Interesting Article On Shifting For 1/4 Drags

I just read this article about shifting. It mainly tell you that we should shift our cars at Redline and not a peak horsepower.

I was wondering if this was true and if some of you disagree or agree on this.


I think peak horsepower give you the most power in that gear but I also think that Redline shifts will give you greater power in the next gear.

Anyway here is the article...

http://www.allpar.com/eek/hp-vs-torque.html

Well i got tired of reading after the 3rd word. So.......... i'll just say this. My car surely doesnt get the best acceleration at my redline rpm. My car redlines at 5800rpms, now do i take it there? Hell no. It runs out of breath a 5200rpms, and i mean OUT. I think the powerband goes something like this.

4,000rpms- 195 horsepower
4,500rpms- 220 horsepower
4,600rpms- 230 horsepower
4,800rpms- 215 horsepower
5,200rpms- 180 horsepower
5,500rpms- 160 horsepower
5,800rpms- 140 horsepower
So in other words my shift point stayes between 4,900rpms and 5,100rpms. Or else i lose. :mad:

I dunno. I haven't bothered to read the article due to what you stated. Some cars actually start to fall on their face at higher rpms (Stock Evo's literally hit a wall at 6,000-6200 rpms). Some guy I know from another chat board has a SRT-4 and he definitely knows how to drive. He coerced a 13.2 sec. 1/4 mile at 102 mph on drag radials. Mind you I believe that was when his car was a stage one mopar. Anyways, he states that he shifts before redline often (I believe close to 500 rpms before redline). Some cars that article may prove to be true for (Obviously a vtec motor would need to be shifted at redline, since the power comes in at the top; more aggressive cam lobes).

My car doesnt fall off until 6500 or so I shift around 6800 after that it falls off enough to where it's not worth it to keep wringing out the gear. I think it all depends on how fast your hp drops and what rpm. As well as what rpm you come in when you shift and what your cars powerband is like once you shift. So your gear ratio would also play a part. A dyno sheet definantley helps.

Top end revs mean death to just about any car. Hell, my current car backs off slightly just before the shift points. My old Colt did the same thing. Best acceleration in my experience has always been right in the middle of the rev range, generally 2500-5000 RPMS depending on how high it goes.

"Not all cars should be shifted at the redline for maximum performance. But it's true for many cars. You can determine optimal shift points by graphing horsepower vs. velocity or transmission torque vs. RPM. Engine torque alone will not determine shift points"

Last paragraph in that whole thing. LoL

I'm with everyone here so far. My engine makes its most power between 4200 and 5500 RPM. I've taken it as far as 6,800 and all it does is start floating valves and falls on its butt. Granted it sounds neat... but it's just tear on the motor and doesn't produce any power.

It mainly tell you that we should shift our cars at Redline and not a peak horsepower.
Actually, that is not what it says.
It says,
"A car accelerates hardest with gearing selected to stay as close as possible to the engine *power* peak, subject to the traction capability of the tires."

... not necessarily at redline. Every engine/car is different.


Excellent read:
http://www.datsuns.com/Tech/whentoshift.htm

Copy/pasted from that site:

Optimal shift points
By Dave Lum - 10/22/98
Looking to get maximum effect out of your car when accelerating? Try optimizing the RPM's you shift your car at. If you're shifting at redline, you're probably not getting the best acceleration out of your car - in fact, the optimum shift RPM will probably be different for each gear. You can calculate the optimum shift points, but it takes two pieces of information : Gear ratios of all your gears, and a chart of your torque curve.

If you don't understand torque curves, you may want to take a look at the horsepower article in my Technical Department before reading any farther.

The trick here is to keep your engine in the meaty part of the torque curve, as your acceleration curve will match your torque curve - meaning if your torque peak is at 3000rpm, that's the RPM your car accelerates the hardest. How do you keep the engine in the best part of the curve? Shift when you will be at an RPM where the car will make more torque AFTER you shift than in your current gear. This may sound confusing, but I will give some examples to help demonstrate this. Gear ratio is important because you need to know what your RPM's will drop to once you shift. EXAMPLE : If you're at 6500rpm in first, you need the gear ratio to know what RPM that will translates to once you shift to 2nd.

Well what do you know! You bracket the HP peak. HP after the shift is the same as HP before the shift. Now we know shifting at the torque peak isn't the answer, and neither is shifting at the HP peak.

The math required : next higher gear ratio / current gear ratio (i,e. second gear divided by first) = X

X * shiftrpm = nextrpm, where shiftrpm is the point your shifting AT, and nextrpm will be the RPM of the next gear at the same speed.

firstgeartorque = torque at shiftrpm times current gear ratio (example, at 6400rpm we have 95ft/lbs, multiply this by our gear ratio in 1st (3:1, or just 3) and you get about 245ft/lbs.

secondgeartorque = torque at nextrpm times next gear ratio (in out example, we have 120ft/lbs @ 4400rpm, times 2:1 (second gear ratio), and you get 240ft/lbs.

Change shiftrpm until firstgeartorque is equal (or close to) secondgeartorque.

Top end revs mean death to just about any car.
Then why hasn't my car died at 197,600 miles ... I redline every egar when I race?

Because, all engines are different. All power bands are different.

The stock turbo MR2, runs out of breathe at 5500 rpms with a 7200 rpm redline.
However, strap a bigger turbo and you shift the powr curve to the right.
My turbo MR2 runs out of breather well over 8000 rpms .... but my redline is still 7200 .... so that is where I shift.

I redline every gear, because that is where my optimal shift point is.