Possible problems with h/p mechanical fuel pump?
Thread Starter
Safety Car
Joined: Jan 2003
Posts: 4,015
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From: Obscurity's Armpit
Possible problems with h/p mechanical fuel pump?
I'm modifying my Q-Jet and I was wondering about upgrading my fuel pump to a high performance mechanical unit. The Holley, Edelbrock and GMPP units look pretty much the same and seem to have the same specs, but I have two questions before I make the change:
1) None of them seem to have a provision for a return line. Is that going to be a problem?
2) They're all rated @ 110 gph. Any chance that'll put too much pressure on the needle & seat?
If possible, please give as much detail in your answer as possible (within reason, obviously :D )
Thanks!
1) None of them seem to have a provision for a return line. Is that going to be a problem?
2) They're all rated @ 110 gph. Any chance that'll put too much pressure on the needle & seat?
If possible, please give as much detail in your answer as possible (within reason, obviously :D )
Thanks!
Team Owner
Joined: Feb 2003
Posts: 30,183
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From: Lake Norman NC
Re: Possible problems with h/p mechanical fuel pump? (PartTimeGenius)
first, those high performance street fuel pumps don't need return lines..as for the return line from you gas tank...just run it down beside the frame(what i did) that way your tank will vent
second, i don't think you need a 110gph pump for a qjet, i think be just as well off with a stock pump. the 110gph pumps preform best for dual feed holleys and demons.
[Modified by REDSHARKONBOYDS, 10:07 PM 5/12/2003]
second, i don't think you need a 110gph pump for a qjet, i think be just as well off with a stock pump. the 110gph pumps preform best for dual feed holleys and demons.
[Modified by REDSHARKONBOYDS, 10:07 PM 5/12/2003]
Safety Car
Joined: Jun 2001
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From: Severna Park Md
Re: Possible problems with h/p mechanical fuel pump? (PartTimeGenius)
The gph rating is the volume the pump is capable of moving, not its pressure output.
I would recomend maintaining yur return line to help prevent vapor lock which can be a problem since vettes have higher under hood temps due to the fiberglass skin creating the canned heat effect. I switched to and aftermarket mechanical pump that also did not have a fitting for return line. I addressed the problem by running a mopar style inline filter that has a second fiting on the outlet side. Its got one going in, and two on the out side. I hooked a hose to the second out fitting and ran it back down to the return. Ill snap a pic and post it later after I get home from work.
I would recomend maintaining yur return line to help prevent vapor lock which can be a problem since vettes have higher under hood temps due to the fiberglass skin creating the canned heat effect. I switched to and aftermarket mechanical pump that also did not have a fitting for return line. I addressed the problem by running a mopar style inline filter that has a second fiting on the outlet side. Its got one going in, and two on the out side. I hooked a hose to the second out fitting and ran it back down to the return. Ill snap a pic and post it later after I get home from work.
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Re: Possible problems with h/p mechanical fuel pump? (Matt Gruber)
How and where do you tap a hole in a pump that doesn't have one or was designed for one ?
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From: central FL, near the beach.
Re: Possible problems with h/p mechanical fuel pump? (MotorHead)
easier way is to screw in a heavy brass fitting; drill it, if you mess up it's only $1 to try again. or use a T fitting, no drilling needed $1.49
Safety Car
Joined: Jun 2001
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From: Severna Park Md
Re: Possible problems with h/p mechanical fuel pump? (PartTimeGenius)
ok heres a pic of my solution to the problem of aftermarket mechanical pumps which do not have a fitting for a return line. Others have also done it by adding a fuel pressure regulator that has provisions for return line. But thats more comlicated and more expensive since you would have to buy a regulator plus the required lines and fittings to go along with it. This filter pictured cost me $3. the you can see how the second line comming from the top curves back down to the return. You can also see how I shrouded the rubber fuel hose with additional hoses sliced lengthwise to protect them from rubbing on block and rupturing.
the link will show a bigger pic of the same thing
http://members.aol.com/o942/return.jpg
[Modified by Jvette73, 2:55 PM 5/13/2003]
the link will show a bigger pic of the same thing
http://members.aol.com/o942/return.jpg
[Modified by Jvette73, 2:55 PM 5/13/2003]
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Re: Possible problems with h/p mechanical fuel pump? (Jvette73)
Possibly I am not getting this, the return line is the same as the line going to your carb ? Could someone please 'plain this cause I am putting an aftermarket pump in soon :D
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Safety Car
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From: Severna Park Md
Re: Possible problems with h/p mechanical fuel pump? (MotorHead)
When the carb is full of gas, then the float closes the needle. Meanwhile the pump is still pumping. The return line allows the pump to send the gas back to the tank rather than fight itself against the closed needle. Someone else could probably add more explanation and do it better than me. The return line fitting on the stock pump does just that. It sends the gas back to the tank when the needle is closed. Matter a fact its always sending any excess volume of gas back to the tank. Since the pumps are usually able to pump more gas than the engine needs at any given time, the remainder is returned to the tank.
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From: central FL, near the beach.
Re: Possible problems with h/p mechanical fuel pump? (Jvette73)
jvette's return filter is a good solution :thumbs:
without a return line my 72 would die in traffic jams on a hot day :sad:
without a return line my 72 would die in traffic jams on a hot day :sad:
