heinrich

Ya know, I've heard this said many times and I don't understand it. My Godzilla broke tyres loose only when i wanted it to. Even with the 2.64. 249 horses, 249 feet pounds.

danglerb

Only time a high ratio matters is when you have traction to match, and outside of a drag strip it doesn't take much to smoke tires instead of go fast.

Cheburator

So the co conclusion is that the 2.64 and 2.72/3/5 boxes suck... Great, I can only see their price going down then...

Abby Normal

Not really. The lower gearing means that if the wheels are spinning, they are spinning at a slower RPM and will have a better chance of hooking-up than a wheel speed that is faster.

GlenL

Huh?

The final drive changes the MPH that you shift at and not the RPM.

On a road course, you want a rear axle ratio that'll let you use all of the engine capabilities. For a track with wide speed (MPH) range that means being between the HP peak and redline in 5th when at top speed.

There are details in the specifics of a track. Could a different final drive prevent redlining just before a corner? But, generally, being in the power band more often puts more torque to the wheels. "More often" => "Closer MPH shift points" => "more gears used"

Ahhh... Saturday

victor25

A G28/11 is from what car? I just bought a used 5spd to put into my 89s4. When I purchased it I was told it was form an 87. Now that I have it cleaned up, and am ready to install, I see it say G28/11. It sounds like the 87/88 cars had the G28/12.

dprantl

G28/11 is from '85-'86 US 928s and has a 2.2 rear pinion. G28/12 is from '87-'89 Euro S4s and '89 US S4s and has a 2.64 rear pinion. '87-'88 US S4s had a G28/13 with a 2.2 rear pinion.

Dan
'91 928GT S/C 475hp/460lb.ft

victor25

thats what I thought. so is there and advantage or disadvantage if with the 85/86 v 87/88. whats the difference? and what about the LSD?

danglerb

The LSD, IIRC is a 12 stamped between the ID and serial number as in G28/11 12 11856

victor25

It is an LSD unit, and your right, there is a 12 stamped between the 28/11 and the serial number.
What I really want to know is ... whats the difference between the 85/86 and the 87/88 trans. I had an 84 928 and it shifted like crap. I hear is has the better syncros, so will it shift nicely like my 89 does, or will this one have the same like my 84 did. I am sure they must have upgraded something from 86 to 87, or they would have the same numbers... yes?

mark kibort

Glen, what???
yes, the final drive changes the MPH you shift at correct. isnt that what ive said for 10 years now???
also, the rear axial ratio will optimize the HP available. you say this as well.

however, if you are looking for top speed, that will happen at max hp optimally, if you have a choice.

now, ive always talked about the "trade offs " at the track. its not just the gear that gets to redlie on the main straight. its the HP-seconds you optimize overall. so , if you have a few straigths where you can hit redline before the braking zone, this will be more often, more valuable than optimiing for the main straight, unless we are talking road ameria, where there are three times you hit the high speeds and there is MORE time spent at those speeds than any other, so that woud be a track to optimize for on the main straights. Again, it depends.

my point is that ALL the gear boxes have the same gear spacing and this is important to understand. However, with the 2.2 you have a wider spaced 4-5th , which doesnt matter unless your track speeds are over 155mph for any given straight, and then gives the advantage of MPG on the way home if you drove it to the track.
make sense??

Mk

mark kibort

no real difference other than the stronger synchros with the 87 box vs the 85. ive had both and they are both excelent, epecially compared to the early boxes without the borg warner sychros.

the extra torque , makes it very hard to control wheel spin, unless you are just blindly flooring a 928, in 1st, where you get wheel spin runnaway with a 2.2. the main trade off is can you get mechanical grip with the 2.75 to take advantage of a lower first. keep in mind, its not as much lower as the difference in rear end would indicate. (i.e this differnce is < the differnce of the 2.2 vs 2.75)

yep, i have 400rwt and 1st gear is just a blur out of the hole.you can only handle about a half throttle launch and even if you do hook up, its for a very short time. If there is a trade off in all the next gears, i would focus on the speed range you generally run at or race at, and make your gear decision about that, unless your goal is strictly about being in 2nd, and having more fun in that gear alone.

