Z06

I have been thinking about shift points, with the long gearing in the GT3,
there have been a few threads about improving the gearing, but why change the gearing and to what gear ratio.

Where would/do you shift at? ..............from what i have read it's just few hundred rpm above peak HP, (will need to find a dyno graph) and after the shift it should land at peak torque.

What rpm drop is there between gears?

From what i can remember i think it's peak torque at 5000rpm and peak hp at 7400, that gives the GT3 a range of 2400rpm, which is a big rpm power range.

When shifting the GT3 does it land at peak torque?

I compete at Ontario Solo 1, it is very competitive and i would like to get the most out of my GT3, there are going to be allot of Corvettes out there including several very quick Z06's

At what rpm do you shift your GT3.

Any thoughts on this topic would be great.

Steve in FL

Z06: I can't speak for the shift points on the street car yet but watching the Alex Job GT3RSRs at the 12 Hours of Sebring they seemed to be shifting at 8700 RPM every time the in-car video w/telemetry was shown. They were running much shorter gears though and 8700 RPM in 6th was showing as approx. 168 MPH on the back straight at Sebring.

Z06

If Rockitman made peak HP at 7300 then we should be shifting no later than 7500 rpm and it should land at 5000 where i believe peak torque is, this is for the best acceleration times.

Rockitman where did you make your peak numbers on the chassis dyno?

Greg Fishman

Shift at redline for the best acceleration.

Z06

If it makes peak power at 7300 rpm, does the GT3 continue to make good power to red line.............. and after the shift how much rpm do they drop?

I guess it is a little different than a Z06, my red line was 6700rpm, peak RWHP was at 6000, and i was shifting at 6200 and it was landing at peak torque at 4400rpm.

mds

Z06, car performance is measured roughly as a weight to power ratio and never a weight to torque ratio. Forget about hitting peak torque, all that will do is make you slower. You do loose something by shifting after peak power, but this loss is more than made up for by ending up in the lower gear at a point with higher power. Greg is correct, shift at redline.

Z06

This is from the Late John Lingenfelter on shift point,

http://www.lingenfelter.com/shiftpoint.asp

1AS

I'm not an autocross expert (having done a lot prior to starting road racing 35 years ago, and having done only 1 autocross last year) but I have a hard time believing that winning in a GT3 is going to have much to do with the upshift point and it's relationship to maximal power.
If the shift point is significant at all, it's the downshift point to avoid lugging in too high a gear. In the most recent autocross I ran, I found gear selection to be most important under corner entry, since you amplify rotation by being in a lower gear.
With corners coming up so quickly, the decision to shift is based more upon how long you can remain in the gear you just shifted into. If your upshift is going to obligate a downshift in another second of two, you'll be better off staying in the lower gear, regardless of power characterisitcs. If your upshift will put you in the right gear to take the corner, then you do it when it keeps the car settled.
If you're good enough for the upshift point to make a difference in winning or losing an autocross, then you're probably too good for any advice here to help. Congratulations AS

Z06

Do you think the GT3 is geared so high and far between gears for acceleration to Top speed 190mph, on most tracks i race on i will hit top speed at 125mph and on the other Mosport 145's.

I am thinking about either changing the 3rd-4th-5th gear or changing the ring & pinion.

On a video i saw the other day the GT3 was in the same gear from corner 2 to 6,

Steve in FL

Considering how tight many autox courses are these days the 8200 RPM redline of the GT3 may mean you never have to shift out of 2nd. May 23rd should be my first chance to autox my GT3 and I report back on my theory afterwards.

rockitman

Very close with your estimates Z06...Peak torque around 5200, peak power at 7300

My dyno graph overlayed with a stock TT's

1AS

Changing gearing works well primarily for pure track cars. A 6 speed for track work is actually a disadvantage for the non-expert, since you struggle to find the "perfect" gear. There are lots of tracks which are primarily 1 or 2-gear tracks. At almost none is the streetable 6th gear worthwhile.
If you are going to drive on the street, you might be swayed by the expertise of Porsche engineering, and leave the gearing alone. For primarily track use, a really long first gear, then tight 2-3-4-5 makes sense, but you'll feel like you're rowing the car on the street. If you're willing to do that, the car will feel like it picked up 100 hp.
Interestingly, my friend Chris Beebe, demonstrates a technique where he uses very few revs and very few shifts, and is really fast by just carrying speed thru the corners. He once shocked a Viper driver by beating his best time using a 3000 rpm redline. In the end, skill matters more than anything. Tires come next. Then set-up. Then gears. Then power. Except at tracks with mile-long straights. AS

Z06

I have been racing in Solo 1 for 6yrs, it's faster than a autocross, we race at local race tracks, the times around the track are 55 to 75 seconds, with my previous Z06 i hold the production car record at Toronto Motorsports Track (Cayuga) and had Fastest time of the Day several times last year, i am getting better at driving with each year and it's allot of fun, and very competitive.

One of the biggest changes to my driving is being smother on entry(this means braking) this allows me to carry more speed threw the corner and apply throttle quicker comming out.
I look forward to competing this year with my GT3.

Z06

Found a similar thread

https://rennlist.com/forums/showthre...hreadid=126801

MJSpeed

To quote Alain Prost (4-times World Driving Champion);

"Generally, the gearing should be as close as possible, and there shouldn't be any "gaps" between ratios, so that the engine remains in operation between its maximum torque and peak power. If the peculiar nature of a circuit necessitates lengthening-or shortening- a ratio to the detriment of the ideal balance, it's least damaing in the lower gears, as the car is travelling more slowly when you shift from second to third than when you go from fifth to sixth. Any compromise should be directed therefore at the lower gears, but given the choice between "too short" and "too long" you should always go for the second: that will be less wearing on the engine, and will allow you to corner more quickly as you won't be slowed either by an over-revving engine or the need to change gear in mid-corner." Alain Prost

Personally, when I was driving in Formula Renault, F2000, F3 and in any other race or street car for that matter, I was always told by the team's engineers to shift up no later than 200-300 RPM's above the max power point in the band. When downshifting to select a gear that will put the revs at the point of max torque so that when you get back on it the engine is at the optimum acceleration point. If one looks at the graph posted by Rockitman, of the power and torque bands for the GT3 there's no point in shifting after 7400-7500 RPM's, both power and torque drop off immensely after that.

These are general rules and can be adjusted according to circuit configuration, such as in an Auto X where it's my understanding that there's very little to no shifting at all. Just my $.10 actually more like $.50...