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IMO, straight cut gears and sequential shifting can reduce lap times, but gear change speed is only one of the elements that need to be addressed. Gear change speed improvements should be part of a systematic approach to gain maximum benefit; i.e. to achieve the greatest reduction in lap times. A measurable reduction can be accomplished with gearing specific to the track, and should be examined no matter what the shifting method. To realize the benefit, information from three sources is needed: 1) Results from dyno testing so the engine’s power band can be established 2) Historical track data so that entry/exit/straight section speeds can be determined 3) A simple PC based gear ratio program to quantify and analyze potential benefits.
There are simple computer based programs that take tire size, final drive ratio, and gear ratio inputs, and output RPM, speed, and RPM drops between gears. Graphic output is best, with RPM on one axis and speed in each gear on the other. I still use an ancient DOS based program called "Ratio" which has served me well for many years. I even used it to determine my gearbox ratios for the Bonneville Land Speed car I’m building. At some point I believe it was rewritten in Windows, but I can't find it on-line. Can anyone help with it or something similar? A good, simple, flexible program is uber handy and a must-have in any serious racer's virtual toolbox.
To minimize lap times using gearing, here’s how I would proceed:
1. Dyno the engine to determine the power band in which you want to stay. Ideally, the power band is that which provides the maximum average HP in each gear.
2. Divide the track into segments, then use historical speed data for each segment and use the program to try various gear ratios, tire size, and final drive ratios. If you’re able to make changes that eliminate a shift (or two), there’s a big bonus since lap times will drop even further. Remember, consider changes in tire size, gear ratios, final drive ratio, and engine tuning.
3. Finally, consider potential improvement with various gearbox/tire/tuning solutions and align with the ever-present budget restrictions.
MM
Last edited by michaelmount123; 01-08-2017 at 01:58 PM.
Understand what you're saying and largely agree with your recommendations. In general terms the stock gearing isn't too bad. This clip is with the 2.5ltr 8v motor which we missed some tq of the earlier 3.1ltr 8v.
Ideally I'd like a shorter ratio dog box that we could get into 6th gear on the track. At this stage we're just over 7000rpm in 5th gear (155mph +/-) on our longest straight. We don't even get into 6th. Not sure what the new motor will give us. I 'guesstimate' and 'wishtimate' at least another 5mph. I'd like another 10mph but perhaps drag and distance will win out. Ultimately any modifications like these need to be reviewed with one eye very much fixed on budget and return on investment. In my mind unless a small miracle happens, or I'm forced into finding an alternative due to the stock components not holding the new motor's power, then I've decided to put a bit more budget into revising the Aero. However, in your opinion what do you think about shot peening or cyro treating of internals?
That's the same one Gustaf uses. To buy and install one of these it would be min $40k Aussie. Nice piece though.
I was directed to that site because I found a Subaru guy in Oz selling his KAPS 6-speed sequential that he bought from them...he was selling it for like $14k.
Wonder if you could whip up an adapter to use such a Subaru box?
alternatively here is a Subaru 6-speed modified with a "dog gear seat" made by PPG.
trans is located in Florida currently but is only $8500, guy seems motivated. https://forums.nasioc.com/forums/sho....php?t=2821451
Thanks Spence. I can see that you were on that forum and asked on my behalf. I think I know that guy and his car actually. Wonder what he's switching to, or is he selling the car? I think ultimately Subies just don't work for out and out Time Attack.
Not just the adapter though. But yeah, it 'could' be possible. I'll send him an email. Looking at the Subie model box though...where do the driveshafts come out?http://eng.kaps-transmissions.com/pr...l-gearbox.html
Just for fun I dug up a few datalogs from a laggy DSM I tuned last year. It shows how quickly boost can recover with a simple No Lift To Shift (NLTS) triggered by a switch attached to the clutch pedal.
This first datalog shows a typical shift when lifting off the throttle. Rev limit is 8500 rpm. Engine Load is boost psi. Like I said, this car had a very laggy turbo. It took 1.8 seconds for boost to reach 30psi after the shift. This was a relatively quick shift, the throttle was closed for just 0.4 seconds.
The next log shows NLTS. Throttle remains at 100% and boost drops slowly during the shift. This was a relatively slow shift to show how boost is sustained, the pink Ign Timing line shows when NLTS was active.
Despite the slow shift, boost only dropped to a minimum of 14psi and recovered much quicker, full boost was regained in 0.8 seconds, one full second and 500 RPM quicker than a regular shift.
Glad to help.
Be aware that a good quick shift might overwhelm tire traction when the clutch is re-engaged. If you shift while turning in a slight bend it might suddenly kick out the back end. Some of the better standalones will let you set ignition timing, fuel afr, and idle valve position when NLTS is active, so you have excellent control over power recovery.
01-02-2017, 04:11 PM
