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Post by pxguru on Jan 23, 2015 9:40:09 GMT
Just had a quick read. Considering the whole tuning job to make all aspects compatible will give the best results.
Good you found the overlap. This is normal. About 10 degrees max overlap for a tourer, where the power band starts low down. For something that revs 10,000+ with a later power band this can be a lot more.
That inlet table in Bell's book is for a piston port inlet. These numbers are not at all related to a rotary inlet. Piston port inlets have many flaws and have to run less degrees, all of which are corrected, and then some, when changed to a reed valve.
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Post by sime66 on Jan 23, 2015 11:04:14 GMT
Using 10° (max) overlap then, and keeping to T-124° at the moment, I can go up to (max) I-128° BTDC from the 118° I had before, which is cutting 10° on that side of the crank (max), if I need to and if it’s worth it. Do you then do another 10° on the other end (harder to cut there?) If getting that close to 10° I’d have to be very careful with measuring and cutting, but with my eyes and ten arthritic thumbs it might be wiser to keep away from the 10 max overlap anyway; no doubt we can pin it down better as we go.
10° would be 128/53 = 181 2x10° would be 128/63 = 191. Your Tourer example was 125/55 = 180, so I don’t need 10°I’M CLOSE TO 118/53 WITH JUST INLET MODS,
125/55 IS TARGET FOR TOURER:
= +7 on BTDC - (CUT CRANK 7)
=+2 ON ATDC – (CUT CRANK 2 – IF POSSIBLE)
IT’S WITHIN 10, SO CUTTING CRANK IS AN OPTION, BUT:
NEED TO ASSESS IF I’M UP TO IT, IS IT BALANCED, IF IT’S WORTH IT, OR IF 125/55 IS NECESSARY IF I’D BE BETTER BUYING A CRANK.
Do I want to take a punt at the exhaust duration, from what we did before, (which I must confess I can’t be bothered to wade through at this very moment – the rules of thumb max/min etc.), or should I wait and measure it on the barrel relative to the transfer port? I was going to do a diagram, which works better in my head than just the numbers do. I knew that table was for piston port inlet; there was rotary side-inlet stuff too (no numbers), but I didn’t find rotary (top-) inlet stuff like ours; I posted that table in case the numbers were similar, but I see they’re not.
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Post by vespasco on Jan 23, 2015 13:18:31 GMT
Good! Youve highlighted a couple of things i wanted to pick up on. Id say it would be best to start with your sip road as this will likely be the limiting/deciding factor on how big/little your inlet needs to be (they are closely related), which would also influence your transfers and exhaust duration too. Once you know how much torque to expect then you can choose your gears. Cutting the crank! As H says, would potentially throw it off balance. Physically grinding/cutting the crank web/flywheel is quite easy... But if youre not splitting the crank then its keeping the grinding dust out of the bearings id be more worried about! For low end grunt and good usable mid range touring set up (which is where youre likely to be riding it most) would require less exhaust duration than a high revver. You will find the more the exhaust port is raised there will be a decrease in mid range power. This is a dilemma i have with my set up..i have good power in mid range which i dont want to loose, yet if i raise the exhaust port (which would ideally need doing) then theres a chance i would loose that lovely power in mid range. With a smaller exhaust port there would be better expansion of gases and higher pressure transfer and scavenging would be needed. Which means possibly opening the inlet and transfers to suit. It will be a happy medium...not to raise the exahust port too high.. i want to keep it limited to below 8000rpm and have the low and mid range power. I actually, ideally want my max peak power at around 7000rpm...in the real world thats cruising at 65mph+ with a bit more in reserve. It runs ok at low revs at the koment too....only just tho' ... Raising exhaust port will affect ths for the worse?! Too much pressure and the fresh charge will flow right out of the exhaust port before its closed.... The ideal rate is for the fresh mix to reach the exhaust port at the exact same moment the exhaust port closes. Too slow and it doesnt push the old combusted gases out. Just right and the fresh charge pushes out the old gas without mixing with them. The fresh mix clings to the cylinder walls ready to be ignited. This is where the exhaust system has a major affect on the running of a 2 stroke. Reliability, longevity will be more down to the compression and setting it up right. The overlap between inlet opening and the transfers closing is something else i was going to look into. Whats permissable etc. The figures i have for, more of a high revver, are similar (15°-30°)... The higher rpm the longer overlap is possible. This is where getting that balance between inlet and transfers is important. And again, the exhaust design will affect this quite a lot. This is one thing that always throws me....whos data/ figures are correct in the real world of vespa'ing!? We are finding out!!! The handy port timing diagram you done for me previously is getting referred to quite alot! Looking at this makes me wonder about how much tolerance can be allowed between the inlet closing and the exhaust opening (i have 20° difference which is loads im sure). Im gonna have a read through those threads you linked to and dig out the Bell/Jennings scriptures. I have another bible but it was written even earlier (1968)!! Although it still agrees with the Japs findings of less can more when it comes to transfer velocity.
