[Darrell]

Well it worked great! My car has never been so consistant. I had 6 runs yesterday and five of them were 12.768,12.780,12.787,12.782 and 12.782. The very first was 12.877 but i forgot to take off my air cleaner.

Hows that for consistant runs? Before the fuel pump I was a tenth or two off each time. I still think I need a bigger fuel line, I was getting a minor bog or miss at the top of 2nd and third gear.

All was good till I blew a U joint!! The car was launching great, I could feel the body twist. I want to thank my good friend 455Grandville and his girl for helping me home yesterday. Hey Bud you went way out of your way for me Thanks.

Another thing on the electric pump I put in a shut off not a check valve (couldnt find an affordable one). My mechanicle pulls right through the elec when its off and it runs fine on the street.
Is this bad to do??

[Darrell]

Well it worked great! My car has never been so consistant. I had 6 runs yesterday and five of them were 12.768,12.780,12.787,12.782 and 12.782. The very first was 12.877 but i forgot to take off my air cleaner.

Hows that for consistant runs? Before the fuel pump I was a tenth or two off each time. I still think I need a bigger fuel line, I was getting a minor bog or miss at the top of 2nd and third gear.

All was good till I blew a U joint!! The car was launching great, I could feel the body twist. I want to thank my good friend 455Grandville and his girl for helping me home yesterday. Hey Bud you went way out of your way for me Thanks.

Another thing on the electric pump I put in a shut off not a check valve (couldnt find an affordable one). My mechanicle pulls right through the elec when its off and it runs fine on the street.
Is this bad to do??

[Cliff R]

Darrell, I was running mid 12's with the stock tank, Comp 140 pump, stock 3/8" lines and regulator. Late last season I sumped the tank, moved the pump behind the tanks and ran #8 hose fittings everywhere. The car picked up .3 in the 1/8 mile thus far. Have been running 7.60's-7.70's at 90mph down from 7.90's-8.0's. I've only ran once in the 1/4 mile and went 12.10's at 112mph in pretty hot/humid conditions.

The interesting thing about the improvements is that the car picked up the same with the Holley and q-jet carbs. I couldn't feel the car nosing over as much with the Holley, but obviously it was leaning out some up near the shift point.....Cliff

[sdbob]

What I did on my 73 I had new stock size lines. At first I tried using 1 tank pickup but I was having problems. So I took the tank out and saw were the stock pickup was located. So I drilled another hole in the inlet and placed another line in the tank in the oposite area of the stock pickup and removed the filter material around the stock pickup Then y'd them to a larger line going to the pump. I might try moving pump and filters to rear of car. Another thing I did was for Qjet I screwed long Buick type filter housing into carb and marked a area on the side for a brass nipple,and brazed this nipple there. to see what my pressure was at the carb inlet.My street car I had for years run the electric thru the mech. pump. Also i can drive car with electric off.

[68lemans462]

Can someone tell me where TomV's electric fuel pump "theory" is. I am having a very similar problem.

[Darrell]

Dan I emailed you what Tom send me

[68lemans462]

cool. I didnt get it yet, but hopefully I will soon. Thanks. daniel.haggar@uchsc.edu

[1968_Injunhed]

Hey Dan, send that my way after you get it. This is Jeff, the guy who bought your T2 intake.

68injunhed@earthlink.net

[Tom Vaught]

First off, I am glad that you are happy with your fuel system modifications.

Second, can you post the brand of electric fuel pump you are using?

Third, If it is a Holley pump you are lucky as most holleys will not allow enough flow, when off, to have the engine run properly at 60 mph.

Fourth, The reason why I recommended a "flapper" type
check valve is:

1) Use of a solenoid will require having a normally open solenoid that closes under WOT.

2) If you have a solenoid that is normally closed, you will need to power it up to keep it open under cruise conditions, therefore it will wear out quickly.

3) The solenoid must close when the fuel pump is on or the fuel will just return to the tank. What type of solenoid did you use?

Tom V.

[Darrell]

I did not use a solenoid Tom just a bypass with a shut off gate valve.

Believe it or not I bought a $35 rebuilt pump from a guy on Ebay htat sells lots of them. He is a super helpful man and I am happy I bought from him. I put my shutoff in the glove box.

[Formula8]

Can someone post Tom's original suggestion? I mean this seems to kinda' defeat the whole sharing of information aspect of the board.

