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I draw these conclusions because the engine seems to loose its strength above 4 k rpm, it seems that it gets short of fuel flow while in the low and mid ranges it shows a strong pulling torque.
What rpm do you have the rev limiter set to?
What do you have the two other dials set to?
At 36* advance, hopefully at 3000rpm or more, you should be fine. No vac can, but that will not cause your 4000rpm flat spot.
A bad coil could easily do this. Hard to test. History? Do you have another to try?
Fuel:
7.5 # at idle is good for a Holley. But your issue is at 4000 rpm, under load. You must test it that way. Rig up a fuel psi gauge with a long hose and tape it to the window if you have to. The fuel psi should not nose dive as you climb in rpms at WOT. Losing 1# to drop to 6# is ok, dropping all the way to 1# means the pump is shot, or you have a clog.
A stock pump should be OK for a 450HP BB, but just. If you can get a good one. New low $ replacement parts have a nortoriously high failure/defective rate.
An aftermarket race pump is probably your best bet. Some are limited to 7.5psi,, not all. Most screw together and can be rebuilt with new diapragms. They generally have a much higher reliability rate.
If the fuel psi is good at speed, and you still have a bog, we need to dive deeper.
Many new builds have Hydraulic roller cams, and some of those have failure of the fuel pump lobe on the cam. They need special pushrods. What was in yours when you changed it?
At that point I would do a plug jetting check as mentioned above, or have someone test it with and AFR probe. It could be very rich, or very lean. The main jets should kick in around 3000+
This NCRS 454 also died at 4000 rpm. This is how they checked it. 3 bad replacement pumps in a row. 4th one fixed it. Bad re-po parts. They are not like old GM parts were.
The 0 6 setting gives you 16 degrees initial plus 20 degree curve assuming you originally had the dials set to 1 7 and set total timing to 36 with a dial back light or timing tape. It also gives you 10 degrees vacuum at 10" load.
Did you set the total timing to 36 with the dials set to 1 7 to lock the advance before setting the dials to 0 6?
The 0 6 setting gives you 16 degrees initial plus 20 degree curve assuming you originally had the dials set to 1 7 and set total timing to 36 with a dial back light or timing tape. It also gives you 10 degrees vacuum at 10" load.
Did you set the total timing to 36 with the dials set to 1 7 to lock the advance before setting the dials to 0 6?
Actually I didnt, I set to 36 with the dials at 0-6, would it had made much difference? Matter is the garage guy didnt know how to manage the distributor and I forgot to tell him how to, I found out that recently, now I'm doing some service to the car but will reset the distributor properly.
If you are doing your own maintenance and tuning, keep it simple.
With a big block putting out 400+ hp, you might be better off pulling out that distributor you have and drop in a simple oem type points distributor or a simple HEI.
Drop in an HEI, set the timing and go.
Even with points, it’s very straightforward and simple.
Actually I didnt, I set to 36 with the dials at 0-6, would it had made much difference? Matter is the garage guy didnt know how to manage the distributor and I forgot to tell him how to, I found out that recently, now I'm doing some service to the car but will reset the distributor properly.
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You DO NOT determine what your engine needs buy the fuel pressure....carburetors want 4 to 6 or 7 psi max. Most are fine at 4.5 psi. Most new EFI conversions want 62 psi...period. Your question should be how much flow do I need?. HP needs fuel. Fuel pumps operate by pressure for the system that feeds your engine and volume for how much it needs to perform. Most systems that are stock use 3/8s line which is an-6. 3/8 fuel line 10 ft long will support 180 gallons per hour. My buddies old Methanol dragster needed two -8 fuel lines to supply enough fuel for it to supply the motor. My 500 hp 427 runs on 4.5 to 5 psi at 97 gallons per hour available which has a return line for what is not needed. The constant flow keeps any fuel sitting in the line cooler than just sitting in the line next to the headers
Take your hp x .5 = lbs of fuel/hr
Lbs/hrs ÷ 6 = gph
I will add links
Last edited by Rescue Rogers; Oct 11, 2024 at 03:33 PM.
I draw these conclusions because the engine seems to loose its strength above 4 k rpm, it seems that it gets short of fuel flow while in the low and mid ranges it shows a strong pulling torque.
I think you need to know what your fuel pressure is when the car is under load at a high engine rpm.
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FWIW: I have an Aeromotive A1000 fuel pump...it is a big fuel pump! I have AN8 fuel lines running from the pump to the engine...one AN8 for fuel to the engine, and one AN8 for a return. (AN8 is 8/16 of an inch, 1/2inch) I also have an Aeromotive fuel pump speed controller, the pump runs slow at engine idle, and then ramps up speed (pump rpm), until 3000 engine rpm, when the pump goes to it's max speed. I have a fuel injection regulator, ~45 psi, but Aeromotive makes carb regulators for the very low carb fuel pressures. The
Last edited by 68/70Vette; Oct 12, 2024 at 12:51 PM.
To everyone pointing at a fuel issue. He did NOT correctly set up the timing curve on his electronic advance curve distributor.
You are supposed to lock the advance and then set your maximum "mechanical" advance". Next you are supposed to select the curve you want to reach that maximum number. Also a second dial is used to set the "vacuum advance".
He had a shop do it without doing the first step. I can only guess that instead of 36 degrees total maximum mechanical he is far exceeding that number by as much as 20 degrees. The engine maybe detonating.
To everyone pointing at a fuel issue. He did NOT correctly set up the timing curve on his electronic advance curve distributor.
You are supposed to lock the advance and then set your maximum "mechanical" advance". Next you are supposed to select the curve you want to reach that maximum number. Also a second dial is used to set the "vacuum advance".
He had a shop do it without doing the first step. I can only guess that instead of 36 degrees total maximum mechanical he is far exceeding that number by as much as 20 degrees. The engine maybe detonating.
I'll definitely correct that iussue and will inform, thanks.
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