Is there any rule or common experience for which cars got the MK6?

From what I can tell, if you ordered a Formula or GTA with a 305 5 speed, then you got the better MK6 tranny and the 3.45 or 3.42 rear end.

If you had a Trans Am with a 305 5speed, then you got the regular 5 speed and the 3.08 rear gears.

Just curious if anyone has more info.

Mark.

 

My 91 Formula with the high output (dual cats) TPI 305 came with the MK6 and 3.42 limited slip if that helps any.....

 

When you wanted certain options and bought the car new it was special ordered with those RPO from the Factory. Not like today,you have to take what on th new car dealers lot and the salesman will say" whats a special order ??". So it depended on how smart of a performance guy the orginal owner was to get the items you quoted by special ordering them.

 

What is MK6? And why is it better?

 

I agree on the special order thing.

I am just finding that you could not order a G92 on a 1987 Trans Am. The G92 appears to give you the better gear ratio and the tranny with the lower overdrive.

Now a GTA or Formula you automatically got the G92 without having to specifiy it.

1987 was a strange year. I think you could have ordered some odd combination with the right dealership.

Mark.

 

MK6 is the world class 5 speed, which is a little stronger than the non-world class version.

 

All T-5 Camaros and Firebirds had the 2nd design trans from 88 up. The different design of trans is not any kind of RPO code. Strictly date-related.

MK6 has to be something else. Perhaps the better 5th gear; .73 instead of .63.

 

Don't think so, but I could be wrong....

I still think that's the 5 speed tranny identifier.

 

Could be that; but it can't possibly be a RPO code for a 2nd design trans, with some other RPO code for 1st design. Which design you got wasn't a RPO issue.

 

Typically (in 87 and 88) when you got a 5 speed, you got option code "MM5". In order to get the lower 5th overdrive, you had to have a second option code, the MK6 as I recall.

My question was ... what triggered the MK6? It seems that the cars with G92 received the MK6.

At some point, GM may have gone to just one V8 tranny instead of the two.

Mark.

 

I don't know that. My 83 car came with the better overdrive, as did every L69 or G92 T-5 I've had; but the lesser cars had the .63. Mostly the LG4 and RS cars were the ones that got the gas-mileage OD gear, that was so low that some of them wouldn't go up hills in 5th, especially with the 2.73 rear gears.

It was amazing some of the things GM did to these cars to deal with the unrealistic CAFE requirements in those days. Between that and emissions, the majority of them really got the short end of every stick there was. You had to try REAL HARD to get a car that wasn't nutted.

 

Don't you mean de-nutted.

 

Well yeah.... nuts removed. What they call "nutted" in the livestock business. I don't think it's possible to re-nut an animal once he's been nutted.

 

The LG4 and RS cars got the transmission designated M39. I've always wondered what the difference between the MK6 & M39
is.

 

MK6 means the lower (better) overdrive.

Mark.

 

Can you define "better"? Which ratio is the MK6, the .73 or the .63?

 

MK6 : TRANSMISSION, MAN 5 SPD, B0RG WARNER, 2.95 1ST, O/D
MM5 : MERCHANDISED TRANS, MAN 5 SPD PROVISIONS
G92 : AXLE REAR RATIO, PERFORMANCE
M39 : TRANSMISSION, MAN 5 SPD B0RG WARNER, 77MM, 2.95

The "better" overdrive was the .73...which came in ALL the 5 spd 1LE cars...MK6 was on the Rpo sheet in order to make the .73 gear to be legal in showroom stock racing....only the 1LE 5 spds got the .73..

A little info on why there are 2 different..adding to what RB said, even with the 3.42's, the 5 speed cars would get walked in 5th gear long straitaways by those LX notch's, so gm added the .73 to better suit the TPI's torque curve..not only did it work it was common to see cam/birds passing coming out of a corner and pulling them down the straits....


With G92 you get the MK6 RPO but you had to have 1LE to get the MK6 .73 gear.....

