Transmission/Diff Input on Upcoming Swap
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Joined: Nov 2015
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From: Western MI
Transmission/Diff Input on Upcoming Swap
Need some transmission/diff input.
I have a '01: 5 speed, sport brakes, and an lsd (i believe is a 4.3). We compete in wheel to wheel with it, and will be continuing to take it on the One Lap of America for the next two years.
We will be doing the new K24z3 swap, and will likely need to detune it just a bit for wheel to wheel competition, and run it all out for the OLOA.
We're trying to figure out what do to about the transmission and rear diff. As is, 2nd is a touch too short, and it screams at highway speeds. We want things to be as reliable as possible, but saving money would be nice too.
So what do we do?
-would the stock 5 speed be able to stand up to the constant abuse and the occasional hard launch from the new-found power?
-go bmw trans and don't worry?
-other options?
Here's what we would like:
I have a '01: 5 speed, sport brakes, and an lsd (i believe is a 4.3). We compete in wheel to wheel with it, and will be continuing to take it on the One Lap of America for the next two years.
We will be doing the new K24z3 swap, and will likely need to detune it just a bit for wheel to wheel competition, and run it all out for the OLOA.
We're trying to figure out what do to about the transmission and rear diff. As is, 2nd is a touch too short, and it screams at highway speeds. We want things to be as reliable as possible, but saving money would be nice too.
So what do we do?
-would the stock 5 speed be able to stand up to the constant abuse and the occasional hard launch from the new-found power?
-go bmw trans and don't worry?
-other options?
Here's what we would like:
- good gearing for the K24z3 on track (better gearing for highway would be nice, but that is secondary)
- reliable for hard launches, on track abuse, and 12 hours of highway/commuting
LMK!
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The 6 speed has a lower top gear so worse. The 5 speed is vastly superior in weight and feel if you are racing. You may want to pair it with a 4.1 for the distance and giving you better gearing in 2nd for autocross.
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From: Los Angeles, CA
This. The higher redline and massive power increase will make the 4.10 feel like a 4.30. Could even explore 3.90 option with as much power/RPM as you'll be gaining.
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For OLOA I would be worried about the longevity of the 5 speed behind a healthy K24. There is a lot of conjecture around what causes them to break and around how to fit it, but they still break, a lot.
If I were going to take a 5 speed car with any real power on a OLOA "Excursion" I'd make sure I had one spare with me, I had practice changing it, and that I identified junk yards near the route who could have spares along the way.
If I were going to take a 5 speed car with any real power on a OLOA "Excursion" I'd make sure I had one spare with me, I had practice changing it, and that I identified junk yards near the route who could have spares along the way.
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Thread Starter
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From: Western MI
We had been planning on doing that all along, however, with the lower overall hp and no plans to go to forced-induction (we race in Gridlife's Touring Cup), It sounds like the 6 speed will be beefy enough and a far cheaper solution.
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From: Los Angeles, CA
For OLOA I would be worried about the longevity of the 5 speed behind a healthy K24. There is a lot of conjecture around what causes them to break and around how to fit it, but they still break, a lot.
If I were going to take a 5 speed car with any real power on a OLOA "Excursion" I'd make sure I had one spare with me, I had practice changing it, and that I identified junk yards near the route who could have spares along the way.
If I were going to take a 5 speed car with any real power on a OLOA "Excursion" I'd make sure I had one spare with me, I had practice changing it, and that I identified junk yards near the route who could have spares along the way.
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I think a lot of those turbo guys aren't doing multiple hundreds-of-miles road trips with repeated track events between them. After 10yrs of playing with Miatas it's just plain annoying to me when people suggest a 5-speed for anything related to track use. They are weak and they're objectively slower than a 6-speed in the exact same car. Period, end of story. Anyone who says otherwise is wrong.
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Thread Starter
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Joined: Nov 2015
Posts: 123
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From: Western MI
I think a lot of those turbo guys aren't doing multiple hundreds-of-miles road trips with repeated track events between them. After 10yrs of playing with Miatas it's just plain annoying to me when people suggest a 5-speed for anything related to track use. They are weak and they're objectively slower than a 6-speed in the exact same car. Period, end of story. Anyone who says otherwise is wrong.
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From: Greeley, CO
If it's coming from him then that's going to be the best combo on track.
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4.30s at minimum. Maybe even 4.44s with only 200whp/160tq. You need to rev the snot out of that thing, constantly, to get it to work.
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Thread Starter
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From: Western MI
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It's a race, you're driving a race car, I'm unsure of what you expected when you got yourself into this mess. I doubt anyone will be able to hear your tiny violin over the sound of the 3" exhaust attached to the K24. In short, sack up 
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Thread Starter
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From: Western MI
doesn't mean i can't be idealistic from time to time.
it's the balance we're trying to strike between on-track performance vs a significant amount of transit driving - while towing a trailer. it's far less about the noise, because we've been dealing with that, and more about trying to have some mechanical sympathy on this car during the transits - which is when most of the oloa cars break.
the 4.3 isn't going to fly with the 6spd as long as we're doing the oloa. but you all have convinced me that the 4.1 will be a better performance ratio than the 3.9 even if it costs a bit on the transits.
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