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Post by sime66 on Jan 23, 2015 13:34:59 GMT
I’ve started doing a port timing diagram, so I can picture the numbers better, but must confess I’m trying to get to a point today where I can leave it for a few hours – don’t go rushing ahead without me though!! Slow and steady; there’s months to get it right. I’ll have a proper read of yours again (I’ll copy and paste so I can look in detail at all your points later), and any posts that crop up later, but for now, as you mentioned it in yours, here’s the port diagram I’m working on. (with the numbers from above – it’s all tweakable; just for discussion and to help me picture it). Lots of variables creeping in; not unexpected, but need to be careful to keep a grip on my understanding of what we're banging on about!
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Post by vespasco on Jan 23, 2015 14:23:56 GMT
With regard as to what your exhaust timing should be.... Id say opening @ around 93°, for 174° duration!?
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Post by sime66 on Jan 23, 2015 15:14:52 GMT
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Post by sime66 on Jan 24, 2015 8:00:36 GMT
From your post, vespasco, now digested in full: (good background info to pinning down numbers, but which can’t really be pinned down yet, which doesn’t matter so much now I have a picture of it in my mind). Did you find any data when you looked at the Sip Road for your scooter? I’ll go looking again, but I think I’ve tried before and not found much. As you say not only who’s figures are correct, but where are they! I’m having a similar lack of data-joy trying to find info on alternative cranks at the moment. Which leads on to crank cutting, which is still up in the air because of those two factors – balance and bearing clogging. We know pxguru wouldn’t be talking about it if he wasn’t confident it was the right thing, so I wonder why you and H both seem to differ – you three between you are my Oracle. (With that matter, and exhaust limitations for inlet duration, this can’t be pinned down right now). There’s’ a similar slight discrepancy in revs too, but I’m letting that one slide for the moment to see where some of this other stuff leaves us. Low end grunt – good useable mid-range – less exhaust duration than a high revver; these words sound more like what I’m thinking for my needs; it really isn’t about top speed. – There is an alternative set-up with no crank cutting and lower transfer timing to tone it all down a bit, but I’m waiting to see what others say on these subjects before I think too much about that. Gears are pretty much fixed now – unless I’m definitely wrong when we’ve decided on the numbers for rpm/torque etc; they are: (21&)/68x21,17,13,12 and 35, 38, 42, 58, not (21&)/68x21,17,13,12 and 35, 38, 42, 57 as original. I don’t think the 1st gear (58 not 57) matters. I could go to 22T clutch if I’ve got the grunt, but that’s about the only change, which I don't expect to be doing anyway, and can be a later change if necessary, not internal.
Your description of how tight your margins are, and the dilemma balancing your engine, is a bit hard for me to follow in detail (as it also became towards the end of the thread where we went into it, and you two lost me at the end), but it serves as a good example of what I don’t want to end up doing, which isn’t practical in the real World, but I’ll say anyway, as a factor in decision making:
I really want this engine to be planned with full knowledge of implications of each decision, and the decisions not leaving me without any margin, then cut about to the best standard my inexperienced hands, and worn-out bones and eyes can manage, put together with all the care I can give it and with the best parts, and then to be put in my scooter, and after some reasonable period of setting up, be rideable pretty much to the expectations of it, without it having to be repeatedly taken out and opened up and tweaked. – I do not want to do this if it means this engine is going to be in-and-out of my scooter for fine adjustments; I’d rather just build my budget-spare than find myself in that situation. I don’t have the will or the facilities to keep swapping engines about, taking them apart, tweaking them, and trying again. The maximum care and attention at this and the building stage, not tweaking and trouble-shooting later. – That’s important; I’m still a rider not a shed-dweller.
I haven’t got any figures for the allowable overlap; I’m keeping to well within my 10° for mine; I’ll keep an eye out for that info while I’m scouring the net for stuff. I went back over those threads I linked to yesterday morning (from Thursday night), and I think most of what I got from them has already been covered here now, so they served to get me asking the right questions, but are probably past their use now. I can do you a new diagram for yours if you give me some numbers; it only takes five minutes to do. I think that’s about it; no numbers pinned down really, or final decisions made, but a very much better understanding of the Inlet Timing can-o-worms than I had a couple of days ago. And a bit of reading and searching for data is needed now. Cheers chaps.
