mark kibort

Really, it seems that you are being a little closed minded, especially since you are responding with the same inaccuracies that have plagued this discussion worldwide! Plus, most of my driving is on the street too!
you keep on CONFUSING "faster and quicker" in each gear, with over the speed range you are in. on the streets, or on the track, (if you cant get the fact that the gear ratio changes mean very little on most tracks due to the speed ranges used to factor out the gear ratio change effects) YOUR acceleration will depend on how much hp you will have available. at any given speed. FORGET ABOUT INDIVIDUAL GEAR PERFORMANCE< as they are skewed speedwise , proportional to the gear ratio change. Now, if you are talking about wanting to to go slower in each gear and accelerate faster in that slower speed range, then YES< YOU ARE RIGHT, but most of us (maybe not) care about what is actually faster for a given speed range. Like, if you want to be a champ from a rolling start to 60mph, 80mph, or passing someone, 60 to 80mph. (most freeway highschool mentality races on the street)

Im asking you to understand its the speed ranges that you are to look at, not individual gear ratios, as they just make you accelerate faster, in each particular gear , but in a slower speed. SO, if you are so intent in racing that Mustang 5.0 from stop light to stop light, and want to break the law in doing so, dont spend money on the transmission change to a 2.72 vs the 2.2, because it wont do much. this isnt me talking here, its simple physics.

you and your 2.75, are ever caught near me when im acting imature on the street, (and both of us have the same S4 HP wise) and we are going 40mph and we go to 80mph, im going to spank you , just as you would spank me if we were racing from 30 mph to 70mph. thats the point,no more , no less.

Hey, the reason i chime in on this, is because changing out a gear box is an expensive job and some expect real results (not just feelings in their pants! )
so, there are some that care about the reality of the mod, personally, i value how these factors effect the race cars, as that always transfers to the street, and I drive a lot on the street with mine. I LOVE to race guys on the track that that change gear ratios and expect lower lap times. It never happens, even after they rave about how their car "pulls so much harder".

mark kibort

Its funny, you can also find the internet simulators that do exactly what i have been talking about, by using the gear ratios and the HP curves. (or torque curves). you can find results of any speed range for any combinaton of gear boxes.. we are talking such small differences, aside from the launch differenes (assuming perfect launching with professional drag racer slip), that it really rams home the fact that gear ratio changes dont do much, but then why would they??? the wider the speed range, the less they can be deemed "effective".

danglerb

0 to X times are about traction more than HP. Same car, same HP, changing the tires and suspension around can make a second or more of difference in 1/4 mile times. Many times the circumstances of 0-60 testing is ridiculously abusive to the cars, so I don't give the seconds derived much respect (unless we are shooting the baloney and talking about MY car).

The 928 is a stupid car to go drag racing in anyway, wheel hop and other issues make it too poor of a performer for anything beyond testing, and there best to be kind to your old ride and don't launch too hard and pay attention mostly to trap speed.

High gear ratios tend to be fun on a street car, but faster will depend on more factors like rolling starts and from what exact speed to what exact speed.

Final whack to this dead horse, I don't care what final drive ratio you have, a 5 spd is way more fun than a AT, but I suspect that most of us would go around a track faster with an AT.

928mac

Looks like someone is bulgarding again

Ispeed

6 speed missing 5th gear, so true.

blown 87

Make it 71 times, see you guys.

dprantl

Mark is a nice guy, but he only has one way of explaining something, and repeats the same explanation over and over again. If someone doesn't get something, you must try other ways to explain it to them.

With regards to the 2.2 vs. 2.64/2.72 rear pinion, if you compare the boxes gear for gear (i.e. 1st to 1st, 2nd to 2nd, etc), there is no question that the 2.2 will accelerate slower. However, depending on the speed range you are in, the 2.2 may be faster. Why? Say both cars are in 3rd gear at WOT, and they have identical power and torque curves, tires, weight, etc. Of course the 2.72 car will be pulling ahead, but then it will reach redline and has to shift. At this point, the 2.2 car is still in 3rd gear and now the 2.2 car is gaining pretty fast on the 2.72 car because the latter is already in 4th gear. Redline for the 2.72 in 3rd is just around 100mph, for the 2.2 it is around 115mph (6600 RPM, 24.73" rear tire diameter). If the two cars were cruising on the highway at 100mph and punched it to 115mph, the 2.2 car would kill the 2.72 car in acceleration if both were in their optimal gears, and that's a fact.

