Shift Points

[Siestarider]

The general rule I was raised on is when attempting fastest possible acceleration, upshift at redline.

However, since this is my first turbo car, and first experience with torque peaking much earlier in RPM range and falling through HP peak on Dyno plots, plus peak HP is well below redline, I wondered whether the Fist should be shifted differently for max acceleration.

Plus my butt dyno had me shifting 3rd-4th and 4th to 5th gears on track around 5500 rpm rather than at redline.

So I used one of my stock turbo 3rd gear Cobb S3 logs and a spreadsheet to obtain tables of torque and hp by gear and by rpm. Graphed both.

Turns out the answer is upshift at redline for max horsepower in every gear. For example, at redline in 3rd gear, car is putting around 240 hp to wheels at redline, which is more than any hp available at any rpm in 4th gear. On this particular log, peak hp calculated for 4th gear is 208 at 5500 rpm.

Going by torque alone, shifting a little earlier 3/4 and 4/5 should work better.

But extracting max HP through the gears should be the best strategy for max acceleration.

Alternatively, I blew the analysis on theory and there is a better answer. Just curious, probably too many variables to test it on a circuit, maybe a drag racer can opine?

 

[juliog]

Yeah. A look at a dyno chart should be enough to figure this out. You want to maximize area under the (horsepower) curve. Upshifting at redline doesn't feel satisfying on this car, but it's still fastest.

 

[dyn085]

Pretty much every good drag racer that I've seen that produces good OEM-turbo numbers shifts well before redline. Hp is not maxed at redline, it has already peaked and dropped in OEM-turbo cars.

 

[frankiefiesta]

I've tried shifting at both redline and before redline. I've found shifting closest to redline as possible produces the fastest time. At least for me.

 

[Siestarider]

Interesting, Dyno85 says what I thought to be true, Juliog and Frankie say what the data show.

Unfortunately HDPE experiences typically do not allow consecutive laps run at the limit to test this, always catching up to someone and waiting for a point by, not that I am good enough to run consecutive laps within a couple tenths anyway.

Drag strip is probably the only safe place to test shifting at HP peak rpm vs redline rpm to get the real world answer.

 

[InsTwin]

Well, are we talking stock power curves or tuned power curves? Because I think on a stock tune, it's best to shift before red line, on a tuned car it's probably best to shift at red line.

My thinking here is there is a less severe red-line power drop after a tune, where as the stock tune has a power dip after ~5500rpm.

I'm just ball parking here as I'm trying to remember the power curves instead of looking them up.

 

[frankiefiesta]

Interesting, Dyno85 says what I thought to be true, Juliog and Frankie say what the data show.

Unfortunately HDPE experiences typically do not allow consecutive laps run at the limit to test this, always catching up to someone and waiting for a point by, not that I am good enough to run consecutive laps within a couple tenths anyway.

Drag strip is probably the only safe place to test shifting at HP peak rpm vs redline rpm to get the real world answer.

Yeah just to clarify I was talking about the drag strip. After seeing how power drops off after a certain point I tried shifting around 5,500 or so. Did this about 3 passes and all 3 were slower than shifting at redline. This is just my findings though. I am not a pro. Might be best to ask those who have gotten stock turbo cars into the 13's

 

[RAAMaudio]

Since I only put about 5 of the first 273 miles on the car before it had the first Cyborg I can only talk about it and the EFR turbo upgrades and not to long from now GT or GTX turbo which all make more power at higher RPM than the stock to small of a turbo which I would have to imagine is far quicker shifting earlier. Doing the math is a very good way to figure it out then actual testing to verify it of course, butt dyno's can be pretty far off though some have a more sensitive one than others it seems.

A tool that could help is using Vdyno and looking at the time it takes to go through the rev range in each gear you use shifting a various RPM levels. Best to do all the runs in the most exacting situation as possible of course, just like tuning runs should be done.

It has been general knowledge in racing for decades to be in the best gear possible for the situation, ratio changes per gear are used by the more successful teams when allowed. That can be more per different points on a track of course when refined that far enough but for fixed gear sets like we have then where you drop into the power band where it is most efficient in accelerating the car in that gear is what matters.

 

[Siestarider]

The data I used in the spreadsheet are from my stock turbo running Cobb S3 V220 tuning. Torque peak 3100 rpm, hp peak 4825 rpm. And all the stock transmission gear ratios vs rpm graphs from the spreadsheet indicate using redline for shift points is quickest for acceleration.

