John Veninger

When you have the right final drive ratio for the type of driving you want to do.

LTCMontana

Interesting debate. However, as MTCARRERA noted earlier, there is another way to achieve lower 1-4 ratios without affecting 5th. You have to start with a pre 85 box though.

The result is quite impressive. While there is a huge gap between 4 on 5, on the shorter (not long straights) tracks, it is a big advantage to get the rpm's up quicker coming out of slower corners. 5th is left alone and can still acieve a high top speed if that is what you're after.

It is a very engenious set up that works quite well. You have to dig into how the trans works to understand the situation. Gears 1-4 operate off of the 5th gear cog as I recall. So, by changing on gear in the transmission, you change the first four ratios.

Slantnose!

So...
What are the available options for a different final drive, anyway?

John Veninger

All depends on year and if automatic or 5 speed. 5 speed is a major change that usually requires a complete trans change unless you get a custom shaft made since the pinion is part of the transmission

3.09 (custom made, only a few out there that I know)
2.75
2.72
2.64
2.54
2.20

I hear there are 2.36 and 2.27, but never seen one.

Vilhuer

2.36 is used in US and Japanise '83-84 A28.01 automatics and 2.27 is optional in same period ROW 5sp to provide extra long 5th for autobahn use.

For modifications early eighties 5sp boxes allow most variations. Its possible to build interesting combination by mixing different diff and gear possibilities. End results just tend to favor ssome particular situation. Its hard to beat US '87-88 S4 manual box as general all around choice. It has 1st through 4th that provide nice acceleration and 5th which is in reality more like 6th. Too bad its not as strong as later GT and GTS boxes.

Slantnose!

Oh, o.k.
I've been really liking this thread...
Regarding my car ('89 S4), is changing the gear a big job and how high can I go?
Have always thought it would make the car alot more fun for messing around town and occasional autocross.

Jim bailey - 928 International

Mark you are still wrong...and admit it " for which we all know a 2.2 is way too high to be useful for any kind of acceleration in the lower speed range. " So why the discussion ??? I suggest that YOU carefully read what you have written...

mark kibort

in my 1984, it came with a 2.226. it already had a pretty low set of 1-4 gears.

generally, it was about 8% lower geared than the S4 or 85 US box, and 5th was near the same.

mk

John Veninger

John Veninger

I love the 2.64 driven by the stroker........ when it doesn't blow up!

mark kibort

Now you are just beeing stubborn. You are like arguing with my 5 year old who just comes back with " no".

Im not wrong Jim. the 2.2 has half to do with lower speed acceleration, the tranmission has the gears that make up the final drive ratios.

right now, its near 9:1. More importantly, its the speed of the redline. at 55 MPH its the same as most all supercars in the world.
with traction and HP being variables, you need to match the 1st gear to the cars ability to apply the HP. if you have street tires and high hp, then a higher 1st will work better. low hp and high grip tires can use very low gears. (think honda civic on DOT drags) again, as i always say, it depends.

you never re-read the posts. if you did, and looked at the comparisons with the simulations, you would clearly see the trade off effects.
the vipers that are shown here (and i could have shown this for the 2.75 gear box vs the 2.2. again, not the bolt on 2.75 rear end alone) are showing the effects of a 16% rear end only change. trade offs are hp applied at start being greater, but from 25mph onward to the end of a 1/4mile the taller set up is faster. it even ends up with a faster top speed. the difference overall with the 1/4mile times are different, but not dramatic. the difference from rolling start to 110mph is different to the same extent, but favors the taller rear end.

its all about application of HP over the operational speed range. along the way after launch its a series of " give and takes". Now, take that viper set up and start appliying reality of grip and the advantages even out of the hole will be even less. assuming that the initial tire slip happened at part throttle anyway!

Jim when was the last time you raced or drove or dragged a high HP car?

Just because your 190hp 928 likes smaller tires by 8% and it "feels" faster, doesnt mean it will make everyone faster for all applications.

again, it depends.

Mk

mark kibort

you coulnd be more wong for track use. having been one of the only racers on this board that has raced the 2.26, the 85 2.2 and the S4 2.2 as well as the 79 and 82 2.75 as well as a 500hp 2.72 928, i can clearly verify that there are trade offs at ALL tracks for a given set of gears, or with varying the HP levels.
PLEASE anyone that doubts ANYTHING i am providing here, needs only to pull out a Carrol racing book and read the section about gearing.

its all about opimizing the amount of time you spend on a road course or drag strip, at max HP levels. to do this you need to know your approx speeds down each straight, speeds out and through each of the turns. one level HP matched with a rear end or set of gears CHANGES once you change any of the variables that can change your speeds in any area of the track.

for example, my gear box is optimized for laguna Seca and road america. but at sears, buttonwillow and willow springs, its a little off. and pretty close to optimal for Thunderhill. once i change my hp to go from 320rwhp to 420rwhp, all things change. going to 520rwhp, things could change right back.
you need to look at how much time at any and all areas of the track you spend at or near max hp and try to increase that. other areas of concern are when shift points are created where you dont want them.

again, it depends.

Once you understand that acceleration = power/(mass x velocity) and that acceleration is proportional to power its very easy to see how to make a car as quick as possible by selecting gears that match your application. lower is NOT always better.

Mk

mark kibort

what are your speeds in each gear. is it a real 2.64 or a 2.2 that has a 2.64 rear end. how did it feel at Sebring. did you reach redline on most of the straights?

How is it going to be at road america? same or different?

mk

Jim bailey - 928 International

Mark does the 2007 400 hp 2007 Vette count ? And perhaps your 5 year old is smarter than his father thinks he is ? You already admitted that you were wrong "for which we all know a 2.2 is way too high to be useful for any kind of acceleration in the lower speed range. " why not accept that fact ! If you define close ratio gears as how many gears do I have to use between 0 and 120 mph lowering the final drive gives you more gears . You have agreed that more gears are better than fewer gears it allows the engine to run at closer to maximum power... And quite frankly Mark your S-4 is not exactly a high powered car either...

mark kibort

Jim, stop and think a minute. closer gears do not equate to "how many gears"
Yes, we agree that closer gears increase the time spent at near max HP.

2nd. i never said my 928 was high hp. although, 400hp flywheel is not low. but i have driven and raced on the track several 500hp 928s.

I dont define how many gears i use between 0-120mph, as close ratios. Close ratios are HOW CLOSE THE GEARS ARE TOGETHER!! this doesnt change when you just change the rear end.
If you lower the rear end and you get a lower set of gears and you end up with a shift at the end of the target speed range that doesnt tap into the HP available, that is a trade off by definition itself! you now have used more gears, but it hasnt bougt you much, except for a better launch (maybe, depending on traction and hp variables). along the speed range, you have a series of comparitive trade offs.

The only facts here Jim, are the ones im bringing to the discussion.

so, to your point of having more gears. the question is how many? what is the limit. 5? 6? 10? where do you stop? with each shift taking .1-.2 seconds there is a cost, that has to be weighed to see if it is offset by operating closer to the hp peak. if it is a flat hp curve toward the end, wider gear spacing can be as effective as a close ratio gear box mated to a peakie HP curve. (assuminng same max HP)

look at the simulations, see what you see. Jim, you are making gross assumptions that the change in rear end has the benifits for all applications. this is a real life situation that didnt yeild a faster 1/4mile time and the owner was puzzeled until i did this chart for him, based on his actual Dodge viper.
why didnt his ET s go up from the 12.5s to the 12.0s as expected?? TRACTION! and driver ability im sure as well.

mk