shift point

[born khatarnak]

hey guys...........i was wondering why is it best to shift at peak horsepower as oppposed to peak torque? wouldnt shifting at peak torque give u more pull?

[rice(er)]

hey dude, im a noobie but i know that horsepower is what keeps you moving, i dont know about you but i only shift at max torque during launching, try it out, try shifting at max horsepower then max torque, you'll know which is better

[thepolishmafia1337]

for best results you should just try to keep the engine in its power band. peak hp and tq are nothing but numbers to brag about.

[drftk1d]

usually the powerband is defined by the area betwen the peak torque and peak hp

you you want to end up shifting to land near the bottom

[kfoote]

The idea is to maximize the araa under the HP and curve for the range that you are in. In most cars, this means shifting just after the power peak, and having the revs drop to either at or just below the torque peak.

[sracing]

Originally Posted by kfoote

The idea is to maximize the araa under the HP and curve for the range that you are in. In most cars, this means shifting just after the power peak, and having the revs drop to either at or just below the torque peak.

kfoote is relatively correct.
The only way to determine the exact shift point is with the output graph of a dyno. (preferably a inertia run on a chassis dyno).

The object is to use the bulk of the HP "under the curve. This means that you always shift AFTER peak HP. After the shift you should end up at a point just prior to peak HP. You can only determine the above points by knowing your HP curves and your final gear ratios.

Of course this is for racing only. Street economy and engine longevity dictate shifts well below peak HP or Torque.

Jim
SR Racing

[nismowu]

Originally Posted by kfoote

The idea is to maximize the araa under the HP and curve for the range that you are in. In most cars, this means shifting just after the power peak, and having the revs drop to either at or just below the torque peak.

how about my car?
the hp peak is @ 6k,
but the torque peak is @ 2400.....

crap!!

[MrPbody]

We have a bit different perspective here. Shift points are decided by the type and output of a given engine. A large cube engine (like a 454) with "street" heads will like to be upshifted 1-2 lower in the band than a smaller engine (like a 350). As the larger engine make s significantly more low-end torque, it can "recover" without slowing it up.

Examples: One customer has a '65 GTO with a 434 CID Pontiac, making right at 500 horspower and a bit more torque. He shifts 1-2 at 5,500, but allows the engine to go to 6,200 for the 2-3 and 3-4 shifts (modified Muncie). We've found his 60' times and overall ET/MPH to be better this way.
Another, a 355 CID Camaro, likes it much better if you rev it well past 6,000 for the 1-2 shift, and the 2-3 shift at the same point. (TH350).

In short, it depends on the engine's ability to make torque at lower speeds. If you can get it into high gear sooner without losing the torque curve, you're going to have lower ETs and higher MPH.

Transmission gearing is another factor that must be considered. A "wide ratio" manual, coupled to a large engine, will outperform the same engine with a close-ratio trans. The reciprocal is true of engines with lower torque output at lower speed.

Another example. A local friend is world-known for his C/E engines. He builds a 290 CID small block Chevy. It makes just over 800 horsepower on gasoline with carbs. He says, if you leave the line UNDER 9,000 RPM, shut it off, as it won't recover. If you leave at 9K, it goes like hell! His car is a '95 (I think) Olds Ahcieva and it goes in the high 7s/low 8s all the time. Pretty scary, hearing that thing at 11,000 RPM! As a "Pontiac guy", I'm lookin' for the door! They live, though. Pretty impressive... Over 2 HP per cube on gasoline. That's not easy no matter WHAT engine you start with.

Just some food for thought, not knocking others' descriptions. More than one way to skin this cat!

Jim

[sportsb4life7]

well is the game need for speed underground at all correct when there is a blue and then green light right before redline and then goes red light and if u dont shift you blow ur engine
(ive never driven a stick shift yet sorry but am trying to learn and learn the best possible way , right away thanks)

[Chiquae07]

nfs underground sux.....sorry but u cant go by that. in that game a fully upgraded spec -V can beat a 'fully upgraded' rx-8.........

[Chiquae07]

sorry nfs undergound sux. nothing is realistic in it....basiclly you shift high enough in one gear to land right in the bottom of your cars powerband.