Maximun thickness gasket case/cylinder...for adjust CR.

[dan67]

what is maximum thickness gasket case/cylinder...for adjust CR?

[Henry Schmidt]

We stock .25mm ,.50mm and 1.0mm base gaskets for most cylinder sizes.
It is very easy to have almost any size made.
We have used cylinder shims as large as 2.80mm for a special long rod engine we built.

[304065]

Dan,

Consider machining the pistons if the compression ratio is too high. Adding cylinder base gaskets is OK but if you go beyond about 1,5mm deck height you could be inviting detonation.

Why do you wish to reduce compression?

[dan67]

all right, good info, its my "doubts Amleticous" for my project engine: 66x92mm "RSR"

(2.0 -> 2.5 Ss?)

with 66x92 JE the CR exceeds 11-11,5 (cit: porsche performance book bruce anderson) I search maximun 10.5 or the best 10.3....I have to buy the P&C 92mm..I do not know what!))
(QSC i suppose..mahle its expensive...)

[304065]

Dan,

What cylinder head volume? This is very important information in determining compression ratio. Early 2,0 heads are around 72cc, 2,2-2,7 heads are 68CC. Using the later heads results in higher compression.

[dan67]

yes, of course, i have 2.7 S heads 68 cc...rsr2.8 (i think) 76cc...this ist the problems)))

[304065]

If you are using JE pistons, why not use a nice shallow dome of 27.5cc? 92x66 with 68cc heads with a 1.0mm deck height gives you 10,3:1 CR. Slightly more combustion chamber volume will result from the twin-plug modification which is a must for this engine. At 69cc you would end up at 10,1:1 CR.

[dan67]

thanks John! perfect! is what I try! this set of JE where can I find? (on JE site the standard Porsche pistons start 95mm ) diameter 92 are custom order?
thanks

[dan67]

opps not corret! I wrong
261666 2.7 92mm 70.4 127.8 34mm 10.5 25.5 418 2mm 866-2500-15-93C JG1006-3622
this kit (261666) its good? for my project engine...

[dan67]

but...Rod Length 127,8 (2.4) i have 2.2 rods (130) ...minimal difference?

[304065]

Dan, the compression height of those pistons you list is wrong-- it is a MAJOR difference as the geometry of the engine must be maintained.

However, you can get custom pistons from JE with about any compression ratio you want.

[dan67]

perfect! thanks John!

[Henry Schmidt]

Piston dome configuration as it relates to cylinder wall and combustion chamber has more to do with detonation with larger deck measurements. To make a blanket statement " anything over .060" is too much deck and it will promote detonation" is way to big a leap for a rational thinker. Large deck measurements by them selves rarely cause detonation.
We have produced engine with substantially more deck than .060" and have experienced flawless performance. Would huge deck heights be our first choice? generally not.
Remember that combustion chamber, piston dome, valve size and location will all play into the detonation equation. Blankets statements are for those not willing to reason through the process.