[Tom Vaught]

I suggested that if you were wanting to keep
your mechanical fuel pump for street driving but were having troubles keeping the float chamber full during WOT you could use a check valve (flapper type) along with an electric fuel pump to correct the issue.

Plumbing would be:

1) Cut the suction line from the fuel tank to the mechanical pump near the fuel tank.

2) Install the electric fuel pump and the flapper check
valve at that location. The check valve and the electric
fuel pump MUST be in parallel circuits.


Operation is:

Cruise mode and low speed operation.

The electric fuel pump is off. Some fuel may be able to pass through this pump but typically very little.

The mechanical fuel pump is working.

The Flapper check valve is open due to the suction of the mechanical fuel pump flow.

Wide Open Throttle mode:

Electric pump is on (either due to a throttle switch,
a low vacuum switch, or a mechanical "ON" switch that
is controlled by the driver. Flow is towards the engine.

The mechanical fuel pump is working and is being pressurized by the electric fuel pump.

The flapper check valve is closed due to the higher pressure of the electric fuel pump being on. This keeps the extra fuel pressure/ volume from returning to the tank and defeating the purpose of the electric
fuel pump.

Benefits:

In cruise mode, NO NOISE from the electric fuel pump.

In WOT mode, you will not hear the fuel pump due to the tremendous roar of a powerful Pontiac engine at
full song! You will also keep the fuel bowl(s) full
which will mean better performance.

Hope this helps.

Tom V.

[Formula8]

Cool, thanks Tom. I'm sure this has already been asked but you got my interest up. I assume we are talking about a system with regulated return or bypass. Using a non-bypass system with a regulator, could you just hook up the electric booster pump to the same vacuum switch or throttle switch?

Due to the vehicle's acceleration combined with the weight of the fuel over the length of the fuel line, I'm thinking all that is needed is to pressurize the suction side of the mechanical pump at WOT to eliminate cavitation. Perhaps a bypass regulator set 1 PSI or so higher than the mechanical pump's output but installed right after the electric pump. At WOT the suction line would become pressurized but would otherwise work similarly to your set up.

[JSchmitz]

Tom, Do you have a part number for a "flapper" type check valve? I'm trying to decide whether I'm going to do this mod or go straight electric. My car is running out of fuel for an instant at the top of first gear.

Also, Does anyone (probably Tom) have a breakdown of fuel pump flow requirement per horsepower? I'm trying to decide what pump to buy. My car weighs about 3,755# w/driver. It has run 12.41@110.88. That's with the stumble. So, assume it will go a little faster/quicker. How much pump do I need?

[Tom Vaught]

Quote:

"Cool, thanks Tom. I'm sure this has already been asked but you got my interest up. I assume we are talking about a system with regulated return or bypass."

No we are not.

The only reason for the check valve is to go around the electric fuel pump so that it does not have to be on ALL the time. There is no bypass function here.

Quote:

"Using a non-bypass system with a regulator, could you just hook up the electric booster pump to the same vacuum switch or throttle switch?"

The electric pump IS a booster pump when it is on.

Quote:

"Due to the vehicle's acceleration combined with the weight of the fuel over the length of the fuel line, I'm thinking all that is needed is to pressurize the suction side of the mechanical pump at WOT to eliminate cavitation."

That is what the system does.

Quote:

"Perhaps a bypass regulator set 1 PSI or so higher than the mechanical pump's output but installed right after the electric pump. At WOT the suction line would become pressurized but would otherwise work similarly to your set up."

Your suggestion does not apply to the way the system works.

I will try again:

From the tank to a TEE, from the tee one side goes to the check valve, the other side goes to the electric fuel pump inlet.

The outlet of the check valve goes to a second TEE.
The outlet from the electric fuel pump goes to the same
second TEE.

frrom the second TEE the fuel goes up the normal fuel line to the mechanical fuel pump.

From the mechanical fuel pump the line goes to a fuel
pressure regulator. (Like a Holley Red one set at 6 psi)
From the regulator the fuel goes to the carb.

There IS NO by-pass in the system.

Tom V.

[GotGTO?]

Never thought about it 'til I started reading this thread.Excellant anti-starvation insurance!My 67 already has a holley electric and the new (used)400 came with a brand new mechanical in the box.Can I just get the check valve at the auto parts store(duh?) and would I be replumbing with larger fuel lines or no? 3/8 or 1/2 inch? What a great idea!

[Formula8]

Thanks Tom, I get it....the check valve allows a greater amount of fuel flow around the electric pump while it is not running. Makes sense. Thanks,