My t/a was previously backfiring due to too far retarded timing. But it would rip on the top end. Pull hard up in the high 5K's, which it never did before I swapped valve springs (I repaired a broken valve at the same time and never adjusted the timing after reassembling it, been at school and visiting home only once a month or so, have had no time), so I figured it was the valve springs. So I readjust the timing on the road with the car, and the car has lost some top end, like a good deal. The car feels ready for a shift at 5000 rpm instead of the 56-5700 before I touched the timing. Will adjusting the timing have this much effect. I know it moves peak torque, but it shouldnt cut what was on the top end, should it? The car was faster when it would backfire every 5th time Id floor it. The heads are 487 casting, the cam is 218/224 @.050 w/ .462/.469 lift. Im wondering if my exhaust is restricting it, but it pulled before at high revs. Ugh, Im getting so aggravated at my car.

 

Computer controlled carb and distributor? What was the base timing before? What is it now?

When setting the base timing did you disconnect the 4-wire timing plug on the back of the cc-HEI distributor? What chip is in the ECM?

 

It is a CCC, and the base timing before was 10 degrees, but it had no top end then, which I attributed a poor intake manifold and 31 year old valve springs. What is the timing now, I dont know, Im stupid, I moved the distributor while driving. The timing was so far retarded that the car would cease to run when I disconnected the 4 wire plug. The chip is stock, as is the ignition module, but I have an accell super coil.

 

If the timing is over-advanced you can actually lose top end. Bottom end will feel ballsy but will drop off in the higher RPMs. This is especially true if the car was an original LG-4 car. Their chips had lousy timing advance in the lower RPMs but still advanced pretty good in the higher RPMs. So you bump up the timing and the bottom end feels good but the top end starts to get flat.

If it's an original LG-4 car/ECM/chip then set the timing at 6* BTDC for starters. If an original L-69 car try 10* initial. This is with the timing wire disconnected, obviously.

Setting timing by ear is not something that will yield good results. I've been at it for almost 20 years and I still can't get it very close to "right" just going by ear at idle speed.