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Smart quod bastardus
 
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Join Date: Oct 2002
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rear diff ratos for 930 4 speed

What are the different rear axel diff ratios available for the 4 speed 930 gearbox?
I have the stock ring and pinion of 9/38 or 4.22 to 1.
I am interested in getting more response and acceleration form the engine with the least amount of expense. This would mean a diff change but I am not sure what is available in terms of gearing that would be lower than 9/38 gears.

Anyone know what else is out there?

fred
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 11-09-2007, 01:50 PM
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Get Bruce Anderson's book 'porsche 911 performance handbook 2nd edition' from Amazon.

In the back he lists both ring and pinion types for the 930 tranny and all the corresponding gears that you can use and the speed each attains at different rpm levels (all on a couple graph charts).

I have the 5 to 1 gearing with the change to lower ring and pinion but everything else the same.

It is insane in 2-4th gear, but 1st gear is almost non-functional. I would change my first gear to about 50 mph if I could, it is like 42 mph now. Redlines instantly right now, too soon.

If you are serious about this, that book will be worth it for those two charts alone.
Old 11-09-2007, 02:54 PM
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I have the 8/39 gear in my 79. It's probably one of the best upgrades for acceleration and drivability you can do for a 4sp.
Old 11-09-2007, 06:37 PM
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I have a lovely 8/41 (5.12:1) in mine... I'll make you a really, really good deal on it. It sings like a drunken tenor, but I haven't determined if that's setup or quality. It's A.M. Engineering imported from Italy. ;-)

I'm tired of the singing and first gear is currently only useful for entertaining the locals with tirespin. I'm going back to stock gears and concentrating on making the powerband wide. If you go with different gears I'm learning that there are compromises...
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Old 11-09-2007, 09:23 PM
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Quote:
Originally Posted by ayglass View Post
I have a lovely 8/41 (5.12:1) in mine... I'll make you a really, really good deal on it. It sings like a drunken tenor, but I haven't determined if that's setup or quality. It's A.M. Engineering imported from Italy. ;-)

I'm tired of the singing and first gear is currently only useful for entertaining the locals with tirespin. I'm going back to stock gears and concentrating on making the powerband wide. If you go with different gears I'm learning that there are compromises...
Mine makes a singing noise in 4th gear. It is not ideal, but not terrible either. It just sounds like a race car.

First gear is not so useful, redlines too soon. But the car sure screams to the redline hard. 60mph to 90 mph is instant.
Old 11-10-2007, 09:07 AM
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Frankly, the whole set up is loud with the lower ring and pinion because your car is always at a higher rpm.

I like a high strung car, that's why I drive it in the first place. I have a zork pipe.

If you want a civilized car than don't change the ring and pinion, but mess around with the individual gears instead.
Old 11-10-2007, 09:09 AM
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I see Powerhaus is advertising a 5 speed conversion for the 930 case. Would this be something you'd consider?
Old 11-10-2007, 10:33 AM
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I see Powerhaus is advertising a 5 speed conversion for the 930 case. Would this be something you'd consider?
I would want to know somebody firsthand who drives one of those before springing for it.

4 speeds is fine for a weekend car if you space them out correctly. A little lower in first, not too much. A hair lower in second, and definitely lower in third and fourth. You can gear fourth to redline at 160 and still have a lot of grunt.
Old 11-10-2007, 10:37 AM
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I have the 8:41 rear end. It is a rocket ship. No waiting for boost. I spin the rear wheels at will, but then it isn't stock. 8:41, 8:39, no real difference besides the few miles at the top. How often do you go over 160? From 70-100+ is one less then one full breath through your nose. My wrench and I decided to buy a German made gear set. No noise. Worth the price of gold.
Old 11-20-2007, 12:26 AM
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So, how do you determine your ratio?

On a chevy is was easy.... spin the back tire one rotation and count the number of driveshaft revolutions ... This Porsche is a tad bit different
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Old 11-20-2007, 06:11 AM
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One issue I have is whether or not you will actually be able to get to 160 with the lowered R&P. I can understand that gearing wise it is the calculated redline but this doesn't take into coinsideration the less than optimal aerodynamics of a 930. As is with stock gears I am tickling 150 (at certain tracks). Would love to have some better response down low and between shifts but don't want to find myself topping out prematurely.
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Old 11-20-2007, 06:58 AM
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I poped 125 to 130mph or so in third (too scare to look closely). the car wanted to keep going when I shifted into 4th. that was with stock gears and rear end. woth the new rear end, I red lline in 3rd at around 120mph without any problems. my 4th gear should be able to pull another 40mph on top of that. who knows, I haven't try. I am too chicken, but always wanted to. One day maybe. My 930 also isn't stock.
Old 11-21-2007, 12:51 AM
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