5.0 Feels Like A Slug

[Klowded]

I have an '89 Gt with an '80 block 302 .040" over with a Comp ThumpR cam, .490/ .475 lift and 297 duration. The rockers are 1.7 rollers, the intake is a Performer RPM, Edelbrock 600 cfm carb, shorty headers, stock re-manufactured heads, MSD mechanical advance distributor, C4 trans with a 2500 stall and an 8.8 with a 4.10 gear.

The problem I have is that the RPMs climb slow and it doesn't seem to want to go over 2500. It drives fine but has no strength like I'm driving into the wind. I ran a compression test and all cylinders read from 120- 135 psi. I found a burned exhaust valve on cylinder two, replaced it and filled the cylinder with air and found no noticeable bleed off. The car seems quieter and smoother but only a slight difference in performance and still won't climb over 2500.

Any ideas?

 

[gearheadboy]

Exhaust restriction? Choke flap stuck? Timing way off? Timed like an H.O. 5.0? And should be like a standard 302? Is it a roller?

 

[Klowded]

Exhaust restriction? Choke flap stuck? Timing way off? Timed like an H.O. 5.0? And should be like a standard 302? Is it a roller?

The choke is wide open, the cam is a flat tappet with 351w firing order, the exhaust is 2 1/2 without cats. I had the timing set at 10 degrees and moved it to 15 and I didn't notice any change. My plugs all look pretty even and they are a medium brown color.

 

[gearheadboy]

1.7 rockers seem a bit steep for stock style valve springs for one, anyone check them for coil bind? Not sure of your distributor set up but when I hear the symptoms I think things like : timing, cam timing and ignition timing, or fuel starvation but your plugs look good. Do you have electronic advance? Are you setting it with the spout connector unhooked? Balancer outside ring move causing wrong reading? Can you do a total timing at like 2500 rpm to about 30 degrees? SO many things. Not to mention do you have another carb to swap out to see if it is interal carb? Was that valve burned or bent? Or bent which after driving a bit caused it to burn?

 

[Klowded]

The springs are a bee hive type the was listed to go with the cam. The valve was burned. I didn't really see anything wrong with it, like it just quit sealing. The distributor has mechanical advance and is using the smallest bushing and the lightest springs. The balancer seems fine. I put another carb on it a 1405 from a 1406 just has .100 jets instead of .098 primary and didn't see any difference.

 

[gearheadboy]

Keep jacking the timing up and see if you can make it ping (rattle) when you accelerate. If thr balancer ring is moved it will make it run better as you advance it and it will look like you have like 40 degrees of timing. Fuel filter? Pump pressure? Carb you need about 7-9lbs. Has it ever run good? Adjustable valves? Too tight?

 

[Klowded]

I just put a filter on a few days ago. It runs 5.5 psi. At that psi last summer I put two lifters in it, either both on the # 2 cylinder or one one #1 and one on#2 I can't remember and I put a "C" ratio shift servo in the C4 and it ran like a race car. I never made a carb or timing adjustment, even reused the same carb gaskets. I was able to lift the back of the intake and slide it out from under the distributor so it was never moved. It was giving tire chirping shifts out of first and second. After a 20 minute drive I had no oil pressure , it dropped to 20 psi. I changed the pump and had to change the intake gasket again and it went right back to the way it was only without the lifter tap. I changed the intake gasket again thinking it couldn't have been the pump considering it reads 62 psi and changed it again with the recent valve swap and I can't come up with an answer. I'm afraid to take it to a shop because I don't have much money and its modified and kind of looks like a nascar inside. The rockers are a pedestal type with shims. They seem to be right the best I can tell.