skinny z

The test vehicle.
Basics are in my signature. Details would include the OEM fuel lines from the original 2.8 EFI engine. There's a 3/8" supply line and I'm using the 1/4" line (from the removed charcoal canister) as a return. I had experimented with a Holley Blue electric pump so there's a 100 micron filter near the tank and a 10 micron filter before the carb. -6 AN stuff from the pump to the carb.
The former pump: Edelbrock 1721.
http://www.summitracing.com/int/parts/edl-1721
Performance:
On the street this pump delivered 6 psi consistently under any and all conditions. AFRs were 12.5:1 under WOT.
At the drag strip, fuel pressure would drop to near zero at the top end. AFRs would approach 15:1. This problem became worse the more laps I put in and the engine had a chance to heat soak. First pass of the night, not so bad. After three runs or so, and hours sitting in the lanes, it was at it's worst. I put that down to a vapour issue as well as dead-heading the pump as the Edelbrock has no return line.
The replacement pump: Carter M6626.
http://www.summitracing.com/int/parts/crt-m6626
I purchased this pump largely based on the 3rd line used for a return. When I purchased it, I was under the impression that it was a 120 gph unit as it was listed as that on several web sites. Since then, I see it's also listed as a 40 gph unit.
Performance:
So far there has been no track testing, however on the street, the fuel pressure tends to be all over the map.
There is a steady 7 psi at idle and cruise, either in town or on the highway, but under WOT, pressure will drop to 1-2 psi. Under moderate acceleration, say 2nd gear to 6000 rpm, pressure will get to 3-4 psi. It has on occasion stayed at the pressure when I resume a cruise condition but will get back to 7 psi after a time.
Not sure what to think. While the pressure is getting down to 1-2 psi, the AFRs are staying steady at 12.5 under WOT. I suspect that at the track, with a full 1/4 mile pass, the low pressure would produce a lean AFR as it did with the Edelbrock. Having said that though, if there was a boiling issue with the Edelbrock, I could see that the bowls on the carb would go dry pretty quickly. If the Carter has eliminated the vapour issue, then perhaps the 1 psi of fuel pressure will be enough to keep the fuel mixture where it should be.
Now my question is, why is this Carter fuel pump not delivering sufficient pressure under street conditions? I can't believe that, even at a 40 gph delivery rate, I'd be using more than the pump can deliver. My understanding of the 3rd line is that the restriction built into the hose fitting (looks about 40 thou or so) is what helps to regulate the pressure. Is it also bypassing too much fuel and causing an excessive pressure drop?
I know how to remedy the situation. There are several options including a helper electric pump or going back to the electric system altogether (can't stand the noise though) but I'm trying to figure what's up with this Carter.
I'm going to pull both filters for an inspection, but beyond that, I'm at a loss.

Night rider327

iTrader: (13)

I think it's pretty simple really. It really is a 40 gph pump and you are just 'out running' the pump.

40 gph pump is not near enough for an engine like yours. Heck it aint even a enough for most stock V8 engines IMHO if the engine is ran at WOT a lot.

skinny z

What gets me is the odd way thing behaves.
While most of the time, cruising pressure is right around 7 psi, if it give it a little gas, say to the top of 2nd, the pressure will drop to around the 2 psi and then recover only to about 3-4 psi even after an extended 2200 rpm cruising session. It doesn't make any sense to me.


I can see that being the case too but how quickly it runs out of fuel is startling. Having said that, at 40 gph, and then considering fuel line losses and starting line g-forces, there probably isn't a lot of fuel being delivered. But what about my former Edelbrock 120 gph pump? Pressure would fall to around 0 at the big end too although on the street, it performed perfectly. Can that be put down to the heat soak issue I had described? Certainly, it's capable of supporting 400 hp (more or less). An interesting point was made in another thread about how the hot fuel, held under pressure stays in it's liquid form but once it's released into the fuel bowl, the pressure is gone and the fuel vapourizes. Makes sense and could account for the odd performance at the track. Maybe I'll try a cool can. Then ultimately I'll probably resurrect my old Holley blue pump. I've got a nice slick installation where the OEM fuel filter was mounted (near the rear wheel house) but the damn thing was too noisy for my taste. I'll have to build up the insulation supporting it.

