[Dragncar]

Can some of you give ballpark CR with 63 cc E heads, 20cc dish pistons and a 4.25 crank. 4.35 bore. Its what I have but need to find out right rod. Believe CH is 1.31.
Thanks for any info.
kicking around ideas for build. I can buy whatever piston I need. But have these new Ross pistons with not much into them. 6 .875 rods and 6.8 billet rods.

[johnta1]

The CR would be around 12.1?

The rods you listed would be too tall for that piston pin height on the piston?
(depending on block deck height, etc)

I show about 6.785" rod needed?
The 6.8" could be made to work OK.

Rod length Calc



Try this:

Piston Pin Height Calc

[Stan Weiss]

Originally Posted by Dragncar

Can some of you give ballpark CR with 63 cc E heads, 20cc dish pistons and a 4.25 crank. 4.35 bore. Its what I have but need to find out right rod. Believe CH is 1.31.
Thanks for any info.
kicking around ideas for build. I can buy whatever piston I need. But have these new Ross pistons with not much into them. 6 .875 rods and 6.8 billet rods.

What head gasket thickness? Zero deck on the pistons?

Stan

[Tom Vaught]

Butlers very common Ross piston (around that Compression Height) is his 1.295" compression height Ross stuff. He has been offering that deal for many years in a BB Chebby rod/ pin size. The 1.31 CH is not a common piston design for a Pontiac.

4.25" Crank could use a 6.7" rod too.

If you cut the block to 10.235" (.005" off deck to square up deck).
use the Butler 1.295" CH Ross Piston.
use the 4.25" stroke crank.
Your rod length is exactly right for the 6.8" long Chebby rod that fits the 4.25" crankshaft.

This deal is ALL off the shelf Butler Parts.

Tom V.

ps using Wallace's compression ratio calculator
http://www.wallaceracing.com/cr_test2.php

you get about 11.73 to 1 compression ratio with the numbers I used.

[Dragncar]

Correction, CH is actually 1.305 . How much that matters ? Guy I bought them from (Milepost) said they were for a 4.375 crank. with the oddball rod available from Eagle at the time.
Not sure I want to trust the Eagle rod to the engine I have been trying to build over the years. If I can not use my 6.875 billets, 6.8 billets or buy a off the shelf 6.7 billet I will just buy a new piston.
The heads will be able to support far more HP than I want to run right now. Good thing is I will be able to up cam, up carb to get stupid power as I need it. When it stops scaring me I just give it more Cam or carb til I am scared again when the lights goes green. Or last yellow if you are a racer. Proven E heads around these parts. Its good to get thrown back in the seat where its hard to keep your right foot on the floor. The list of things that are better than that, well, there is a list but its not a long one.

[johnta1]

Use the rod length calculator I posted.

Depends on the block deck height.

If it is around 10.23" you could use the 6.8" rod with your other specs.

Best would be to measure the specs of the block and crank for accuracy.

[Tom Vaught]

Originally Posted by johnta1

Use the rod length calculator I posted.

Depends on the block deck height.

If it is around 10.23" you could use the 6.8" rod with your other specs.

Best would be to measure the specs of the block and crank for accuracy.

X2 Until you measure some stuff and get real numbers, you are just "Spinning Your Wheels''.

Tom V.

[Dragncar]

It looks like the best bet is to just get new custom pistons for my exact needs. 12-1 is too high for 91 CA gas anyway. I know some get away with it where you can get 93 octane. That way I can get my CR of 11-1, 11.5-1 with the 63cc E heads and run the 6.875 rods. They are Crowers and would rather run them vs china billets.
Make someone a deal, brand new Ross 4.35, 20cc dish pistons, 650$. But you get the Total Seal file fit rings, tool steel pins and spiro locks. The pistons alone went for over 900$ when bought.