Hello everybody, I tried some searching before making this post but couldn’t seem to find somebody that had a similar set up to me. I have an 86 firebird base with original LG4, original 700r4 (maybe? I’m the 5th owner) and 83 10 bolt open diff. 200000 miles. Brand new edelbrock 1406, brand new fully loaded accel dizzy vac advance, Holley street dominator spreadbore intake, basic spreadbore to squarebore carb adapter, summit 1065 cam and lifters (duration 284/284, lift 458/458, LSA 110), dual coil valve springs but unsure of what they are, po installed them, and unknown bottom end. Stock exhaust manifolds, cat delete, flow master exhaust, brand new oem Carter mechanical fuel pump, Mr gasket adjustable fuel regulator. If it helps sometimes fuel pressure drops after driving for some time (goes from about 5.5 to 4 relatively). When I start the car in normal temperatures it idles fine with relatively snappy throttle response, after letting it warm up a bit it will chirp the tires a little pulling out of the driveway with a little throttle. After the car reaches about 140 degrees on the dash gauge, it seems to lose a good bit of power. Throttle response is low and will bog and hestitate if snapped, and seems sluggish going up hills or accelerating in general. Sometimes has trouble getting to 2k rpm but once it gets there acts somewhat normal? I know a bit but am still learning. Drove my friends 84 vette and felt a good difference in torque and power. Any advice is appreciated, and sorry about the essay

 

go over timing first, check jetting with a wideband O2 if you can, make sure you’re not heat soaking the carb, all edelbrocks NEED the thermal spacer to run right with today’s gas or else they will try and vapor lock when driving (which is what I’m leaning towards)

are you getting preignition or detonation? That’s a good indicator that you’re either running too much timing or the cylinders are getting very hot, running lean could do that or a flat cam lobes on the exhaust.

Run the engine with the valve covers off just to be sure, could also be as simple as an issue with the valve lash setting if adjusted too far in

If it’s a flat cam lobe on the exhaust first you’ll start to notice sluggish acceleration then preignition, then you’ll back off the timing, it’ll go away then come back, you’ll back the timing off more, rinse and repeat until you’re running 2 degrees of timing have no more cam lobe, flat intake lobe would cause compression problems and make it act like a dead cylinder, which could be your problem, maybe it’s worth a compression check

 

I’ll try to go through the timing tomorrow; as for the heat soak there is no thermal barrier on there now. There is an aluminum adapter from the spreadbore intake to the squarebore eddy. I can’t seem to find a similar phenolic adapter and engine space is limited in our cars so I might have to get creative.

havent noticed any huge signs of pre ignition or detonation, but I’ll check the spark plugs if I’m gonna have them out to compression test anyways.

very possible the heat soak you mentioned could be causing it to run lean; opening the second barrels seem to do nothing. Would like to hope it’s not the cam like you mentioned in my other thread, but if nothing else it’s an excuse to throw more racing parts at it

i also just found out that I have non-original 2.41 gears, which is probably not helping the power situation. Thanks for the response I’ll hopefully update tomorrow

 

Is the choke adjusted / operating correctly?

 

Yes, I recently fixed it.

 

I adjusted the initial timing, the shop I had do it had it set way high BTDC, managed to get it around 10 ish before the vac advance canister hit on my brake boost vac hose 🤦‍♂️. Took for a drive the way it was (fully warmed) and it drove infinitely better. Gonna do some research to see what I can do with the brake booster to manage a couple more degrees. Thanks for the help and I’ll update when I readjust

 

My useless 2 cents. Adjust the timing to what make the engine "happy". Or that is what has been said over and over again. (Sofa's words are echoing in my mind). Toss the timing gun since base timing was set for the sticker on the car with a factory equipped engine. You have altered that factory equipment (and there is no harm in that as it is your ride). Set the timing so the engine cranks smoothly (no stutters, grunts, or whatever) and then slightly advance from there to find a "happy" place. As a for the advance on the distributor clearance? Sounds like you are one or more teeth off. That means pulling the distributor, finding TDC, and the rest of the process. When installed correctly, the HEI top pack should be about square to the engine bay (or so I have been told.)

 

Weak coil breaking down ?