worf928

MK, I personally would have used a phase that describes a small difference rather than similarity in the interests of precision. Regardless...

It seems that you are fixating on a GT w/3.09 while I originally targeted the 2.20 rear for the 3.09 'upgrade.' Remember that this thread started on the topic of LSD conversion with the additional question of a f/d change.

Replacing the 2.72 in a GT/GTS with the 3.09 is probably silly since - yes - it is a small change. Better to spend money on something that yields a bigger change. But, if you (not 'MK you' but the anonymous reader) have an open-diff with lower-than-2.72 f/d, and if you can get a limited-slip with a different f/d for less than the cost of a GT/GTS box and you can pick the f/d, AND you've decided that you want to spend your money in that part of the car, then... why not pick a f/d numerically equal to or greater than 2.72?

mark kibort

no, Im fixating on ANYONE that would do a change to a 2.2 or 2.75 gear box, to gain a imaginary gain, or in other words, a gain that will be less than 3%. Best to change to a limited slip rear end, as this is an easy change with the 2.2 open diff. now, the 84s have the best gears in my opinion, next to the GT /GTS gear boxes with the 2.73 rear end.
Now, as you so acurately posted a few posts ago, (ive copied the chart below), you can see that a 3.08 S4 creates a gear box, that is very close to the GTS gear box, but the problem here is the first gear becomes even more UNUSEABLE. (ie max speed in 1st of 35mph) coincidentially enough, the rest of the gears almost match to a T the S4 gears. but you would be using 3-5thgear, instead of 2nd through 4th HOWEVER, one big problem !!!! the 4-5gear drop internal to the S4 and 2.2:1 rear end gear boxes, would give the S4 like result a BIG disadvantage in the shift from 4th to 5th. THERE IS A 50% drop in rpm where normally, the spacing in most all gears are in the 75% range. this is key, if you racing or otherwise, as going up to 97mph and then having a 50% drop in torque, would kill its performance, even though the top speed would be close to the S4 in 4th gear in stock form. anyway, you can see the ratios. just do the math and make the assesment. from my eye and experience, its a no brainer to leave the stock gears alone, unless someday, AS KIM SAID, we can get that GTS with a 3.09 but make the transmission gears all closer together and make 1st gear taller too!!

The S4 and 84 S boxes are nice. dont mess with them. dont call them "EPA" gears either. from 2nd to 4th gear, they are very close to most all high performance street cars. its not until you get to the fuel factory race cars where the gears get to be in the .8 to .85 drop, like in the 996 cup cars or the PGT BMWs. the C5, M3, and others are alll in the same range as our cars now. why would you want to create an S4 gear box for a GTS gear box (by the 3.09 conversion) why would you want a 84s gear box, out of a S4 gear box, with a 50% drop from 4th to 5th gear???
and this mod on a 84 2.226:1 with a 3.09, is a big problem!! dont even go there. (plug in the ratios if you want, but it is even a bigger mess)
even a change to a 2.72 on a 2.2 makes a mess of a gear box. better than the 3.09 but a mess none the less.

MK






It seems that you are fixating on a GT w/3.09 while I originally targeted the 2.20 rear for the 3.09 'upgrade.' Remember that this thread started on the topic of LSD conversion with the additional question of a f/d change.
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Based upon the above I'd say that a GT w/3.09 is basically like an S4 box

Replacing the 2.72 in a GT/GTS with the 3.09 is probably silly since - yes - it is a small change. Better to spend money on something that yields a bigger change. But, if you (not 'MK you' but the anonymous reader) have an open-diff with lower-than-2.72 f/d, and if you can get a limited-slip with a different f/d for less than the cost of a GT/GTS box and you can pick the f/d, AND you've decided that you want to spend your money in that part of the car, then... why not pick a f/d numerically equal to or greater than 2.72? [/B][/QUOTE]
code:--------------------------------------------------------------------------------
RPM 4000 6400 4000 6400 4000 6400 4000 6400
Gear GT 28.55 S4 28.13 GT (3.09) S4 (3.09)
1st 26.9 43.0 30.9 49.4 23.7 38.0 22.0 35.2
2nd 40.3 64.5 46.2 74.0 35.6 56.9 32.9 52.7
3rd 56.6 90.5 64.9 103.9 49.9 79.9 46.2 73.9
4th 74.8 119.7 85.8 137.3 66.0 105.6 61.1only if a GT box is also 'basically' like an S4 box. [/QUOTE]


__________________

Carlos

Mark, you may have a point as relates to road racing. But in a drag race, all things being equal, the 3.09 gear car will win. ET is all about 60 foot time & the 3.09 car will have a significant advantage. If my calculations are correct, my S4 would go 209 at red line. All the calculations on earth will not change the fact that geared to go 160 or so, that same car will provide more torque to the rear wheels hence better acceleration.

mark kibort

I have to say, wrong. at best you would look at an equal deal.

again, look at the ratios that come out of a 3.09 GT box. same as s4, except a lower 1st and a slightly talller 2nd. 3rd and 4th almost identical. so, going to 110mph or 120mph, (depending on the rear wheel hp) will require the S4 , 1s through 3rd gear and the GT with 3.09 1and 2nd (as I said, these both would have only an 8% average lower ratio combined, yet you only spend about 1.5 seconds in an S4 1st or the 1-2nd GT 3.09, PLUS you have a shift. do the math, a shift would equal , easily, the 8% gain in those two gears vs the S4 1st)

you also have to think about what gear allows for better hook up. tires and other factors will be very important. Having done standings starts in both the 2.26 and the 8% different 2.2 S4, I can tell you both are pretty scetchy with grip, even with hot race tires. Im in first, for shorter than you can imagine. (with 300rear wheel hp, and more hp would mean even less time in 1st gear)

dont be fixating on the final drive ratio or "gear number" and the top speed. they dont matter. its the total ratios that count. doesnt matter if you are using 1-4th on a 3.09 vs 1-3rd on an S4. if the total ratios are the same , the torque to the wheels will be the same.

in summary. S4 equals the Gt 3.09 for all practical purposes.

If not, show me why!

MK