mark kibort

so, to make this easier to understand for everyone. just tell me what the new max MPH would be in each gear.
as i mentioned, a 3.09 in a GTS box, only really changes 1st gear as compared with a stock S4. the rest of the gears are almost the same, except one disadvantage, you loose 5th gear for a 1st gear that is basically useless.

On the track, ive been able to use my stock S4 2.2 first gear on occasion. (ie traffic slowing me down in a hair pin, SpeedGT Standing start , etc) but with an even lower gear for 1st, i couldnt see a need for it, especially since with big race rubber 1st gear is right on the limit for keeping traction with 300+rwhp.

the MPH for the S4 2.2 stock gear box is:
1st 50
2nd 80
3rd 118
4th 150
5th 225

for a 3.09 in a GTS box (from memory)
"sub" 1st 39mph
1st 55mph
2nd 80mph
3rd 115mph
4th 155mph
no 5th

the above is reasonably close for sake of argument. the bottom line is, its all about the speeds in those gears and how they relate to redline.

Now, some very skilled drivers could be able to take advantage of a "sub" 1st, with the right tires and power levels. for most of us, it could just be an advange to keep the car in gear in traffic without having to push in the clutch when crawling along in LA traffic

mk

Jim bailey - 928 International

Once and for all let's get this straight....first gear in a 2:20 rear geared 928 is for ZERO to about 50 MPH ! Up to about 30 MPH the engine is running below 4,000 RPM so it is much down on power. Unless you slip the clutch the engine boggs down when the wheels stop spinning after the launch and the wheels slow down to match the speed of the car at which time the LONG SLOW pull up to redline approx 50 MPH Put in a lower final drive and you get through 1 st gear much faster and spend much less time below 4,000 Rpm and maximize the time above 4,000 RPM. Quick cars are measured from zero-50 mph , fast cars from 50-100 mph , and most 928s from 100-150 mph To understand the effect of gearing on acceleration you need only try a drag racing start by starting out in second gear ! To feel quick you need lower gears ... 0-40 MPH it is ALL about gearing ! Road racing where you seldom go slower than 40 MPH it is a very different discussion.

Scott M.

Mark;

You know i'm just screwin' with ya, right? The devil makes me do it.

Gary;
Sorry, I was thinking Gary Rovelto (auto) but typing to Gary I. (5 spd)
One option to improve the bottom end slightly from a gearing perspective is to drop in a trx from an 85-86 Euro w/ the 2.72 ratio or change the ring/pinion from an 83/84 with the 2.34 ratio. Not many would go to such trouble though.
I put my 84 on a 400 lb diet and am now impressed with it's bottom end pull.

Shane

^^^What he said^^^


Thank You!!


By the way max speeds for 2.20 box using 2.72 gears with a shiftpoint @ 6500rpm:

1st-44mph
2nd-67mph
3rd-93mph
4th-123mph
5th-180mph (if you have the HP to push it there)

mark kibort

most draggers are never caught below 4,000rpm, and for all practical comparisons, real draggers have such large soft rear tires that im sure most are redlined at 50mph too! (equating the same gearing as our 928s)
that aside, your right, if you dump the clutch and have to wait the long wait as you say to 50mph in a 928 1st gear. however, you have to also think of the next shift and the time spent in that gear. its all about HP seconds applied, and as you mention, staying near the max hp available. Im sure with some tallent, a 3.09 GTS could have a better launch and have an edge to 39mph as we simulated with the computer and also keep the lead to the 1/4 mile race. (dending on a few factors though, how much HP and the resultant speed at the end of the 1/4 mile dictating the final most important gear. if you dont redline in the final gear of the 1/4 to the finish, the guy next to you could be pulling hard and catch up and pass. you see this all the time.

the rear end effects and shifts the entire equation. it could help, but then again, it could hurt . If you could play with all the ratios independently, then yes, you would pick the best 1st gear and space the rest to get redline at the end based on your hp levels. Plenty of guys change out the rear ends only , and dont really change their times in the 1/4mile as it becomes a game of give and take. The Vipers guys are notorious for this.

Mk

mark kibort

no worries, I know! i just need an excuse to write:

acceleration = Power/(mass x velocity)

Mk

mark kibort

That does become an interesting road racing gear box. still never using 5th and never really using 1st. (i cant remember the last battle i was in where i even used my 1st gear)

but the speeds below match up wth some of the tracks i visit. however, i would get killed for any track over redline at 123mph. (ie thunderhill) and not be able to take advantage of the most used gear in the gear box, 3rd with a top speed of 115, where it is used to redline and mid sweepers more than any other gear. adding up the time i spend in 3rd, vs the advantages in 4th, it would be a net gain at the tracks i visit.

