1996man

what is the top speed for a 6 speed ZF6 vett? im not talking about stock top speed i mean horsepower aside what is the fastest speed you could do in 6th gear if you had all the power in the world till you ran out of gear

MYCoupe

It's well over 200 MPH, but a ZF6 would not live very long at high RPMs in 6th gear.

Nathan Plemons

That entirely depends on the redline of the motor and the final drive gear.

If you're talking about a stocker with the 5800 RPM redline and 3.45 gears you've got a max speed in 6th is 257 MPH.

If you go with 4.10 gears it drops to 216.

Raise the rev limiter to 6500 and you're at 288 and 242 respectively, depending on gear ratio. Oh, and tire size plays a role too.

If you can open a Microsoft Excel spreadsheet I think this will answer many of your questions http://www.wku.edu/~nathan.plemons/calc.xls

1996man

why not? i thought it was pretty much bullet proof? what does the number work out to mathmatically? im trying to win an arguement that a late model C4 top speed gear limited is much higer than a 90 300ZX TT which is 207 (it only has 5 gears and a high rear end)

Nathan Plemons

Well the problem with your argument is that the gear reduction is the limiting factor in these two cars. You can go much faster in 5th gear than you can in 6th gear. I know you said to ignore the horsepower issue, but that means you're just changing the terms in order to win the argument

5th gear top speed for a stock LT1 vette is 171

1996man

nathan i thought you could only go faster in 5th gear unless you were putting out some incredible hp like over 500.

Nathan Plemons

The gear reduction kills you. Even with extremely high horsepower levels you're probably gonna run into clutch slippage issues. 6th is for economy only.

1996man

hmmm i see. but our 5th gear top end is still higher than 207 on the nissan isnt it? thats all i want to know! I love his Z very much but i know deep down that Vettes are better!

Nathan Plemons

Nope, 171 is all she wrote.

BAM92

Same with my 6spd Trans Am, you can reach a higher top speed in 5th than 6th.

1996man

171 is the gear limited top speed? why can ZF equipped ZR1s go over 180?

Z-07 freak

Car and Driver Oct-88 issue, page 41

"With six ratios, the ZF unit provides five gears for performance and a sixth, extremly tall top gear for fuel-efficient crusing. At 70mph in sixth, the engine is turning only slightly more than 1600rpm. In theory, that means that the ZR1 should be able to reach 306mph at its 7200rpm redline in top gear.
In reality, of course, the ZR1 isn't quite that fast: its estimated 180mph top speed actually occurs at about 6500rpm in fifth gear."

VAHROOM

Find a Hiway Patrolman, and go as fast as you can by him. He will let you know how fast a C4 can go. He can also tell you how fast you can go.

On the serious side, there are so many limiting factors. Theoretical and practical seldom meet exactly. A helpful theoretical tool can be found at Gear Calculator.

Nathan Plemons

Simple, the engine is capable of a higher RPM.

Take a look at that spreadsheet.

rocco16

Top speed for the stock LT4 in fifth is 169 at redline. (according to my 1996 copy of Car & Driver)
Is the LT4 'slower' than the LT1?
I know the LT4's redline is higher so that means that the LT1's rear end is higher than the LT4's AND it has the power to pull it at redline in fifth. I'm impressed.
(aren't all ZF6 car's rear gears the same?)

Larry
code5coupe
(slow day at work....)

VAHROOM

Tire size makes a big difference also. Make sure you are comparing apples to apples. For instance my buddy's LT1 convertible has taller tires stock than my LT4 convertible. Does that mean his is faster than mine? You just have to make sure that EVERYTHING is the same when you compare. EVERYTHING

88Blackonblack

Well having owned a 90 tt 300zx and a highly modded 91tt300zx, I can tell ya that no way did vettes hang at 160 mph plus...also according to my engine management computer in the 91, with the factory 245,45 16s my best top speed run was 191 mph in my Z...that is from the speed sensor not the speedo..Twin turbos own at high speed...

just passing that along.

JCD

Yeah, it's cheating to say the 6 spd vet is faster because of gear ratios.

It's a big PITA to try to figure out theoretical top speeds, and dangerous and illegal to figure out real world top speeds.

The problem with finding the top speed is that your power (ha-ha, I mean torque) is not linear, you can't just say: I have 300 HP, therefore I can displace about 300 HP worth of wind resistance.

You have 300 HP at only 1 place in your RPM range, but you have to get there first, what happens if you need to displace 250 hp worth of air when your dyno says you only have 250 hp? You stop accelerating.

So you need actual dyno results of each, exact gear ratios (including tires), coefficient of drag, and front cross sectional area (or whatever it's called). Then you can do some math.

It is possible that a higher rear end gear ratio will be helpful for top speed (it raises your RPM range thus getting more available power to fight wind resistance in 5th gear).

Check out these web sites:
http://auto.consumerguide.com/auto/u...ex.cfm/id/2347

http://www.supercars.net/cars/1996@$Nissan@$300ZX%20Turbox.html

Looks like they've got about the same horsepower and weight, looks like the vet wins the 1/4 because of better torque (16.5 seconds to 100 mph? slackers). C4 will out handle it.

Hope you didn't offend your friend too much!

JCD

rocco16

Then someone isn't stock.
According to the reference COR-VETTE SPECS, all '92 LT1's had 275/40-17 rears. All post-92 LT1's and LT4's had 285/40-17 rears. So, you see, no LT1 had taller rear tires than an LT4...stock.

(Finally got to use this $30 book....)

Larry
code5coupe

1996man

what do you mean when u say that in no way did the vetts hang with a 300ZX TT at 160mph? one was walking away from the other? are you saying ur zx had that much top end and the vett didnt? what kind of power were you putting out with the Z? Please give me more details on this