4.10 would hurt. I have stock 3.42. If i had a 4.10, id top out at 140

 

I'm talking about 6th gear mang. The C6 Z06's 196mph run was in 6th.

 

you sure? i can see 6th getting like 5 mph extra, if that. what gear is in teh new Z?

 

http://www.f-body.org/gears/

Heres a calculator. 194mph with 3.42s in 5th. 4.10s knock it down to 162 in 5th. 225 with 2.73s. All assuming stock tire size and 6200 redline and the coupe trans. 6th gear is not big enough to support the load of a top speed run. At least not in a c5.

203 for the new Z with the calculator in 5th gear.

 

475-500rwhp would be a pretty good average I'd say. Some cars could do it with less power, but with perfect gearing, improved aero (lower car, remove mirrors, tape up gaps).

If you just took a plain jane stock C5 coupe and gave it roughly 500rwhp it would hit 200 in 5th gear pretty easily I'd say. 200mph is roughly 6400RPM in 5th with stock sized tires and 3.42s. I'm sure any C5 with 500rwhp would have the rev limiter moved up so that wouldn't be a problem.

Dope

 

With respect to the Z06 crowd (heck I’d have one if the top came off); I believe that while the Z06 crushes the coupe down low, the coupe actually hit more MPH on the top end, perhaps internet fiction???

 

Its true. The z06 has the m12 trans while the coupe has the m6. Slightly different gear ratios give the edge to the m6 cars up top.

 

Thanks for the info, that's what I thought. The Z still pours on the power pretty darn quick!

 

Top speed is dependant on 3 things only... horsepower, drag, and gearing. Weight of the car has nothing to do with top speed... all cars will get to the same top speed regardless of weight, but the heavy ones take longer. Its all about resistance... aerodynamics, tires, internal moving parts, and once that force matches the force put out by the engine in HP, then the car stops accelerating and reaches terminal velocity. The best thing to do is find a 5th gear or a 6th gear that ENDS where you want your top speed to be (6th is better). This approach will get your car to your desired top speed the quickest, for it is the last gear that takes the longest to get through, so you want to make sure that gear is the most efficient it can be and your cars peak hp RPM is calculated to fall on your desired top speed (200). Having 5th gear end at 180 is pointless.... unless you have 700hp, and you are after the 230 mph mark in 6th gear. TORQUE MEANS NOTHING... look at an indy car, no torque, all HP. 400 rwhp is capable of 200 I think. 450rwhp definately is. Lowering your car makes a big difference... its all about how much air you have to displace, and every inch counts, but the most important part is gearing bc if its off, youre done.

 

As far as the posts saying 5th gear is the best, perhaps in stock transmissions... but if you were going to modify the gears, 6 is always better than 5, and to prove my point try to get to 200 in just 5th gear from a dead stop... it takes longer. Now do it with 2, then 3 then 4 then 5 gears... the more gears you add the more often you are putting your engine at peak hp along the way... not rocket science. So setting your 5th to end at 165 (rough guess) and having 6th take you the rest of the way in would be an option. Idealy, if you wanted a top speed car, you would have tall first - fourth gear, and a short 5th and shorter 6th.... thus maximizing your engine through those last 2 gears.

 

The right way to work this problem is to determine what the theoretical top speed would be for your car based on it's peak dyno RWHP and the aerodynamic and rolling resistance characteristics of the car. There are formulas that work very well for this calculation if you know such things as Cd, frontal area, air conditions, etc.

Then, once that top speed is calculated per above, work backwards to find out how the gearing should be setup to make full use of the RWHP by making the peak RWHP and theoretical top speed coincide with each other at the top speed obtainable (by RWHP) with he appropriate gearing. In other words, the car can only go as fast as the peak RWHP will allow it to go, but only if the gearing is setup to allow full use of the car’s top speed potential which is really based on its RWHP.

 

While you're technically correct, 6th gear is impractical to use on a C5. Figuring in factory height tires, and the lowest gear ratio you can purchase (4.10 as far as I know), 200mph is roughly 5100-5200rpm. Far from the peak HP of a car that makes enough power to hit 200mph.

For all practical purposes, a C5 going for 200mph will do it in 5th gear. 6400rpm in 5th is 200mph and would be right at, or close to, the HP peak of a car making high enough power to hit that speed in the first place.

