Lavender

Some presumably retarded bean counter wanted to save 1 dollar 39 cents per car... I hope so at least because if its not the case then.... then it is not good!

PRE-Z06

Gotta understand the rules they’re trying to play by then…
http://fbaum.unc.edu/lobby/_107th/126_CAFE_Standards_2/Organizational_Statements/GM/GM_CAFE_Fleet_Requirements.htm
https://www.reuters.com/business/autos-transportation/stellantis-gm-pay-363-million-us-fuel-economy-penalties-2023-06-02/
https://gmauthority.com/blog/2023/10/gm-could-pay-6-5-billion-in-fuel-economy-standards-penalties-by-2033/amp/

AzDave47

1:38, not all that impressive now but that was 25 years ago and my first time there.

AzDave47

Yesterday I ran the Gila Bend 1/2 mile with the C8Z. We did have a ~15 MPH head wind. I was expecting 155-160 before the wind forecast. I did get one run in at 155.17 MPH. but even the top of 4th was slow to come and 5th for the last ~10 MPH was very modest, even more so than my C6Z after the 4th to 5th shift, but that was almost 20 MPH higher at 160+ when it was stock.

gsxriannew

Head winds are tough on ANY car at that speed!

AzDave47

My last run was against an HCI C6Z like my 09. I got him off the line good even though he started first and the starting line paving was really poor. I could see at about 125 that he was starting to catch me. He went by when I was doing 145 and trapped about 10 MPH faster than I did. I went and talked with him after and told him the run went as I expected, getting him good from a did but in a 1/4 mile I would have had a better ET but he would have trapped 4-5 MPH higher.

NORTY

I have no doubt that GM is listening to you. So, first thru fifth gets you 150+. So, since this is "only good for the top of fifth" the car needs to have longer gears to make the GM CAFE numbers. Having those gear steps close would give you only incrementally better pulls. It would NOT be "night & day." You'd have better luck taking 1000lbs out of the car. (This would certainly have a positive effect in "speed change" tho.)
The CAFE fuel standards are something that NO manufacturer wants to get a violation of. Would you be happy with your LT5 turning 4800RPM to make 75MPH in top gear? Think about the accelerated wear, the excessive heat build-up. Now, the car gets 20-21MPG on the freeway. Would you like to get 6MPG? You'd now have a cruising range of 100 miles. Is that good for you? All to spin the engine, needlessly. Would it be worth an additional $10,000 for this "benefit?" That's about what the fine from EPA would be, if amortized across all the C8Z06's. (Missing the CAFE standard by 2/10ths of 1MPG costs $50,000,000. And this was 15 years ago. Who knows what the fine would be, now that the current occupant at 1600 Pennsylvania Ave has devalued the dollar to record lows...)

Besides, how often do you "bury" your speedo? Exactly.

AzDave47

I only went over 150 MPH 7 times yesterday in my C8Z, and each time I wished for better gearing.







7 passes in the 1/2 mile NFZ event at Gila Bend AZ.

Ragtop 99

I don't think it would have that much impact on total rpms for vmax in 6th. Wide ratios encourage the use of higher rpms because the next gear is sluggish, so the car is slower to upshift. When gears are closer spaced, the ecm can set the part throttle shift points lower because the drop between gears is shorter. Even if they had to shorten 8th by 5% to accommodate vmax in 6th, the difference is less than 100 rpm at 80 mph. Maybe across all usage, the car uses 5% more revs over 100,000 miles, but in automatic mode they can control the average rpm used through the tune.

For scenarios with vmax in 7th or 8th, it would be an interesting issue because 8th gear would be significantly shorter.

jc123

I'm surprised nobody mentioned this already, but CAFE aside, GM could be saving the proper gearing for the ZR1/Zora to give it an extra edge in performance stats and lap times.

AzDave47

Presuming the ZR1 is TT, they will get torque that way. Zora with TT and electric motor, plenty of torque and front wheel traction, too, so neither will need gears for acceleration. They may do different gears to handle the added torque, though.

PRE-Z06

You’ve done a lot of high speed events, ever tried running a wide body Corvette with narrow body wheels to see how much of a difference it makes on the big end? I know skinnies make a difference in the 1/4, but curious how much rolling resistance matters at even higher speeds?

AzDave47

No, Just about all the Corvette runs I've done is with the OEM sized tires front and rear. I did run a wider set of front Nitto NT05s as my first aftermarket set of tires for my C6Z. They were OK, but the OEM sized PSS had more grip by a lot. I drive 100-500 miles to events on the tires I am going to run so being safe on the highway is important to me as well and also limits what tires I am willing to run.

This event was 150 miles away and I ran the OEM PS4S ZPs. It was 29* when I left my house. In warmer weather I might run the Cup2R ZPs that I have mounted on the OEM rims. Alternatively, I could drive down to the Valley the afternoon before and stay overnight. I will likely have to do that for the road course event in February. It is typically 15* cooler hup here in the high country than down in the Valley.

Red Mist Rulz

And the fact that they couldn't find a manufacturer who was willing to build a bespoke manual tranny for such a small market had nothing to do with it, I guess....

GM doesn't profit off dealer repairs. In fact, warranty repairs cost them money.

Back to gear ratios:
Tadge has publicly stated the engineering team want different ratios but management and the bean counters told them no, for cost saving reasons.

RapidC84B

Please show me where Tadge said this… he hasn’t AFAIK. He did comment on a higher top speed than we received.

348SStb

If that’s the case, I wonder if it’d be possible to swap that transmission into a Stingray/Z06.

RapidC84B

C8Z gearing is something I’d love to hear from Tadge. We know they know how to gear a car. The C6ZR1 box has shorter 5th and 6th so it can run hard up top and goes well over 200. You can watch roll racing videos of them walking Carerra GTs. Then we get a C7 ZR1 that will do freaking 212. Now we have a car that sounds neat, but is really flat up top.

348SStb

People talk about him by first name — is he a guy who is accessible or whom we could contact? Does he post around here? I had to look up the name Tadge and I am just finding out he is the chief engineer for the C8 project. Certainly it would be nice to ask him about this (and other matters).

rawbar

He used to participate in the forum in "ask tadge". He no longer does and hasn't for a long time. No, he is not accessible to the average joe. He also works for a massive corporation and thus is severely limited in what he is allowed to say. He's not going to speak poorly of other divisions within his own company (ie if bean counters or product team overruled technical decisions).

Lights ZR1

The C7 ZR1 has the same MH3 gearset as the C6 ZR1, with the addition of a 0.48~ 7th gear. And then there's the 8 speed auto.