 

Prior to the 1LE cars, the Players Challenge Cars in 1987 and 1988 also go the MK6 tranny. I'm sure some were also build for the US based firehawk series too.

Mark.

 

I don't know anything about getting "walked" by Mustangs; as I described, my 83 car, from the days when the best Mustang you could get was about a half-second slower, came with it. I doubt that anything to do with Mustangs had anything to do with it.

I know it had it because it was in there the first time I tore it up and had to rebuild it, in 86. About the same time I obtained a lunched T-5 (mainshaft snapped off right in front of the splines) for parts, out of a 84 L69 car; also with the .73.

I'd suspect it was the other way around..... that is, the .73 is the "right" ratio, most suitable for actually moving the car most effectively; but for CAFE they used this other ratio in as many cars as they possibly could, that produced higher gas mileage numbers on the tests regardless of whether it actually worked well in the real world or not, and forced you to go out of your way to special-order the more suitable ratio which lowered the results on the test and hurt the product line's CAFE.

 

hahaha, nice. I have an 86 tranny in my car and I turn 1750 rpms at 70mph with 2.73's, that would be .63 right? 2 things 2.73's dont suck for, 30 mpg or 90mph in third gear, heh.

 

i copied this directly from www.1Le.org

http://www.1le.org/1le's.htm

This was not enough to motivate the heavy Camaro's past the lighter Mustangs, and passing was impossible in the high speed straights. The lack of Fifth-gear torque was a direct result of GM trying to improve fuel economy and emissions for the everyday car buyer. Originally, GM equipped all five-speed manual F-car transmissions with a 0.62:1 overdrive Fifth gear. This gear was too tall and the Camaros couldn't even get out of a Mustang's way on the long straights. A steeper 0.74 gear ratio was slipped quietly into all five-speed transmissions slated for installation into the 1LE Camaro's. The gear swap was combined with an aluminum driveshaft to lighten the car and decrease the drivetrain's rotating mass saving power. This all became a factory-installed option, thereby meeting the rules and keeping costs down as well.


i dont know anything about those pre TPI cars, and i wont pretend that i do nor will i argue about the fact that your 83 had the better 5th gear, but as i said the .74 5th gear (IN TPI CARS) came from being WALKED by mustang down long straits....
if you didnt have 1LE then you DONT HAVE the .74.....

 

GM did many things back then. While it is true the 1LE cars came with the .74 gear, so did many other cars.

All Player's challenge cars from 1987-up came with the 0.74 5th gear except for 11 or so of the first 1987 Camaros. All other had them from the factory. This was part of the A4U option package of the time. As these cars were built exclusively for the showroom stock racing, all the parts had to be GM, although there wasn't any rules that they had to be production.

In 1986, the cars came with 3.73 or 3.70 rear gears, so the 0.6x overdrive was more useable. In 1987, the gears dropped to 3.45, which created some problems.

The 1LE group of options was ultimately born out of the Players Challenge racing series and the firehawk series in the US. There were many early version of these options that are not well documented. You can discuss 1LE for many hours on what was and wasn't included. Bottom line ... GM did many things each year. Suffice to say ... if you have a 1LE, you got the good stuff. If you don't have 1LE ... you might. My 1988 Trans Am, which is not a 1LE car, came factory equipped with the 1LE front brakes ... one of the first cars to leave the assembly line. I have documentation and I have spoken directly with GM and the people that installed them. The only reason 1LE came out in 1988 was to make the heavy duty brakes "production" and thus make the cars legal to race in certain races. Chances are all of the 1988 1LE production was very late in the year ... well after all the race cars proved them to be a "production ready" option.

Mark.

 

L69 cars got the good gears (.73) as well as, appearantly, the 1LE cars.

MK6, IIRC, was the RPO for the actual trans itself, and MM5 was the RPO for all the other stuff the manual trans required.

 

My 84 Z28 has MK6 and MM5 on it's SPID sticker, and was powered by the mighty LG4. It had the .73 OD and the GU5 3.23 rear.

 

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