Hello! I have this problem with my newly tuned 455. When i kick down from drive or 2, the car shifts down but only slowly builds the revs, it actually was quicker before the engine work.
But if i floor it in 1, it just shreds the tires and goes like hell.

The setup is: Ported big valve C heads, edelbrock performer intake, edelbrock 750 carb, flowtech headers and dual 3 inch exhaust with 2 mufflers, Lunati 10420286 camshaft, dual roller timing chain and a Thunder HEI distributor with 8 mm accel cables.

It also runs very poorly at idle, adjusted the 2 screws on the front of the carb and it got better, both idle and driving it, but not at all good, still worse then before the tune.

First thought is i might have done something wrong with the ignition, so long time ago since i adjusted ignition properly. But pulled some plugs today and all of them were perfect, light brown.

A 750 carb should be enough for this setup right?

Any ideas are welcome, it shouldnt be possible that the car runs worse than it did before, haha

 

What did you set your timing to? Points or electronic ignition? When you adjust your carb, you should use a vacuum gauge and adjust to highest vacuum, or a tach to the highest rpm. With a cam I prefer a tach.

 

I belive i set it to about 12 degrees on idle with the vacuum removed and plugged. It has electronic ignition, HEI.
How do you mean to the highest rpm with tach?

 

You need to advance your timing a bit. You'll find your engine will like it. Do you have a dial back timing light?

Do you have a tach and dwell meter? With it hooked up turn your idle/air scews out about 2.5 turns each. Then turn them in 1/8 turn at a time and watch the rpm's when you get to the point where the rpm's drop, back each out 1/8 turn. They need to be pretty even on the amount of turns each.

 

Cover the throat of the carb with your fingers, does the rpms increase?

If yes, then a vacuum leak.

 

2nd on advance the timing. 12 degrees is nothing with an aftermarket cam. Spec's are out the window. With Edelbrock heads, not C's I am running 17 degrees, 3 grand rpm or so with my dial back light,@ 37. Of course aluminum heads will take a little more but I still think you need to advance some. I have tried both ways up or down with mine and it likes what it is set at now.
Edit- I am running an HEI. 20 degrees advance.

 

Do a compression check. You may have more preload than you need.
then dial in more initial timing but be careful of the total. You can still detonate even a low compression engine.

 

Have you tried less initial timing?
Just got back from the dyno and my engine liked only 8' initial at 850 RPM.

 

68442, what is your total timing?

 

oldcutlass 37' @ 4000.

I'll probably change to lighter springs after it's in the car.

 

Are you still running points? I always shoot for the 36 and let the initial fall where it may. If I want more initial I have to limit the amount of mechanical to compensate.