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Old 06-19-2017, 11:39 AM
beasleysteven beasleysteven is offline
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Default Barber Motorsports Park Diff Gear Ratio

I have a WRL race coming up at Barber in August. My S13 has a 1uzfe in it with approx 275 hp. At the last race at Road Atlanta I had plenty of power to pull virtually any one out of the corners but the car was lagging on the top end. Toward the end of the back straight I would begin to get left behind by many of the other V8 cars. Coming into 10a/b complex I would be at about 6k RPM right before lifting for the braking zone. Same on the front stretch. I was running a 4.08 on a stock welded diff then. I have since picked up a 3.9 gear set that I can put into one of my other diffs. I was going to weld that one up also. We are running a stock KA transmission so 5th gear is .71 if I am not mistaken. I also have a 4.6 on a VLSD but I usually use that only at very short tight tracks. We have the race coming up at Barber and having never ran that track before with he V8 so I am not sure which gear to run. Does any one have any experience with that track with these kind of HP numbers?
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Old 06-19-2017, 11:44 AM
T-Rex T-Rex is offline
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I run a 300zx in Improved Touring at Barber. I run a 4.6 and make less HP than you do, but I don't run out of gear. Having said that I think I may get into 5th on the far back straight and the front straight.
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Old 06-19-2017, 12:22 PM
Matt93SE Matt93SE is offline
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Not much help today, but go find yourself a 5th gear from a Hardbody pickup. they are like 0.85 or something like that. way better than the stock 5th gear.

The OD is so tall on these transmissions that any engine will pretty much fall on its face when put into 5th.
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Old 06-19-2017, 01:09 PM
Def Def is offline
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Where does the 1UZ make peak power? You want to start getting around that range a few hundred meters/yards before the braking zone of the longest straight to maximize speed.

The hardbody 5th gear will help, as you won't bog down so bad going from 4th to 5th (which might be more what your experiencing).

Maybe a 4.36 would suit your power and top speed a tad better, which would be easier than the hardbody 5th.
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Old 06-19-2017, 07:58 PM
beasleysteven beasleysteven is offline
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It makes peak power in the mid 5k range.

So from what it sounds like you guys think I am going the wrong direction for Barber. I need to go up instead of down for that track.

T-Rex what is your speed down the front straight and that short hop on the back stretch just looking for a reference.

I have a 4.6 that I usually use at Atlanta Motorsports Park but I figured that was way to short for there. But depending the speeds it may work out.

What does the 4.36 come out of?

Also this may be a stupid question but is the hardbody trans the same as the 240. They both ran the ka?
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Old 06-20-2017, 04:21 PM
Def Def is offline
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Hardbody trans (D21 I think) is the same as a KA, with different ratios.

Anything you can do to get a bit more top end power? Sounds like that could be your root cause, but the big gap to 5th can't be helping either.

4.36 didn't come in any US cars. Commonly found in JDM S13 Qs and Js NA cars and A31 Cefiros. There are some others like some years of R32s I think.
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Old 06-23-2017, 11:14 AM
icantdrift icantdrift is offline
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The straights at Barber are quite a bit shorter than Road Atlanta so you can definitely gear the other direction. There's also a lot more slower/tighter corners than Road Atlanta so the lowest gear you can run will help a lot. The 4.6 gear with that tall of a 5th will get you to around 148mph with a max of 6500rpm and a 25" tire guesstimated. I don't remember my actual speeds there but back when I ran my S13 there with a lot more power than you have it wasn't anywhere near 150mph, maybe around 130 or just over.

Tremec has a pretty decent gearing calculator on their site you can use to figure it out based on your actual max RPM and tire size http://www.tremec.com/calculadora.php
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Old 06-23-2017, 12:57 PM
T-Rex T-Rex is offline
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I went back and looked at video, and I never do get into 5th. So I'm running a 275/40/17 tire and running a 4.6 final drive. I'm definitely not running out of rpm when in fourth. I'm making quite a bit less HP than you are, but am NA, so probably rev higher. YMMV.
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Old 06-23-2017, 05:29 PM
beasleysteven beasleysteven is offline
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I am running a 245/40 17 tire. The height of it is 24.7". I will look up the height of your tire to see how it compares. Probably a little taller if I was to guess.

It has been a couple of years since we ran Barber and blew a ka maybe an hour into the race so we didn't have time to collect much data. If I remember right we were still running the stock 4.08 then. And may be even open diff.
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Sponsored by Pallets and Crates LLC Gainesville Ga
04' Chevrolet 3500 Tow Vehicle, 02' Dodge Ram 1500 Truck, 87' Toyota 4 Runner "Top Less",
15' Toyota 4Runner, 07' Honda Fit
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Old 06-27-2017, 11:05 AM
ZainRacer ZainRacer is offline
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No sure if this helps but here is one of my laps from Barber a couple yrs ago.

https://www.youtube.com/watch?v=X3HnIdYAjsM

This is a SR20 at ~240whp. 225-50-16 tires with a stock S14 sr20 Trans and 4.08 gearing. I never got into 5th gear.
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