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Discussion Starter #1
This last weekend while at the drag strip I was losing all fuel pressure at about 4,500 rpm. At least that what it felt like.

First thing to mention was that is was 112 degress outside (HOT!). During my runs, the engine started to sputter, as if not getting enough fuel, as the RPMs reached 4,500, so I up-shifted to get the RPMs lower and all was fine until the motor hit 4,500 again sputter repeated, so I up-shifted again...).

My fuel pressure guage usually reads 5 3/4psi at idle, but after a couple of runs it read only 4psi at idle. No adjustment to the fuel pressure regulator would get it above 4psi. BUT - when I got home (where the outside air temp was in the mid-70s) the fuel pressure read 5 3/4psi once again.

Do you think this might have been a heat-related issue? Or do you think my mechanical fuel pump (Holley High Perf) is not up to par?

BTW - Carb is an Eddy 600 cfm.

Any thoughts would be greatly appreciated. Thanks!

FYI - drag racing thread in Track forum:
http://forums.vintage-mustang.com/showtopic.php?tid/1514453/
 

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you might need a small electric helper pump best located near the gas tank.

Other than that, do you have a insulating (not aluminum) spacer like a phenolic block between the carb and intake? That would help keep the gas temp down. And you might need to use some insulating around the gas lines. Any speed shop sells these fiberglass covers w/ a reflective outer surface. They work great for lowering gas temps.

Z. Ray
 

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Are you using points in your ignition? Sounds like you were having ignition problems. If you're running out of gas the motor usually just lays down.
 

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Discussion Starter #4
Thanks guys. I do have a 1/2" phenolic spacer between the intake and carb, and am running with an MSD ready-to-run dizzy and Blaster 2 coil with no MSD box.

I used to have vapor lock problems without the spacer, which went away once the spacer was added. And the ignition combo works great on the street - never had any problems with it. But then again I never run it that hard (i.e. never go above 4k) on the street.

I thought the issue was fuel-related because of the significant dip in fuel pressure reading after my runs - but the problem could very well be ignition-related.

Any thoughts?

And do you think if I had the car dyno-tuned they would be able to figure this out?
 

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Rorin67 said:
................... And do you think if I had the car dyno-tuned they would be able to figure this out?.................
if they could duplicate the track conditions, yes. But I doubt they will working the dyno when it's 104 degrees.

I do know when it's really hot outside, the likelyhood of problems such as gas boiling in the lines, vapor locks, etc. is greatly increased. Using the mechanical pump alone will often be insufficient to overcome the heat related issues. But just a little more pressure from an electrical pump (helper) can seem like magic.

Z. Ray
 

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Discussion Starter #6
Thanks guys. I agree with all of the above. Since the fuel pressure is back to normal now (at normal outside temps), I'm inclined to believe it was a heat-related issue.

Maybe I'll hit a freeway onramp in 1st and get the RPM's up there again to see what happens while in normal temps. If the car acts up again at 4,500 rpm like this past weekend, then I'll know it's not a heat related issue and begin to look elsewhere (ignition, etc.).

I'm going to fix everything else up on the car and still get a dyno tune before the next NHRA Street Legal Drags session on Oct 31st. I figure it should be normal temps in the desert on Halloween (in the 70's), so the heat issue won't be there anymore.

In any event, street legal drag racing has me hooked! :)
 

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Your carb was heat soaked. Fuel was boiling out of the bowls and lowering the fuel level. Plus probably some vapor lock as well.
 

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I would try the engine over 4500 rpms when it is not heat soaked and see what happens..I had a bad plug wire(brand new)that caused me a similar problem..I kept thinking it was fuel related but it was not in my case..
 

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Discussion Starter #9
In reading another post ( Link to Post ), I'm wondering if my loss of fuel pressure was due to fuel starvation from the fuel tank. That day at the track I was running with about 1/4 tank of fuel (to keep wieght down).

Since the fuel pickup is at the front of the tank, do you think it is possible that during a drag run that the fuel pickup didn't have any fuel to pick up, since the fuel was jammed at the back of the tank because of acceleration forces?

Hhhmmmm..... :shrug:
 

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If your fuel tank is otherwise functional, I seriously doubt that you're uncovering the pickup. I ran 13's and 14's (and over 7Krpm when running 4.57's) for years back in the 70's in a '67 and never had such an issue once; I always maintained the tank at 1/4-1/2 while at the track, since I was poor and racing fuel was expensive. I added weight in the trunk with my tool box and an extra spare tire. Weight transfer ;) I started with an OEM mechanical pump, later switching to a Carter pump at the tank.

Just put an electric fuel pump back at the tank if you're going to run the car hard. Add a spin-on type fuel filter back there too.

If the car doesn't vapor lock on hot days normally, say after driving on the freeway and pulling up to a stop light, then I doubt it's doing it at the drag strip. Regardless, install a phenolic carb spacer. It keeps things more consistent.

BTW, what is your ignition setup?

Lastly, have you ever noted this issue under normal driving conditions?

Pat
 
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