Originally Posted by 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!

Originally Posted by dcrasta

I think they put the 2.2 boxes in for 'fuel economy' aka CARB standards. All things equal, a lower numerical rear ratio will turn lower RPM's at the same speed (given the US speed limit is usually 55 MPH) and would translate into increased fuel savings.
More RPM's at the same speed = more fuel burned. Of course the tradeoff is faster acceleration (all other things equal).

For a race track application often the rear gearing is changed to suit the track. When I was racing motorcycles we would often change the sprockets on faster tracks, larger front sprocket for shorter tracks (quicker acceleration from corner to corner) or smaller rear sprocket for more top end.
Life is a compromise.

Originally Posted by dprantl

Yeah, but you also switched from auto to 5-speed, which gives you a larger mpg gain than the loss going from a 2.64 to 2.2 rear pinion. My former '86 5-speed with a 2.2 got 25 - 26 mpg on the highway going ~80 mph. It was also a very strong example of a stock early 32v car. I guess the point is that 5th gear is not meant to scream, even on most tracks it is not useful, so why not make it a more economical highway gear? You can still make it scream in the other 4 gears if you want, and with the 2.2 that will get you to ~140mph in 4th.

With that said, a stock 2.64 or 2.72 928 with today's performance 265+ wide tires will be able to hook up in 1st gear, so will be able to get a slightly better 0-60 and 1/4 mile time than a stock 928 with a 2.2. It's too bad the 2.64/2.72 didn't have a 5th gear with 0.8:1 overdrive, although that would make a pretty big RPM drop from 4th to 5th

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

Originally Posted by blown 87

As far as the gas mileage, mine actually went up about 2 MPG going from a 2:20 auto to a 2:73 manual.

Originally Posted by blown 87

What it really needs is a real OD, or just one more gear, just for cruise.

Originally Posted by dcrasta

I think they put the 2.2 boxes in for 'fuel economy' aka CARB standards. All things equal, a lower numerical rear ratio will turn lower RPM's at the same speed (given the US speed limit is usually 55 MPH) and would translate into increased fuel savings.
More RPM's at the same speed = more fuel burned. Of course the tradeoff is faster acceleration (all other things equal).

For a race track application often the rear gearing is changed to suit the track. When I was racing motorcycles we would often change the sprockets on faster tracks, larger front sprocket for shorter tracks (quicker acceleration from corner to corner) or smaller rear sprocket for more top end.
Life is a compromise.

Originally Posted by DougM

I knew I had seen the info that I requested somewhere before and I figured it out. Old magazine articles from the Brooklands Portfolios show speed in gears in the old road tests from R&T, MT etc....
C&D did a test on an '87 US model with a 2.20 ratio
speed in gears are:
1st(6100rpm): 49
2nd(6100rpm):73
3rd(6100rpm):102
4th(6100rpm):135
5th(5100rpm):165
From Autocar test on a '84 Euro S with 2.75
1st(6200rpm):43
2nd(6200rpm):67
3rd(6200rpm):90
4th(6200rpm):119
5th(6100rpm):158

Not exact, but gives an idea of difference in speed through the gears.

Originally Posted by 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

Originally Posted by GlenL

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

Originally Posted by 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!

Originally Posted by 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

Originally Posted by mark kibort

the only thing fuel efficient about the 2.2, is the 5th gear, 1:1, so you can chug along at 65mph at under 2000rpm. the ONLY racing disadvangae of the 2.2 box , is above 155mph and 175mph. If you are not racing at these speeds, the 2.2 is generally a better racing gear box. ....

Originally Posted by heinrich

How does this make sense? I know that in my 2.2, I was able to maintain hundreds of revs lower in 5th at freeway cruise, than the 2.63/4. That should make for better fuel economy at cruise. And might I add, a lot less droning sound.

Also, racing above 155mph should lose you some legs on a 2.63/4 as opposed to a 2.2 at that speed with more to give?

2.2
4th(6100rpm):135
5th(5100rpm):165

2.75
4th(6200rpm):119
5th(6100rpm):158

Originally Posted by DougM

From Autocar test on a '84 Euro S with 2.75
1st(6200rpm):43
2nd(6200rpm):67
3rd(6200rpm):90
4th(6200rpm):119
5th(6100rpm):158

Not exact, but gives an idea of difference in speed through the gears.