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Post by sime66 on Dec 3, 2014 11:55:45 GMT
Vespasco, I need to read back through this to refamilarise myself with where you two lost me on this thread; it was about the time where you saw the light about your compression ratio calcs, but you and pxguru shot off talking about your exhaust port, and lost me. I wonder if you have time to write the measurements you used and the calcs you did to get the figures you got for your compression ratio. I will probably work it out myself with a good read back, but I thought I might catch up on this thread while the MicroDyno thread is waiting for data.
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Post by sime66 on Dec 5, 2014 7:16:36 GMT
Vespasco: Repeat of yesterday's request above; I was intending to work this out myself yesterday, but I got bogged down with pxguru's and the your MD test reults - is it at all possible that you spend a couple of moments to put some of your barrel and head measurements into these formulas for compression ratio and corrected compression ratio to help me on the way to following what you did? If not I'll spend my time on this while you hone your MD method in the other thread.
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Post by pxguru on Dec 5, 2014 11:56:49 GMT
Just talking about compression and totally ignoring squish band, clearance or angle. Corrected compression is sometimes called trapped compression, which describes it better. This is what actually matters. The full volume divided by the head volume gives a figure like a 4 stroke. This is a guide as a higher number will perform better until you have too much. There is also the supercharge effect from an expansion which is a major factor if you have an expansion that works over the same range as your power band (porting).
To calculate trapped compression is the same as the usual way but the cylinder volume is only measured from the top of the exhaust port. This gives a figure for static trapped compression.
The 200 standard barrel from the factory gives a trapped compression of 6.5:1. IMHO this is like the minimum for any 200 tuned or otherwise. This is not particularly high compression when compared to motorcycles but still takes some skill to set up the squish, carb and timing to avoid the dreaded pinking!
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Post by sime66 on Dec 5, 2014 13:27:48 GMT
Righto, thanks. What I want to do is just use vespasco’s measurements to reach vespasco’s results; these, I believe: Here are my final figures! No more editing! Top of Exhaust port to top of cylinder - 37.3mm - 170.21° - ideally ° would be more Top of Transfer port to top of cylinder - 47.3mm - 127.06° - ideally ° would be less Blow Down duration - 21.57° - ideally ° would be more Exhaust port height - 23.3mm No base gasket 0.6mm Deck Height
Squish gap 1.6mm - 60.6mm to bottom of ports (60mm stroke); With 25cc Combustion Chamber volume Uncorrected compression ratio - 9.98:1 Corrected - 6.49:1 Existing head is 26cc (I think that’s where we settled – before tweaking).
It’s probably there now, I lost track before with all the tweaking; just going to have one more bash at it to get it done.
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Post by vespasco on Dec 5, 2014 17:20:29 GMT
i can confirm,,,,this is my set up (at present) with no base gasket, to try and get the transfer timings as low as possible.... Next, i will aim to advance the peak revs higher up the rev range by fitting a 0.5mm base gasket (which hopefully will bring my performance back to where it used to be, as im sure i used to have a 0.5mm gasket! Figures...not shown head volume without piston = 31cc Piston displacement volume = 5.3cc head volume for calc purposes - 25 or 25.3cc - (depending on how much the barrel is raised) ive not actually re-measured the head volume,,, i lapped the head a little so would be slightly less than before... ive taken it into account for both these charts above When i saw the light - compression ratios.... It seems everybody likes to use the uncorrected ratios for the stats but apparently it dont mean a lot! Guru ji enlightened me by confirming that its the corrected ratios that matter, not the uncorrected. (i kind of knew that before although i didnt know why etc...im not sure i still know exactly!!!) bvut the important thing is the Corrected ratio anyway! Id worked out my head volume by using uncorrected ratio, trying to get it close to a stock p200...9.8:1 Guruji suggested that the stock p200 Corrected ratio is the one to aim for...., the figure he gave for a stock px200 was 6.5:1 ... so this told me i could actually increase the compression in the head and still be under the stock Corrected (and within a nats whisker of Uncorrected ratio)... I lapped the head as much as i could (by hand) to achieve a 'perfect' compression ratio and fitted the cylinder with no base gasket, to keep transfer duration to a minimum.
