hotairgypsy

I do not know specific hp/tq numbers but for my question i will make some up. Lets just say to be in the interstate at 75 mph with cruise control set the car is at 100 hp/125 tq. REMEMBER made up numbers..lets say it is flatland so we take hills out of the equation. If memory serves me correctly when doing 75mph I am running like at 2800 RPMs with the automatic tranny.

Well I am installing a Saleen SC in a few weeks and I am told it starts producing boost right away. So i assume i have a bump in HP/TQ from 1000RPMs and up. Well if without FI it took 100hp/125tq at 2800RPMs to maintain 75MPH I would think i would see 100hp/125tq at a lower RPM. If so what would that new RPM be and is it noticable in the MPG. I know if your foot is in it all the time that last question is pointless but lets just say you baby it for a full tank of gas.

hammeron

excellent choice with the saleen.

when you're just cruising along at a steady speed, you're
in vacuum.

boost builds, when you move the gas pedal down

hotairgypsy

so if i understand you then when i have cruise set at 75 the SC is not doing a thing as if it was never there

hammeron

it's there and it's spinning, it's just not
creating boost.

it is also taking horsepower to turn it, just like
any other accessory on the belt system.

moosestang

You'd only be making 40hp if that while cruising at 75mph. The engine isn't under much load when cruising, idling, etc. That's how you get such good gas mileage. I'm just going by the numbers on the aeroforce gauge by the way.

jlaurens06gt

informative post. thanks

drbobvs

I'm not sure if I'm understanding your question so i don;t know if I'm answering correctly but... You're speed on the highway with the t/c locked up is now a function of your gearing. Once you overcome drag with hp, which is minimal, the 40 hp moose stated could be close to correct, it wouldn't matter if you had 100 or 1000hp at that rpm, you'd still only be going 75mph at 2800rpm due to the gear ratios. By this answer, am I understanding your question?

Gene K

RPM wont change at 75 mph. Thats set by the gearing not hp.
Engine load will only be slightly more because when your under vacuum (light throttle)
the bypass in the SC opens and the SC just freespools.

On a Roots (Like Roush, Magnuson) it takes like 1/3 bhp to spin the rotors when bypassed.
On a Screw Type like a Kenne Bell, Saleen, or Whipple I think it takes slightly more but still not much.

slySTANGguy

Very good posts, this gives me a question to ask.

I thought the amount of boost made by the supercharger was a function of crankshaft speed? I thought this because its hard connected to the pully system.

Can a supercharger produce vacuum and boost at the same RPM under different conditions?

hammeron

no. the s/c does not create vacuum, the
pistons do.

the s/c's job is simply to move and compress
air