Manic Z

iTrader: (1)

I ran the holley blue, and I too found it very noisy. They also crapped out on me every 2-3 years.
I switched over to the black gerotor design (PN 12-150 & 12-125) with a return regulator, and am very pleased with the much quieter design. Been 2 years so far, and it's still going strong....

skinny z

I think that despite still having the Holley blue pump installed, once I make a decision on what I'm going to do with the car going forward (supercharger, LS swap...?), I'd like to go for one of Aeromotives Phantom in-tank pump kits. That is, after I've sorted this fuel delivery issue out and get a decent time slip before the season ends (which is mid-October in these parts).

http://aeromotiveinc.com/products-pa...antom-340-kit/

That would give me the flexibility to do just about anything engine-wise.
I'd also go for the access panel cut into hatch area for easier access should the need arise. Dropping the tank on these cars is a PITA.

Night rider327

iTrader: (13)

I think you hit the nail on the head man. The 40 gph is not enough, but your 120 gph non return pump was causing fuel to over heat.

Try the 120 gph pump with a return reg. setup. It's been years since I done it so I'm alittle fuzzy on details but you can take a cheap holley $25 deadhead reg and use a holley carb jet and convert it over to a return style reg.

The cool can is another idea and it does work but was always a pain to drain, refill, etc. Maybe if you insulated the can better (or for that matter used a small drink cooler to make it from) and used dry ice it would work better.

Or try a fuel cooler... You know kind of like an external trans cooler mounted on bumper side of rad... Just plumb your fuel lines up to one

Or use a dual fueling system.. Like you said the holley blue is too noisy for street use, and your 120 gph pump worked great on the street.

Put a cut off valve on your main supply line before the mech. pump... Add a 2-5 gal fuel cell under the hood, and mount blue pump up there... Run that holley blue and fuel cell at the track and the mech. 120 gph pump on the street

Alot of the nitrous guys runs systems sort of like that. Once I put the N20 system on my car, that's what i'm going to do. 2 gal cell mounted between nose and rad., holley blue pump on driver strut tower, deadhead reg for it mounted off rad. Dump 2 gal of 110 octane fuel in cell

Night rider327

iTrader: (13)

Hey Skinny... I just thought about this one... My 1st pump on my car was a stock parts store replacement for the 70/71 LT1 370 HP camaro/vette. It's a 3 line return style pump and flows around 75-90 gph (never checked mine and never could find a real answer but that is the range I found on it)

It's under $20 new and might be worth a try at least

Night rider327

iTrader: (13)

Cater M6215 65 gph 3 line pump
http://www.summitracing.com/parts/cr...make/chevrolet

skinny z

That was suggested by another racing friend of mine. Just need the details on how to put it together.

Based on Brake Specific Fuel Consumption formula, and 400 hp it looks like 40GPH is the bare minimum. The problem is, GPH ratings are free flow. Put 7 PSI in there and I can see why this M6626 doesn't cut it.
90 GPH would probably do it.

Not sure about 65 GPH though.

I think I'll try the Edelbrock again with a bypass regulator and jet. The Carter has what looks to be a .040" restriction in the return so I'll try a jet around that size to start. Have to figure out a way to install the jet though.

skinny z

More testing has shown that the Edelbrock (at 110 gph) is giving up, even on the street.
I had a suspicion that at least one of my fuel filters might have been clogged but that wasn't the case. Not sure what's going on but I'm guessing that I'm just outpacing the delivery capacity of my fuel system. That includes the lengthy and multiple bends of the OEM 3/8th fuel line. Over and above the factory arrangement at that.
I've got a Holley 12-803BP regulator on order and will put my Holley Blue Pump back into service. I've got two weeks before that last race of the season and I'd like to see a 108 mph trap speed again. (I'll need good air to pull that off regardless).

five7kid

iTrader: (14)

Do you know for a fact that your entire feed system to the pump is up to snuff? No kinks in the line, pick-up sock not clogged, no rubber lines collapsing, etc.?

skinny z

At the time of the latest installation (years ago) and having had a decent look at it when I serviced the fuel filters yesterday (a 100 micron filter located near where the OEM EFI filter was and a 40 micron between the mechanical pump and carb) , I can say that from what I saw, it all looks good.
The 3/8" factory line follows the EFI route along the drivers side frame although I've added an additional length of bent up steel line that follows the cross member across the chassis and connects to the mechanical pump. What I can't say for certain is that the length of rubber from the tank to the rear filter location is still 100%. I would hope so. The pickup in the tank, (which I traded for with you years ago, EFI for carbed versions) was installed without a sock into a new tank. Examination of the filter elements in both filters yielded no signs of debris.
It may be a simple case of the Edelbrock pump having a hard time, especially under hard acceleration, sucking enough fuel the length of the car plus the piece I've added across the front. I don't recall this being a problem in the past, then again I've been working through a lot of issues. The fuel pressure gauge is a relatively recent addition so the data doesn't give me an indication of what was going on before.