Hey guys, i'm seeing about 12psi out of my 355/f1a combo with a 7.6 crank and 4.25 blower pulley. I have a 3.40 pulley already but i'm not sure if that would give me more than I want.
What do you guys think I would gain from this pulley swap, or should I go somewhere in between?
Looking to be around 18 psi when said and done with meth.
Thanks guys!

 

A 3.4 inch pulley will make 18+ psi, depending on your cam/head combo. I have the same pulley combo you do, and made 11 psi.

 

Looks like we have similar setups. I don't have a 9 inch yet but I got a big front mount. I wonder how my numbers would stack up to yours? I'd be thrilled with that much power on this setup!

 

19psi widh a 3.55" (if i remember correct) on oure 383.

 

It made 623 rwhp on 11 psi, twin highflow intercoolers, and a moser 9 inch. I have the 7.65 crank, 4.5 inch blower pulley...You sure you need a 3.4? Thats maxing out an F1A! I dont know what your bottom end is made out of, but if you dont have a bottom end made out of kryptonite, you will likely not need a pulley that small...keep in mind...when that F1A is spun that fast, it will make a sh*t ton of power. They are screamers on the top end...

Instead of shooting for a given boost level, you should shoot for a certain rwhp mark instead. I wanted 600+ rwhp, and reached my goal with 11 psi...depending on your h/c setup, who knows what 18 psi will make? The best way to do it will be to try a 3.75 (assuming they make them in this size, if not, something in this ballpark) and see what it does..but that all depends on how much power your looking for and what times your trying to run.

 

Thats the reason for this thread, wasn't sure what the 3.4 would get me so just figured i'd ask since I have one and a belt. sucks paying for these 12 rib belts. My bottom end should be fine, I had speed inc build it and told them my plans of 700 plus rwhp. Maybe i'll get somethin like a 3.70 and see how that goes. Elevation here is around 4500 ft so that don't help much.

 

I've been running a 7.6 --> 3.4"pd pulley setup on a 383 - D1 Procharger for 2 years. I had the 4.25" pd driven pulley, but, the rate of boost increase, and air flow from the 3.4"pd pulley was quite addictive. I tried to pick a cam and pulley combination that would be compatable. I ended up with a cam motion 231/240*... .538/.558"@ 114lsa, with rpm range of 3500 to 6800. At 6500 engine crank rpm, the D1 impellar is @ 65000 rpm. I was considering purchase of a F1A and would machine a custom driven pulley of 3.8" to 3.9" pd to drive it @ 6500 engine rpm. I've since been playing/ experimenting with a GZMS VP103 vac pump and was very pleased with the added cylinder pressure and blow-by control. (97ss - 383 - D1) B.

 

So how much boost were you making with that combo?

 

14 to 15 psi. Manifold pressure (boost) is a function of flow resistance. So, many have commented that lower boost pressure is a good thing. The lower the air flow resistance (intake/ heads/ exhaust evacuation), = more gain in adiabatic efficiency and HP.

 

I think it may come down to a 3.70 or 3.55 for me. I'll throw my car on the dyno and let you guys know how it goes with this current setup.