jhunt@huntinter

Agreed, if you mess up... and it is easy to with the backlash if you aren't experienced you may end up with a tranny that lasts a week.

Brent 930

Patrick Motorsports in AZ does a conversion for around $7k but you still have alot of labor. I doubt the clutch comes with it either, so that's why it's big money.

As for the R&P I got the David Brown (from England) through Carquip and they also installed it, it's been great. Again, don't even try to install it yourself if you decide on getting one.

Paul

The strength of the standard G50 R&P is borderline for turbo power. The G50/50 has a far stronger R&P, although the gearing is probably a bit on the high side.

PT

Brent & John,

Just curious - why not DIY for the R&P, or for interpolating what you imply, tranny rebuild?
Is it WAY more difficult than, say, an engine rebuild (where scary tolerance like <.25mm difference needs to be guaranteed across the timing chains)?

thanks...

Paul

Unless you have the tools to measure the specified pinion depth within .001" and unless you set the backlash to .007", the R&P will be noisey and/or self-destruct.

Brent 930

PT,

Don't try to compare setting up a R&P to an engine rebuild. You have no chance of doing it right and I'm assuming you don't have the special tool needed which is ALOT of $$$. Realize this, the labor is around $1k to do the job!!! Now I just found out the R&P's have gone up in price ALOT and your looking at least $1800-2200.

PT

Guys, thanks for the heads up... To be honest, after my DIY rebuild, I'm really tired of working as opposed to driving the car. But, I also want to know more about how things work. Nothing beats hands on experience

A friend of mine who motivated me to do my rebuild had also done this himself. No drama or issues. Yes, everyone's skill set is different & mine is certainly not up there. So will keep that in mind when I decide on what to do.

Thanks again...

Rob S

I think the G50/50 is the best way to go for a street/track car. It's *so* expensive, though. For the track alone, a regeared 4 speed can work quite well. It's a little marginal for street use, though if you make radical changes to the gearing (as I've done!). If you regear the 4 speed, you gain the advantage of selecting your ratios just as you like, and you can keep the 9:38 R&P, which is much stronger than the 8:39. The strength may not be an issue at 450 hp, but if you go EFI and see 600+, you might begin to see problems. I regeared mine, and I spent between $600 and $750 for each of three gearsets. Below is what I wrote on the Rennlist thread entitled "4 speed vs. 5 speed" from about a year ago. You might want to read the whole thread. By the way, when I wrote it, I expected horsepower in the 450 range. I'm now looking at numbers in the mid to upper 500s.

Here's what I wrote:
In my trackified 930, with horsepower somewhere in the mid 400s, I've chosen to put in a 4 speed with different gears. Though I actually had a 5 speed in it for a while (a 915), I was concerned that I may run into trouble with it under the sustained high loads of track duty. My understanding is that you'd have a hard time breaking a 930 gearbox, even with massive amounts of power under track driving conditions. But I really didn't like the gearing in the stock four speed -- the ratios were just awful for the tracks around here. I suspect that they'd be pretty worthless on most any track. Stock first is too low for even the slowest corners and fourth is too high for the fastest straights. What you end up with is essentially a two speed box. So, I decided to abandon any utility on the street and I made mine an "active" four speed, with a taller first, stock second, and a shorter third and fourth. I wanted to use the 9:38 because I understand it's much stronger than the shorter R&Ps. Besides, as Steve W said, the big problem is the spread between the ratios, and that isn't solved by changing the final drive ratio. Here's what I used:

1st - 1.736 (taller than stock, revs out at 72 mph)

2nd - 1.303 (stock, revs out at 97)

3rd - 1.000 (shorter than stock, revs out at 126 )

4th - .767 (shorter than stock, revs out at 165)

I'm running 315s on the rear and using a 7000 RPM redline for comparison. With these gears, I have very similar gearing to a late 915 (which I considered to be perfect for a 930), but without first gear! It makes it a clutch burner to get started, but it's fabulous once you hit about 30 mph. I use first in the slowest corners and get deep into 4th on the fastest straights. There's 1600 RPM drop between all shifts, and 4th is tall enough that you can still drive it on the highway for a track day at a distant location. The cost of the gears (and the Guard LSD) was not trivial, but I think the total cost was still far less than a G-50, and it's absolutely bulletproof, which the G-50 (or G50/50) is not.

PT

RobS, thanks for the insight... indeed I do agree that changing 3 of the gears would very likely much more satisfying than doing the R&P, though cost is getting up there too...

I rode with a student recently who changed his otherwise stock (engine-wise) 930 with a set of 935 gears (he assured me that is from a 935). Wow, does the car perform!!! It seems to be on power everywhere.