Shawn, you are one of the few who actually get it! good for you.
yes, 2nd gear is a feather gear, 1st is way too much, even with heated up 335 size race rubber. i can ony go full throttle with 1st, when im already going 40mph, and the car is pointed straight. if you notice on my race videos, 2nd gear corners require a little bit of finess to keep from spinning the rear wheels on turn exits.

in the the end, all the gear boxes serve different speed ranges. pick the range, and thats the gear box you will need. no one vs the other is better overall. the 2.2 does have the advantage of the tall 5th for fuel economy, and keeping the rpm down, at no real cost vs the others. (unless you actively spend time accelerating from 155 to 170mph, or are a drag racer. )

ive said it before and ill say ti briefly here again. how the gear vs speed over lap happens. (why gears dont buy you HP), is because when the higher ratio rear end shifts, having its 10% advantage vs the lower rear end ratio, it then has a 30% disavantage for a 10% of the shift speed differences. (e.g. if i shift out of 1st at 45mph with the higher rear end ratio , the one that shifts at 50mph in 1st will have a 30% adantage from 45 to 50mph when it then shifts to 2nd, even though it had a 10% advantage up until that shift point.) repeat through the gears and all the HP , to the wheels , should be even, or near even. again, this is why a IVT runs at max engine HP rpm, not at max torque.
So, the closer the ratios, the more advantage the gear box takes of the available HP. in otherwords, if you have a close enough gear box ratio set, the rear end becomes a non factor, except for drag racing in 1st. this is because
acceleration = power/(mass x velocity) . as long as you are ever at the same HP level as your opponent, (or other gear ratio comparison), you will always accelerate at the exact same rate, even if one has a 10% mechanical gear ratio advantage. think about that one for a second. If you understand that, you graduate and understand the essence of gearing!

(example would be two 928s one with close ratio gear boxes, even with one wiith a 2.75 and the other with a 2.2. If the RPM drop of both is only 10% (like a cup car), then both engines are always between 5500rpm and 6500rpm, which is usually two ends of the HP curve peak. car A at 6500 making 300rwhp and car B making 300rwhp at 5500rpm, will accelerate exactly the same at all speed ranges, even though one has a 10% mechanical advantage over the other one. note: assume an even arc HP curve before and after 320WHP peak at 6000 in this example)

victor25

Ya know guys there is a very simple answer to this often disputed ratio thing. look at the specs for the 88 and 89 s4. Same engines and power, just different trans... RIGHT?. So now look at the 0-60 and 0-100 times. Who is faster?!? duhh

mark kibort

you still dont get it, do you ?? just read and try and understand what I wrote above and you will.

all gear boxes have some subtle advantages. none "suck" as you point at the 2.2 earlier. as someone that requres maximization of the HP i have, i would gladly have swapped out my 2.2 for something that made my car faster, but nothing in the physics world pointed to any reason that this would be true for the tracks i drive at. in fact, all the math points to trade offs for the speeds i race at . (i.e. 40mph to 155mph at the very fastest). so, i could fine tune by using the 2.64 at thunderhill, the 2.2 at laguna and the 2.75 at sears, but that would be a lot of work for very little gain, dont you think, PLUS, there might even be some non optimal gear shifting speeds that could hurt lap times, or rpm levels in turns that could hurt the engine.

blown 87

Sadly Mark, it is you that simply does not get it.

As far as the 2:20 VS the 2:73 I have in mine, it is pretty simple, it will accelerate faster in EVERY gear, and has a higher TOP SPEED.
How freaking hard is that for you to get?

Personally, and I can not speak for any one else, it was interesting reading your thoughts on gearing the first 3-4 times I read it, but dude, after about 70 times of you talking the same thing, about a race track that pretty much only you drive on, well sir, it kind of gets old.

I drive on the streets, and I suspect that others here may also drive on the streets, and a 2:63 or a 2:73 is quicker, and faster on the vast majority of the 928 on this board that do not have high dollar strokers or blowers.
It really is pretty simple.