It would be a terrible gear box at road america, where you would have to use 5th, where you would get killed. also, it would be bad for anyone doing a stroker and had more HP to get to the 130mph range on some tracks.

It would be perfect for drag racing where your top speed at the finish could be near 120+mph. (ie 11+ second ET ranges)

mk

Jim bailey - 928 International

Mark yea shifting is bad ! "It has often been said that a Pro Stock car is one of the most difficult cars to drive in all of drag racing. Indeed, Pro Stock drivers stay plenty busy during each six-second run. Beginning with a carefully orchestrated pre-race procedure that includes a tire heating burnout, a Pro Stock driver carefully inches his car to the starting line. Reacting to the first hint of a yellow light from the Christmas tree, the driver quickly releases the clutch pedal and then must make four separate gear shifts. Each shift must be perfectly timed in order for the car to achieve maximum performance. As if staging, leaving the starting line and shifting wasn’t enough, a Pro Stock driver must also concentrate on keeping the car as straight as possible during the run before finally deploying the twin parachutes which slow the car from over 210-mph at the end of each quarter-mile run...." They use ALL 5 gears, rev to over 10,000 RPM and set up the clutch which is ONLY used on the launch to SLIP to allow the engine to carry high RPM through first gear. Like I said if you think gearing makes little difference just try a quick standing start in 2nd gear , third gear, 5th gear for that matter, once that sinks in you might see the benefit of a lower gear

Shane

It is not a track car, but a street car, and the way it is makes it a blast to drive.

On the 1/4 mile track...might be fun but an auto would kick my *** because I'd be shifting too much.

I'm happy that you are happy with your 2.20 box on the track...

Steve Cattaneo

On a 5speed the differential pinion is part of the Trans main shaft. If the contact pattern on the ring gear is not correct, the differential will sing.

You will need one of these to tame that new found rear wheel Torque.

Shane

That is pretty cool Steve!

I haven't noticed any abnormal noises coming from there, and mine has a mechanical limited slip on it. Is that Quaife compatible with our trannies?

Steve Cattaneo

No, it’s not compatible (I tried it) with a 928 Differential carrier, the MB carrier is bigger, as well as the side bearings.

mark kibort

I never said gearing makes little difference, i said changing the rear end may not do what you think it will just for making it numerically higher! there are trade offs, especially, if you are only moving the shift points up and down, and keeping the spacing constant. We are not talking about launching in 2nd or 3rd gear we are talking about a launch that balances clutch slip, tire spin, grip and power available. for many stock cars, this can happen effectively with a stock 1st gear that redlines at 50 mph. If you do some research on 5 speed drag machines, its not uncommon to see them hit redline in 1st gear at 50mph. If so, they are geared very close to the S4 stock 1st gear.

The gears are used to keep the engine as close to max hp ave as possible.

mk

6.0-928S

"If you do some research on 5 speed drag machines, its not uncommon to see them hit redline in 1st gear at 50mph. If so, they are geared very close to the S4 stock 1st gear."

I've been drag racing for almost 40 years & I've never, ever, seen a 4 or 5 speed drag car reach 50 mph in 1st gear. Unless the engine can spin 15,000 rpm! How can a car with a 4.56 or 5.13 rear cog (& most have a 3.05 first gear in the trans) go 50mph in 1st ?
Hammer

mark kibort

10,000rpm and big drag slicks. what's the diameter of the rear tire on real drag cars again?

I forget the statistics, you may have them at the top of your head if you have been doing this for 40 years. 4.56 could do it, especially if you had a real drag slick on a drag car! (corrected per Jim)

With a 4.56 and 3:1 transmission 1st gear, that would be 13.6:1 total ratio. if the tire is 32", then effectively, the top speed all other things being equal would be near the same as our GTS with a 10.5:1 ratio as far as top speed. If the rpm was higher by 10+% to near 7500rpm, then the top speed would be identical in 1st gear at redline. If both cars, the S4 and the dragster were putting out the same hp and shaped curve, the torque at the rear wheels through the gearing would be the same for the entire 1st gear run for both cars. Thats comparing a 2.2 vs a 4.56 !!!

MK