Ok I know all the tuning nightmares that lie in the carb and boost combination, but have seen that it can be made to work, and is something that I am considering for a 383 build up (distant future ).

I have a question though about the fuel pressure. If I put the whole carb in a box (with sealed cables for the throttle and fuel lines in it) and pressurize it to say 5 lbs with boost (not even a whole lot), then won't that drop my effective fuel pressure (the pressure that the needle and seat see in the carb) by that same 5 lbs?

I plan on running a Mallory return style regulator that has boost compensation (adds one lb of fuel pressure for every pound of boost), but the pump will only put out so much pressure. I do have a Mallory 140 which is supposed to be a race type pump and has a max out put of 14 psi (if I remember correctly) . But even at 14 psi, if I have 5 lbs of boost and loose 3 psi due to lines and filters that only leaves me with 6 psi to the carb, and I'd like to keep it at 7-9.

Of course this gets worse if I think about 8-10 psi of boost (still not all that high).

So what kind of pumps are people using with these things? If they are using standard pumps maybe this is part of the tuning nightmare (because they are not getting the same fuel pressure under boost as they are not under boost).

 

I don't have an answer to your problem but I'll definitely confirm that your theory about what will happen with fuel pressure is dead-on.

Logic says that the only way to keep fuel pressure up at higher boost levels is to have a pump that is capable of more than ~15 PSI. No way around that.

Maybe a higher pressure EFI-style pump that can give 30+ PSI. Maybe Holley has a pump that's designed for applications like this. Start calling tech support lines and asking questions unless you have someone you trust who has done something similar.

 

I just was not sure if using an EFI pump would wear it out, or heat up the fuel because so much is going to be returned by the regulator. I also wonder if the volume will be enough with a bunch being returned by the regulator....

yeah a few calls to some techs are in my future, I was just wondering if anyone had actually done it....

 

You'd use a boost referenced regulator. What is normally a vent to atmosphere, is now tied in to see boost. If you dial in 6psi of fuel pressure, it will stay 6psi above reference. A Mallory fuel pump puts out around 14 psi, but can be increased if needed, so you'd be ok in that respect.

 

I just looked through my instructions on the 140, and all it says is that the pump is factory set at 12 psi, and needs to be run with a return style regulator (which has a boost reference). So I'm not even sure it can do 14 psi....

I under stand how the regulator works, but the regulator can't make the pump put out more pressure, it only bleeds off pressure. You said it could be increased on the 140, any idea to what? and how? (I have already bypassed the internal return, but have not checked what pressure the pump will put out).

 

I'm not up on the 140, but on my Mallory Comp 250, it's adjustable, even though factory preset at 12lbs. I believe I can go up to 20lbs, but I'd have to double check the paperwork on that.

Mallory also makes a device that changes the voltage to the pump, therefore regulating pressure by changing pump RPM. If the demand isn't there, the pump slows down and saves wear and tear.

 

look here

you can use a carter 120 mechanical pump and boost reference it.
look under Budget Twin Turbo 351w

http://www.toohighpsi.com/

also others

http://www.boards2go.com/boards/boar...ser=huntracers

http://www.boostedhorsepower.com/Blowthru/Forums/

 

not sure I want to go with the first links methods of fule meetering (blindly turning on an enjector, installed in the intake tubing before the carb, at anything over 4lbs boost).



ok, for playing with a junk yard motor, but I plan on building up a motor that I want to last.

but the other boards look interesting...

 

YZ- I am installing a Mallory adjustable FP regulator on a 92 Camaro that was originally fuel injected, but now has a carb. It's a return-style regulator. The return orifice/valve is HUGE. I have no doubt that thing could be made to drop the pressure from even a high pressure (fuel injection) pump down to a carb-friendly ~6PSI without getting "pressure creep" at low RPMs (many former TPI guys have used it in similar applications).

It's also got a vacuum line fitting on it for boost-referencing your fuel pressure. Comes standard.

Possible solution.... forget the Blue pump and get a serious in-line fuel injection style pump (T-rex, or whatever) and use this regulator or something similar to it. You'll never run out of "headroom" on fuel pressure with an FI-style pump and this regulator looks like it could keep things in balance with no problem.

 

been reading up on the other board, and learned a lot already. Found a guy with the motor I want to build and even in the same car!!

I think I'll run what he is running:
AEROMOTIVE A1000



puts out up to 45 psi, and is even listed as useable with carbs (with a return style reg of course)