Michael_Philippi

I have read several articles about the differences in gear ratios between the USA G50 trans and the European G50 and RS G50 trans. The USA trans has taller gears with more of a spread between the ratios. All of what I have read says the Euro transmissions would result in much snappier performance. So, I am thinking, why not just change the final drive? It should be cheaper than a whole transmission full of gears, and essentially achieve the same results.

I got a quote for $2200 (ouch) for a 4:00 ring and pinion. The car currently has the stock 3:44 ring and pinion. Has anybody done this type of swap? Am I barking up the wrong tree in my search for more performance. Incidentally, I don't really care about top speed. The car is street driven. I just want to make sure that new Mustang, etc. gets a good view of that wonderfully sexy Porsche rear end

Thanks for all responses.
Michael

Viken

The final drive will make all the gears shorter and will not change any spread between gears. It will also make first ridiculously short. It's a half *** solution for a real problem, if you ask me. Spend the money for the right gears and leave the final drive alone.

GrantG

Michael - That won't really fix the problem (the wide spacing of the gears). You will still have the same rpm drop when shifting which is what really slows you down, it will just happen at a slower speed. The key is to keep the motor in the heart of the power band (5k-7k). You would have far better results by swapping individual ratios and making them closer. It's been suggested that a good way to go is to use the stock 5th gear as 6th (requires some machining), leave 1st and 2nd gear alone, and make 3rd, 4th and 5th closer together. Steve at www.rennsportsystems.com can hook you up...

Glen

It works great, not ideal as it makes first irrelevant but it makes top speed about 155 in a 993. It also reduces the gap between the gears, specifically the 2-3 bog gap in US spec boxes. It also of course reduces the gap between all gears as a result of the lower top speed. Only real downside is first is a writeoff and You have to be careful not to launch the car hard in first as it can destroy things quickly(but You would not do that in a 911 anyway would You...). I have built 4 different boxes, 993 short box, 993 custom, 996 Cup short and 996 03-05 Cup delivered box in addition to the short R and P. In a street driven, autocross/de car I would do the R and P swap, put in 3,4,5 steel syncros, leave brass at 1,2 (steel too expensive as they are a 3 piece syncro) and 6 never fails. If money is no object, regear. R and P is a great shortcut for the $ though and does remove and reduce the gap problem.

GrantG

Glen - Do you have any gear charts to illustrate the point? Whenever I have graphed a gear chart, changing the R&P (or tire size diameter) does nothing to improve the rpm drop after upshift. You may feel that the car is more lively after the shift, since there is less wind resistance to overcome at the lower vehicle speed at gear change, but I don't think you'll be turning higher revs after the shift...

TroyN

It would be more the effect of having a less steep gear to climb per gear that you would feel, vs. reduced wind resistance. It seems that for every gear but first (and maybe even first, for a nice hole-shot!) you'd be faster - in a straight line at least. Whether it translated into usable gearing for street or track is a question.

Glen

Just my experience for what its worth. It works great, sold the R and P box to another lister and the custom box to a different lister. Perhaps they will pipe in with their firsthand impressions. In fact if I remeber correctly the short R and P box was quicker than the custom box to the 60-70 range while the more active box was better in road race type apps, of course I did put a 47 mph 1st gear in the active box The short R and P was run behind a stock 3.6 and a Andial 3.6 while the active and short were run behind a 3.8 and a TT so the stock 3.6 with the short R and P was quicker than the 3.8 with the active box in street/de/autocross situations.

Glen

If You choose to go the regear route and want to save $, then use the stock 1,2 ala Grants recomendation, use 3,4,5 from a G50/21(cheaper than G50/32 or PMS gears and move stock 5 to 6. again, not ideal but a nice option.

JasonAndreas

This mod is really only useful for auto-crossing, racing on a track or bench racing your forum signature. Straight line acceleration on the street will basically be unchanged...

Steve Weiner-Rennsport Systems

Amen!


Michael:

You need to address the root cause here; the gear ratios are simply too far apart and engine RPM's fall off too far at each shift. Changing the R&P doesn't address any part of this issue.

Regearing the transmission with close-ratio gears is akin to adding 50 HP to the performance envelope of the car.

As Viken said: do this the right way, do this once, and you'll not have do it all over again later.

kev

I am the person in question that bought Glen's 8:32 R&P. I also have a Cup car with short gears and stock R&P.

I understand what everyone here is saying, but like Glen, my experience on the track is that the gear drop does seem less between shifts. And for certain, the revs really pick up between shifts (but I also have a very light flywheel). On a short track (MSR) its actually sort of a pain, you're at redline so fast. My shift points are sooner in my track car with short R&P than my Cup car with short gears. How that translates into lap times I don't know.

I'd still spend my money on a proper regear before a R&P swap. Also keep in mind that if you go club racing one day, only the R&P and LSD is fair game for prepared transmission upgrade. You're not supposed to touch the gears. I wonder how many 993 racers would pass tech if PCA cracked open gearboxes . . .

Michael_Philippi

Steve:
...and others who replied. With several muscle cars I have owned in the past, swapping rear end gears to a shorter set resulted in quicker accelleration. That is precisely what I am after here. I completely understand that just changing the ring and pinion will not have any effect on the effective "gap" between one gear and the next. However, if the final drive is shorter, then by definition, accelleration in each gear should be quicker.

As I said, this car will be street driven, thus I am not that concerned with "power shifts" or banging one gear to the next. I would prefer a quick, but non-abusive shift from one gear to the next, but still have a marked improvment in accelleartion. If it turns out that changing the gear ratio spread is better than changing the ring and pinion, then that is the way I will make the change. It still seems less expensive however, to just change the ring and pinion.

Now, if this results in making 1st essentially useless, then I will probably not persue this, because a "5 speed" box with six gear sets is not what I am after. It is because of the collective wisdom and experience that I ask these questions here.

Thanks for the continued imput.
Michael

JasonAndreas

Check out THIS thread, it would be nicer if we had actual timed measurements but its interesting nevertheless.

Flying Finn

Guys, I don't necessarily disagree just changing R&P is "halfass" solution and for sure you'll get better results with changing gears.

However, surely by changing R&P only will shorten the "gap" between gears, or am I missing something here?

Just thinking it mathemathically, when you calculate the final ratio of one certain gear, you need to know the gear and R&P, and calculate them both, no?

When you take difference between two gears alone, that of course is still the same but when you combine that difference with different ratio R&P, the total is different.

Result: gap between two gears is different with only changing R&P.

flatair

In a street driven car, changing your R&P will make your car *feel* quicker and more responsive, and in-gear acceleration will be greatly improved....BUT you're going to have to shift more. That will negate most of your in-gear acceleration gains - given you shift pretty quickly you'll end up getting to 100mph at the same rate. Oh your gas mileage will go to crap