 Another Transmission Gearing Question |
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| 914Bryan |
 Feb 10 2012, 02:00 PM
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#1
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Member  Group: Members Posts: 190 Joined: 6-June 11 From: Orange County Member No.: 13,162 Region Association: Southern California  |
Howdy, I know that our fifth gear is considered an overdrive, but has anyone gone a bit lower so as to lower the rpm for extended freeway driving. 3400 is about 75 mph and I was wondering about dropping it below 3K to increase mileage...Any thoughts? (IMG:style_emoticons/default/confused24.gif)
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| AZ914 |
Feb 10 2012, 02:03 PM
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#2
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914 Dumbass Group: Members Posts: 1,459 Joined: 6-January 03 From: Sunny Tucson Member No.: 98 Region Association: Southwest Region |
When I had my trans rebuilt last summer, I had 4th and 5th swapped for lower gearing. I put an X in 4th and a flipped H in 5th. There is another thread (Gear ratio chart) currently discussed that shows the various ratios. I think the flipped 5th probably lowered my RPMs by 400-500 though I can't be certain. I'm very happy with it.
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| Dr Evil |
Feb 10 2012, 05:17 PM
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#3
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Send me your transmission! Group: Members Posts: 22,999 Joined: 21-November 03 From: Loveland, OH 45140 Member No.: 1,372 Region Association: MidAtlantic Region 
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Root Works did the X and flipped H for 4th and 5th and loved it.
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| shoguneagle |
Feb 10 2012, 05:22 PM
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#4
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shoguneagle Group: Members Posts: 1,180 Joined: 3-January 03 From: CA, OR, AZ (CAZOR); New Mexico Member No.: 84 Region Association: Northern California |
I have had Doc Evil build my road machine transmission with the same thought; lowering the 5th gear to somewhere below 3200 rpm at 70 mph; not in yet, but I think it should lower it somewhere below 2800rpm at 70mph.
Since these are oil cooled engines, you probably will not want to lower them too much without having an external oil cooler to take care of the lacking of cooling air and oil to the engine. I am running a 3.2 Carrera engine and the whole transmission has be build close to what the engine demands per each gear. I am also running a 911 oil tank along with the external oil cooler which gives me somewhere around 24 quarts Mobile-1 in the entire system. I feel I can run across the Mojave Desert or down to Phoenix without too much trouble of any overheating from the lowered rpm.. Now you are seeing the reasons I built my car this way. It is anticipated to be a road cruiser with great acceleration, quickness, and speed getting great fuel mileage. If you are running a four cylinder, the building process could be something else. You can always down shift and run slower if your car is overheating. I will let everyone know this summer when I get the transmission changed, project finalized for road, and do some test runs. My resident expert is Doc Evil who you can find on this board. Steve Hurt Hope the above helps |
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