Ok I pretty much thought I had a decent understand of HP and torque. Today I deceided to do some browsing and came across this site that gives you the equation to figure out hp and tq etc.

It says that torque = hp x 5252 / rpm and hp = torque x rpm/5252.

I was just pluggin in some numbers and some things just werent adding up to me. On the window sticker of my G it says 306hp@6800 and 268tq@4800.

If you do the equation on the site. 306x5252/6800 you get 236 lb/ft of torque. I dont quite understand this fully yet as its late and im pretty tired from work. If the G is supposidly only putting out 236 lb/ft at 6800 rpm then wouldnt you actually want to shift slightly before that?

Another thing that im curious about is take a car like say the honda s2000 which is 242 hp @ 7200. If you plug those numbers into the formula above it actually says that it produces 162 lb.ft of torque which if im not mistake is exactly what honda says, so why is the G so far off then?

My main reason for checking out this site was trying to figure out shift points and actually how to increase torque without F/I. I always just bring my car to redline if i wanted to acheive the fastest acceleration, but it seems like after reading this, thats not the case. If seems to me that by going off these calculations that higher in rpms you go past peek, the more the torque drops off, therefore hurting acceleration times. Am I wrong?

People with real knowledge on this subject please respond.

 

I would think you want to drive through the peak torque to a certain point, then shift down to where you are at or near your peak torque, so shifting at 6800 RPM or greater the next gear you are back near peak torque.

The best way I've done this is just by repeated driving and feeling where the car stops pulling as hard, then shift at that point. Typically it just before (500 - 1000) rpm before redline. But then again I've only driven turbocharged 4cyl, until Last Tuesday.

 

This is the definition of horsepower. There's no question about that. Just keep in mind that this equation only holds true when torque is measured in lb-ft.
Yes, so we know the engine makes 268 lb-ft of torque at 4800 rpm and the torque drops to 236 lb-ft at 6800 rpm.
It depends on the torque multiplication factor, which depends on gear ratios. For convenience's sake, suppose 2nd gear is exactly twice as tall as first gear. Even though torque has dropped off by (236 vs 268) 12% of the peak figure as you approach redline, that's still a lower loss than shifting to second, where you would lose 50% of torque multiplication. Of course, this depends on the gear ratio spread. Shifting from 5th to 6th on a racing gear box might only drop the torque multiplication by 10%, in that case you wouldn't keep revving higher if you'd lose more than 10% in torque.
That just means the rpm at which the max HP occurs is close to that of maximum torque.
Again, it's the torque at the wheels that matters, and you must take gear ratios into consideration. You should upshift when the torque at the wheels is higher for the next gear than the current gear. To calculate this, you'd need the torque curve of the engine and all the gear ratios. In most cases, revving to redline yields the most torque to the ground.

 

Shifting before redline on the HR drops you to lower wtq in the next gear than the current gear, at least for the first 3 shifts(that's all that I've calculated).

 

this is always what i assumed myself. Just because of the simple fact that higher you bring the current gear, the higher in the rpm band you will be in the next gear, therefore being closer to the peak.

I guess all these numbers are basicly useless though unless I do a dyno (or just read someone elses on the HR) and see exactly where the curve is.

 

At the track, when I was fustrated with not hitting 13's the first time out, I shifted 200 into the red and lost some mph. I think 7600 is only useful to take advantage of future modifications.

 

Here is a story with an unrelated car- but it is related to the topic-

I used to have a 90 Mustang GT- 225hp 300tq from the factory- 5500 RPM redline-

If I shifted at redline, the car ran 14.7s- if I shifted at 4250-4500RPM the care ran 14.2s and 14.3s-

so just because there is a redline, does not mean that is always the best place to shift

 

1) Looking at VQ35HR dynos, the optimal shift point for our car is DEFINITELY at redline.

2) It doesn't matter that you are making what seems to be not enough torque, as long as you are making it at high RPMs. Say I had an F1 like-tranny and was making 150tq@15000rpms, that would mean at that point I would have ~430hp. As long as you can make decent torque through out the entire RPM band, you'll have low end and high end power.

 

by reading the dynos i was thinking about 6300-6900 was about rite...ill have to look again.

 

Shifting too early, which 6300-6900 definately is way too early, will bring you down to a lower torque curve after your shift. Shifting too late will also bring you down to a lower torque point at the next shift.

Point of shifting is to shift into the next gear at the highest possible torque, which is why you want to shift at 7500 on the HR's.

Same goes for the Revup

The HP vs Torque debate is never an easy subject unless you really understand physics.

.

 

yea well i always bring it rite to redline anyway....what actually made me look into this subject was that my tires chirp harder when i shift earlier then 7500 rpms, which led me to believe that I might be getting more torque out of the car If i shifted a little earlier.

 

Since it seems that the autos have been on point for 1/4 mile, what rpm does their computer shift them at? Might be a good reference for us M/T guys.

 

in DS mode, it goes out to 7500 in every gear. i only get to 3rd gear, and i don't remember what rpm i'm at, but it's a consistent 98mph at the end of the 1/4.

i've tried shifting myself at different points, and not taking it to redline or damn close (7200-7500rpm) will slow you down slightly. when i shifted at redline like the DS mode, my times were the same.

 

just get a huge tach and mount it in front of the LCD screen...

 

the slower speeds you ar are getting when your shifting for youself could be do to a slight lag when you dont let the computer control it. I know most tip-tronics have this lag, even if its minimal its still there.