Cosworth piston issue... photos inside
That 8.8 may be with the factory head. If the Cossie head has 3ml larger chambers, that will lower it a little.
FWIW, increasing compression reduces emissions, not the other way around.
FWIW, increasing compression reduces emissions, not the other way around.
sorry for not reading all of the posts, nor for doing the math, but a common mistake is to not account for the original 'volume' when calculating CR. Basically you have to add 1 after doing the math to account for the 'starting' volume of air. Again, without doing any math on the measurements, could that have been forgotten?
added: just did quick math and 8.14 appears to be what it is.
added: just did quick math and 8.14 appears to be what it is.
Last edited by 9sec9; Oct 23, 2008 at 10:28 AM.
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From: Evoland
I bought a repair gasket set for EVO 9 directly from Japan.
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From: Evoland
In your case if you want additional compression ratio - perhaps you can conisder to deck the head and the block slightly
I am not sure about the specs on the cosworth Evo pistons, but on the Subaru side they are really very good pistons
Low compression is not that big a deal IMHO with turbo cars although something closer to 9 / 1 may be better
AL
I am not sure about the specs on the cosworth Evo pistons, but on the Subaru side they are really very good pistons
Low compression is not that big a deal IMHO with turbo cars although something closer to 9 / 1 may be better
AL
8.1:1 CR is way to low I need to find something else to do.
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From: Evoland
Cosworth makes only one compression ratio piston, according to their catalog. It is 8.8:1 compression ratio.
https://mzmperformance.com/CW-PA2689.htm as an example.
They also make the same piston, but for a 2.4 stroker crank, so make sure you got the right part number.
As long as everything was correctly installed and with the right parts, you have what you have, and it's like Cosworth intended.
I'd not consider decking the block. If you need to change compression ratio, it should be done by changing the pistons, if that's a huge concern to you.
Decking the block changes the distance between the crank centerline and the cams, which alters the timing.
https://mzmperformance.com/CW-PA2689.htm as an example.
They also make the same piston, but for a 2.4 stroker crank, so make sure you got the right part number.
As long as everything was correctly installed and with the right parts, you have what you have, and it's like Cosworth intended.
I'd not consider decking the block. If you need to change compression ratio, it should be done by changing the pistons, if that's a huge concern to you.
Decking the block changes the distance between the crank centerline and the cams, which alters the timing.
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From: Evoland
sorry for not reading all of the posts, nor for doing the math, but a common mistake is to not account for the original 'volume' when calculating CR. Basically you have to add 1 after doing the math to account for the 'starting' volume of air. Again, without doing any math on the measurements, could that have been forgotten?
added: just did quick math and 8.14 appears to be what it is.
added: just did quick math and 8.14 appears to be what it is.
V = 85mm Bore x 88mm Stroke = 499cc
C = Combustion Chamber = 48cc
P = Piston Dish + Deck Relief= 9.5cc
G = 1.2mm Gasket for 85mm Bore = 6.8cc
SCR = (V+C+P+G) / (C+P+G)
SCR = 8.76:1
1. how far down is the piston from the deck? it looks ~1.0 mm
from a power perspective, that isnt ideal.
deck the block & time the cams accordingly.
measure the piston pin height & rod c/c to figure out where the discrepency is, relative to the oem pieces.
i would feel safe running a piston to head clearance of 0.74mm if spinning to ~9k or so.
GL
from a power perspective, that isnt ideal.
deck the block & time the cams accordingly.
measure the piston pin height & rod c/c to figure out where the discrepency is, relative to the oem pieces.
i would feel safe running a piston to head clearance of 0.74mm if spinning to ~9k or so.
GL
I think another reason the US evo gets a thicker headgasket is because the octane level in the US is generally lower than Europe.
Mitsubishi lowers the compression ratio in their latest model years. Have a look at table 2:
http://www.mitsubishi-motors.com/cor...007/19e_13.pdf
Perhaps this is why the US evo 8 had a 1.3mm headgasket and the US ix has a 1.5mm.
Mitsubishi lowers the compression ratio in their latest model years. Have a look at table 2:
http://www.mitsubishi-motors.com/cor...007/19e_13.pdf
Perhaps this is why the US evo 8 had a 1.3mm headgasket and the US ix has a 1.5mm.
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From: Evoland
SCR=8.05:1
Something does not sound right to me. You are telling me that the piston dish is 6.5cc. Ok.
The measurement of the deck height looks like 1.3mm. If that is true, that works out to be 7.4cc, but you've measured 9.5cc (see 9sec9's comment) With the engine running, it should be 7.4cc = 8.27:1 SCR
Are you sure your deck height measurement is accurate?
Are you sure the piston moves no higher in the bore?
Are you sure your 9.5cc figure is correct? How did you isolate the piston dish from the rest of the deck space?
I have not ruled out the possibility that there may be some inaccuracies that are clouding the real figure.
And of course, a 1.2mm gasket will compress somewhat to a reduced height when torqued.
The measurement of the deck height looks like 1.3mm. If that is true, that works out to be 7.4cc, but you've measured 9.5cc (see 9sec9's comment) With the engine running, it should be 7.4cc = 8.27:1 SCR
Are you sure your deck height measurement is accurate?
Are you sure the piston moves no higher in the bore?
Are you sure your 9.5cc figure is correct? How did you isolate the piston dish from the rest of the deck space?
I have not ruled out the possibility that there may be some inaccuracies that are clouding the real figure.
And of course, a 1.2mm gasket will compress somewhat to a reduced height when torqued.
Last edited by Ted B; Oct 23, 2008 at 11:16 AM.