Art_Z

Is it just me or does it seem that the SC options seem to generate much more HP rather than torque? Is this typical for any type of forced-air type setup?

MarkRobinson

That's common for centrifugal SC's. Twin-screws make a much more even curves/amounts. Turbo's build more torque down low & hold it longer than SC's, & make about as much HP as the SC's do up top, or possibly more if intercooled.

Of course, blower/turbo sizing has a lot to do with those curves as well. Same engine, same boost pressure, a small turbo on a V8 will always make more torque than HP. SC's will always make less tq than hp, though the the same boost on either setup will yield similar HP, all similar factors considered.

pmotts

Can you explain the science of this a bit? I know it's true and that custom exhaust influences torque/hp but what is the main reason the different FI systems act so differently?

hacker-pschorr

I'm confused, my 81 is making 311rwhp & 321lb-ft rwtorque.

FlyingDog

hp = (torque x rpm) / 5252
If you have a perfectly flat torque curve from beginning to end, the highest HP will be at the highest rpm measured. If that peak rpm is above 5252, peak torque will be below peak HP. The only times that does not happen are when torque falls off well before 5252 (environmentally friendly American V8s of the 80's, or a boosted car with an undersized compressor) or the engine never gets to 5252 (most diesels).

pmotts

Well... almost always

Kevin Michael

Which is more important tq. or hp?

pmotts

I would guess most people would say Torque/grunt.

Abby Normal

You trying to make this a blood-bath?

Abby Normal

That motor made more tq than hp in in the first place?

You had 220hp/265tq stock..not knowing what that meant at the wheels, however your hp increase was still more than your tq increase.

I'm guessing here.

Kevin Michael

Abby, I really, and sadly, do not know the answer. I heard so many conflicting opinions I don't know. I have an idea but I don't know.

hacker-pschorr

Yes, so does my 79 non supercharged car.

pmotts

Larry928GTS

There's a an explanation of the relationship of torque and horsepower and how they affect acceleration at:
http://www.cannell.co.uk/Technical%2...tq_explain.htm

I think Mark Kibort will appreciate it.

MarkRobinson

W/o making a long & boring post, Abby is on track: your motor made quite a bit more torque than HP in your beginning run. On most 5.0 928's making 280/280 roughly (same HP & TQ for the most part), the boosted power is always producing more HP than Torque. why? Because the Supercharger is belt-driven & geared for max boost @ max rpm. The TS's design allows for much more boost down low, resulting in more torque.

The turbo, being driven soley off exhaust gases, comes on boost dependent to it's size to the engine (in short), and makes peak boost immediately. So where an SC is making 3psi boost @ 3500rpm (assuming), adding roughly 20hp per PSI: 270 + 60 = 330rwhp, the turbo is making 6psi @ 3500rpm, & adding another 50rwhp to that number to make 380rwtq (as per my dyno scan: SC compared to Turbo, done on my cars on the same dyno, same year 928, making within +/- 5rwhp before boosting). 5psi vs 5psi, no ic, no ic.

Boosting via SC adds HP and about .93 Tq compared to HP. A 400rwhp SC will make about 375rwtq, on a normal 5.0 with about 5psi boost, given that a normal healthy 5.0 is about 270/270 to the ground. Since your motor made more torque, you maintained a torque lead, though if you look at the ratio Hacker, the spread is less since the torque factor is less (than your base run). Gotta finish work, ya'll go ahead & play.

Yes, my torque did fall off fast with the turbo: a 1/8" boost leak @ the throttle housing will do that.