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Post by pxguru on Jan 24, 2015 10:26:21 GMT
Not much time right now but just to clear up one point. Vespasco, your blowdown duration is a few degrees under the allowable absolute minimum. This will cause a power loss in from low mid range to high rpm. Fixing this will increase power everywhere
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Post by henri on Jan 24, 2015 11:50:07 GMT
i'm still reading an following an digesting all of that ,but 1 thing i caught is sime pointing out me/vespaco/guru differing on stuff , welcome to the world of tuning where nobody agrees on the day of the week never mind anything else , an as vespaco is reading a 68 bible ,i'm stuck in the 80's an i'm thinkin guru's round about 2005 ,maybe later ,weve all got more modern info n trends mixed in aswell so we will differ.aswell as its horses for courses ,every engine is different an can be tuned differently with the particular end use in mind , a potential confusing minefield ,will sit down a go thru later n see if ive anything useful to add to the mix ,H
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Post by vespasco on Jan 24, 2015 12:27:53 GMT
Of course, you are right guruji!! Id kinda forgot the blowdown was not enough!! Yep! Makes sense. Heres the figures for sime that i guessed at. 124* transfers 8000rpm 25(.5)* blowdown 174* (175*) exhaust (going under rather than above as its a tourer). Although heres still room for more (or less if desired?!) exhaust duration to raise blowdown. Sip road data... This is where a dyno comes in handy!! Scooter centre?? Most dynos ive seen do not go past 8000rpm with the sip road. And most of what i saw would be for 200. Id be suprised if you went past 8000rpm anyway. Not sure if theres much difference between 125 and 200 pipes. Id imagine theyre the same inside to keep production costs down if nothing else. Im not saying you should not cut your crank..... Just , if you do, they are the things to look out for! Did you consider a stroker crank?? If you end up buying a new crank then surely the stroker should be considered!? Otherwise use your stock crank. It will be fine. Id also look into just how much of the sealing pad can be ground out before it breaks the virtual seal with the crank web. (You need to keep the pressure in the crankcases)! Overlap figures ive seen are 10*-25* and 15-30 and also, keeping them opening/close at exact same time for a broad power range. More overlap would give more max power but at the expenense of mid range power. A small amount (7*) of overlap would be fine for you sime, id say. Setting the inlet for your exact motor and needs is a little trial n error than fixed, definite figures but im sure youll get close enough with the figures abailable. You can go even further with the figures and work out your port time-area figures. (See Jennings)!! It would be great to get all the theory right, put it into practice and ride off into sunset. It doesnt always happwn first time as theres no substitute for actually doing/trying it for yourself in the real world. But im sure we can get the engine right without the need to split it after its built. Yeh! Ill take you up on the offer of the crank diagram. Ill check my figures again and post them. I did also notice you used a 57mm crank for the distance in mm (i have a 60 stroker, i bought it from a stoker, from the coast of Kuala Lumpur). Cheers! Fuijo Nagao. Hes the man!! edit...... I missed your post there H!! Yeh youre right. Each to their own etc. however i do think we are all saying pretty much the same thing essentially , just from a different perspective. Its then down to you sime on how you decide to interpret it all and what makes sense. If we all thought the same it would be a boring old world!! I have and refer mostly to the 2 bibles, (whichever edition they are?) The '68 edition of 2 stroke engine design i also have is rarely used but for the sake of variety i dug it out the other night. All say 'about' the same thing,,, altho as has been mentioned before 2 stroke technology and knowledge has come a long way since the 60s !!!
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Post by sime66 on Jan 24, 2015 12:46:28 GMT
reply to H - vespasco, you've slipped one in above while I've been composing; I'm going to post this and go away and read yours: There’s just as much to be learned from the bits you don’t agree on, H. it’s all still worthwhile conversation and debate, and understanding the factors in deciding is just as important as the decision – no time pressure to make any decisions. For me with this crank, I see several options, and it can wait anyway; I’ll just tweak the plans and numbers as I get closer to getting it pinned down, they are: 1) Just do the case mods, and stick at the approx 118/53 I reckon I can get with doing that. 2) Do the crank mods too, to achieve the 125/55 (if necessary – refer to revs and exhaust points above). 3) Find a suitable better race crank to achieve similar to the 125/55 (if necessary – refer to revs and exhaust points above). · The exhaust matter is something I hope to sort out by just spending some time searching for tech info on Net. · The revs thing is not something that’s not bothering me too much right now, other than to try to get as close to an agreed figure as I can. I’m prone to being cautious, not being too bothered about top speed and wanting to maintain my low-down grunt, but am open to persuasion. I think there’s a bit of confusion still (on my part anyway) where some are talking about max revs, and others might be talking about revs at which max power is achieved. It’s all good; as long as you lot don’t get bored or frustrated with my clarifications, I’m picking up info all the time – sometimes even managing to remember some of it! My engine is back in it’s box for now; I’m waiting for gears, which are floating around on a truck somewhere between here and Glasgow, and a carb, which should be here, but I think is still sitting in a shed in Kent. The barrel supplier hasn’t even got my € yet in case I change my mind before ordering it; the listing ends on Thursday. I’m well happy with where we’ve got to, and the bits we’re discussing now. With the disagreements, I’m trying to get as close to a consensus as I can and understanding the reasons for it if you don’t agree, because at some stage I will have to make decisions, but that isn’t yet. Vespasco: This one? NOT a little gentle bedtime reading – looks like a head-spinner : Fuijo Nagao The Effect of Crankcase Volume and the Inlet System on the Delivery Ratio of Two-Stroke Cycle Engines: www.bridgestonemotorcycle.com/documents/crankcase_volume6.pdfI’ll look at Jennings port time/area stuff as well; just for the shear joy of the feeling of a numb, overloaded brain, and words and numbers passing my eyes and not going in. Cutting crank discussion is in hand; absolutely agree re: sealing pad; do not want to be getting that wrong, or so close that a slip causes me major agro. My thinking changes to-and-fro as we pin it down, but at the moment this engine is looking like being the better of the two, and if it’s the one I do end up as the keeper in my scooter, then another £100 or so for a crank isn’t a problem, if I need it, and as long as the engine remains within the (loose/vague) requirements of it that I’ve said. - Cutting the crank, buying a crank; both still options. Re: 57mm, not 60mm; you mean just when I was checking your port timing data and results? I see 60mm on my sheet for your scooter – otherwise our numbers wouldn’t have agreed at the time. Is it something that’s affected the numbers you’re using now? I can’t think what else you mean? Do explain. ‘Ideal World’; agree, but see above ‘ in my scooter’ is where the engine wants to be, and ‘ out and flying about’ is where my scooter wants to be; not in boxes, sheds, back gardens or skips! I’ve made the point already, and I’m having a joke now, but some of the tweaking can be designed-out with care and attention at this stage. I know it isn't real-world, but tweaking/trouble-shooting is the bit of this lark that I enjoy the least, and want to keep to a minimum. Give us your numbers and I’ll do you a diagram, once you’ve checked and tweaked it, I can email in whatever format you like, to put on your tablet or print; whatever.
