FI and rear gear choice
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07-13-2006, 11:57 AM
#4
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Your powerband is much smaller with a centrifugal supercharger, only a couple of thousand RPM where peak power is really high, and you need a gear that will not take your motor outside of it. Example: Suppose we have a 700 rwhp LS1 with a Procharger with over 500 rwhp from 5k to 7k rpm. You're going to want to have a gear that, shifting at 7k, won't drop you down to a point where you're making significantly less power.
Turbo is a whole different story because the powerband will DIRECTLY differ depending on the rear gear choice, i.e. load.
I would never run over 4.10's with a positive displacement blower on a street car. With their wide powerbands (Maggies & KB's), I wouldn't want to be shifting too often and instead I'd let those low-end torque monsters do the work for me.
Turbo is a whole different story because the powerband will DIRECTLY differ depending on the rear gear choice, i.e. load.
I would never run over 4.10's with a positive displacement blower on a street car. With their wide powerbands (Maggies & KB's), I wouldn't want to be shifting too often and instead I'd let those low-end torque monsters do the work for me.
07-13-2006, 12:41 PM
#5
Rear Gear saying 373's, 411's or any gear work fine with a supercharger, all depends on how much boost you want to make, how tall of a tire, and what size pully is on both the crank and blower. If you have large pullies on both a tall tire then yes possibly you can run 411's. if you have a smaller pulley and shorter tires then you might have to run a shorter gear like 342. I run a D1 Procharger with a 7" crank Pulley, 3.75 Blower Pulley with 26" tall tires and a 373 rear gear. At the end of the quarter my RPM is right where I want it, around 6000 with 12lbs of boost....
07-13-2006, 01:04 PM
#6
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So if I were to do 3.73 gears it would be a good thing with my power? Since my power is directly related to my rpm I would think climbing rpms faster would be helpful. But people tell me to keep the 3.42s so it pulls in the gear longer... What do you guys think about this one?
07-13-2006, 01:04 PM
#7
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With my old blower combo I ran 3.50's/T400/680rwhp/shifted at 6800-7000. Calcs suggested 3.65's.
If you are M6 on 26's I would not run more than 3.73's, I would never suggest a 4.xx gear for anyone making over 450rwhp with a blower since you will not leave a lot of room to upgrade later.
If you are M6 on 26's I would not run more than 3.73's, I would never suggest a 4.xx gear for anyone making over 450rwhp with a blower since you will not leave a lot of room to upgrade later.
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07-13-2006, 03:59 PM
#9
Originally Posted by Drewstein
So if I were to do 3.73 gears it would be a good thing with my power? Since my power is directly related to my rpm I would think climbing rpms faster would be helpful. But people tell me to keep the 3.42s so it pulls in the gear longer... What do you guys think about this one?
Again, It all depends on your TOTAL setup. if your power is all over with at say 6000 RPM then you do not want to go through the traps at 7000 RPM, this is spinning your enging for nothing. Also you have to calulate boost since it is proportional to rpm. If I run a 4.11 gear then my boost is to high with my current setup, I would have to change the size of the pulley or run a taller tire, so you have to understand the combined effort.
