TOO much compression, warning: long & boring story, i've got a couple options, what have you done? Options

[orange914]

looks like i've added 1 too many cans of compression to my 2056 build...opps...
heres the deal. we're building a 2056 for my sons 1.7 that dropped a seat... this is kennys car and he's covering cost so we're doing it on a bit of a budget. got a good deal (from a great 914r here on the 914world) for the 2.0 short block, spent money (well worth it) on 2.0 heads, located ALOT of misc. needed like tin, intake conversion parts etc...
problem is the heads are 55cc and i will need a not recomendedly (is that a word?) thick set of cylinder shims to knock the k.b. flat top 96mm pistons compression down to 8.0-8.5:1. (around 0.1 thickness)
if we dont shim (or partially shim) we have a few recomended fixes and they are:
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A valve pocket .075 deep intake and .050 deep exhaust for 42X36 valves would give you the 3ccs you are looking for.
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Or we cut toss a hemi-cut at the chambers.... As long as the CR stays up the hemi cut should help with tuning.
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has anyone done this on 96mm k.b. flat tops or on the chambers, with what results +-?

mike

[Joe Ricard]

The valve pocket thing would be the best choice
IF THE PISTON TOP WILL SUPPORT IT

What kind of valve to piston clearance do you have?

What's the matter with higher compression? 9.5:1 is perfectly fine

My motor will bump out to 10.1:1 as i figure it right now.

[orange914]

The valve pocket thing would be the best choice
IF THE PISTON TOP WILL SUPPORT IT

What kind of valve to piston clearance do you have?

What's the matter with higher compression? 9.5:1 is perfectly fine

My motor will bump out to 10.1:1 as i figure it right now.

the cam is a raby9550 and i will be using the d-jet. jake recomends no more than 8.5:1. seeing the r&d he has done who am i to say otherwise (IMG:style_emoticons/default/slap.gif) i wouldnt mind higher compression but not if it compramises this build, besides ca. gas and what we will be using this for i'd rather build in engine life over additional h.p.
one thing that can be compramised if i lower c.r. by shimming only is quench. i'm not even exactly sure of what that means... more research i guess, this build has been alot of fun and a learning process too!

[jd74914]

There isn't anything wrong with compression, but IIRC he is building a 2056 with D-Jet and a 9550 cam, its can't handle that CR.

[Demick]

What's wrong with shimming? That's the standard method of setting C.R. My 2056 with flat top KB's also had 55cc heads IIRC. I shimmed with .030 or .035" shims to bring the CR down to about 8.25:1

Demick

[Jake Raby]

You are walking the high wire at 8.5:1 with the 9550 and D jet. D jet has a very hard time supporting the higher efficiency capability of more CR and camshaft and at over 8.3:1 things start to change in my experience with this cam and D jet.

Give up on trying to make it perfect- not happening and the more you try the more sleep you'll lose and the more you'll be discouraged.

I say build the damn thing straight up as it is with a .060 deck and run it, just watch the temps initially.

You can't be afraid of the effects of engine modifications or your project will be doomed from day one.

At worst you'd have to pop the heads off and have Len use our Hemi cut that is used when these types of issues pop up from time to time? How will it effect the engine? Well it'll get the CR down and won't effect the flame front nearly as bad as super tall deck or valve reliefs that can shroud the intake charge.
Build it. Run it.

[orange914]

You are walking the high wire at 8.5:1 with the 9550 and D jet. D jet has a very hard time supporting the higher efficiency capability of more CR and camshaft and at over 8.3:1 things start to change in my experience with this cam and D jet.

8.3 it is, just attempting to see what'll get it there properly. i've got a wtb ad out looking for 96mm dished pistons- if they are out there-'

Give up on trying to make it perfect- not happening and the more you try the more sleep you'll lose and the more you'll be discouraged.

not shooting for perfection just a good build, got permission from the wife to build it, so i gotta do it right or i'll never get the opertunity again (IMG:style_emoticons/default/happy11.gif) besides i dont discourage easy

I say build the damn thing straight up as it is with a .060 deck and run it, just watch the temps initially.
At worst you'd have to pop the heads off and have Len use our Hemi cut that is used when these types of issues pop up from time to time? How will it effect the engine? Well it'll get the CR down and won't effect the flame front nearly as bad as super tall deck or valve reliefs that can shroud the intake charge.
Build it. Run it.

i think the hemi cut is a good idea to minimize shim/quench issues? how long does it take to get you custom shims after order is received?

[Jake Raby]

We have most all shims in stock, the odd sizes take 10 days to make up.