86 406

My set-up, 86 T/A, 406, Vortec Heads, Comp Cams 268 xe cam, Edelbrock RPM Air Gap Intake, Demon 750 Carb, Edelbrock TES and Catback. For fuel I have 110 gph Electric pump boosting a factory 3 port mechanical pump. I had to use the factory 3 port pump with the return line to cure vapour lock problems. Will this system support a 100 shot of nitrous?

Damon

Nah nah nah. Factory pump isn't designed to work without the return hooked up. And how disconnecting it could possibly cure a vaport lock problem I have no idea- returning fuel back to the tank keeps a ready supply of COOL fuel flowing through the lines at all times.

What kind of electric pump are you running? It shouldn't make more pressure than the mechanical fuel pump itself is (~6PSI) unless that return line on the factory pump can return enough fuel to keep fuel pressure down to acceptable levels at idle and part throttle (which it definitely can't now since you plugged it).

In theory that setup could probably support a 100 shot, depending on how much the motor itself is making to begin with. But that assumes you've got the fuel system working properly. I'm going to say that you might want to think about what you're doing with that fuel setup before you start spraying it.

First thing I'd do is get a cheap remote fuel pressure gague, T it in near the carb's inlet, mount the remote gague somewhere you can see it WHILE DRIVING (I duck tape mine temporarily to the windshield), make a few runs and see what's going on with your fuel pressure currently. If it's dropping off in the upper RPMs you definitely WON'T be able to support a shot of nitrous. If it's climbing through the roof at idle that will definitely cause starting problems (flooding) and drivability problems.

It is IMPOSSIBLE to tune around fluctuating fuel pressure.

86 406

The return line is in service. I tried to use a Holley 2 port mechanical pump at first, but vapour lock made the car undrivable in the heat. I swapped back to the factory 3 port pump with the return line hooked up, and the vapour lock problem was greatly reduced. I got the idea to use an electric pump for a booster from your (Damon) response to one of my previous posts on fuel starvation. The electric pump is internally regulated to 6 psi. Thank you for the advice, it solved my fuel starvation problem. With a T in the fuel line just before the carb, hooked up to a pressure guage taped to the windshield, the fuel pressure runs about 6.5 psi and will drop to 5 psi at wot. Race wieght for the car is about 3750 lbs. My best run on motor so far is 12.7 at 109 mph. This is through a built 700r4 with 3.73 gears in a Strange 12 bolt and BFG drag radials. The elevation here is 2500 ft.

MrBrooks

you would be better off with a 4port(return style) regulator on the carb and then use the mech pump as a stand alone pump for the spray. Of course that means running a new fuel line to the mech pump.