Should I expect to see a drop in fuel pressure at wide open throttle? Currently, pressure is around 6psi; however, at wide open throttle I can watch the pressure drop to slightly below 3psi. Only happens at wide open throttle. No issues with part throttle acceleration or idle. Car does not bog, but I believe I am hearing some pinging only at wide open throttle and thinking engine may be starving for fuel and leaning out. Current setup is: Edelbrock Performer 750cfm Running out of the box main jets (#1432 - .110") One stage richer metering rods (#1455 - .073"x.042") Two stages richer on secondary jets (#1433 - .113") stock fuel lines flushed with all new rubber lines Tested with 1/2 tank of gas Holley pressure regulator set at 6psi with stock return line to tank, installed between filter and carb Stock replacement pump installed. Not sure of brand as it has been a while since I purchased, but as very little mileage (maybe 1,000 miles). Is this drop in pressure normal? If not, is there a better mechanical pump I should purchase or should I be looking to move to an electric pump? Thanks Doug
Total timing is at 30* all in by 3000 rpm I am running an MSD distributor setup with the purple stop bushing (19*) and 1 light silver spring and 1 heavy silver spring. Timing curve looks like the following: 750 (idle) - 11* initial timing 1500 rpm - 15* 2000 rpm - 20* 2500 rpm - 24* 3000 rpm - 30* 3500 rpm - 30* The vacuum advance is currently plugged as it was adding too much advance. MSD says it should only add 10*, but I found it was adding 13-14* above 2500 rpm. If you think my fuel pressure is normal, then I will go back to playing with the timing curve to eliminate the WOT pinging. Thanks
Depending on your dynamic compression and cam specs you may be able to run a bit more total timing with good 93 octane gas. As for vacuum advance, Accel makes an adjustable vacuum advance canister that can go from zero to as much as 30 degrees. It's adjusted with an allen screw through the vacuum port. Here's a chart of the adjustments vs. vacuum that are possible. May get you a bit more cruising economy.
Thanks Ray. I am running 93 octane and my current total timing of 30* is down from where I initially started at 35* at 3000 rpm. I reduced the total timing and slowed the advance curve to try to eliminate the pinging at WOT. Unfortunately, I do not know where my compression actually landed for this engine. For the vacuum advance, I made a stop so I can adjust the amount of advance added; however, I have not added back the vacuum advance until I can figure out why I am pinging at WOT.
3 psi will not cut it, especially if you have a Q-jet, and especially when you add some acceleration G forces into the equation!
does any one know for sure if more than 3 psi is needed, mine was always around there never leaned out. robbmc makes a high volume one if needed they are on v8 buick. vacuum advance does not add timing at wot
i would do a cranking compression test, to see how much compression you really have. really don't think it's leaning out.
You and I are running similar set-ups. My 401 has about the same compression. I switched my fuel system to an in tank pump with 3/8 line regulated to 7 psi because I struggled with getting adequate fuel flow at WOT. I never have issues with detonation, even with a factory style vacuum advance giving an extra 12-13 degrees. I run 93 octane fuel also.
that's not to much maybe about 9.5 compression. must have something else going on. you should be able to run 35* total. can you get it to come all in at 3400 rpms just to see if timing advance is an issue. check to make sure your damper is right and didn't slip. how bad is it with 30* any power. how do the plugs look ?
I will start playing with the advance curve to push out total to a higher RPM and see what happens. Engine feels strong throughout the RPM range; only issue is the pinging at WOT. Damper was rebuilt along with rest of engine a little over 1,000 miles ago, so I hope it didn't slip. I am also going to look into upgrading the fuel pump. Not sure I am ready to go electric, but will look at the Robbmc pump. I never liked the replacement pump I bought. The line from the tank is 3/8", but the inlet to the pump is 5/16". If I pick up the Robbmc pump I can use a 3/8" inlet fitting and upgrade the pump to carb line to 3/8" as well. Here are some plug pics. These plugs have 150 miles on them.
Why are you running a regulator on a stock mechanical pump?if its the $40 one best thing to do is throw it in the trash. Chris
Your plugs look fine! The color change over point is pretty darn good. a 5/16” bottle neck in your fuel system is a nightmare! A 400 cid motor with a 2 bbl making only 300 hp will not have access to enough fuel volume thru a 5/16” restriction.
was told not to run platinum plugs in an older car not sure if that is true or not. plus platinum plugs run hotter and they look like a hot plug and also they look like there running hot by the side electrode, looks like the heat mark is by the bend of the electrode if i can see right. I like the ngk xr5
Sounds like I have some work ahead of me. Yes, I am running platinum plugs. I have a set of fairly new conventional R43S's I can swap in to see if it makes a difference. I will also continue to play with the timing. Finally, I'm going to order the Robbmc pump, as I have never been happy with how the fuel system dropped down to 5/16"and whether it fixes the issue or not, it will remove that concern from my mind. Thanks all
I've been running Bosch platinum plugs for years with no issues. I did a poor man's in tank fuel pump conversion. Search my posts for more info. Basically I put an F150 low pressure pump on the end of the stock pickup. I've been running it for years without a problem but will likely use a higher quality in tank conversion some day when my conversion fails.
It's great that your Ford pump had served you well for years, but how much HP can it support? How many gallons per minute can it pass?
They were used for years in all gas powered F150s, so I imagine it works just fine for most stock nailheads. The OP is running the same set up as me, more or less, so my comments are geared towards his use.
Get rid of that fuel pressure regulator, it’s NOT needed. Pinging at WOT has nothing to do with vacuum advance, BUT Everything to do with total timing
