savyboy

Agreed, none of the slick Porsche Marketing Machine BS spew. GM and Viper are giving straight talk, no nonsense, direct to the enthusiast discussion.

"A car set up for track perfection"
"If you want a street legal track car...this car is for you"

Oh man...

jumper5836

Rev matching feature on the new Corvette. At 6 min into it.

Porsche has down-shift but Corvette matches up shifting. I think the PDK would not have so much advantage over manual's during the up shift if they had this feature.

GrantG

I don't think the upshift rev-match will make a manual as quick as PDK (almost seamless), though it's more fun...

Rev-match will smooth the shift, but not quicken them.

jumper5836

I speculate that it would close the gap. The shift is still faster with pdk but not losing rpm is why the pdk gains a 3/4 car length per shift or was in 1/2 car length can't remember.

GrantG

Nope - you're a little confused. To quicken an upshift, you Need to lose rpm's for a smooth shift. That's why the Keonigsegg has a brake on the input shaft of its gearbox to slow the revs for the next higher gear on upshifts. Having a light flywheel on a manual helps this.

The Vette just cuts fuel to the engine on upshifts - this does nothing to speed the shift (just makes it a little smoother).

The software on the PDK of the GT3 keeps the revs higher than normal on upshifts to give you that little shove in the back - reminds one more more of a manual, but is harder on the equipment.

jumper5836

So as I understood it. You move the gear shifter towards the gear and it either lowers or raises the rpm to match that gear. Wouldn't it be doing the same thing as pdk.

GrantG

Yes, both systems do rev-matching which improves the smoothness of shifts. But the speed of PDK comes from handing off from one gear with one clutch to another gear that is pre-selected on the second clutch - this advantage of PDK is not closed by the rev-match feature on a manual.

jumper5836

It didn't mean closed, I meant closes. Which I believe would still be the case. How slow do you really figure we are shifting it. It's not like were taking sips of our drink between shifts

GrantG

Instead of "closed", I should've said quicken. I don't think rev-matching quickens shifting at all. It can prevent a spin or loss of control on downshifts, if someone otherwise doesn't know how to heel-toe. And it makes upshifts smoother (and less likely to upset the handling balance during shift), but I don't think it helps the speed of shifts at all, up nor down (given a good driver). i.e. Laptimes should be unchanged.

jumper5836

I agree it doesn't quicken shifting. RPM drops as a side effect of slow manual shifting. This would negate that and keep rpm matched for the gear it goes into. Decreasing this is what is keeps the momentum up and allows less loss of acceleration during up shifts.

Z356

Thanks GrantG. This is an example of what makes membership in this forum so worthwhile for me. I am clueless about how new technology actually works at the mechanical level and I am learning quite a bit from reading these discussions!

Saludos,
Eduardo

GrantG

My pleasure. Also, I might've added to my explanation that downshifts might actually be a little quicker with Rev-Match than even a good driver who heel-toes. However, the time it takes to brake for a corner is much longer than the time it takes to downshift during that braking zone, so this is why laptimes are unaffected.

Rev-Match on Upshifts is really most beneficial to a driver who is very slow on upshifting - who pauses long enough for the revs to drop lower than the optimal point, at which juncture the computer can blip the throttle for a smooth upshift. For a fast driver, there really is no benefit on upshifts (without some sort of engine braking mechanism).

GrantG

Yes

StirlingMoss

So this is really for the Vette's "cars and coffee" crowd and not the "heel and toe" squad?

On a more serious note, great explanation. Even more impressed by the Swedes in the hangar now

C.J. Ichiban

I think the z/28 is awesome- for an american car company to release a 50k track car with light weight options pre-installed (I know it's a big car anyway but you need to challenge yourself to drive around it) just shows that there are some enthusiast targeted cars still being sold and not merely the bling crowd being catered to...

500HP and 470LB/FT with carbon brakes, 1.05G lateral and 1.5G braking is really impressive...for 50k it is a steal!

that is cheaper than an audi A5 cabrio