I just got my current combo in the sig running a month or so ago. Well everything has stayed pretty much the same, but it acts strange. I havent tuned the carb yet, sense im waiting for headers to come in latter this week.

The car idles fine in park ~700-750 and in drive it sits at 450-500. Pulls 12-15" vacuum, but bounces with the gauge hooked up to manifold vacuum. The car drives awsome around town, and feels great when the power comes in around 2500-2600, but falls on its face once it hits 5200. This is my first performace oriented car, that wasnt factory. The power is there, and it pulls hard, then all of a sudden its like I let off the gas. I shift, and the power is right back. I checked fuel pressure and it sits at 7-8 at idle with a Mr. Gasket AFPR (speed shop was closed, so I couldnt get a holley) and it never dropes below 4.5psi, even when im running 5k in 3rd for 20+seconds.

Could the LG4 maifolds, and open Y cause it to shut down like that? The valve lash is set close to right, I dont hear any ticking. Im going to reset it when I put on the headers. I dont know exactly where timing is, as I think the balancer has sliped. I can run 42* with out vacuum advance, and it still doesnt ping. I hooked up a muffler to quite things down alot, and I had a few experienced guys ride along and they dont think the timming is too far advaned. Im going to find TDC and remark the balancer, or just get a new one. When I got the heads, they had used performance springs on them. I know they are stiffer than the stockers, thats for sure. Could it be valve float? Maybe im slightly off on lifter lash causing the valves to stay open.

Any tips on where to start looking? I wouldnt think the cam would die off that quickly or that early. According to DD2000 the cam I picked offers me a nice broad power band, with not much gained form going larger, and alot lossed down low.

 

Its the manifolds/Y-pipe combo. I have seen otherwise stock LG4/L03 305 cars pick-up 30 RWHP just by doing a full exhaust from the head ports back.

 

I see myself gaining no less then 40hp by switching to the hedman LTs and a free flowing exhaust. I just wonder if its something else that stops me dead in my tracks at that RPM. Im hoping to have them in and installed on the 12th, and then possibly hit the track later that night. I tried to do a few 0-60 runs with my Gtech and my best was a 6.75 spinning till 55. Its funny, when I just hit it from an Idle it would start to spin up around my power band, and I could only muster 7.0-7.4's.

 

yes, ditch those manifolds.
Also, how is your ignition setup? Could be a bit weak, they usually lose steam over 5000RPM unless you've upgraded it.

Float level ok?

 

Well the ignition is a 70's vacuum advance unit, with the MSD HEI upgrade, so it has a MSD module, coil, cap rotor, and I set the rev limiter to 6200. The vacuum can is a MR gasket unit I think, and I have a centrifugal advance kit on it, that brings in20-22* by 2900-3100, with 15* inital. I have some cheapo wires on it that get burned here and there every once in a while, those will soon be getting replaced. New autolite plugs, that look like they are brown on one side, including the proceline, and then clean on the other.

I need to check the float lvl. I have too much fuel pressure at idle, so I need a better regulator (stock replacement mech fuel pump) and the car stalls out when I make sharp turns, but does just fine braking.