So tired of hearing HP/L (Page 2/2)
Zac88GT JUL 13, 11:34 AM

quote
Originally posted by Xyster:

Q. How ridiculously low is the S2k geared to compensate for the lack of torque?
A. Very. 3.1 in first and 4.10 in the diff.
Corvette numbers for example are around 2.3 in first and 3.42 in the diff.



Fiero M19: 4.1 diff, 3.53 1st
G6: 3.55 diff, 3.77 1st
Cobalt: 4.05 diff, 3.38 1st
NA Miata: 4.1 diff, 3.136 1st
NB Miata: 3.909 diff, 3.76 1st
2013 Supercharged Camaro Auto: 3.23 diff, 4.03 1st

All of these cars have combined gearing that is higher than the S2k in first. What does this mean? It doesn't mean anything on its own. The gearing choice is very application dependent. Some cars will have a tall 1st gear so they can have a close ratio gearbox with a higher top speed, and some will have a short 1st for traffic congestion or towing.


quote
Originally posted by Xyster:

I am so tired of hearing about HP/L and not BMEP.

BMEP is (for those of you wondering) ft-lbs/cid*150.8. This number is based what the engine does and the only way to improve it is to build a better engine.

Engines produce torque. Hp is a function of torque at a given rpm. So, if you can't produce torque, spin the crap out of your engine and use hp/L to make it sound like you made a good engine. Heck, Honda does it and all the magazines love their high NVH/short life span engines.

So, now for those thinking, it takes a "better engine" to turn higher rpms, remember, GM, Ford and Mopar engines are cammed for street use, not ads showing a tach at 8k rpm. [/rant]



As with the gearing above, a "better" engine depends on what the application is. If you're towing something then yeah, you'll want more torque.

For performance it's not quite so simple. I prefer HP/L rather than your TQ/L because it gives you more information. An engine that produces tons of torque but doesn't rotate (completely static) is useless in a car, but would do well according to your formula because it doesn't take rotation into account at all. At least HP/L gives us an idea of how fast the engine can transfer the fuel energy into vehicle speed (the main goal of a performance car). Lets take a look at that formula of yours.

2013 Golf 2.0L TDI:
BMEP = (236 ft-lbs*150.8)/122 cid = 291psi
HP/L = 140 hp/2.0 L = 70hp/l

2006 Toyota F1 2.4L V8:
BMEP = (202 ft-lbs*150.8)/146 cid = 208psi
HP/L = 740 hp/ 2.4L = 308hp/l

What engine is "better"? Again it depends on the application. I consider the F1 engine the better engine because I'm interested in speed and acceleration. What you need to do is define what you think "better" is. Are you referring to better as in performance, towing capability, efficiency?

And for your Corvette vs. S2000 comparison

2013 Corvette 7.0L:
BMEP: (470 ft-lbs*150.8)/427 cid = 166 psi
HP/L: 505 hp/ 7.0L = 72hp/l

2000 S2000 USDM:
BMEP: (153 ft-lbs*150.8)/122 cid = 189 psi
HP/L: 237hp/ 2.0L = 118.5hp/l

The S2k is better than the vette on both accounts
FieroGT42 JUL 16, 09:30 PM
HP / L is kind of stupid. It's a technical bragging point, but only if that's what everyone involved in the argument wants to compete in.

HP/lb is more realistic, but torque/lb might matter more, and both even those are only peak values not taking into account the power curves, broadness, flatness, redline.

It's all relative to how your'e trying to make the car perform , for what role, and then there's reliability of course. 1000 hp is great, but if you have to rebuild after every race like actual race cars do...
Xyster AUG 01, 08:58 PM
Accleration Calculator

Drag the blue bar to match your dyno chart.

[This message has been edited by Xyster (edited 08-01-2013).]