RonBrooksGA

My questions is simple but I can't find a graph on the internet. All I want to know is the engine rpm on a '94 Corvette at 70mph in a manual transmission equipped model. My '95 Porsche 968 has an LT1 engine transplant and the prior owner put in a track gear pack from 3rd-6th and the end result is 3000 rpm at 70. Great fun for acceleration up the gears but I do a fair bit of highway driving and I want to change 6th gear out for a taller gear and would like to know what GM had in the engine's original installation.

Thanks,

Ron B.

leesvet

depends on the rear end ratio...

RonBrooksGA

I should have said that I am referring to the original stock ratio, not any performance ring and pinion factory or aftermarket application.

1991Z07

The factory ZF6 had a .54:1 final drive ratio with a 3.54 differential gear.

Mine runs about 1800-2000 I think at 70 MPH...at 55 MPH it is around 1300 RPM.

You've also got to factor in rolling diameter with that...I run a 285/30Z18 on the car...slightly bigger than stock factory tires.

96GS#007

5th gear is 0.75
6th gear is 0.50

Rear ratio depends on year. Early ZF6 years had 3.33 (my 1990 for instance was 3.33). A very limited number of cars had optional 3.54s. Later cars all had 3.45s. As I recall, all the ZR1s had 3.45s. Clear as mud?

rocco16

In sixth, with standard 3.45 rear, I will be turning about 1700rpm at 70 mph. I know because it drones until it hits 2000rpm and that is at about 82-83mph.

QCVette

That is very close to what I get also.

I thought that the 0.50 6th gear ratio with a 3.45 rear ratio is on almost all of the C4 6 speeds. I have only heard of a very few different ones.

Like 96GS#007 said though the early ones might be different.

WVZR-1

The most important thing for you to do is ID the trans that you're using currently for us, the tire size and the rear axle ratio that's present. I can't say that anyone that I know of off hand used 6th for a "cruise" with regularity. I would assume you would try to attain maximum drive-ability in 4th (1 to 1) in the trans and 5th and 6th are a +.

You don't mention the gear @ 70MPH just RPM's. There's not many gear packs available for most of the transmissions and there's I believe 2 vendors that offer packages that use different combinations.

The intention of the original drive-train was to move let's say a 3400 lb car both economically (CAFE) and with some appreciation of the power by the driver.

An axle ratio, tire size (rolling radius), and an RPM/MPH chart for each gear 4 - 5 - 6 is required to help you really or even to offer up comparisons.

Everyone has posted "I think" or "about" - you need to start with where you "ARE" and determine the changes needed with "your car" to get to where you'd like to be. It's that simple.

First requirement I'd think would be do a speedometer/odometer check by GPS and maybe confirm that with some measured miles. If the speedometer isn't accurate the numbers ain't worth "squat"!

With rear axle ratio, tire size and if you measured the rolling radius, confirmed the speedometer, and did 60MPH drives in 4th, 5th and 6th I believe the transmission ratios could be calculated and a comparison gear pack done from there. Whose rear axle is in the car? If we know whose and you just do the 1 tire rotation and count the rotations of the pinion, matching that to brand should be a confirmation of the real rear axle gear.

Thirty minutes of your time plus the speedometer/odometer check with 60MPH drives should make it very easy to determine where you "are"! Depending on rear axle maybe the change actually needs to be the rear gear!

QCVette

I use 6th regularly for cruise on the highway. It drops the rpm down and that is when I get the best mileage. On my '94's with a 6 speed and 3.45 ratio I could get 30+ mpg. If I used 5th on the highway I got about 3 mpg less. That is really about all the 6th gear is good for. On the stock LT1 cars top speed is done in 5th gear.

WVZR-1 makes some good points to check out what yours is. I have used the GPS to check the speedometer as a first step and then check the rpm.

WVZR-1

6th gear is all about "location" "location" "location"! My car has seen 6th maybe a handful of times in 10 + years, 5th frequently but NOT what I'd say "often"! I would say I could go for weeks without seeing 6th maybe months! Really!

Photomania

My 1990 coupe with a manual transmission was around 1800 to 1900 rpm at 70 mph until recently. The tachometer began malfunctioning about a year ago and now it says 3,000. Eventually, i'll replace the part of the system causing the problem.

Phat98

Had the Tech2 plugged in the other day doing some troubleshooting...stock '96 LT4, 3.45 rear gears, stock tire size...in 6th gear, at 70MPH on a level road, the RPMS were 1650-1680 RPMs.

Churchkey

From ZF Doc's web page:

ZF S6-40 General Specifications:
Gear ratios - 1st-2.68, 2nd-1.80, 3rd-1.29, 4th-1.0, 5th-0.75, 6th-0.50, Reverse-2.50
Description - 6 Speed 95 mm Fully Synchronized
Weight (w/shifter) 145 lbs
Lube Capacity ~ 2.2 Quarts (engine type oil P/N 1052931 or BMW P/N
07510009420)
Reverse Lock Out Mechanism - ('89-'95) On-shift handle pull-up to release, ('96) Crash-thru (force required ~15 lb.)