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  #11  
Old 10-03-2012, 12:46 PM
gbeaty gbeaty is offline
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Originally Posted by Matt93SE View Post
My stock KA tranny has.. hmm.. several hundred hours of track time on it. I built the car in 2006 and drove it daily for about 2 yrs. It has been a track-only car since then, and I've put about 20k miles on it- ballpark of 250hrs. I finally wore out the 2,3,4th gear synchros at a rough track, but I was beating the bejeezus out of the car at a huge event and only needed it to last the race.
The datas I've seen indicate transmission temperature takes a long time to reach an equilibrium, still climbing at the end of a world challenge race, for example. So I'm not sure you'd see the same sort of failures in sprint racing.

In any case I'll find some way to track temperature (probably caliper temperature stickers) and report back. It'd suck to have to run a Z32 trans in the car; those things weigh a ton.
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  #12  
Old 10-03-2012, 06:51 PM
djsilver djsilver is online now
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Originally Posted by djsilver
I picked up a fair amount of power between the old 5,300rpm HP peak and the 6,800rpm rev limiter by retarding the stock exhaust cam 5 degrees for more overlap. It moved the peak up about 300rpm but didn't really loose any bottom end. A JWT sprocket is pricey but there are DIY's on the net for making your own. It'll also make for an easier peak compression if you go with the SOHC pistons.
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With what cams? Do you happen to have the graphs posted anywhere? Edit: I assume you have 248/248s; how much did you change the intake cam timing when you installed it? Seems like people advance it 2.5 or 5 degrees?
I'm running the stock 240/248 S13 cams and the intake position is stock. Retarding the exhaust cam 5 degrees increased overlap from 3 degrees to 8 degrees. The SOHC cam has 15 degrees of overlap stock. I don't have a dyno chart handy but it just stretches the top end out a little, nothing fancy. Around 165rwhp with that and CAI/JWT ECU/Hotshot header/2.5" catback. I do have over 150 ft/lb of torque over a 3000 rpm spread and that's nice.
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  #13  
Old 10-03-2012, 07:43 PM
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Quote:
Originally Posted by gbeaty View Post
The datas I've seen indicate transmission temperature takes a long time to reach an equilibrium, still climbing at the end of a world challenge race, for example. So I'm not sure you'd see the same sort of failures in sprint racing.

In any case I'll find some way to track temperature (probably caliper temperature stickers) and report back. It'd suck to have to run a Z32 trans in the car; those things weigh a ton.
It's chumpcar, weld some aluminum fins all over the case for a redneck heatsink/trans cooler.
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  #14  
Old 10-03-2012, 10:26 PM
gbeaty gbeaty is offline
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Thanks djsilver.

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Originally Posted by Def View Post
It's chumpcar, weld some aluminum fins all over the case for a redneck heatsink/trans cooler.
...that is pretty much exactly what we were thinking
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  #15  
Old 10-04-2012, 06:00 AM
240sxTTC 240sxTTC is offline
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I've heard there have been some 5th gear failures later (after 12hrs) in Lemons and Chump car races seemed to be caused by heat. So any way to reduce the trans fluid temps would help.
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  #16  
Old 10-04-2012, 08:00 PM
Sleepy_Steve Sleepy_Steve is offline
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Kind of obvious, but heat wrapping the exhaust as it goes by the trans probably also helps out some. I know I stopped the wrap at the end of the header.

But then again, HPDE's and back roads cruising on an NA power plant doesn't seem to kill hardware.
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  #17  
Old 10-07-2013, 08:52 AM
gbeaty gbeaty is offline
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Originally Posted by 240sxTTC View Post
I've heard there have been some 5th gear failures later (after 12hrs) in Lemons and Chump car races seemed to be caused by heat. So any way to reduce the trans fluid temps would help.
Well a friend of mine's 240 just got 3rd place at the ChumpCar 14 hours of Sebring. No transmission issues at all, though for much of the race the drivers weren't using 5th gear (it was faster to leave it in 4th).

Our Z broke a shift fork (or perhaps a shift fork was broken; I hear those things don't just break themselves) about an hour in. Sigh. We've yet to have a Z transmission last more than 1.5 races.
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  #18  
Old 10-07-2013, 02:49 PM
gbeaty gbeaty is offline
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So, here is how the 11:1 (DNJ, factory replacement SOHC) pistons worked out for a friend of mine with a 240 ChumpCar:

From the get-go, the compression numbers were around 180 on all cylinders. We knew this was low, but thought cam timing checked out and figured that it was maybe the gauge reading low For whatever reason we couldn't get the car on the dyno and needed to try and track-tune it. We'd started with base timing at 14, which was pretty slow. We upped it to 18, which was an obvious improvement.

The car then got a few hours of track time put in it, but based on our daq it was clear it wasn't making good power at all. AFR was good, so we figured the only thing left to try was ignition timing. So we upped base timing to 22, and the motor blew on the warm-up lap. A compression test showed 180-ish compression on all cylinders except #4, which was 120-ish. When we pulled the pistons, every single one had broken ring lands. Nothing else was damaged, so the owner slapped new pistons in it and put it back together.

While it was being put back together, the owner noticed the center cam sprocket was a crank-tooth off. Whoops. This probably accounts for the low power and low cranking compression. He put it back together with factory pistons, and the car made 162whp (167 without power steering). This is with a 4->1 eBay header, cone filter, stock S13 cams and obviously a racing exhaust.

Me and another friend are building another KA for ChumpCar and NASA, using used OE SOHC pistons. We'll see how that goes. I hope we can run MBT timing on 93.
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  #19  
Old 10-08-2013, 11:15 AM
Tower240sx Tower240sx is offline
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I built 1 highish compression KA24DE, SOHC pistons and a 1.3 (i think) headgasket,

I had 248 cams in it and didn't use the JWT gears, I moved it 4 teeth (or whatever the math I did said was right)

I made 155 at the wheels on a big roller Dynojet. the car had ALL factory induction, factory manifold/header to a 2.5" muffler shop exhaust. Only issue I had was when I took it to the track on too hot of a range spark plugs...still ran fine until it ate thru the exhaust valve seat pocket on cylinder 4...
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  #20  
Old 10-08-2013, 11:27 AM
Sleepy_Steve Sleepy_Steve is offline
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So... word is still out on hitting MBT with SOHC pistons?
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