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Join Date: May 1999
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tranny options for a V6 conversion



I'd like input on the options I have for reducing engine rpm via a tranny change (or gear change) on my 914 (side shifter) The engine in a Buick 3.8 V6.
What changes can be done to the 901 tranny to improve (reduce) engine speed?
What about other trannies?
What about reliability?
What is the cost for parts?

Any advice will be appreciated.

Dave San Jose, CA

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Old 01-19-2000, 08:23 PM
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Probably the easiest way to do that is to buy some bigger wheels, without getting smaller tires. For instance, if you went from 15" rims to 20" rims, and ran 205/50s on both, you'd wind up with about 20% taller gears across the board.

Smaller changes, and changes to specific individual gears, can be made by swapping the gears themselves. You have to open up the tranny to do this, of course. There are more different gear ratios available for the 901 tranny (the 914 is a type of 901) than for just about any other that I can think of. But that doesn't mean the gearsets are cheap, or easy to find. Just that they're cheaper and easier to find than for most other trannies. Bring money--lots of it.

You can also find some alternate gear sets for the 915. Bring a *lot* of money just for the gearbox, another lot of money to have it set up for running in a mid-engine car, *another* lot of money if you want to convert it to a side-shifter, and *yet another* lot of money for any of the alternate gear sets.

Actually, depending on how you do it, it may be cheaper to get large wheels as well!

--DD
Old 01-20-2000, 06:11 AM
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I'd like to see your V6 conversion. If that would be possible would you drop me a line at jenelson@sr.hp.com? Thanks.
Jeff
Old 01-20-2000, 08:52 AM
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Try giving Andy a call at Renegade Hybrids in Southern Calif. They have done many conversions and he does have a 901 Trans fix for bringing engine RPM down. You can find his website at http://www.renegadehybrids.com
Old 01-20-2000, 09:29 AM
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Can someone shed a little more light on this subject for me? It seems this subject pops up more often from guys doing conversions than by guys staying with 4 or 6 cylinder porsche motors. Comparitively, do porsches have longer strokes than other manufacturers? Or most often are tire diameter changes the problem? It seems to me that a simple tire change could remedy most gearing problems.
Old 01-20-2000, 07:45 PM
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Stroke has nothing to do with it. The only real question is how may RPMs you want to be doing per MPH on the road.

The early six-cylinders like to run at high revs. The 2.4 S hardly even gets moving until you wind it up to 5000 RPM, and redlines at something over 7000!!! But the four-cylinder cars have a more sane redline and a nice fat power band. They have 95+% of their max torque from 2500-4500 RPM, and max power just under 5000. Redline at 5600 or thereabouts.

Hmm, I sidetracked myself there... Anyway, the wheels and tires are the easiest way to change to overall gearing. I still can't see what the stroke has to do with the gearing.

--DD
Old 01-20-2000, 09:04 PM
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You kinda answered my question.
(I think)Stoke is one component of torque. (right?)Torque, being optimal at different RPM ranges. Fuel consuption, and harmonics are also a factor, I guess in drivablity and driving comfort. As I see it, the chevy guy's seem to find the harmonics unacceptable at the mid RPM range. The long stroke motor has to fire more often than a short stroke to produce the same revolution, Right? This equals RPM's which equals the unacceptable harmonics. I think? I'm probably way off on this one. Anyway I agree, change the tires.
Pheeewww
Old 01-20-2000, 09:38 PM
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There is no replacement for displacement. A small block chevy puts out more power at idle than a four banger does at redline. You don't need to run the hell out of a big motor to get usable power out of it. A 3.8L Buick will follow the same logic on a smaller scale. Gas mileage, longevity, and driving comfort are greatly inhanced by lowering the RPMs at highway speeds.
Old 01-21-2000, 07:13 AM
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Stroke, bore, compression, valve size, and cam profile have everything to do with it. Those variables create the torque, horsepower and power band of an engine. Unless your trying to getting every last bit of power out of an engine for racing, it should be running in the mid-range at freeway speed in top gear regardless of how many or how big the pistons are. Tires and wheels are the easiest and cheapest route for an overall gearing change. Last time I checked, they wanted 5-6 hours labor just to set the ring and pinion, at $65/hr. I'm running 205 60 15's which equals about 2800 at 70mph.
Old 01-21-2000, 12:01 PM
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