A couple of 3.9 questions

[greenstream]

Hi

1. Whats the thread size in the block for manifold studs ?

2. Im going to use a swirlpot in the fuelline and then I will need a fuel pump. Which should I choose for the above engine in a challenge truck thats destined for MS in the future. And what kind of psi ?

Thats all at the moment ;-)

Morten

[tacr2man]

usually a two pump system , a low pressure pump from tank to pot , and then high pressure from pot to injectors HTSH

[dirtydiesel]

Exhaust manifold thread size is 3/8 unc I believe.

Walbro 255 makes fora good hp pump.

Try these www.injectortune.co.uk

[FridgeFreezer]

If you're buying studs you can get them with 3/8" UNC one end and 3/8" UNF the other, with brass bolts. I think Minispares sell them, or possibly Namrick. Saves the threads in the head from damage / cross threading when fighting with exhaust manifolds.

Walbro 255 is fine, as is just about any fuel pump from a fuel-injected petrol car of similar BHP. Almost all petrol fuel injection systems run at 45-55psi, which is regulated by the fuel pressure regulator not the pump - the pumps can hit 100psi if you clamp the return hose off!

It's worth putting a restriction in the return line from the swirl-pot so you have some small pressure feeding the high-pressure pump - a small inline filter does two jobs at once there.

[greenstream]

Thank very mucho.

The thread size for the studs, wasnt for new studs, but because I've left the remains of one stud in the block :-(.

But as I'm at it, then it sounds like a brill. idea to change the lot for a better version.

Morten