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Post by henri on Dec 5, 2014 18:01:46 GMT
have to say i agree totally with pxguru's statement above on compression alone ,6.5/1 as a min , but with todays petrol you cant really go much higher before a scoot engine will pink ,but the difference is in squish depth , to high/big a squish leaves a large fuel load in the band an this can lead to detonation before the flame-front arrives , from the rapid pressure rise/fuel load present , with a carefully adjusted squish the compression ratio can be raised by quite a margin , i'm guessing this is vespaco's reason for re-profiling an searchin for diff heads , but your going into the ranges where a 4 stud head wont be reliable at not blowing ,hence the fancy-dancy 8 "prisoners" heads n barrels on the market today , if your worried about pinking with your new head vespaco i'd suggest retarding your timing a nads or so, as theres a pressure spike on ignition that travels infront of the flame front ,which can cause detonation in the squish as its not quite as its smallest/lowest fuel load yet , actually where is ya ignition set i'm afraid i cant remember ,if youve said it, an also as ya mentioned lapping , ive discovered recently that shops arent allowed to have plate glass anymore its got to be laminated safety stuff, an as plate was best for lapping stuff on ,i dont know bout laminated , an its best only used 1 or twice now seems to be the time to lay in a stock off it , an got to say ,thanks for going into this stuff lads ,ive visited sum well dusty corners of my brain trying to keep up ,but am struggling not to catch tuneittis agin from this , vespaco your saying earlier bout a .5mm base gasket an maybe re-introducing it , is ya engine feeling low compared to before ,or are ya reckoning thats where the "sweet spot" lurchs , H
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Post by vespasco on Dec 5, 2014 21:11:38 GMT
Numbers for the compression ratios:
ECV = (3.142 x 69^2 x ES) ÷ 4000
ES = 37.3mm (exhaust port height) - Static deck height 0.6mm = 36.7mm
ECV = 548926.4003 ÷ 4000
ECV = 137.232
Corrected compression ratio = (ECV + 25) ÷ 25
CCV = 162.232 ÷ 25
CCV = 6.489:1
The above is what i believe i have at the moment. (+/- 0.5cc on the ECV, as i lapped the head).
I think there will always be difference of opinion on which ratio to use...but i notice you tuning guys, 9/10 times, will always talk of/use Corrected/trapped ratio.... It makes sense to me now that Crrctd/trapped would be a better figure to work with, as who knows exactly how much volume there is when the exhaust port is open, with gases coming in and out at different rates, etc... Theres an easy answer isn't there?... Use both??!! In favour of your choice!?
My Pinasco wont need the 8 prisoners...its deliberately low compression, for various reasons i wont go into now. (I can if you want to know)! The head i have, and have used with great success, has only been lapped by hand, by a small amount only, which accounts for only a small rise in compression. But as its already a 'low compression' head this gives me plenty to play with. If for example, i had a screaming, high compression Malossi, with a head designed for max compression (without going over) then it would be a different matter... but Im quietly confident i can use this same head without changing things drastically and it will still give good compression and wont ping. My timing is only set to the marks i made when i stripped it (19°). It still needs checking / tweaking, ive only got as far as marking the timing using a strobe, nothing more... It only pinged once after i first rebuilt it. It never returned although ive not really done much to change it! Shopfronts use lami, lami is just 'float' (plate) glass stuck to another bit of float glass so for your purposes it would be fine... The thicker the better. Ideally you want at least 6mm thick, 'normal' float/plate glass,,,, keep your eyes open for doors with small sections of glass, it maybe 6mm if your lucky! And a nice small size. Most (house) windows you see will have 4mm thick glass, which is ok,,,,good enough for me anyway! I can get loads of it!! Shame you werent closer H! Yeh,my motor is feeling low! I want my sweet spot higher up again,,, at around 5500-6500,,,this would be around the speed i would generally be at on most roads around here,,55mph going upto 65mph gives me enough to overtake comfortably and still have a little left. Right now i feels so slow....i think the power band is too low....but thats ok..i was kind of expecting to put on a 0.5mm at some point! But i do believe at lower revs its much smoother...i can cruise at 25mph/2400rpm in 4th gear very smoothly! Which is nice for a 225! So really, all kits must have a sweet spot.....it just depends where you want it!? If you want a high revver high speed machine, chances are you want the sweet spot quite high, along with a good choice of expenasion pipe n carb to achieve the revs you need. If you want a torquey tourer on a sip road its likely you want your sweet spot where you need it most, a little lower down the revs, where youre likely to be most of the time.