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Post by sime66 on Jan 24, 2015 19:06:07 GMT
A couple of things for you blokes to have a look at if you feel inclined: Spreadsheet for checking porting: (based on Jennings, Bell, and Blair) PORTING DESIGN CHECK ON TWO-STROKE ENGINESwww.330.dk/It’s a downloadable Excel file; not much use if you don’t do spreadsheets, but I’ll have a play when I’ve got some numbers to put in. Couple of two-stroke design books by Gordon Blair: Gordon P. Blair The basic design of two stroke enginesdocs.google.com/uc?id=0BwCDki0jowhAODJWWmFVMHhqZ00&export=download(Has to be downloaded) Gordon P. Blair The basic design of two stroke enginesdocs.google.com/file/d/0BwCDki0jowhAODJWWmFVMHhqZ00/edit(read online) Gordon P. Blair Design and simulation of two stroke engineswww.dragonfly75.com/motorbike/2StrokeDesign.pdf(read online/download) ------------------------------------------------------------------------------------------------------------ Unrelated to that; does anyone know how to read this on the tech data for a 57mm mazzucchelli race crank? Obviously it’s the Timing short seal face 196°, long seal face 173°, but how does that relate to the 110° I measured on my crank? Faffed if I know. Is it the cut + length of seal face (pad), if so what’s a short seal face, and a long seal face? Is that the roughly 60° (measured) of my pad?, which would make my crank now 110+60, in which case the 173° seems rubbish, so it can’t be that then, but if the 196° means something, that's useful. Any clues, ideas, hunches appreciated: Not buying one, and if I do it won’t necessarily be this one; just trying to find out the right numbers for it, or any non-standard cranks that have data I can read. Another point I noticed about this crank is that Wasp say that Mazzucchelli recommend a 1.6kg flywheel or lighter; my new one is 1.8kg (still with option to take off start-ring. – just thought I’d throw that one in. Got data and info from Wasp and Scootercentre, but for this the cheapest I’ve found so far is SIP; £76.87 (cheap!): www.sip-scootershop.com/en/products/racing+crankshaft+mazzucchelli+_45000000That’s all folks!
