Didn't say sequential wouldn't work, it's the millisec rpm change without a slip element that's the problem. Instant rpm increase when downshifting is a huge deal given the T56's gear spreads and typical V8 rotating weight. Try clutchless downshifting a rwd V8/T56 combo while entering a decreasing radius corner with the weight transferred the front.

"Clutchless" shifting generally means you are not manually actuating the clutch, but that clutch still needs to slip as instantaneous ratio change causes either durability or traction problems. Even in the bike world where rotating assy weight is minimal, the clutch still needs to slip for effective clutchless downshifting.

Grant

 

Downshifts done correctly with a sequential box and throttle blip will be very smooth, and far better/safer than any attempts with an H pattern which can unsettle the car.

You're choosing to do them incorrectly from your description. Of course that is a bad option. Dont choose bad options.

 

You keep defending sequential, I have no problem with that. The part I have a problem with is with your claim of superior millisec clutchless shifts, as if getting the clutch to slip much longer than millisecs wasn't an important part of making it work.

I have an engine that gains no-load revs at a rate of 11,500 rpm per sec. My calculator says a full throttle blip for a "smooth" rev-match of a clutchless 1700 rpm ratio change would take around .15 sec. On a scale of "0" sec being an insanely abrupt shift and ".15" sec being a completely smooth shift, it's easy to see that millisec shifts require a carefully matched clutch capable of slipping when it needs to.

Grant

 

What a load of *****.

Have you ever driven or raced a car with a sequential ? And just exactly how are you going to get a clutch that slips only during a shift, but not at all other times ?

Your device for slipping on launch does have it's merits, but wishing to encourage a clutch to slip under full power when you want it to grip, is just silly. Likewise during a shift..ffs may as well just go back to an H pattern and using the clutch !

And who said anything about a "full throttle blip" ? Who on earth applies full throttle to try and achieve a smooth downshift ? That's just nonsense.

 

No different than my bike, unload power flick the lever power on.. Unless I'm really trying then it full throttle and bang the shifter hard..

FWIW,,, if you keep an eye on some of the SE venues in the fall, you can buy used NASCAR transmissions for very little, there are a couple outfits that freshen them up and sell them for about 1500 to 2500 depending on the box..

The clutch doesn't slip when you shift a road race dog box, you shift as you transition power in and out of the turns and upshifts on the straight are just a pressure on the shifter blip throttle gear is shifted back on throttle..

 

My whole point was doing clutchless downshifts with a sequential.

On a moto as you are talking about, downshifts without the clutch will cause the rear wheel to lockup or at worst temporarily unload the rear tire. If you have a slipper clutch on your bike (which is basically a one way sprag clutch that will unload during downshifts) you wont have an issue and your bike will down shift cleanly without that hard clunk you probably noticed.

If you are road racing your bike and do a clutchless down shift without a slipper clutch right before trail braking, you are almost guaranteed to highside the bike and if your lucky, lowside it right at the apex. Granted, there are beginners that are on the brakes so long before turning that its not an issue, but faster riders are in danger withought clutching.

Heres a quick overview of what a slipper clutch does https://www.motorcyclistonline.com/m...theyre-awesome

In a car, there is no such thing as a slipper clutch that will unload the torque on the transmission during hard downshifts on the track (road racing). There is one way to do a downshift without electronics and that is to lift off the gas, clutch in, heel toe your rev match and execute the shift when vehicle speed matches input shaft speed and it just drops in.

If you are in a honest to goodness sportscar and thousands of a second per shift could equal seconds less per lap, you are going to go with electronic shifting aids that not only handle the shifts, but also handle torque delivery during them.

This video shows just how fast downshifts are done in the C7.R. If anyone thinks they can downshift that fast and smooth without electronics while keeping the chassis entirely stable on corner entry, I dare them to prove it.

 

The .15 sec long wot blip was a hypothetical scenario for rev-match to get a completely smooth downshift without using the clutch. Opposite that was the "insanely abrupt" hypothetical instant shift with a clutch that doesn't slip and no time for any rev match. Those set both ends of a scale for estimating how harsh a downshift might be depending on shift duration without any slip.

It's not about making the clutch slip under full power, the trick is getting the clutch to slip enough to smooth the rpm change without slipping too much. To get a clutch to slip only after clutchless upshifts, one way is to closely match the torque capacity of the clutch to the engine's output. When rpm drops after the shift, that energy release will then cause the clutch to slip a bit until revs match. Excess clutch capacity beyond the engine's torque is basically what determines how long it slips.

Grant

 

Except you do not need it to slip. Just use proper shift controls, upshift cuts and downshift blips, and life and the box will run smoothly.

Simple, tried and tested and it works.

 

Oh I agree,, just kinda depends on the level of gain your looking for,, Like your saying if its a pro .001 seconds per lap are worth serious coin.. For me,, I'll stick with a dog box and use some finesse. I'm pretty easy on a transmission, I don't like to break stuff and lose.. I've had clients that had me swapping transmissions every weekend because they ham fisted the tranny so hard they'd break stuff.

I worked on a sports 2000 driven by a paraplegic guy with hand controls and a air shifter, the box was a sequential, working out the timing and adjustments was non trivial to keep the box alive.

 

It shouldnt be difficult, but I guess it depends on what you're trying to control it with.

If you need an idiot proof system that doesnt require any great skill to tune, Geartronics is what you need. But the full kit is pretty damn expensive.

But a proper sequential should be worth a lot more than 0.001s per lap. Every gearchange would be worth more than that, nevermind over an entire lap, plus the fact it will make the car easier and smoother to drive.

Or for a retrofit for these that cannot operate controls themselves, MME offer flexible kits based around pneumatics for all sorts of boxes, and can also incorporate a clutch actuator too if needed between shifts, although dont think it covers from standstill.

http://www.mme-motorsport.com/en/pro...paddle-shifter

 

Yeah I was talking thousandths (probably hundreths) per shift equaling SECONDS per lap.