The only practical way I could see doing it in 6th would be to run 4.10s and enough power at lower RPMs to be able to pull 6th gear. Boost or a big stroker/427 could do it I suppose.

Dope

 

It will be much easier attainable with the G-Force gearing which switches out the 5th and 6th gear. 6th gear, 6200 RPM's will bring you to 202mph. I have just built myself a car aimed directly at accomplishing this goal. I will report back in several weeks when I give it a shot as I am still working out some kinks.

And for all thinking about doing this, don't forget, you need to drop this car for that kind of speed, I would and did upgrade the suspension, brakes, wheels, and tires.

Good Luck, I will post vids!!
Dan

 

not trying to be argumentative, but I had a lingenfelter vette, I wasnt gear savvy back then, but top speed on it (in 6th gear) was 165. it was geared for the drag strip, had 550rwhp, and would rev limit in 6th gear. I thought it was a 4.10 gear ratio, idk, maybe it was even higher. My point is, 6th gear is not obsolete by any means, and yes, there are gears out there that will drop 7200 rpm's in 6th gear well below 200mph. The forum works better when people speak from experience.

 

Which brings up a good question, which provides more rear wheel torque, sticking close(er) to 1:1 ratio and a tall rear gear (ex, .74:1 5th gear in MN6 and a 3.15 or 2.73 rear) or running way OD (6th, .50:1 and 3.73, etc)?

I would think one would want to stick closer to 1:1 (say the M12 .84:1 ratio in 5th) and a 3.15 rear gear, as opposed to running a shorter rear gear (3.42, etc) and a really tall OD. I'd be leary of dumping a ton of torque on 6th gear under sustained load.

FWIW the .74:1 MM6 5th gear and a 3.15 rear gear and stock height rear tires (~26.1) is good for 217 mph @ 6500 rpm, 233 mph if you can make enough power to rev to 7000.

 

As I originally stated, you want to gear the car tall in the first 4 gears, and short in 5th and especially 6th. Therefore, a 3.15 or even a 2.78, and then swap out 5th and 6th with shorter lower gears. If 5th and 6th werent swapped and kept stock... it would be geared for 240mph or somethign rediculous, but by swapping out just 5th and 6th, 1-4 get you up to taller speeds so by the time you swits into 5th and 6th, they have less mph distance to climb to get to 200, and then 5th and 6th magnify the engines power between very short ranges.... hopefully this makes sense and the poor guy who started this forum doesnt get told that a corvette cant be geared below 200mph with 4.10 gears in the upcoming response

 

High speed runs in 6th gear are not the way to do it. 6th is the smallest gear in the box+huge forces against the car going 200mph = Melt down.

Coupe are faster sorry FRC guys.

Randy

 

The C 6 ZO6 has a higher redline, so per gear it extends the top speed in each gear. I.E 62 mph in 1st,as oppossed to what ever the C5 1st is around 52mph. Also the TQ in the New Z may peak at the same # as some H/C cars but due to the cubes it has more under the curve especially in the lower RPMs and can pull 6th better.

 

Hmmmm I'd be very curious to see this T56 gearset that allows you to be well below 200mph in 6th gear at 7200rpm with 4.10s and roughly stock sized tires.

The only aftermarket 6th gear I've seen was .62 vs stock .50. The M12 in the Z06 has a .56 6th as well. You would need something like .80 6th gear to achieve what you're talking about - which is shorter than the stock 5th gear. It would have to be something like a 1:1 4th, .9 5th and .8 6th? That's pretty hard to believe. The only T56 I've heard of that could do that is the prototype sequential 6spd from Australia based on the T56. It had a .8x 6th gear and a 1:1 5th gear. I don't even know if they ever even made any production units.

They don't make shorter than 4.10s for C5 diffs (that I've ever heard of) so that couldn't have been a factor either.

Do you have some documentation or links on this?

Regardless, I can see that you're new here, I recommend not acting pompous. The entire question here, if you read the OP, was explicit in specifying stock T56 ratios. Hence, the different opinions posted in this thread centering around just rear gear changes and power levels.

Dope

 

To do it right, the tranny gear ratios and/or diff gear ratio need to be changed to "fine tune" the gear ratio to match the top speed potential defined by the car's RWHP and aero characteristics. The rear tire diameter also play a part in the overall "crank to wheel" ratio.