Quadcammer

You have an M96...I'd shift it about 300-400rpm short of redline, as I do with my m96 powered boxster. Not the absolute quickest, but with that fragile motor, every little bit helps

NYoutftr

At my last DE, I noticed a big percentage of the DE cars and dedicated track cars had shift lights, just got one, but have not installed it yet.

Blue Chip

Which did you get?

PorscheAddict

Are any of you guys actually short shifting the DFI motors for longevity concerns? I shift at 7,600 (3.4L Cayman). I did have to short shift it last summer, but that was temperature-driven rather than concern for the engine life (oil and coolant got too hot due to lack of third radiator, which I've fixed). Just curious how many people are taking it easy on the DFI cars.

mark kibort

just calculated from the gear ratio change from a common shift. usually 2nd to 3rd or 3rd to 4th. generaly, the RPM drop is about 73 to 85% i(if close ratio) of redline or shifted RPM

what i found is most cars make about 93% off their peak HP during redline shifts. figure out your average and you can weigh the sacrafices of short shifting for an effort to increase engine longevity. most engines can handle redline shifts no problem

NYoutftr

Is the 73%-85% a goal for racers or something proven.

It sure seems like that is what a sequential gear box would produce or some racer with perfect shifting skills.

It seems there are so many variables in gear changes.
I am referring to clutch disengaged / engaged, how much to back off on throttle during shift, etc.

I know my shifting feels different in the higher rpm range after I installed a LWFW and stage II sprung sachs clutch disc. I don't know what is different, but it surely is.

NYoutftr

I got the Ecliptech II, it has some great features.
The folks at their company explained that in addition to progressive lights to upshift, it can be set up to flash a different color at another predetermined rpm to indicate the need to down shift.
In addition it can be a second idiot light for engine temperature that will flash.
Expensive, but if I can figure out on how to wire it for all of those functions it will be worth it.

mark kibort

Aside from style of the actual shift , which is a timing /feel thing.... I was referring to the spacing of the gears in the gear box. it becomes less important with a wide HP curve, but if more peaky (like most small engine cars) a close ratio gear box can keep the RPM in the max HP range better. this gives you a higher average HP available to use , over a lap. or through all the gears. sequential gear boxes help with the dwell time between shifts (much shorter)

Blue Chip

Does my math hold up here? Standard 996 6MT has the following ratios:
1) 3.82
2) 2.20
3) 1.52
4) 1.22
5) 1.02
6) 0.84

With that said - on the upshift - is it a reasonable expectation that, say, at 6500 in 4th gear and shifting up to 5th my expected RPM in 5th would be just over 5400? I based that on the 16.4% difference in ratio between 4th and 5th....

By my math the difference in drive ratio also drops from 31% (2nd to 3rd) to 16.4% between 4 and 5. The inverse holds true as well - which is why on a straight (headed into a turn) similar to Sebring turn 7 where you go from 5th to 2nd in a short amount of time - that 3rd--->2nd downshift has caused a bunch of people a bunch of money.

NYoutftr

That is an interesting way to look at it with all the numbers of each gear, if those are the ratios of my 2003 996
Then there would be no hurry on long straight to go from 4th to 5th to gain MPH, like NJMP Lightning or the Esses at WGI
Am I understanding that correctly?
The reason I am questioning, is I can pull away from cars (Green Group. LOL) 2/3 of the way up the Esses, but as soon as I upshift, they are on my bumper. Then I down shift twice, 5th-4th, 4th-3rd and go through the Bus Stop at nearly redline in 3rd and I can pull away again
My favorite place so far coming into the Esses, what a feeling looking at that view !!

NYoutftr

My favorite place so far coming into the Esses, what a feeling looking at that view !!

DTMiller

NYoutftr, I went back and looked at the video you shared with me -- you are shifting to 4th at about 90 mph and to 5th at 100. 4th gear is good to about 130 in your car (roughly, we don't need precision for this discussion right now).

For you in your car where you are developmentally as a driver right now, you don't ever need to go to 5th gear at WGI at any point on the track if your goal is to lower your lap times. Indeed, if you did nothing else, making that change would lower your laptime.

NYoutftr

Thank you for that.
Watching my videos after the fact, makes me have so many questions for myself
What was I thinking shifting at such low rpm, but in my head, I think I was calculating and came to split second decision that I should go to higher gear for a faster rate of acceleration .

Duh, I know from drag racing, that rate of acceleration is measured in G-Force.
But my little brain, thought road racing only used G-Force meterics for deceleration, braking and cornering.
I should have known better, so now I am all over this, trying figuring out before I go to my next DE, where I should shift.

I try and drain so much knowledge about how to drive from my instructors, I don't need to have this be something taking up space in between my ears.

Thundermoose

Again you should stay in lowest gear for as long is possible. so yes no hurry to go to 5th unless (1) you're hitting rev limit or (2) you'd have to upshift in a spot that would be sketchy. For example, I will short shift from 4 to 5 right after 2 as I want both hands on wheel through 3 and 4.

Also to your just before this one, highest acceleration is at highest hp. HP = mass x velocity x acceleration. So when deciding between 4 and 5, at the point of the shift mass and velocity are the same, but once you shift you're now at a lower hp so be math you will be at lower acceleration. This is true for nearly all cars and certainly for any car that has steady and increasing hp to redline. The gearbox is the velocity vs acceleration compromiser. At some point you hit rev limiter and cannot get any more velocity without upshifting but this always comes at the cost of reduced acceleration. Simply put, for nearly all cars, max acceleration is at lowest gear you can run.

mark kibort

Yes, ,your RPM drops are 83% of redline RPM for 4-5th and 69% of redline RPM for 2-3rd. this makes your resultant RPM from redline to be 4500 or 5500 depending on the gear. obviously, your RPM drop is lowest with the closer gears of 4th to 5th.

acceleration = Power/(mass x velocity). This means at any same mass and vehicle speed, acceleration is proportional to power, and inversely proportional to speed. so, the name of the game is to maximize power whenever you can on the track for max acceleration.

in summary, all you need to do is make sure your shifts are as close to redline as possible, and confortable and you will be utilizing the most amount of hp avaliable. that is the name of the racing game!