Anyone here used CP 9:1 pistons before?

[EVO-00X]

Hi guys, doing a rebuild for someone and the question of forged CP pistons was brought up and I have never used them before let alone know anyone who runs them in a street car. I've noticed their 4G63 variant is a 9.0:1 comp ratio and a little too high for my liking as it would make tuning a bit more difficult with higher boost levels, but with the higher comp ratio it would be better off boost. I'd rather stick with 8.5:1 JE pistons as the motor will see up to 28psi boost I expect but wanting to hear from any CP boys out there first I am told that the rings they supply with them suck and they will need custom rings to suit the pistons? cheers

 

[DOUGMO]

i have them rob, have not run the car yet though.

my static comp is about 8.3 with a multi layer gasket (about 1.2mm)

the rings are very fine and a bit fiddly to put on but seem fine.

a mate runs the same type of piston iin his cosworth escort and
they have handled massive abuse and he also used the supplied rings

 

[steve]

What cams are you going to use? Don't make your decision on pistons based on the static compression ratio, instead work out the dynamic compression ratio (the general rule is to aim for about 7.5 - 8:1 DCR) and choose your piston/cam combo based on that.

I run 9.3:1 static CR (wiseco 9:1 pistons, thin copper headgasket) and stuff 22psi down her throat on pump fuel day in, day out. Add good fuel, and there's no reason I won't be able to jam 30psi into it. The difference between 9.3:1 and the old 7.8:1 pistons I had previously is like night and day.

 

[DOUGMO]

i have bc 272s

we cc'd the engine to come up with that comp ratio

 

[steve]

Yup, but the static compression ratio and the dynamic compression ratio are two totally different things.

Keep in mind that while the inlet cam is still open and the piston is rising, compression isn't occurring. Dynamic CR is calculated using the volume inside the cylinder once the intake valve closes after bottom dead centre. This is what will dictate how much boost you can run.

Two identical engines with slightly different cam profiles will give different DCR ratios. Take the 6-bolt 4G63 for example - while they were all 7.8:1 static compression ratio, there was a few different cams for the motor, with the inlet valve closing anywhere from 43 - 51 ABDC. This varies the dynamic compression ratio from between ~7.1 - ~6.8 depending on the profile.

 

[EVO-00X]

Yeah I'm talking static CR. The VR4 motor has HKS 272's and a GT35R and will see some C16 and high boost on the strip. Obviously it will drop back to 98 octane for most of its life for street use so sort of wanting to know if 23-24psi boost levels are OK with the 9.0CR on pump (pretty sure the headgasket is a Cometic 0.51). What thickness gasket are you using Steve? So anyone wanna endorse the CP? :lol:

 

[ENGINR]

I'm using them Rob, with 272/272 cams. Absolutely no complaints with them sofar. They have a shorter skirt than the Wiesco pistons I compared them to and actually felt a bit lighter too (but this was just me holding one of each and comparing so not super accurate...)

Great throttle response off boost with a 9:1 too - very perky.

 

[steve]

Rob, I've got a 1mm (copper, doesn't compress) headgasket .. and the deck height isn't standard either.

I don't have any direct experience with the CPs, but I'd avoid wisecos if I were you - we were very careful with the tolerances on my motor, but they're still noisy as all fuck on startup.

 

[The Godfather]

Rob, I've got a 1mm (copper, doesn't compress) headgasket .. and the deck height isn't standard either.

I don't have any direct experience with the CPs, but I'd avoid wisecos if I were you - we were very careful with the tolerances on my motor, but they're still noisy as all fuck on startup.

what didnt you like about the wisecos?

 

[steve]

but they're still noisy as all fuck on startup.

This part mate.

Actually, I had wisecos in my old VL, and in the 4G before this one and they were quiet, I guess I just got unlucky this time around. The piston slap is horrendous until it's got a bit of temp into it.

 

[shadow]

I got recommended on the Wiseco Pistons as a mate built a stroker and said he could barely hear them.

 

[EVO-00X]

Just did some more reading up on Arias, Ross, CP, JE, Wiseco, Mahle, and Venolia pistons and fark me, 2618 alloy/4032 alloy; high silicate/low silicate; tight bore clearances/looser clearances; expansion rates; fuel and oil emissions; blowby; you name it. What I have come to believe in years gone by has changed. Each brand has its advantages and disadvantages as you can have a low silicate with tight bore clearances, then a low silicate with loose clearances and the same for high silicate pistons as well with both characteristics.

As for finding a good medium? well.. thats what I'd like to know :lol: Might do a bit more digging in regard to the CP's and suss out the Venolia's as well .

 

[steve]

I have heard nothing but good things about Venolias - but there's more from a strength/weight/construction point of view than how quiet they are.

I get next to no blow by and the pistons have shut up by the time the water temp has reached the bottom line on the temp guage (I don't drive the car before that anyway), but those first few minutes are still annoying as hell :lol:

 

[FRANK-E]

I have heard nothing but good things about Venolias

same here

 

[EVO-00X]

Jackson Auto Machine have designed a Venolia piston and ring set for 4G63's but at 7.5 CR its more suited to somebody running big boost on the strip :lol: Price on here is installed.... https://www.jacksonautomachine.com/html/shopping/list_section.cfm?sectionId=29 .

And price of the Venolia pistons and rings alone as per JAM's specs is pretty damn good too: http://www.dsmtuners.com/parts/prod...=bd0626712ac1dd8cf18fea38394ae5f9vendor_id=34

 

[3zercrowd]

PAGING Josh_Tsv :lol: , Josh to the Forum please. Josh to the Forum.......