FDDYNAMICS AND THE MID ENGINE CORVETTE, A CAUTIONARY TALE

 MID ENGINE CORVETTE????????? 

The September Road and Track interview of Tadge Juechter / Chief Engineer 2020 Chevrolet Mid Engine Corvette was highly relevant to the FD.

ROAD AND TRACK'S first question:

WHY Mid Engine?

"Biggest was the limit of performance. We knew we were in trouble bringing out the 638 hp (542rwhp) C6 ZR71 and we had a hell of a time beating the 505 hp (429 rwhp) Z06 0 to 60. It was only because of the Michelin tires that we were able to... We couldn't hook it up. So that was kind of the start of it. Fifty-fifty weight distribution is great when your not power limited. That's why race cars evolved with the engine in the back. You really want more like 40/60 so you can get the power down."

With 215 rwhp our 50/50 FDs, as well as the Miata, have no traction issues. Unfortunately it is all too easy to add power and a 350 rwhp single turbo setup is considered conservative, 400 still not crazy, 500 is sporty and 600 is within reach on pump gas and meth AI with pretty good durability.

Yet Tadge is saying that 429 rwhp is about the limit for the 3130 pound C6. at 50/50. The 638 hp version ended up with 335/25 tires on a 20 by 12 inch rear wheel. weight was 3353 with a 51/49 distribution so the all important rear weight was 1643 pounds.

The mid engine Corvette weighs 3566 curb weight according to Autoweek/November. Mid engine cars generally range from 56.5 to 59.3 (as per August Car and Driver) so let's use the middle:

3566 X .579 = 2065 rear weight... so a primary reason for the mid engine Corvette was to gain 422 pounds of rear weight.

FD rear weight 2862 X .5 = 1431

recap:

2013 Z06 505 flywheel/429 rwhp, 3199 curb weight, 1600 rear weight, 335/25/20. 3.73 pounds rear weight per one rwhp

2013 Z06 ZR1 638 flywheel/542 rwhp, 3353 curb weight, 1643 rear weight, 335/25/20....3.03 pounds rear weight per one rwhp

2020 mid engine Corvette 495 flywheel/421 rwhp, 3566 curb weight, 2065 rear weight, 305/30/20... 4.90 pounds rear weight per one rwhp

FD

255 flywheel/217 rwhp, 2862 curb weight, 1431 rear weight, 225/50/16... 6.59 pounds rear weight per one rwhp

let's solve for same FD rwhp per rear weight relationship matching the 505 FWHP Z06:

1431/3.73 = 384 rwhp

Chevrolet had to upsize the rear tires on the 638 hp C6 to barely "hell of a time" beat the 505 hp Z06 which is the equivalent of a 384 rwhp FD!

Obviously there are many qualifiers here but there is some truth also. Ask most really experienced track (we are talking road courses) guys and they will tell you that they really don't need much above 400 rwhp to get the most out of the FD chassis. Additional hp sort of goes up in tire smoke and becomes extremely difficult to manage. There is nothing wrong with additional hp and it certainly results in faster times in the quarter mile but on a road course physics rules.

As you get up above 500 rwhp, given our rear weight it does become easier to go sideways or lose traction. Of course you can engineer around almost everything but for many of us in this web based world where everyone wants 600 rw (bigger is better?) perhaps, given our 1430 rear weight a bit of judiciousness might be in order as we contemplate our FD mods.

My background is road racing and I have always considered front weight to be evil, which is another way of saying rear weight is good. i have around 52% rear bias. i do recall talking w a 630 rwhp 20B FD owner at the Rotary Revolution. He had his car running well with a smallish turbo to limit the power (630)  but said he had to be very careful as even at 140 mph his FD could go sideways unless he was very careful with the right pedal.

Having power is one thing, being able to efficiently use it may be another. Now that we better understand tractive considerations let's just look at power to weight... what do we FD pilots need to beat the hottest cars in a straight line?


answer: not as much as you'd think... (thanks Mazda for the 2860 curb weight)


Consider these comparative rear wheel power to weight ratios:


2019 Corvette ZR1 LT5 3560/ 642  = 5.55

2019 Corvette Grand Sport  3428/391 = 8.77

2018 Porsche Turbo S  3550/ 516 =  6.88

2018 McLaren 570S 3300/ 478 =  6.90

2018 Merc Benz AMG GT C 3804/ 468 = 8.13

2018 Accura NSX 3868/ 425 =   9.1

Nisson GTR NISMO 3920/ 510 = 7.69

2019 Aston Martin Superleggara 4100/ 608 = 6.74

2018 Ferrari 812 Superfast  3593/ 671 = 5.35

2020 Camaro LT1      3685/387 = 9.52 

2020 Camaro ZL1 3883/552 = 7.03

2020 Mustang GT 350  3662/447 = 8.19

2020 Hellcat Redeye (797 flywheel hp)  4429/677 = 6.54




1993 Mazda RX7 2862/ 215 =  13.31

1993 Mazda RX7 2862/ 350 =   8.18

1993 Mazda RX7 2862/ 400 = 7.15

1993 Mazda RX7 2862/ 450 =  6.36

1993 Mazda RX7 2862/ 500 = 5.72

1993 Mazda RX7 2862/ 550 =  5.2

1993 Mazda RX7 2862/ 600 =  4.77


Feeling better about your 450 rwhp FD? it will beat all but two of the supercars, although with only 1431 rear weight traction will be a consideration.