I still have no clue.. I am off to bed, but tomorrow afternoon ['round 3 ish] I can type up this info page on self diagnosis if you would like. If someone else wants to type it up sooner that'* fine too.


-justin

Your car was built in February '91, as was mine

Hokay: lets clear the air a bit:

ME9 is the order code that the dealer checks for a 4 spd/OD automatic

F79 is the installation code for a 4 spd/OD trans with 2.97 ratio final drive. This code is found on the option sticker either under the hood or in the trunk. Other 4T60/440T4 sticker codes are:
F17 - 2.84, FP3 - 2.73, GX3 - 3.33, GW9 - 2.93

Then there is a four digit alphanumeric code that is found on the transmission itself (many many). e.g. 1990 Bonneville with GX3: 9pah, 9pbh, 0wxh, 0pah

Finally, there is an eight numeric digit part number for the transmission that is how the transmission is ordered e.g reman 1990 SE with 2.97 gear trans: 24212204

Finally, the best place to find a 3.33 GX3 is behind a 2.8 or 3.1 engine from something like a Grand Prix or 6000STE. 3800s usually received longer gears.

Ok... I just need some things cleared up...

With a final gear ratio of 3.33, does that mean a higher top speed, or I just get upto speed quicker then someone with a final gear ratio of 2.73?

Higher numeric gear ratio (go from 2.97 to 3.33) means higher rpm for any given speed. Will get to speed faster. Will probably result in lower mpg. Can calulate on any four function calulator e.g. 2000 rpm @ 70 mph with 2.97 = 2242 rpm @ 70 mph with 3.33 - about 10% difference. Don't forget the understood "to 1" as it is a ratio not an absolute number - for every 2.25 complete revolutions of the engine, the drive shaft goes aroound once (am not going to get into differentials).

Terminology gets confused since often people refer to drag race ratios as "lower" even though they are "higher numeric" and why I make that distinction. This is probably because "lower" gears (first, second, third) result in higher numeric ratios e.g. first is often around 12:1.

Keep in mind that 2.97 is the final drive ratio. Since 4th is an overdrive ratio of .76 (or is it .78 ?) this means the *overall gear ratio* is 2.97*.76 or 2.25:1, a really long gear aka a "high" gear.

A lot of the mpg in modern cars is because the pumping losses (go up with square of rpm) are minimised by a slow turning engine - back in the bad old daze, the 400 cid engine in my '72 station wagon was turning 3200 rpm at 70 mph from the three speed THM 400. Is a lot of the reason it got 12.5 mpg and this was with a 3.08 "economy" gear.

Today we have a 234 cid engine turning 2000 rpm at 70 and getting 25 mpg. With decent performance. Of course if that is not enough I have 400 hp and a 4 speed in the garage that gets 11 mpg of 93 octane (and boosters) through a 3.55 posi axle and 255x60x15s on 8 inch rims. Have to feather first and second to avoid smoke. Of course since I only use about two tanks a year it doesn't matter too much.

Lower top speed, higher acceleration.

Have seen cases where a lower (numeric) gear meant a higher top end. Bonneville may be a case in point since with 35 mph/1000 rpm, at 4800 rpm (hp peak) it would be running 168 mph. Of course three factors limit that:
1) 160 hp won't get you that fast
2) At WOT lockup does not occur
3) The fuel is cut off by the PROM at 125 mph (stock tire limitation of SE, may be lower in LE, dunno).

So the theoretical top speed with a 2.97 in a '90 is 125 and the same speed is reachable by a 3.33, the computer is probably the limiting factor (nonwithstanding, the effective top end is probably more like 110-112. They do cruise nicely at sane speeds though 8*).

Wife had some kind of rental rice burner on her recent trip. Said yesterday it was nice to be back in something that could accellerate.

SO technically it is possible to go 120 with a 3.33 right? Does that include that the tranny only goes into 3rd at WOT? Also, is there a chip available for the Vin C to get rid of the limiter?

a) only drag/hp is limiting speed below 125
b) 125 mph cutoff is just a byte in the PROM, changed mine at same time I revised the fan turn on speeds to keep engine under 190F. (Cannot just do for people, am on travel too much and have only a few reprogrammable memcals).
c) think WOT just keeps it from locking up (TCC), not out of 4th but never had mine beyond 3rd at WOT. Anyone know for sure ?

If I play with the pedal I can shift to fourth and get 111 before it shuts down, 3rd should hit the speed limiter before it hits the rpm limiter though.