 Transmission gearing advice needed, I have some choices to make |
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| DNHunt |
 Oct 4 2009, 08:43 AM
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#1
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914 Wizard? No way. I got too much to learn.  Group: Members Posts: 4,099 Joined: 21-April 03 From: Gig Harbor, WA Member No.: 598  |
2380 Type IV, redline at 7000. Best power from about 3600 to about 6200. Street car some AX. 205 15 tires street and R compound. With the stock box on the AX courses we run 3rd is just too tall so I know I want a shorter 3rd. ZD 5th is just right or a little low for the highway so I don't want to change that. So I can change 3rd and 4th.
I tore down a 902/02 tranny and got M, S, X and I have N, V, ZD from the stock box. I'm tempted to build a A, F, M, S, ZD box. I could build a A, F, M, V, ZD box. To complicate it more I know where there is a brand new L gear with hub. I am really tempted to build a A, F, L, S, ZD box. I think it makes the most sense to stretch from 4th to 5th. What do you think? Dave |
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Replies(1 - 11)
| J P Stein |
Oct 4 2009, 09:16 AM
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#2
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Irrelevant old fart Group: Members Posts: 8,797 Joined: 30-December 02 From: Vancouver, WA Member No.: 45 Region Association: None |
I have a very nice GA 2nd F/S. That is good to 60MPH @ 7k.
The Flipped ZD is good to around 75 @ 7K and the shift drops right into the guts of your power band. That will cover 98% of the autocrosses you'll find. This would leave a pretty big spacing to 4th, I realize, but so what. 4 & 5 are basically cruise gears on the road. Your motor has good torque, use it. Short of going to a 904 mainshaft and a C first there's not much to be done with 1 & 2. Frankly, these gears really suck for a built motor. They louse up the whole box. |
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| DNHunt |
Oct 4 2009, 09:51 AM
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#3
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914 Wizard? No way. I got too much to learn. Group: Members Posts: 4,099 Joined: 21-April 03 From: Gig Harbor, WA Member No.: 598 |
Ah JP, my favorite adviser. You always give me good advise. The only bad advise I've ever got from you is the advise I haven't listened to.
I hadn't thought about the GA main shaft but, looking at the guts and doing a little figuring I see you can change input shafts without changing pinion shafts so pinion depth doesn't need to be reset. I'll have to ponder. I always short shift to second. I've also considered launching in second cause that dogleg shift is slow. F would be better for that. Dave |
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| race914 |
Oct 4 2009, 09:56 AM
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#4
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73 914-4 Group: Members Posts: 1,006 Joined: 31-October 05 From: Nipomo, California (Central Coast) Member No.: 5,027 Region Association: Central California |
Here are a couple of model runs. These help me to 'visualize' the gear setups related to MPH, shiftpoints, etc. I'm not sure if you shift at 7000 in 1st or 2nd so in these runs, I set 1st at 80% of redline and 2nd at 90% of redline...
A-F-L-S-ZD  A-Ga-Ka-V-ZD (Ka = Flipped ZD)  You can download the model and run more setups here: http://www.914world.com/specs/regearing_901.php Hope this helps with your gear set selections |
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| J P Stein |
Oct 4 2009, 12:36 PM
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#5
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Irrelevant old fart Group: Members Posts: 8,797 Joined: 30-December 02 From: Vancouver, WA Member No.: 45 Region Association: None |
We do use F 2nd to launch and the flipped 5th. The F works good (not great) if you have the motor to pull it. There have been AXs that it is all you need. We've yet to run out of 3rd gear......good damn thing cause there ain't no more. (IMG:style_emoticons/default/biggrin.gif)
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| ConeDodger |
Oct 4 2009, 09:52 PM
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#6
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Apex killer! Group: Members Posts: 23,613 Joined: 31-December 04 From: Tahoe Area Member No.: 3,380 Region Association: Northern California 
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JP has given you solid advice since you seem to drive that thing to and from the AX events and don't track drive the car much... I am going MSX for 3,4,5 to give me track day options since I generally tow the car to events. All autocrosses are at least 50 miles for except one...
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| charliew |
Oct 5 2009, 12:28 PM
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#7
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Advanced Member Group: Members Posts: 2,363 Joined: 31-July 07 From: Crawford, TX. Member No.: 7,958 |
I must have missed the tire diameter. I for some reason thought the normal tire dia was about 25.0, is that too tall for the 914 or is the 23.4 just a good racing size?
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| r_towle |
Oct 5 2009, 01:43 PM
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#8
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Custom Member Group: Members Posts: 24,591 Joined: 9-January 03 From: Taxachusetts Member No.: 124 Region Association: North East States
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leave 4th and 5th alone...you need them to drive to and from the events.
Get a spare 5th gear set from someone and flip them around to replace your stock 3rd gear. This is perfect for most autox's. You will spend most of your time in 2nd and third.... With alot of torque, you can go with the smaller third gear and get out of most issues. Rich |
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| J P Stein |
Oct 5 2009, 02:16 PM
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#9
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Irrelevant old fart Group: Members Posts: 8,797 Joined: 30-December 02 From: Vancouver, WA Member No.: 45 Region Association: None |
A 205 X 50 X 15 is about 22.5" in diameter.......which just happens to be the same diameter as my ex rear slicks.
I gots spare 5ths also. |
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| r_towle |
Oct 5 2009, 04:04 PM
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#10
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Custom Member Group: Members Posts: 24,591 Joined: 9-January 03 From: Taxachusetts Member No.: 124 Region Association: North East States
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I had the flipped setup for a few years...its really a low cost, decent setup...
Its a bit of a climb from 3rd to 4th, but its really not outrageous... The best part is 2nd to 3rd is close enough that you can stay in third with all your torque and not waste a second or even two seconds to downshift, then upshift again.. Rich |
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| J P Stein |
Oct 5 2009, 08:30 PM
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#11
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Irrelevant old fart Group: Members Posts: 8,797 Joined: 30-December 02 From: Vancouver, WA Member No.: 45 Region Association: None |
QUOTE(r_towle @ Oct 5 2009, 03:04 PM)  I had the flipped setup for a few years...its really a low cost, decent setup... Its a bit of a climb from 3rd to 4th, but its really not outrageous... The best part is 2nd to 3rd is close enough that you can stay in third with all your torque and not waste a second or even two seconds to downshift, then upshift again.. Rich True, You can run thru sections where hard acceleration is not really needed....more like just maintain the speed you have. My car is more controllable at 5k in 3rd than 7k in 2nd...slaloms are good examples. |
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| Chris Pincetich |
Oct 5 2009, 09:00 PM
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#12
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B-) Group: Members Posts: 2,082 Joined: 3-October 05 From: Point Reyes Station, CA Member No.: 4,907 Region Association: Northern California |
Wow, nice collection of extra gears (IMG:style_emoticons/default/beerchug.gif)
I did the cheap ZD flip in 2008 for AX, luv it for racin 20-60 mph AX courses. Driving around town in my 1.7 with small tires (195/50s) I often go from 2nd gear to 4th, and have enough torque to cruise 35-45mph over small hills and curves quietly in 4th. My stock engine never sees oil temps over 210 even in traffic after long drives. A shorter 4th might be nice....but you won't race with it unless you are on the big track at 70-90 mph. |
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