On 2001-08-22 11:44, Rippied.Z06 spewed forth this drivel:
Pat, thanks much! I am making about 320 rwhp and 380 rwt at 4400 rpms. Sounds like it would be enough to pull 6th at those speeds. Since you are good with ratios and rpms, what speeds would be pulled in 2nd, 3rd, and 4th at 6600 rpms with 3.90s? Thanks. /phpBB/images/smiles/icon_smile.gif
If your car was geared to drag limit at the peak HP RPM of the engine, it could 'theoretically' go 177~178 MPH. This is based on a Cd = 0.31 and a frontal area of 21.3 ft^2 for the Z06.
At true top speed where you are drag limited, the available RWHP is equal to the sum of the aerodrag + rolling resistance to maintain that speed. In the model case of the Z06 with 320 RWHP, it will go 177~178 MPH in ~70 deg air at sea-level. Of the 320 RWHP to the ground, 240 RWHP is to overcome aerodrag, and 80 RWHP is to overcome the rolling resistance of the car on the pavement.
Stock Z06 gearing says 176 MPH in 5th gear at 6500 RPMs actual (not indicated, which could be off alittle bit). Peak RWHP is at ~6000 RPMs, so it seems that most stock Z06s will be able to pull near red-line in 5th gear which is what your seeing.
If you put 3.90 diff gears in it, the RPM at 178 MPH is ~5000 RPMs, which is below the peak RWHP hump. Therefore, I would say it will NOT pull any faster (and probably slower) than 5th currently does.
IMO, GM has already set the Z06 up to drag limit at near peak RWHP in 5th gear /phpBB/images/smiles/icon_eek.gif. Of course, if you had some mods and extra RWHP, then using 3.90 gears would get you more than 178 in 6th gear. My calculations say that even a 2002 Z with 350~355 RWHP would not benifit from 3.90 gears. Putting 4.11 gears in a Z with 355 RWHP would pull nearly 185 MPH in 6th gear.
pmontelo -- I think your numbers are a hair high. I get 264 MPH in 6th gear at 6500 RPMs with 3.42 gears, and 176 MPH in 5th.
On 2001-08-21 15:18, Rippied.Z06 spewed forth this drivel:
I saw in West Coast Corvettes latest that they carry 3.90 gears. Would a Z06 with 400+ rwhp and 400+ rwt be able to pull 6th past my current 177 mph top speed in 5th with the stock rearend? If so, what would you estimate it would pull before it became drag limited?
It would take a Z06 with 403 RWHP to go 194 MPH if geared perfectly, and you had a LONG road to get upto top speed. My calculations show that 3.90 gears may do it in 6th (194 MPH = 5450 RPMs), BUT 4.11 gears would probalby work better (194 MPH = 5750 RPM, closer to peak RWHP point).
If you plot out engine RPMs vs. Speed in Excel, you can see that there is a HUGE gap in the gear ratios when going into 6th gear. I don't think GM ever intended 6th gear to be a top speed gear. If you where actually only interested in top speed runs, it would actually be better to gear the diff UP and stay in 5th gear. As you can tell, gearing is all dependant on how much RWHP you have -- every time the RWHP goes up, typically so can the gearing to take advantage of the extra HP. Unfortunately, for a stock Z06, 5th gear is already at or close to it's rev-limit at drag limit, and 6th gear is a far cry too tall compared to 5th. The best solution might be to change 6th gear ratio in the tranny if possible.
BTW - I like crunching numbers if you couldn't tell /phpBB/images/smiles/icon_biggrin.gif
