Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Idle problem

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dlphil10:
Thanks, I need to do some checking and verify some specs.

dlphil10:
I pulled the motor and have checked it out. The heads are around 72CC-73CC. I did find that the pistons are around 0.041" in the hole. This is not the only issue, but I would say this is one of the main issues (lower compression and poor quench)

I found a 400 block that I think would be a better choice. I see D dished pistons in my future.

Thanks for the help, I appreciate it.

Cliff Ruggles:
.041" in the holes with .040" or so head gaskets just will NOT work well.  Not only does that lower the compression nearly half a point, combustion efficiency is very poor, as you were finding out.

For our engines here, we shoot for .035" quench, and NEVER over .040" for any reason.

Finishing up a Pontiac 455 Super Duty engine in the shop this weekend, pick of deck height attached.....Cliff

dlphil10:
Thats sweet, is the deck machined down to be flush with pistons with zero deck, or are there other ways?

What head gasket do you use to get 0.035" quench?

Given my beginner status, whats the max CR you would recommend to stay on top of the tune? I would like to reuse my heads on a 400, but still run pump gas. That would put me around 10.5:1 - 10.2:1. Im going to have to find a relatively large dish I feel. Is 9.5:1 still pushing it for a beginner wanting to play it safe?

Thanks for the information, I'm trying to do this right.

429bbf:
not a pontiac guy ,i don't know what they like for compression . I'm a ford guy and they like about 10.7 or so and they run great on 91 pump gas with about 14 degree advance .maybe pontiacs just can't handle the compression (just joking )i don't want to be throw off the site. there are a lot of pontiac guys on here including the guru cliff.fwiw

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