I'll take your points and happily pocket them under my user name

Yeah, 9:1 C.R. with the forged pistons.

10 Browny points to Capt. Tav!

IIRC Accralite 1341 pistons give a CR of 8.5:1 with metal head gasket.

http://www.accralite.com/accralite/Search/Pistons.asp has the dimensions but no mention of comp ratio...hmmm someone will know for 100%

Yeah, 9:1 C.R. with the forged pistons.

10 Browny points to Capt. Tav!

IIRC Accralite 1341 pistons give a CR of 8.5:1 with metal head gasket.

More like 9.3:1 with the thinner metal gasket, i.e. a bit on the high side for forced induction and an 8v cylinder head.

Wossner pistons retain the standard compression ratio

wossner i think are £4-500 a set

these any good? thinking of getting some when i strip mine down end of year (or someone else will - i'm too bloody lazy!)

Some would say that Wossner pistons are the best available in that price bracket. G-Werks use them in their G60 engine rebuilds.

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This seems a little confusing.. does anyone actually know for CERTAIN what the compression ratio for the 77mm 1341cc Accralites are?

Ahh excuse my stupidity .... i was having a comlpetely thick moment whilst holding on to the wrong end of the stick. The compression ratio of the Accralites DO up the CR to 9.0:1 - by fitting a thick metal head gasket you can bring this figure down a little... My aplogies.

The metal head gasket isn't thick...it's thinner, so the higher CR gets even higher...

Ahh excuse my stupidity .... i was having a comlpetely thick moment whilst holding on to the wrong end of the stick. The compression ratio of the Accralites DO up the CR to 9.0:1 - by fitting a thick metal head gasket you can bring this figure down a little... My aplogies.

the metal head gasket (the usual ones for mk4 polo) is thinner

Will i ever get this car right??????

I thought there was a thick metal gasket available to bring down the CR.. no?

It's quite simple Accralite 77mm pistons to give 1341cc are 9:1 CR - i.e. high.

The metal HG people use is thinner than a stock one, so ups the CR a little more. PSD used to quote an extra 0.3 CR with it fitted (giving 9.3:1 on a 1341cc rebuild) - I've never bothered to do the maths myself though.

A company called Ferriday engineering will make up metal spacer plates or custom HGs if you need something thicker.

It's quite simple Accralite 77mm pistons to give 1341cc are 9:1 CR - i.e. high.

The metal HG people use is thinner than a stock one, so ups the CR a little more. PSD used to quote an extra 0.3 CR with it fitted (giving 9.3:1 on a 1341cc rebuild) - I've never bothered to do the maths myself though.

A company called Ferriday engineering will make up metal spacer plates or custom HGs if you need something thicker.

Thanks Andy...

I was under the impression that there was a thicker metal gasket widely used with the 77mm accralites (other than the mk4 version) but i must have been mistaken...

This throws my plans out the window..

I was hoping for a lower CR than 9.3:1 - gonna have to have a re-think big time - i'll have a look at Ferriday sounds like a possible plan!

What do you recon is the best route to go down for reliabliity? A spacer plate?

cheers again...

Jez

If you've not bought pistons yet, buy some Wossners @ 8:1 CR. I regret not having done that.

Would the 77mm Wossners @ 8:1CR be a good choice for a Turbo PY, I'm not sure which ones to get and are the Accralites worth the extra?

This is my problem - i have and have fitted Accralties to my bottom end already!!

Had i have known this from the ourset then i would have saved the extra pennies and gone with the wossners!!

What pistons are you running then andy? And how?

andy's is a 1341 accralite with a k03 if i remember correctly.

the 'stroked' g40 accralites - are these actually 1w pistons?

Would the 77mm Wossners @ 8:1CR be a good choice for a Turbo PY, I'm not sure which ones to get and are the Accralites worth the extra?

Personaly I would go for the 9:1 ones, a bit more responsive off boost, but a tad more difficult to tune/map, as it is more sensitive to how well porting is performed and a bit more picky when it comes to cam choice. I'll be fitting accralites in my 1W big valve 38/33mm K03 engine, with cutouts for the bigger valves obviously

Mathers recomends something in the middle, eg a a piston with 8,5:1. They are £675 from Jabba, but if you can do a bit of research yourself, you can find custom JE's on ebay.com for 600 USD

http://cgi.ebay.com/ebaymotors/JE-CUSTOM-P...37062QQtcZphoto

Need to fill out this form though

Edited 19 September, 200817 yr by G40NUT

With 9:1 CR and a supposedly suited cam, my car will detonate BEFORE it reaches MBT. Chassis dyno proven - mapping doesn't really come into it there.

Solution: lower the compression, use methanol/water injection, or fit a significantly more efficient (i.e. 16v) cylinder head.

Hence I think that 8.5:1 is probably as high as I'd go in an ideal world with an 8v Polo cylinderhead. 9:1 works, but it's not ideal.

What would be the best pistons to use with an eaton conversion then?

All this CR talk is way above my head!

(sorry to hijack)

All this CR talk is way above my head!

Get onto google/wikipedia and type in compression ratio and you might get an idea...

Thanks for your in-put guys.. Having thought about it i think i would like to reduce the CR to 8.5:1 for peace of mind. I think I'm going to look into getting a de-comp plate made up by Ferriday as you mentioned Andy.

Is/has anyone used one of these plates on a G before?