Its all given me a much better understanding of how/why these things work , which makes this thread... well.....excellent!
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Post by vespasco on Dec 5, 2014 21:56:43 GMT
Taken from MicroDyno thread.....
Im 75% sure it will be back to normal using the 0.5mm packer. Then it will be the same set up as before, inc the SIP road, i just couldnt work out why, when i rebuilt it, it was not giving me max revs in 4th... The small tweaks id done, made little improvement. From feel alone, if anything it felt a tad slower. Speedo also agrees with my feel! But the changes were not so big that i cant go back...i hope!...The thing i cannot put back is the lowering of the piston inlet port, that was a small amount yet it felt so right!!
The sip road can just about handle 7300rpm + a little. Which is my max revs, by coincidence or because of the sip road, or because of this or that. It revs in 1,2,3 at 7300, so should be able to handle it 4th!? Although....... By me lowering the barrel, effectively makes my, already low, exhaust port timings even lower! At BDC the piston is not fully opening the exhaust port.. This could be one reason why im not getting max rpm in 4th!? Especially whn you compare the results to using a 0.5mm packer, allowing the low duration of the exhaust port its full potential to open.....fully, which still only gives no more than 172°. And even worse is, by raising the barrel 0.5mm, it raises transfers by 2.5°! (0.5mm packer raises the exhaust just 2°). My pinasco can (or used to)! handle it, in 4th @ 7300rpm , giving me 73mph! With the sweet spot just where i wanted it, around 6000rpm +/- 500rpm. You could well be right h!
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Post by pxguru on Dec 5, 2014 22:55:41 GMT
I think it will be an interesting experiment to fit the 0.5 packer. What I expect is that at less than max rpm it will go better than before. in third certainly rev higher but in 4th it wont rev out. Even worse than now. this will be due to the below minimum blowdown duration being even more below minimum once the barrel is raised. Raising the exhaust with the packer will increase the exhaust duration but the exhaust duration alone is of no importance to anything. The exhaust duration just provides the blowdown duration which once the barrel is raised will be even shorter, so would most likely clip the top of the power curve even more. Will make interesting results for the other thread. When you doing it? Next experiment is to get the exhaust port raised 2.5mm then it will go like a train
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Post by sime66 on Dec 6, 2014 7:31:30 GMT
I could see this thread becoming relevant to the MicroDyno one, which is why I wanted to get BACK up to speed with it. By the time vespasco is ready to do barrel mods, we should have the tools to accurately measure the changes he makes; it’s going to me (even more of) an education!
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Post by vespasco on Dec 6, 2014 11:01:53 GMT
I will be dping as soon as i physically can. My body says no at the moment. From what weve learnt , it wouldnt make sense to raise the barrel. Yet From past set up, wich worked really well, by raising cylinder to 0.5 worked really well.... Unless theres something else which has changed. Something i cannot find. First i need to get considtant results on the microdyno so i can reliably compare the 2 readings/set ups. Then hopefully the experiment will be over!? If both prove unsuccessful its either ; raise the exhaust port, or look for the cause of low power elsewhere, probably crankcases?!
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Post by pxguru on Dec 7, 2014 12:53:51 GMT
What I am seeing from your power curves is exactly the shape would expect when there is insufficient blowdown.
Raising the barrel now will make it feel better. The torque will go up and it will ride better, as long as you keep it under 6000 rpm! If you want it to go better at high rpm and mid range, then you need much more blowdown.
The numbers are never that far different from the reality of how an engine actually runs.
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Post by vespasco on Dec 7, 2014 20:55:14 GMT
Ive done a few dyno runs on the MicroDyno app and now im confident of consistant accurate results... Heres a typical curve, showing around average readings (12Ps, 16.2Nm) I now know what i need to do to gain power higher up the revs - raise the exhaust port...but this is not going to happen soon! Maybe not at all?!? Id like to for sure, but then ill end up with a non stock looking exhaust and probably need a larger carb too, so that wont be happening!
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Post by vespasco on Dec 7, 2014 20:57:56 GMT
And here's the very same curve as above... but in more detail!!
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