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915 transaxle
Hi all,
Need your advice, I have a 915 transmission 8.3:1 pinion from a 911 1980 SC, I am planing to used it in street track racing with a light sports prototype 2 liter car, the 911 stock tires are 25" in diameter, using 22 1/2" diameter tires will it work? these are from the Pro Formula Mazda slicks Thank you PK |
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11-24-2014, 08:11 AM
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Registered
Join Date: May 2012
Location: Troy, Mi
Posts: 1,937
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There's a downloadable gear chart sheet on InstantG's Home Page near the bottom. Might want to double check the ratios, but it's pretty slick. Gives you rpm for each gear at all speeds.
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Matt - 84 Carrera |
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11-24-2014, 10:25 AM
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Hi Tom,
I check it a while a go, and to get a maximum of 120 mph (the maximum street track speed 120 mph) i have to use till 5th at 5500 rpm's, in theory will work, but I don't know if its going to be good to make a lot of gear changes. With a tire diameter from stock 25" to 22.5" its just a 10% reduction. I will recheck it again just to be sure Thank you Last edited by pedrok; 11-24-2014 at 12:49 PM.. |
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11-24-2014, 10:51 AM
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gearhead
Join Date: Nov 2007
Location: Loverland, CO
Posts: 23,597
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It's all dependent on what you think your top speed will be. The gaps/rpm drops are pretty decent on 2-3-4 on a stock 915. The 4-5 shift is a little long but with high rpm rev limit engines it can work. You just have to chart it and decide if it works for your application.
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11-24-2014, 06:42 PM
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Driven97 & Matt,
Thank you for your answer it really helps, I check again with the gear chart and yes it's only about 10% reduction, about 5 mph less in 1st gear, 8 in 2nd, 11 in 3rd, 15 in 4th and 17 in 5th, not too bad I think it will work well. I remember using mainly 2nd & 3rd and a little bit of 4th at this street track with a 2nd gen RX7, in this case this new car will be lighter about 1500lb with around 250hp, for sure I will see higher speeds. |
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11-26-2014, 06:30 PM
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Join Date: Jan 2002
Posts: 650
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With a 2.0 liter wouldn't you want a 7.31 (pre 75 trans) as the ratios would be better suited due to the low torque of the motor?
 Tinker |
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11-26-2014, 08:39 PM
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Tinker,
I did not mention it, but actually its a turbo motor. I check with Wevo and they told me that I should not have more than 250-260hp before 4,000 rpm with the 915 or the trans will not hold racing conditions Happy Thanks Giving Day!!! Last edited by pedrok; 11-27-2014 at 09:45 AM.. |
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11-27-2014, 08:17 AM
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Join Date: Feb 2004
Location: UK
Posts: 2,230
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Do you really want a transmission that has a relatively slow shift.
You would be better off with a real race car transaxle such as a Hewland or similar. |
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12-07-2014, 10:01 AM
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