Doing high performance tricks with a fuel injected car always seems to be a disappointment. Either the computer fuel curve, the fuel rail pressure, or the injector size needs to be fiddled with, and each effects the other so eventually you end up hot rodding all three!!!!
If your Stang had factory horsepower, you are probably running a 110lb hour fuel pump delivering 40 PSI. This will basically turn your Demon carb into a gasoline fountain.
You will want to run a pressure regulator, with a guage!!!! and make sure you set it to provide no more than 7 lbs pressure at WOT. I like 5-6 just to be safe. If the inlet needle is forced off the seat, fuel rises and gets sucked raw into your intake. Rarely will this damage the motor, but it sure does make for great fires.
The Demon probably is running double downleg HP boosters. Check to make sure. I would jet the primary at 68 and the secondary at 72. Set the power control valve at 6.5.
If this is going to be a street highway car, I would change the front boosters from double downleg to annular. That way the primary circuit will come in sooner, and you will atomize fuel off idle almost as effectively as fuel injection. This is what I do with my modified Holley. Annular boosters up front and double downleg HP boosters in back.
I would lose that mechanical secondary carb. Go to a Holley 750 and contact me again. I will help you modify it for your rig. The Demon carb is for quarter miles and circle track. It is not a good street/ highway carb.
For a strictly racing carb set up, I like to run two 75 gallon fuel pumps and two 1/2 inch fuel lines from the tank and individually feed the primary and secondary fuel bowls. I run the pressure at 4-5 lbs. This will feed a 500-700 HP engine safely. It also makes feeding the NOS monster easy, since you can just boost up the secondary pump rating to match the HP you are tuning for.
If I hear one person say this is overkill, then when have you run 8 to 9 second quarter miles? Sit down, shut up, and hold on.
Before you give up on the fuel injection. You should try the new trick flow upper and lower intake with the 90 mm MAS, a good chip, and 36 lb injectors. That should get you from 350-500 hp and be great on the street. I port the intakes on all my race cars. I like the ports to be 1 5/16 wide by 2 1/8 tall. This is very close to CJ 428 size, and should support 400+ horsepower.
When you add nitrous, a 200 HP boost will make you want to go through NASA training- I KID YOU NOT.
