Overdrive.

 

90 GT, 2.73:1 rear end, ~3000 rpm at 80 mph.

The rpm/speed in gear chart is in the '90 owner's manual.

 

Just checked my owner manual... It shows 2300rpm at 62.5 mph (ie. 100kph). I couldn't reach the GTS's and chose not to transfer from wheelchair in to car just to grab the OM to check on that one. I'll be driving it tomorrow so I'll confirm on the GPS and in the OM on engine speeds at 60 mph and 100 kph...

 

For explanation why 4th in 4sp automatic is 1:1 see for example A28 Transmission Description of Operation.pdf in transmission section of Jim's tech CD1. Factory documents have all the info why 2.20 diff cars should run significantly lower rpms than 2.54 versions.

 

 

The true answer to the OP's actual question is simple: The S4 is a Rogerbox and the GT has that stickymabob. You can always tell one from the other on the highway because the Rogerbox is out front! Now, lets talk THAT one up!

 

Then there's Paul's car. You can tell it's Paul's because it's sitting in Davek9's driveway!

 

Where did you find 275/35X17 tires?

Driving back from SITM with 2 GT's few years back. My 2.20 final drive netted me about 22mpg while the GT's got 19mpg.
Was loafing around 2400 revs while the GTs were at nearly 3000.
Not sure what it was like driving for 8 hours at 3000 revs.

 

Yeah Andrew, you're right. I guess I'm just a poser right now. Hopefully, I'll be able to pick it up this Sunday for the 100 mile trek back to Saginaw. The weather looks like it MIGHT co-operate.....Ice & snow = no drive. Dave has had my car more than I have in the past 2 years and now I'm only $10K away from having a $12K 928. But I'll suprise you someday and show up with a completed ride that runs great and looks great inside and out. I have to admit though, back in the day I've been in some fast MF automobiles (panteras, cobras , street rods, etc.) and your SC/GT rocks!

 

Glad to hear you're getting back on that horse again. That car runs really nice now. It's amazing how 2 bad injectors and old wires can affect how well it runs. I think you'll be very pleased. Now it;s just a matter of getting the body work and interior done.

 

AO, just two injectors and wires? Did you forget about the water pump, all new cam gears, PK tensioner, all new belts, fuel lines, vacumn lines, injectors, plugs, caps, rotors, intake refresh, TPS, crank sensor, knock sensors, fuel pump, relays, coils, battery, all new hoses, new radiator, new rotors, pads, ss brake lines, tie rods & boots, shocks, Eibachs, X-pipe, all new fluids and filters and a bunch of of other WYAIT stuff besides, that were put in that car in the past year!!! You were there. I'll need new shoes (and socks) the interior is waiting to get installed after I get the dents from some Yee-haw's pickup truck out this spring. Then I'll be able to cruise (but not compete) respectfully with your beast and the rest of the Michigan 928 OC.

 

No no... I didn't forget. Just since the last time I touched it when we were trying to find the miss. I know Dave did some other work after that, but that was a real head-scratcher. The old wires had tons of corrosion at the ends, so that was part of the issue. Then two of the new injectors you had him put in were not working. Just goes to show you that even new parts can cause issues.

You'll be crusing in style soon.

 

Actually in my GT with xpipe and RMB....the 3000 rpm range is way better than the 2400ish in my old 87S4 with the same xpipe/rmb. There seems to be a resonance that develops around 2400 rpm that is really annoying..so in the S4 you either go slower ... or faster.. With the GT it all nice and mellow sounding at 3K and the car feels like its right on the edge of "jumping" at your will...

 

I need a 4.5 gear between 4 and 5.
Like those electric overdrives 5th gear Volvo's had back in the day.

 

Heres chart easier to look at on ratios.
https://www.928gt.com/t-928trans.aspx