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Old 07-19-2010, 01:43 PM
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circle track 355 fuel issues.

Running an imca stock car, with a 10.5:1 355, aggressive cam (.520 lift), 1.75 headers, 2bl holley carb. Problem: after a few laps fuel pressure drops from 6-8 to 2-3, then it won't pull like it should. Running 74 jets, turning around 6200-7000 rpm.

Question: would a stock fuel pump lay down at high rpm like that? Thanks.

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Old 07-19-2010, 02:20 PM
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I'm surprised you're running a stock pump. Do the rules allow you to run an electric pump? 6200-7000rpm is asking a lot from a stock pump...especially if the rpm is constantly up there...
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Old 07-19-2010, 02:51 PM
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Quote:
Originally Posted by BigRoy1978
Running an imca stock car, with a 10.5:1 355, aggressive cam (.520 lift), 1.75 headers, 2bl holley carb. Problem: after a few laps fuel pressure drops from 6-8 to 2-3, then it won't pull like it should. Running 74 jets, turning around 6200-7000 rpm.

Question: would a stock fuel pump lay down at high rpm like that? Thanks.
What is you delivery system like. Line size , filter, tank/pickup, regulator, what type pump.
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Old 07-19-2010, 02:55 PM
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fuel pump

there is no way a stock pump will take 3500 cycles per minute which is what the pump seeing at 7Gs. Do a google search and type high performance chevy fuel pimp, i cant remember the website or the companys name but i bought a piston style pump for a racer a couple of years ago. worked very well I belive W.O.Outlaws cars use this style pump,I assume u have checked all other possibilities such as fuel lines sucking shut, trash in fuel cell, vent plugged up, bad fuel regulator etc.
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Old 07-19-2010, 03:04 PM
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http://www.speedwaymotors.com/Carter...-Pump,186.html

One of these or similar to start and then insure line size and filters and such will accept that much flow..The race pumps flow approx 170 gal/hr and a normal stocker is about 100/120 gal/hr

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Old 07-19-2010, 04:14 PM
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Because of fire, electric pumps generally aren't allowed in circle track racing.

The OEM pumps can -and DO- float, just like a valvetrain at high RPM. I'd agree w/topwrench and OneMoreTime to use a high performance mechanical pump if all other causes for the pressure falling off have been examined and eliminated as the cause.

Also, there are lightweight push rods available that lessen the chance of fuel pump float at high revs.

The piston type #1500 Race Pump has 50 psi pressure for carbed applications, they say "This pump is designed for use with carbureted fuel systems. A Race Pumps fuel pressure regulator is required with this pump".

Good luck.

Last edited by cobalt327; 07-19-2010 at 04:24 PM.
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Old 07-19-2010, 05:52 PM
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This pump will do the job, a stock pump will not.

http://www.allstarperformance.com/product.htm?prod=549

lightweight pushrod is not required for your app but wont hurt either.

Check that the cell is vented properly. Check for foam in the pickup tube. Check the pick up tube for indication that it is collapsing internally, as well as the line from the cell to the pump. I have seen the pump lobe worn off the cam act this way, so check that when you replace the pump.

I also recommend a filter

http://www.allstarperformance.com/product.htm?prod=320
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Old 07-19-2010, 09:43 PM
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Dang! Lots of responces!

Its a 32 gallon, bottom feed cell with no foam. Line size is 5/8 to the filter, stainless steel screen type, then 3/8 to the pump and carb.

Can't use electric due to rules.

Piston pump, like to have one, but too pricy for me!

I put a stocker on after my good one died. It only does it on the longer track we have here, no problems on the 3/8's track!

I did find something tonight when I was pulling the trans. The fuel line looked like it slipped down, being right in the path of the exhaust. The line was a little bubbled on the surface, from heat I'm guessing. I'm also guessing that the heat could have caused this? Vaporizing the fuel? Thoughts?
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Old 07-20-2010, 06:37 AM
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I would still get a racing fuel pump.

The damage to the fuel line could be your problem.

The longer track makes alot more demands of the fuel system.

1/2 mile dirt track? That is some fun.
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Old 07-20-2010, 09:26 AM
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Yeah, I was thinking that the immence heat could have vaporized the fuel, or boiled it, causing it to not pump.

Its amazing, especially when there is only one groove that will hold the car. Makes for some intense racing!
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Old 07-20-2010, 10:57 AM
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If you replace the pump, make sure you pack the spring cavity of the pump with moly or break in lube. Most of the time this is overlooked. on SBC`s they don`t have a direct supply of lube, that`s why it`s important they get pre lubed. If they aren`t lubed before installing, the spring will get really hot and we all know what heat does to springs, makes them weak which will quickly cause them to compress instead of pump when RPM gets to 3000 or better.
Even if it seems the stocker pump has been doing the job, it`s more than likely border line. I would replace it with the pump recommended, after you install it, you will more than likely have to retune the whole combo which tells you quickly the new pump has made the difference.
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Old 07-23-2010, 10:52 PM
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ok if you cant afford a piston pump then try this and i think it will help
check the fittings and entries in and out of the pump, enlarge the entries and exits and use large radius hose ends and not pipe fittings, the deal with the burnt fuel line, I believe was a big contributor to your problem,fix that, anytime I ever had a problem in a racecar i fixed that first!! run as big a fuel line as you can to the inlet of the pump,if you are using a holley make sure the flow is split adequalty(i know i spelled that wrong) make sure there is at least 3/4 inch clearance over the top of the fuel vent tubes at air cleaner.check the fuel level at the float bowls,I know you have narrowed it down to fuel pressure, these are just some of my other suggestions.
Good Luck!
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