The largest difference you will see with these two boxes is when the 2.72 has to shift from 4th to 5th gear. That is around 130mph, whereas it is around 150mph for the 2.2. If you punched it at 130mph, the 2.2 car would leave the 2.72 car IN THE DUST, then at 150mph the 2.72 car would reel it back in.

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

GlenL

Perhaps someone can list the effective gear ratios for all 5 gears on these transmissions. That'd be interesting.

dprantl

2.72
-----
10.2666
6.8513
4.8818
3.6930
2.7272

2.64
-----
9.9244
6.6229
4.7191
3.5699
2.6363


2.2
-----
8.9476
5.9711
4.2546
3.2185
2.2

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

Red Flash

Hi All

Mark's arguments sound perfectly clear to me, and I don't even know enough about this subject.

What interests me more, is what Porsche was thinking when they sold the 2.2 gearbox only in the US? (And I think this was the case.) Did they assume Americans would be doing more highway cruising? For sure, driving in most places in Europe, the 2.64 and 2.72 would be better for the speeds and traffic conditions, where cruising is just not as easy as in most parts of the US.

I did learn after I bought my GT that traveling 16 hours at 80 mph in a car with a 2.2 gearbox is more comfortable than the 2.73! Especially, if the exhaust is not stock... That having been said, my GT is "perfect," so I certainly wouldn't change it...

Cheers, John

PS-Thanks to Flying Dog for making that table and To Andre for posting!

GlenL

Thanks, Dan.

A quick run through Excel shows the ratio between gears. I was curious about the 2.2 4-5 ratio people have mentioned. Looks like a big step down in RPMs when making that shift. People have complained over the years that going to 5th puts the engine too low in its power band. That last shift goes from 6K to 4k, for example.

2.72
-----
10.2666
6.8513 0.667338749
4.8818 0.712536307
3.693 0.756483264
2.7272 0.738478202

2.64
-----
9.9244
6.6229 0.667335053
4.7191 0.712542844
3.5699 0.75647899
2.6363 0.738480069


2.2
-----
8.9476
5.9711 0.667340963
4.2546 0.712532029
3.2185 0.756475344
2.2 0.683548237

ShawnSmith

> 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.

Well, that probably relates to my car having around 400 hp and more than 400 ft-lbs

stock, 1st gear was just at the limit of traction with stock 16 inch wheels.

I grew the motor, and 1st gear became useless.

I added 50% more rubber in the rear and now 1st gear hooked up good.

Then I stroked and bored the thing (or had Greg do it for me).

Now 1st gear is back to requires-throttle-modulation-to-be-useful, and 2nd is just perfect for limit of traction. Greg asked if I wanted a numerically higher drive... I asked why on earth I'd want that unless I needed to hit specific trap speeds at 72 mph or 104 mph that peaked in a certain gear.

Stock, especially in earlier years with limited torque, I can see the case for more aggressive gearing. Later years, with any meaningful improvements to the motor.... I don't get it. 1st gear is there for stunts, not launching, other than maybe with drag slicks.

heinrich

Shawn, with that much torque you cannot use anything less than a 2.2. I must have missed where you said it had so much torque, sorry Anyhway I don't think the OP has that much?

victor25

New Tranny is in, and the 2.2 works great. Acceleration is great, cant tell a difference, and 5th gear is sooooo much better. Wow is it easy to pitch the *** end out around the corners (= (=
This one does not downshift as nicely as my other one did, but oh well, you cant have everything... LOL
I now have wheel hop though ?? Never had that before, but then I didn't have an LSD in the 2.63. Is there anything I can do about it? Is this because of the LSD or what?

danglerb

I don't think wheel hop is "directly" associated with the LSD, but the LSD is perhaps allowing a bit more torque to reach the wheel with best traction.

As I understand it, wheel hop, comes from some energy storage occurring, something acting like a spring, from the torque, and when the wheel slips it unwinds with some force in the vertical plane. I'm not sure if there is a straight forward solution above some level of torque and a factory suspension, its a common complaint.