From my experience, I can live with the ratio spread. Its the very tall 2nd-4th that really kills me. Coming into a 70mphs corner, I need 2nd but need to hold it @ redline pretty much from apex on. So, based on feedback from one of my fellow instructors who did the R&P, and my calculation for the tracks I usually run at (Glen, LCMT, Mosport, Shannonville), changing the R&P seems to address the issue by enabling use of 3rd gear in many of the "medium" speed corners and let me keep the car in the power band easier.

Good news is that I still have time to decide what I wanna do - my tranny is likely coming out since I'm starting to get stuck coming OUT of 3rd. A rebuild is probably needed anyway unfortunately

So - dilemma again

BTW - why is 8:39 much weaker than the stock 9:38?

Thanks...

Brent 930

A good 8:39 will hold any CIS power but it's weaker since you have only 8 teeth instead of 9. Heads up a R&P now will run you at least $2 plus labor. While the gear change is best for the track you end up with a 70+ mph 1st gear which can't be worth much on the street. You might be able to re gear with 1st in the 60 mph range and still be pretty good so you can drive on the street. You can't have your cake and eat it too with the 4spd.

Rob S

PT,

I agree with Brent in all regards, here. There's no free lunch with only four gears. You'll be giving up something somewhere to get what you want elsewhere. It's all a matter of personal choice and priority. Also, as he said, the smaller pinion on the 8:39 means that the fewer teeth on the pinion are more highly stressed than is the case for the 9:38. Same thing when comparing the 915 7:31 to the 8:31. The 8:31 is much stronger...

If the R&P change does just what you want, or comes close enough, it may be simpler to change it rather than restack your gearset. But in fact, the R&P change ought to be done by a pro who really knows what he's doing, as has been discussed. The gear change is, in some ways, less critical and easier to do. After all, if you're going through your gearbox anyway, to change synchros and bearings and such, it's a natural time (and easy) just to swap in new gears. Plus, it's fun to be able to choose the exact ratios you want.

I'm not the expert here, but my understanding is that the gears for a 930, 935, and 962 (and maybe others) are all virtually identical. I know for a fact that's true with the 962 gears, because I have a first and fourth gear from a 962. The physical differences are small -- the 962 gears are a bit lighter (which is really trivial), and they come with racing dog teeth. I changed mine to street dog teeth anyway. The biggest difference I've heard is that the factory gears run a bit quieter than the aftermarket gears made by Paul Guard or Powerhaus II. I have no basis for judgement yet. And in my case, that's not a big deal because the car will be so noisy anyway. If I were doing it again, I'd just focus on finding the ratios I want, and I'd be happy to go with aftermarket gears. There are tons of ratios out there -- just call one of the vendors and they'll work with you to dial it in. My guess is that if your friends car had 935 gears, and was fast, it has nothing to do with the fact that they're "935 gears," it's because the ratios were right for his car and the application. There were many 935 ratios, and some of them are likely to be exactly the same as 930 ratios.

It would be a shame if you had to change all four gears to get what you want. That would start to get expensive. There are some tricks -- some people can get away with running the factory third gear in the fourth gear position. But that shortens it up too much for my application. Also, you could perhaps leave first and second alone, but shorten third and fourth. If you brought third significantly closer to second, it might solve the problem you're having. In my case, I decided to use 2nd gear as my basis, and change everything else around it. My first gear is very radical, I'll agree, and I wouldn't do that if I had any aspirations of street use. You wouldn't have to go so extreme, necessarily, but I wanted a true active four speed, and I felt it was the best way to go for the tracks around here. But interestingly, it's quite comfortable to drive in that configuration on the street. It wouldn't be a good stoplight drag car though -- which I couldn't care less about.

Sameer

Guys,
How much would a set of 8.39 R&P cost today? How many reputable makers are there? How about Quaife?

Sameer

also what would be the difference between the Andial R&P and the Guards R&P?

A930Rocket

Where I track my car, I mostly run in 2nd and 3rd, but would like to shorten 3rd and 4th. They are a little tall. There are places I run out of 2nd, but if I shift ti 3rd now, the car is a dog until boost kicks in. I'd like to be able to shift into them and be in the power.

Any suggestions? Move 3rd to 4th and find a gear in between? Or would this be too short, as I hit about 150 or so on the back staights.

125shifter

I'm planning do some gear changes after I see how my new engine set up works. I believe Andial sells the R&P for about $1500 and I got a quote to change it for $1000 if I bring in just the tranny. You can buy gears for about $800 each from Powerhaus II which you could change yourself easier than the R&P. The problem with a gear change is the optimum gear changeout with what's available puts you right about where the 8:39 R&P would put you. The one upside to new gears is you keep the stronger 9:38 R&P.