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Post by vespasco on Jan 24, 2015 19:27:58 GMT
Im not entirely sure which things you've picked up on that makes you think we disagree. its probably just me not explaining myself clearly! No worries though, it's all food for thought and will soon get corrected (hopefully)! if anything is wrong. thats how we all learn. I dont mind playing the fool. Inlet/crank mod's... Id say you want your inlet opening @ 118° minimum. That would be your starting point anyway, so as to match your transfers closing, but ideally they'd be a little overlap, around 125°. If you can do that on the crank alone then happy days. It would be better than altering the sealing pad. Altering the size of the inlet, (either on the sealing pad face or on the carb box gasket face) will have an effect on the velociy of the incoming mix. Without flicking though the guides again i cant remember how a longer inlet duration affects that exactly. Once my head stops spinning i'll take another gander @ Mr Nagaos papers. The answer will be in there i bet! One of the guides i have is by an italian 2 and 4 stroke engine designer,(for Alfa Sud and Komet (karting) amongst others)). Its not as clear/informative/easy to read as (the revised in the 80s, maybe even later)?? Bell (or Jennings) guide which everyone seems to refer to in our vespa world. Mine is translated from italian! I actually think that, especially with your skills on a pc, you will quickly figure out your time-areas. Jennings shows you how to map it out in his guide. Theres no reason why this engine should not be the better of the 2. Compared to your current motor i mean. If you end up with Dr. Kit for this build, at least you will know EXACTLY what to do to your current motor when you tune that. It would be a good comparison to have. And will be a similar set up to your current motor. You could try one thing on this motor, and transfer it/update it/leave it off the other motor. Keep in mind....You tune this new motor well and want to keep it in your scooter. Would you actually want to sell your other engine? The one that matches your scooter? Some people arent fussed. Some people like to see matching serial numbers (near as damn it). Unimportant really. But worth pointing out. I had a similar dilemma once, in the end, I found that the engines peformance far out weighs the need for matching serial numbers!! Haha! Buy a cut crank!! Haha! Andreas at Worb5 was very helpful when i wanted to design/profile a cylinder head. Im sure theres a few other tuning shops in the uk who could help if you sent them an email asking for details of timings. It may prove quicker/more reliable than searching endlessly. I never found much conclusive data when i was searching for a crank. Im sure by the time you come to build all the creases will have been ironed out and all that will be left to do is fine tune the usual...ignition timing and setting the carb. Which should be easy enough. Im quietly confident youll fire up your newly built motor on 3rd kick, with no major surgery required My 57/60 crank thing..its no biggy.. Its only on the crank diagram you kindly made that I was reffering to, i mean the figures beside the diagram, the mm ATDC...(converted from x° ). These are given for 57mm crank....easy enough to work out on a calculator tho'! It threw me for a sec until i spotted 57mm at BDC! For the sake of continuity these are the figures with no packer, 0.6mm deck. Which i think is the one ive been referring to recently when talking of my motor. To confuse things, atm im still using the 0.5mm packer, but Im going to be changing that back to a 0.1mm packer sooner or later!! So, with 0.6mm deck, (0.0mm packer, 60mm stroke, 110mm conrod, exh - 37.3mm, trans - 47.3mm, both from top of cylinder, 69mm dia bore): My inlet is 107°/74° (+/-1°) Trans open @ 116.5° atdc for 127° duration Exhaust opens @ 95° for 170° Theres not a huge amount i can do to alter these figures for the better. (With exception to raising the exhaust port of course)! Ideally my inlet would open at least 10° earlier which would be very beneficial. And close a little earlier too. (This period, from TDC to inlet closing is where you are likely to suffer blow-back if the timings are wrong). Ive suffered from blowback before, but thats a totally different story from way back, involving a diggery-doo-dah!! %D Bhoom Shankar!
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Post by vespasco on Jan 24, 2015 19:29:15 GMT
Ah!! I knew i should have checked for a reply before i posted just now!! Didnt see your latest post!
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Post by vespasco on Jan 24, 2015 20:21:07 GMT
Bit of a guess but...
Size of rotary seal face - 193mm = 165° (98mm x π etc) minus your 42° inlet = 123°
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Post by sime66 on Jan 24, 2015 21:00:18 GMT
LOADS!! To read there, which will need the morning brain for concentration, which is beginning to wander tonight. I quickly knocked up your port timing diagram, but I’m wondering if you meant something else, with the talk of 60mm etc., ‘cos that’s not involved in this; it’s just your degrees. Anyway, I’ll read it all better in the morning. Tell me if this was what you meant, if it is have a quick check, and I’ll alter it or email to you. (The angles are ‘associative dimensions’, so if I move the inlet and outlet bars on the drawing, the degrees update automatically, so it is easy to fiddle with – no problem if you want to change it.) I do see what you mean about the Inlet opening being earlier. (But you’re concerned about areas/velocities if you open it up? – still to read it properly)
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Post by vespasco on Jan 24, 2015 21:50:44 GMT
Xcellent cheers! Dont worry about the 60mm crank thing. Im was looking at an older diagram. Sorted thanks. Yeh the inlet...(i would cut the crank not the inlet). But whatever i did it would make the inlet duration even longer. Its long enough already id say (chorttle!chorttle!) Tha was the main concern for me. Enlarging the inlet on the pad was what i was concerned about doing - making the hole bigger - would that affect the flow too much? In the same way a bigger carb venturi would affect the flow. ?? Keeping it same area is no problem.
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Post by vespasco on Jan 24, 2015 21:55:20 GMT
Ive suffered from blowback before, but thats a totally different story from way back, involving a diggery-doo-dah!! %D Bhoom Shankar! pass the chillum sime's way!!! jebus christus that would be a giraffe Ive had a few of those too. With a few Baba ji /saddhus. And it always passes to the left. Whichever way that is from here. Who's next? Bhoom!
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Post by sime66 on Jan 24, 2015 21:59:43 GMT
Still only skimmed over yours, but picked up on that about worrying about the area of the opening; if you go back a page or so, I recall pxguru saying that the (main) limiting factor on our engines is that opening size, so I reckon you'll find there's room to open it up. Also maybe it explains why Piaggio put the extra hole in sometime as an 'afterthought'. I suspect that opening it up is going to be beneficial, not just to inlet timing - just guessing from what's gone before though. Need to do those other calcs you mentioned too - loads of loose ends. I have taken on board about cutting the crank (or replacing for longer inlet crank) rather than cutting the cases though; all up in the air still........ Also about keeping the same age engine with the frame; noted, but no reply yet My frame is 1983; the engines 1982 and 1984, so all close. There's still loads to read through, so I'll leave it there for now.
