billschroeder5842

I have a question what is the "optimal" shift point on my car. I have a 04 Z06 CE that is bone stock.

I've been looking at the dyno charts on these with similar stock Z06s and see different peaks for HP (5000ish) and Torque (6-6500ish).

I drive pretty sane, but the looooooong On Ramps for Texas freeways are just too tempting to ignore. I'd like to get as much as I can during those brief runs.

So what is best to shift? Follow the HP or Torque curve?

lbzraptor

I shift just under redline. My hp peaks at 6500 rpms and holds that to 7000. So shifting right at redline I still have a little more torque than I started with at 3000 rpms.
son says the gears come about as fast as a crotch rocket doing it this way.

jrp1588

I believe "engineering explains" has a video on this. If memory serves, he recommends the HP curve.

neutron82

hp, if you have a dyno sheet for your car then look to see where the power starts to nose over and drop off and shift a couple hundred rpm before that point

apex26

There used to be occasional articles about this, and in checking whatever car I had, which was always the high performance motors, it usually came back at redline. I think my 1972 LT1--a solid lifter peaky motor came back at 5,800, a bit surprising. You can google it, but the formulas are way complicated. I was told by an engineer that short shifting the C5z leaves a lot of speed on the table.

lionelhutz

No matter the gear, HP is HP and the HP reaching the wheels is the engine HP minus the losses. So, look at the before and after RPM and pick the shift point so you maximize the HP at all times.

Most likely, the car will be faster if you go past the HP peak and shift after the HP has started to drop off. This happens because after the shift you gain more HP than lost before the shift.

ASRoff

to do this properly you need to dyno your car to create a "puc calculation" (Power Under the Curve)

check post #90 in this thread for an explanation...

https://www.corvetteforum.com/forums...ossible-5.html

NSFW

This.

FASTFATBOY

5-10% past peak hp has always been the general rule.

Dbl_D718

Yes, his video is a good watch if you don't understand why to shift based on horse power versus torque. In most cars, shifting near redline is going to maximize power under the curve and give the best acceleration.

FASTFATBOY

Where you shift is based on where the tach ends up AFTER the shift, not where it is prior to the shift

neutron82

exactly, that is why I would shift a little before peak

sstonebreaker

Best way to illustrate hp vs torque is this:

1990 6sp C4 TPI L98 engine had 250hp/345tq. 0-60 6.0 sec, 14.5 sec @ 96 mph

1992 6sp C4 LT1 engine had 300hp/330tq. 0-60 5.0 sec, 13.6 sec @ 104 mph

Both stats were from Car and Driver so I assume the conditions were as similar as possible, weather permitting.

Basically, it comes down to gearing. The L98 car hit its peak hp at 4000 rpm and redlined at 4800. The LT1 car hit its torque peak at 4200 rpm, peak hp at 5000 and redlined at 5500. This means that the LT1 car can hold each gear higher in the rpm band, benefiting from that gear's torque multiplication longer.

Extreme example of this is F1. Those tiny 1.0 liter engines only make 250tq or so, but being able to do that at 19,000 rpm means they can use ridiculous gearing to multiply the torque to the rear wheels.

lionelhutz

Nice stats, which again show why HP is such a widely used number. If you put more HP to the ground you win the race. The LT1 with 50 more HP will win if the car is built to match the engine.

Supercharged111

Good way to lose in a straight line. Do the PUC method above.