Originally Posted by Diver944

These are very interesting comparisons and I'd love to be able to see them both in the real world rather than on our tabletops but let's get back to these two specific charts.

944J I didn't start my comparison before 3000rpm because when driving fast I never use revs below that. I see now that you were leaning towards a standing start whereas I was leaning towards track driving or fast road.

I do still take issue (in a genial manner ) with your figures though because I think you have forgotten that the S/C chart is measured in Nm whereas the Turbo is in ft-lbs. So I have redone my charts to include HP from 1500rpm where the S/C starts and have converted the torque into ft-lbs from 1000rpm where the torque starts. The Turbo chart does not start until 2000rpm so I don't think you can just say it has nothing under that

The red text illustrates where each car has the higher figure

HP First

S/C ---- rpm---- Turbo

50----- 1500----
80----- 2000---- 50
115---- 2500---- 100
150---- 3000---- 150
180---- 3500---- 250
220---- 4000---- 320
260---- 4500---- 360
280---- 5000---- 380
320---- 5500---- 380
335---- 6000---- 340
350---- 6500----
360---- 7000----

Torque in ft-lbs

S/C ---- rpm---- Turbo

162---- 1000
177---- 1500----
207---- 2000---- 140
222---- 2500---- 200
251---- 3000---- 270
266---- 3500---- 370
281---- 4000---- 425
296---- 4500---- 420
296---- 5000---- 400
296---- 5500---- 370
288---- 6000---- 300
281---- 6500----
266---- 7000----

Coming back to your drag race, I agree that this S/C will make a better start off the line in first gear. However once both cars are past 3000rpm the Turbo will start to close. When they change to 2nd gear and drop down to 4000rpm for the Turbo and 5000rpm for the S/C, the Turbo will make more power and torque than the S/C through every gear until they both get to the top of Fifth gear and the S/C will start to claw back.

We need a very long piece of tarmac to do this race for real

Oh and I still think this S/C cars figures are at the crank and not the wheels

Originally Posted by DVC

944J- I didn't read all of the thread, but I can offer you some observations based on my experience (not P-car) with replacing the stock Eaton with a KB 2.3L twin screw. First, the KB did a good job of lowering the discharge temps, therefore safely allowing more boost and spk adv on the same octane fuel. Second, it makes significantly more top-end power than the roots, without increasing lag. It is in a way like a turbo without the lag...but, not really! Yes, it lowers the parasitic drag on the motor, but has been known to show maybe only a 10hp savings in this aspect.

The twin screw will usually squeeze out an additional 1-2 lbs before redline, so you have to be careful with your pulley choice. This may be part of what contributes to it offering broader power than the roots.

Also the sound of the KB is sinister and addictive. It almost sounds pissed off and evil. I've been told you can hear my KB screaming a half mile away or more.

One of the disadvantages of a twin screw, is fitment. The I/C must be positioned under the blower, with a heat exchanger and pump used. This will take up some space in a '51 bay, and require a different hood. I think this would also be heavier than the turbo setup.

BTW, awesome car Paul. Please post more pictures when you can!