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Post by vespasco on Jan 24, 2015 22:04:34 GMT
Now youve said that i do recall noting that its the inlet duration BEFORE tdc thats more important! So, I'll think about doing that!
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Post by vespasco on Jan 24, 2015 22:57:51 GMT
Oops! I posted previous post early by mistake! My tablet didnt like that spreadsheet! Pretty useful tho'! Good find. I had to take a bit of a guess with the exhaust port radius as mine is a weird shape, (an uneven oval). According to Jennings im not tooooo far out but none the less there's room for improvement. But i do need to take into consideration that, ultimately my motor's builtt as a long distance torquey tourer!! Mustn't forget that when looking at all these figures! As mentioned earlier, the drilled hole is not an after thought. It just looks like it thats all. I imagine its this hole (or lack of more like) that is restricting the modern low emissions px. (Along with the stator etc etc).. So no worries about the engine numbers! Build this one right and no doubt it will stay! Any comments on opening the actual hole in the sealing pad and what effects it would have on the volume/velociy of the mix being sucked in to the crank case? Would i end up needing a bigger venturi for instance if it was too large? The size of this inlet hole has got to be related somehow. Or is it simply that it would only affect the inlet duration on our simple motors!? (To our advantage) I dont want to get this confused with the cranking pressure / flow to the transfers. Gaz, I dont think i could handle it anymore, most of the Baba ji that ive met are never seen without one on the go except when asleep in bed. And its quality too! Believe me its true, thats something i DO know for sure! Haha! H@ppy daze :0 Sorry sime, back to your thread! Hahahaa
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Post by sime66 on Jan 25, 2015 7:03:30 GMT
It will go ok with a standard inlet like everyone elses does but opening it out will make a differance.
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Post by sime66 on Jan 25, 2015 7:04:16 GMT
Another differance between 200 and 125/150 casings! The drilled part on both is like you say, an after thought. The cast hole is too short and the drilling corrects it.
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Post by sime66 on Jan 25, 2015 7:05:25 GMT
To get the most fuel in the crankcase the inlet needs to be open as early as possible and close as late as possible. So, longer time (without going over)is what is needed here. The area of the inlet hole is a limitation on Vespas. With the hole as big as possible on a 200 this is about the area of a 30mm carb (Any carb bigger than 30mm should have a reed valve conversion (and and carb smaller than 30mm shouldn't!!)). On this 150 job to get a reasonable inlet time, the maximum inlet hole size and a little ground off both ends of the crank should do it.
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Post by sime66 on Jan 25, 2015 7:14:24 GMT
^^the point I'm making by reposting those is that, although I will look at the calcs you mentioned before, I think we already have that answered; I suspect it is less of a factor than the fact that the inlet hole on the cases is too small.^^ We have, in the past, got too carried away and bogged down in the books, and gone too theoretical when the obvious is already there - perhaps this is the case here. Regarding the smoothing out of the carb->carb box->case inlet is concerned, I'm talking about smoothing out the edges and corners caused by the mis-match between the openings on those three items; those can't be beneficial to airflow with the friction and turbulence they are creating, and tidied up they're still smaller than the carb venturi - I think that's the point. I have done some drawings of those transitions, but I'm holding-back with them for now. The other stuff; I'm going to wait for the dust to settle, the others to catch up, and do do some quiet, sensible reading; including your last couple of posts - too many distractions at the moment to keep track of what's worth following up.
