I just reassembled my olds 455 and want to get to the bottom of a problem im having. The Previous owner had the motor rebuilt .040 over and i have no idea if the heads or block were decked/milled. I installed a comp XE256H-10 Intake .453 exhaust .456 cam which comp said would work great for my low compression motor.

So I got the motor running and it runs good/smooth but not great. It has issues that I suffered before the cam swap. It only runs good WAY advanced (2 inches advanced of the timing tab) and super lean. The holley 750dp airbleeds are adjusted only 3/4 of a turn out. I have an hei setup and the firing order is correct. It makes very little power considering its size and estimations. My concern is the pushrods may be putting to much preload on the valves and im loosing compression, hence power, hence ultimate frustration. Has anyone dealt with these issues or adjusted your valves with shims or had to swap your pushrods. Thanks for reading. I really want to correct this and get my cutlass on the road.

Also, I just rebuilt the carb because of this and am running headers.

 

[QUOTE=F15david;540807] My concern is the pushrods may be putting to much preload on the valves and im loosing compression, hence power, hence ultimate frustration. [/QUOTE]

Did you actually do a compression check? If not then do one first.

 

I'm in the middle of dealing with this now. Compression check was 125 +/- a couple lbs. all the way around, but #8 cylinder is not seating fully. I had to do a leak-down test to get any kind of real idea how much leakage I had past the valves.

TDC compression stroke, rockers torqued, about 20% leakage. Loosened the rocker nuts, leakage dropped to about 10% on that cylinder. (Cheap HF tester, I don't trust the actual numbers at all, but the change was consistent across a few tests.)

I really couldn't tell any problems from driving it; it felt strong.

 

Im going to try to shim the rockers this weekend and see if this effects the overall running and performance. I will let you guys know

 

You might have a few things stacked against you:
Milled heads'
Zero-decked block,
and Uncut valve stems.
Might be better-off going with adjustable rockers, and/or the correct length pushrods.
I've heard nothing good about shims.

 

Did you degree the cam in ?
That cam is real mild.
Going to the adjustable rockers would be an improvement.
Comp makes the adjustable rocker kit. You should make sure of the push rod length, if you use the kit.
If you try to degree the cam now, it will be a tuff job.

Gene

 

I did not degree the cam when I installed it. I should have bought the degree wheel but I did not. I did shim the rocker arms and noticed a slight difference but not enough to tell me it helped. I am going to invest in the adjustable rocker arm kit so I will see how that goes. Something is off, I'm just stuck trying to figure out what it is. Thanks for reading