Since Frankie has the only real world report,and his report agrees with spreadsheet data for gear ratios multiplied by torque and hp at rpm, I will conclude that quickest overall acceleration is obtained by shifting at redline in every gear.

Butt dyno caught lying again. Lol. So next track day I will shift at redline (6700) on the back straight, see what real world data say. I have enough logs shifting at 5500 on back straight for a reasonable comparison.

 

[frankiefiesta]

The data I used in the spreadsheet are from my stock turbo running Cobb S3 V220 tuning. Torque peak 3100 rpm, hp peak 4825 rpm. And all the stock transmission gear ratios vs rpm graphs from the spreadsheet indicate using redline for shift points is quickest for acceleration.

Since Frankie has the only real world report,and his report agrees with spreadsheet data for gear ratios multiplied by torque and hp at rpm, I will conclude that quickest overall acceleration is obtained by shifting at redline in every gear.

Butt dyno caught lying again. Lol. So next track day I will shift at redline (6700) on the back straight, see what real world data say. I have enough logs shifting at 5500 on back straight for a reasonable comparison.

I know my experience is just word of mouth. I had the slips, never thought of posting them. Unfortunately tossed all my slips sitting in the center console before bringing my car in for service

 

[Siestarider]

I know my experience is just word of mouth. I had the slips, never thought of posting them. Unfortunately tossed all my slips sitting in the center console before bringing my car in for service

Talk about an abundance of caution. I am laughing. But I pull all the HDPE stickers and numbers off my car before I leave track, so we are on same page.

 

[RyFiST]

I use to drag race alot with all my other vehicles I use to own. From my personal experience, winding out all the gears to redline with very quick shifts in between gears nets the faster ETs than shifting before the powerband drop off. You may see a very slight mph change but usually the ET will suffer. I will state, I am no expert. I'm just experienced.

Example: Pre-technology tuning, 1999, My stock turbo, 90 GSX with minor bolt ons netted a 13.7@98mph using the shift early method. Then I followed up with a 13.3 & 13.4 @ 99mph just by shifting at redline. And that 14b turbo dies fairly early, almost equivalent to the FiST.

 

[dyn085]

Interesting, Dyno85 says what I thought to be true, Juliog and Frankie say what the data show.

Unfortunately HDPE experiences typically do not allow consecutive laps run at the limit to test this, always catching up to someone and waiting for a point by, not that I am good enough to run consecutive laps within a couple tenths anyway.

Drag strip is probably the only safe place to test shifting at HP peak rpm vs redline rpm to get the real world answer.

Actually, that's also based on my experience as well. My fastest time in the FiST was shifting right around 5500 rpm. But I'm also very green when it comes to racing as a whole because I don't have the time to invest into it.

Unless someone is extremely consistent it's very difficult to keep variables in check. Admittedly, my times can be skewed by that factor as well, but my fastest ST friends that hit the track consistently shift early (shortly after the hp starts drops) and wind out fourth. Ymmv.

 

[RAAMaudio]

I highly respect drag racing, always have, always will

BUT, the scope is focused much more narrowly than a quick canyon run, autocross, rally, road race track, etc, where things become far more complicated due to so many more variables.

Being in the right gear at the right time is paramount to being fast and being safe for the driver and or the car so knowing when to shift into the right gear for the moment is what is key.

 

[Beans]

Bumping this, shifting at Red line optimal for a stock car or 5500-5800 to get more into the torque curve? I'm sure 1st and 2nd for getting out of the hole, but does short shifting improve times?

What about launch procedure? 3k, slight slip, preload? Stock wheel/tire.

 

[Siestarider]

I now have enough track data with stock turbo to know shifting from 3 to 4 to 5 near redline produces my highest max speeds on longer straights. PBIR has a long back straight. Out of turn 9 in 3rd for me, I have compared 5500 with 6500 and the higher shift point generates highest terminal velocity. Difference about 5 mph just past 300' brake cones into turn 10 at that track.

Time difference using higher rpm shift points is around 2 sec a lap at that track. Spreadsheet wins.

 

[Beans]

Good to know, thanks! Plan on making the maiden voyage down the track Wednesday.

 

[Siestarider]

Have fun, and turn off TC. Save brakes from eating themselves. TVC will still intervene enough to use fronts hard, rears will run much cooler.

 

[Intuit]

5500RPM / 60 sec = 1 stroke every 0.0109 of a second.

So your piston moves up and down 91.7 times per second.

Those are some amazing stresses.

 

[Quisp]

That's all day interstate rpm on a 2 wheeler. And the stress goes up exponentially with rpm.