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Post by sime66 on Jan 25, 2015 7:43:45 GMT
These are 'Work-in-Progress' but maybe it's time to use them to illustrate that the carb is the biggest opening, but the fuel/air from it is whacking and bouncing all over the place, not flowing smoothly into the crank case, and that it's getting strangled through the casings too:
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Post by vespasco on Jan 25, 2015 13:10:59 GMT
Im probably looking into this too much... Opening inlet will make it go better. But thats more due to the timing of the opening not necessarily the size of orifice/opening itself. The 'after thought' drilled hole is part of the design, its not actually an after thought. It just looks that way as its not part of the original casting and has obviously been done after the casting process due to reasons highlighted by guru ji (you wont get the cast out of the mould if it wasnt like this) and as it's not been cleaned up it looks even more like its an after thought, made by a previous owner!! Opening inlet for longer time, without going over. - Opening my particular inlet earlier might just make it go over? as its closing late enough as it is - although this is not so important). Let me put it another way.... If the orifice (stock sealing pad hole) is smaller than the venturi, but is the size of a 30mm carb when opened up fully, would i then need to match this with a larger 30mm carb? That would be like 'inverting the 'cone" of the inlet pipe! The main point im making is i will retain the stock 24mm carb regardless (and the sip road exhaust) Yes it would go better with a larger inlet and larger carb, (+larger exhaust, ports)! I looked into using an si26/26 before but got put off as i learned some people found it made their motors worse, i believe due to a decrease of mix velocity? and made their motors very difficlut to dial in. Is it such that a stock 200 inlet orifice is equivalent/same area as 24mm venturi? Do they need to match/be bigger/smaller to work most efficiently? Mr Magoo has the answer and i must have read it last night!! Ill have another catch up of the posts here too. I guess its a basic science question really, which i cant think of the answer atm. I probably done this at school! Hahaha!! Im not going to get bogged down on this little trivial matter anymore! So i guess the question is.... can you suck more mix through a (24mm diameter) cone, an inverted cone, or a straight cylinder! (Ie. the 24mm inlet pipe). Thats what i was really trying to find out. Schoolboy stuff im sure. I bet Gaz can help with the answer. I reckon hes sucked on a few cones!! Hahaha! Smoothing out the inlet is fine. Ive done it to some of my motors. But i deliberately never touched the size/timing of the sealing pad orifice. Out of curiousity, does your software tell the area of your stock inlet orifice by any chance? (Sealing pad) ...fully opened up we know its equivalent to a 30mm carb on 200 cases. Nice CAD work sime!! That does show it clearer! Shown like an 'inverted cone' almost. The (my) crank diagram looks cool.. Wouldnt mind a pdf of that if possible Sorry guys,, that was a bit long winded and i probably repeated myself a couple of times. Time for a cuppa!!!
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Post by sime66 on Jan 25, 2015 14:26:00 GMT
In reply to your's, vespasco:Im probably looking into this too much... – I’M HOPING WE LOOK AT IT ALL IN DETAIL, BIT BY BIT.Opening inlet will make it go better. But thats more due to the timing of the opening not necessarily the size of orifice/opening itself. – I THINK IT’S BOTHThe 'after thought' drilled hole is part of the design, its not actually an after thought. It just looks that way as its not part of the original casting and has obviously been done after the casting process due to reasons highlighted by guru ji (you wont get the cast out of the mould if it wasnt like this) and as it's not been cleaned up it looks even more like its an after thought, made by a previous owner!! – I MEAN AN AFTERTHOUGHT AS IN A DESIGN ADJUSTMENT, WHEN THEY REALISED IT WAS TOO SMALL, IF IT WAS JUST FOR WITHDRAWAL THEY COULD HAVE TAKEN GREATER CARE NOT TO EFFECT THE OPENING SIZE, IF IT WAS GETTING TOO BIG; SOMETHING LIKE A LOLLY STICK SHAPE WOULD HAVE DONE FOR WEDGE WITHRADRAWL – THIS LOOKS LIKE A DELIBERATE INCREASE ON WHAT THE ORIGINAL MOULDS WERE.Opening inlet for longer time, without going over. - Opening my particular inlet earlier might just make it go over? as its closing late enough as it is - although this is not so important). – NOT GO OVER IN TIMING; WE CAN CHECK THE VOLUME IF YOU’RE STILL CONCERNED WHEN PXGURU HAS COMMENTED. CAN WE SEE YOUR CRANK INLET AND PAD? MAYBE YOU CAN INCREASE JUST THE FIRST EDGE TO OPEN EARLIER? AND THEN CHECK THE AREA IF NECESSARY.Let me put it another way.... If the orifice (stock sealing pad hole) is smaller than the venturi, but is the size of a 30mm carb when opened up fully, would i then need to match this with a larger 30mm carb? That would be like 'inverting the 'cone" of the inlet pipe! - THE 30MM VENTURI IS EQUIVALENT TO A 200 OPENED TO THE MAX (THAT ISN'T CHECKED). – WE CAN CHECK AREAS IF IT IS CONFIRMED AS BEING CRITICAL.The