Shift around peak tq or hp?
 

Hey folks, I've been thinking about this for a bit and I'm looking for some input from the more experienced people out there. If I'm drag racing, should I be shifting around peak tq or peak hp? When I look at my dyno results, my peak tq is at about 4500 rpm and peak hp is closer to 6500 rpm. I have a manual so there's a fair amount of variability in when I actually shift anyways, but what should I be aiming for? Thanks.

If racing, you want to shift at either the spot on the horsepower chart where it stops increasing (goes flat) or red line if it does not go flat.

If you want to do an impressive burn out shift at max torque.

Shifting later allows a longer use of the lower gear ratio which acts as a power multiplier.

dont ever shift at peak TQ. for drag racing and the best average HP through each gear you want to shift about 10% past peak HP. so if the car makes peak hp at 6500 then shift it at 7150. you can adjust it up or down a few hundred RPM and see if it goes faster at the track. but shifting at Peak TQ will have you looking really silly.

Ben Weishaar
Gwatney Performance Innovation

I'm not sure about my build, but with the TSP 231/246@112 LSA and all the good valve train goodies needed, except for stock rockers and stock bottom end, and a 4200 stall and an LOD X-1 intake, I have it set to shift at 7200 and redline at 7400. On the dyno we pulled it out to 7500 and was STILL making power, but we stopped there for safety sake. lol. But she sure sounds good up there and the car pulls like a bandit!!

You are looking for the best shift drop, Ben's comment about 10% past peak HP is a good guide. You want to have the RPMs in the best part of your power band.

I know this is an old thread now, but I have a good visual to share on this to help you think about maximizing average power through each gear. This chart shows where you going to land with shift recovery on a 3-4 shift in a regular TR6060-M10 combo. Yellow is shifted at peak hp (6500rpm), green is shifted at about 700rpm beyond that, 7200rpm. It's not hard to see why shifting at peak power is leaving significant performance on the table, you're going to be buried on shift recovery much further down in the RPMs, where the car develops less power.

This is why I get so frustrated at dyno operators and tuners that run the car out to where-ever it peaks and then quit. That doesn't tell the whole story, and that 500-1000rpm beyond the peak is crucial for determining where the best shift point is gonna lay. Given the choice, I pull the car out as far as I trust the motor to routinely go - because that's your real potential operating range, and will help dictate what the best shift-point will be.

Another thing to keep in mind for this discussion is stick-shift vs. auto. Auto guys are faster for a lot of reasons, and shift recovery is one of them. The torque converter will reduce how far back down the rpms drop after a shift. This in turn means the car doesn't need to be pulled as far past the peak. Depending on what the curve looks like, you could very well shift 2-300rpm beyond the peak and not be giving up much. On the other hand, stick shift cars have zero slip once they make the gear change, and drop rpms much lower. So, they must be pulled MUCH deeper beyond the peak to make the best average power through the gear - like as shown in my graphic.

I hope that helps.

Hey cammer, so good to see ya back on again!! And as always, you provide some GREAT info on everything you post to keep us informed. You rock brother!! Stay well sir..Thanks.

It's good to be back. I'll try to sneak on here a little more often!

Very cool sir!! And love the color and brightness of your Camaro. :thumbup:

What Matters More for Acceleration: Horsepower or Torque? https://danielmiessler.com/study/horsepower/

So my tuner set my shifting at 10% beyond my peak hp and I have an automatic. Is this still ok?

Impossible to say, it completely depends on the shape of the curve, and how your particular combination acts on shift recovery - which is in large part influenced by the torque converter, as well as transmission and rear end gearing.

A general rule of thumb for these cars is that with a healthy streetable cam and stock intake manifold you can expect peak horsepower to fall in or around the 6100-6500 range. With an automatic car going 10% (650rpm) beyond that number with a decent converter is like more than enough to yield good shift recovery. A stick car on the other than likely need to swing at the very least that 10% beyond, if not more like 15% over (975rpm) to give best average power. Most stick cars are likely going to target a shift point based on the max RPM the valve-train can stand.

It's all very combination based though - the curve head of and after the peak will really dictate what is going to yield max performance. A stick car with a stock intake and mild cam might not leave much on the table shifting at 7000rpm. An aggressive cam and short running intake on a stick car needs to see north of 7500rpm to maximize performance, and we're back to discussing practical limitations of the valvetrain.

Here's my dyno chart. Let me know what you think. Thanks
Attachment 1074855

I love VVT - peaks, and then just rides out strong after the peak. Graph gets a little weird up top, not sure why it's so jumpy, maybe just a glitchy pull. I'd probably shift this thing at 6800 if it still has the stock converter in it.