TheSamba.com :: View topic

Sun Jul 27, 2025 8:38 am

Alright motor guys, the time has finally come to actually start on my turbo project. Keep in mind that this motor was originally assembled by a shop. This is the first time I've been into it.

I pulled it down to short block status to do the maths for the compression ratio. My deck height is only .020-.020". The combustion chamber is 55ccs and there was a. 060 copper head gasket in place, netting me a compression ratio of 9.2-1. A little high for a turbo street car.

As I can't put the cylinder out any further, do dished pistons make any sense?

Be well

Sun Jul 27, 2025 10:51 am

( assuming were talking about the 2276 in your signature) youve got .080 deck then, the guys are going to tell you to fix that for sure.
You could dish the pistons, or open up the combustion chambers, or both. Depends on what CR your after but if your going to tighten up the deck and want the CR below 9:1 your going to have to find a fair amount of cc’s somewhere.
To run .050 deck and 8.5:1 CR youll need 67cc chambers.
Or keeping your .080 deck you could run 62cc chambers to get 8.5:1.
All depends on what you want, what you want to spend or how scared you arent to go hogging out some heads and dishing pistons, and how much boost you plan to run.
Most i ever pulled out of a set of heads was right around 10cc, possibly a little over, (i dont remember the exact number now). But they are a completely dished chamber like you see on some boosted LS’s.
If your only going to run 7 - 8lbs of boost then id say to just run your 9+ CR.

Sun Jul 27, 2025 12:53 pm

Check. I understand that I have to set the deck height closer to 40-45 thou. I REALLY don't want to hog out my heads or semi-hemi them either. Ultimately it comes to dished pistons for me. Are they suitable for a street car and less than 15 pounds of boost?

Sun Jul 27, 2025 2:02 pm

You don’t HAVE to set deck at 40 - 45, obviously, youve been running at .080 and plenty of ppl have run with more than that.

And you’re not going to get 12cc out of dished pistons.

Sun Jul 27, 2025 2:03 pm

Here is a 4cc dished piston . Gonna have to be a bigger cut
If you want more

Sun Jul 27, 2025 2:23 pm

BFB wrote: You don’t HAVE to set deck at 40 - 45, obviously, youve been running at .080 and plenty of ppl have run with more than that.

And you’re not going to get 12cc out of dished pistons.

Here in the classifieds, Gene Berg has offers a service to cut 15ccs out of a 94mm piston. Aren't they suitable for turbo use at that point?

Sun Jul 27, 2025 2:25 pm

Call Dan Lawson at cevw
Available in 040", .060", .090" and .125" thicknesses.
Done

Sun Jul 27, 2025 2:56 pm

Do you really want to be making the piston crown thinner on a turbo build? How about a shorter stroke crank? Suddenly everything is happier. Run some numbers on CB's calculators and see what stroke allows your current pistons to be suitable.

Sun Jul 27, 2025 4:46 pm

It’s not like piston manufacturers don’t have piston blanks available that are forged with enough material for a reverse dome or dish. Contact Icon or whoever and get whatever dish volume you need, done.

I have custom Ross forgings in my Pontiac V8 with a 27cc dish, what’s the big deal? Of course you don’t take a lightweight flat top forging and cut a big dish in it, you start with the right forging blank designed for a dish.

Sun Jul 27, 2025 4:54 pm

This is the calculator I use . Really great and can enter any value even with a decimal point .

https://www.rbracing-rsr.com/compstaticcalc.html
Turbo motor won’t care if it’s .040 or .100 deck in my experience

Mon Jul 28, 2025 11:28 am

How much boost are you planning on running? Is this for the 2276 with a w125 cam? I am building a turbocharged 2332 with a w125 for my daily driver and will be setting compression at 9.2:1. Mine will be a blow through system with intercooler, water/meth injection, and a J&S Safeguard knock sensor system. The plan is pump gas, 20psi boost. I was doing it with a much smaller cam at 20psi and 8.4:1 (242 duration @ 50) and it ran great.
Don't forget- that cam has alot of top end and the turbo will just push that up.
When I ran a w120 in my old 2276 it would want to pull past 7800rpm with 16psi boost.

Mon Jul 28, 2025 11:45 am

Hi Daniel,
Yes. It's going on my 2276. I have a forged rotating assembly and will be sucking through a DCOE 45. I hope to see 15 pounds of boost on occasion. Nothing more high tech than the MSD to control timing and an electronic boost controller.

Wish me luck!

Tue Jul 29, 2025 4:48 am

slayer61 wrote: As I can't put the cylinder out any further,
Explain please. Conventional wisdom is to set the deck with shims at the bottom of the cylinder and not with copper rings in the head.

Tue Jul 29, 2025 6:17 am

oprn wrote: slayer61 wrote: As I can't put the cylinder out any further,
Explain please. Conventional wisdom is to set the deck with shims at the bottom of the cylinder and not with copper rings in the head.

Upon disassembly I found that one of the studs wasn't fully engaged with the head nuts. I found that I could back that stud out a couple of turns. Problem solved and shims and gaskets are on order

Tue Jul 29, 2025 6:22 am

oprn wrote: slayer61 wrote: As I can't put the cylinder out any further,
Explain please. Conventional wisdom is to set the deck with shims at the bottom of the cylinder and not with copper rings in the head.

aside from whatever slayer is talking about, you can set the deck "conventionally" with shims at the bottom of the cylinder , or set deck with the copper head rings. say if your piston to top of cylinder is 0 and you use a .040 copper head ring then your deck would be .040.
the rings just technically extend the cylinder.

Tue Jul 29, 2025 8:21 am

The path of least resistance would be heads with the correct cc for what you want to do..
Seeing how much you can lower the compression and then building the turbo system to suit it, is sorta bass ackwards. Usually you just get what you get, not what you wanted.. not to say I haven’t done the same thing. But I usually wish I had just done the obvious thing to start

Tue Jul 29, 2025 8:40 am

esde wrote: The path of least resistance would be heads with the correct cc for what you want to do..
Seeing how much you can lower the compression and then building the turbo system to suit it, is sorta bass ackwards. Usually you just get what you get, not what you wanted.. not to say I haven’t done the same thing. But I usually wish I had just done the obvious thing to start

Yes Sir. I get that. I'm trying not to spend the additional $$$ on new heads. I'd love to have some Tim's heads with big chambers, but I'm trying to work with what I already have, my empi gtv stage II heads and welded, ported manifolds.
Maybe next time.

Wed Jul 30, 2025 10:37 am

slayer61 wrote: oprn wrote: slayer61 wrote: As I can't put the cylinder out any further,
Explain please. Conventional wisdom is to set the deck with shims at the bottom of the cylinder and not with copper rings in the head.

Upon disassembly I found that one of the studs wasn't fully engaged with the head nuts. I found that I could back that stud out a couple of turns. Problem solved and shims and gaskets are on order
For what it's worth, you can get longer studs that allow strokers to get full engagement.

Wed Jul 30, 2025 1:51 pm

What about going to thick wall 92 P&C?

Wed Jul 30, 2025 3:35 pm

Michaellatini wrote: What about going to thick wall 92 P&C?

NO. 8)