Well You will see boost at lower RPM's the difference is you will only see max boost close to redline as opposed to a roots type blower where you will see max boost as soon as you lay into the gas. I guess what I meant to say is that a centrif unit works best when kept above 4500 as it is an RPM based s/c where the positive displacement does not need RPM's to make boost.

I had a procharger D1 on my GT running 14psi and I had boost at lower rpms but it didn't hit 14psi until I was at about 6500 RPM(built motor with raised rev limiter). in the 2-4K range I might have been pushing about 6-8psi which is good don't get me wrong but it would have been nothing compared to lets say another car with a KB pullied for 14psi in the same RPM range. My car was set up for drag racing so low RPM boost was not an issue for me, once I got out of the hole the car didn't drop below 5K until I hit the traps.

 

I can tell ya this, my Procharger starts pulling hard from around 2000 rpm. and doesn't stop until I get off it. Since I don't really race my truck, I'm usually getting off the throttle at 4500 rpm, makes me a little nervous. The whistle of the blower is most noticable at lower rpms. Once you get on it, the exhaust will drown it out. Cruising on the highway, I barely hear it, kinda sounds like a little jet engine. It's freakin cool!

https://www.f150online.com/galleries....cfm?gnum=7238

 

What is your max boost? At what RPM do you see max boost? How much boost are you putting out between 2K & 4K?

like I said I am not saying you won't get boost and extra power at lower RPM's what I am saying is that a Roots and or Twin screw will provide more boost and in turn more power at lower, or daily driven if you will, RPM

Example 2 trucks both pullied for 9PSI max boost one has a Pro Charger the other has a roots blower like the HD for example.

Centrif Truck Roots Truck

RPM: 2500 Boost: 4PSI RPM: 2500 Boost: 7-8PSI
RPM: 3500 Boost: 6PSI RPM: 3500 Boost: 9PSI

So if the two were riding next to each other at the same speed cruising at lets say 2500 RPM, and they both slammed the pedal to the floor...Which one do you think will pull harder?

 

what would you guess the 1/4 for with my truck stock vs. the procharger 9psi, with bigger injectors and fuel pump and intercooler?

 

To answer 01TruBluGT, I wish I knew. I don't have a boost gauge yet. All I know is that it pulls hard until I get off it. I agree, the roots blowers put out more low end torque than the cents. I went with the Procharger because I pull a big boat (9000#) I was worried that the roots blower would too hard on my drive train at low rpms. What I like about it is when I get it moving, then I have alot more power available.

To answer fordbyfour, Since I've never raced my truck I don't have any official times to quote. What I've heard from others on this site that have some experience, A 6500# truck with that set-up would do times around 14.5 and somewhere around 90 mph. in the 1/4 mile. I believe stock is like 17 or so. I sure would like get behind the wheel of one of our trucks with a roots blower just to feel the difference. If there's anybody in the PHX. area that would give me a ride, please, give me a shout.

 

That's true. I prefer to have the graduated power and the top end pulling hard, that's where the speed is.

fordbyfour- I knocked 1.4 seconds off the qtr in my 4.6 2v at 9 psi air cooled..... your results may vary.