main point im making is i will retain the stock 24mm carb regardless (and the sip road exhaust) Yes it would go better with a larger inlet and larger carb, (+larger exhaust, ports)! – I AGREE 24 & SIP FOR ME TOO I looked into using an si26/26 before but got put off as i learned some people found it made their motors worse, i believe due to a decrease of mix velocity? and made their motors very difficlut to dial in. Is it such that a stock 200 inlet orifice is equivalent/same area as 24mm venturi? – DON’T KNOW – PERHAPS YOU HAVE DIMENSIONS FOR YOUR/A STOCK 200 INLET?Do they need to match/be bigger/smaller to work most efficiently? – TO HAVE NO EFFECT ON VELOCITY, THEY’D IDEALLY BE THE SAME WOULDN’T THEY? I THINK AT PRESENT THEY ARE SMALLER; I DO TAKE YOUR POINT THOUGH.Mr Magoo has the answer and i must have read it last night!! – HAVEN’T TOUCHED MR MAGOO, OTHER THAN TO GLANCE AT IT AND DECIDE IT’S GONNA BE A CHALLENGE; I HAVE A HUNCH WE’VE GOT THE ANSWER – DON’T WANT TO GET LOST IN BOOKS UNLESS IT’S CONFIRMED AS NECESSARY (WILL DO IT AT SOME STAGE OUT OF CURIOSITY THOUGH).Ill have another catch up of the posts here too. I guess its a basic science question really, which i cant think of the answer atm. I probably done this at school! Hahaha!! Im not going to get bogged down on this little trivial matter anymore! – NOT SAYING IT’S TRIVIAL; JUST NOT SURE, FROM WHAT’S BEEN SAID BEFORE, IT’S A BIT WE NEED TO WORRY ABOUT; GURUJI SEEMS CONFIDENT IT CAN/SHOULD BE MADE BIGGER; I’M WAITING FOR HIM TO CHIP IN.So i guess the question is.... can you suck more mix through a (24mm diameter) cone, an inverted cone, or a straight cylinder! (Ie. the 24mm inlet pipe). Thats what i was really trying to find out. Schoolboy stuff im sure. – YOU DON’T HAVE THE OPTION OF A CYLINDER; IT HAS TO BE A CYLINDER ON TOP OF TWO CONES/WEDGES – THE CARB BOX AND THE INLET (THE WIDTH OF WHICH IS DICTATED BY THE WIDTH OF THE PAD AND THE CRANK WEBSmoothing out the inlet is fine. Ive done it to some of my motors. But i deliberately never touched the size/timing of the sealing pad orifice. – NOTED; I STARTED DOING THOSE DRAWINGS A WEEK OR SO AGO, BUT GOT STEERED AWAY TO LOOK AT INLET TIMING AND TRANSITIONS; I WILL GO BECK TO THEM TO TIDY UP SOMETIME. FOR NOW (AT THE BOTTOM OF THIS POST) IS A LITTLE VERY QUICK SKETCH OF THE SORT OF STACK OF CARB, CARB-BOX, AIR INLET; IT’S UGLY, AND ANY SMOOTHING MUST BE BENEFICIAL – IT’S EVEN WORSE THAN I’VE SKETCHED BECAUSE I HAVEN’T SHOWN THE EDGES AND CORNERS THAT NEED CUTTING.Out of curiousity, does your software tell the area of your stock inlet orifice by any chance? (Sealing pad) – YES I CAN GET ANY DIMENSION, AREAS, ANGLES, CROSS-SECTIONS ETC – THE ACCURACY OF THE MEASURING AND DRAWING DICTATES THE ACCURACY OF THE DATA BACK FROM THE DRAWING – FOR THESE I’VE JUST USED MY RUBBINGS....fully opened up we know its equivalent to a 30mm carb on 200 cases. – WE CAN CHECK IF WE HAVE YOUR PAD AND INLET OPENING.Nice CAD work sime!! That does show it clearer! Shown like an 'inverted cone' almost. – SEE BELOW; IT’S JUST A VERY QUICK SKETCH THOUGH; I HAVE LEFT THE DRAWINGS FOR A WEEK OR SO, BUT WILL GO BACK TO THEM SOMETIME.The (my) crank diagram looks cool.. Wouldnt mind a pdf of that if possible – NO CHANGES? IF NOT I'LL SEND THIS ARVO, I CAN STILL CHANGE IT AS YOU TWEAK, AND MAYBE ADD IN THE OTHER DIMENSION DATA WHEN YOU’VE FINISHED MESSING ABOUT.Sorry guys,, that was a bit long winded and i probably repeated myself a couple of times. Time for a cuppa!!!SIMPLIFIED SKETCH OF THE TWO TRANSITIONS UNDER THE CARB FOR THE CRANK INLET:
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Post by pxguru on Jan 25, 2015 16:01:21 GMT
I think maybe you are over complicating this a little but at least it irons out all the wrinkles The area of the narrowest part of the inlet hole just needs to be bigger in area than the carb. The timing of the rotary inlet is related to the porting of the barrel being used and the purpose it is being used for. Standard inlet timing doesn't suit anything else but a standard barrel being used for driving around an Italian city, with a girl riding side saddle on the pillion
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Post by sime66 on Jan 25, 2015 16:11:08 GMT
I had a feeling you were going to say that pxguru; I thought it was getting too ‘numbery’ after the pointers you’d already given us . As it happens, I’ve just done a quick look at the areas along the path from carb to crank, so I’ll post them now – I was going to check in the morning before posting, but as you mention it: Cross Sectional Areas in mm² at known points on Carb to Crank Inlet Transition (before cutting) - Taken from pencil rubbings of components, not from precision measurements:Bottom Outlet Si24/24e – 475.8 Bottom Outlet Si20/20d – 410.3 Upper Side of Carb Box – 464.9 Underside of Carb Box – 427.9 Crank Inlet – Top of Casing – 495.5 Crank Inlet – Inside of Casing – 374* *This was rubbed on the arc of the inside of crank case, so is actually slightly smaller in cross section – not yet drawn accurately, but it's clearly the narrowest point and needs big holes cut in it!!. In case it helps identify which areas I’m talking about above:
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