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Old 11-01-2007, 02:50 AM
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Practical tq limit of 4L80E

I want to know how much tq/hp a 4L80E is capable of handling... and I don't mean in race trim once a week, I mean in daily-driver street duty. I have a duramax diesel project that (depending on how I tune it) can make anywhere from 250hp/550tq up to 500hp/900tq. I just want to know with all the things I can throw at a 4L80E, how much can it take and be reliable? And when I say reliable, I mean 50-100k of real street punishment in a 4500-lb car with occasional (careful) 3500-lb towing.

I know the 4L80E was installed in vans behind Dmaxes tuned to about 250/550 so I know it will take that much. I'm not looking for fluff answers, I want real, practical limits. If you tell me that 550 is the max, I'll look for another tranny, but the 4L80E would be the easiest.

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Old 11-01-2007, 09:18 PM
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check out www.ckperformance.com a stock 4l80 should handle like you said 550 on the high end. these guys got em up to about 1800lb ft. hehehe. but there are various minor upgrades, valve body, servos and line pressure kits that are relatively inexpensive to buy(not cheap,just inexpensive) and can be installed by a smart person like yourself. get a good low stall converter for that diesel though. they dont like to rev.
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Old 11-02-2007, 01:40 AM
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Great, thanks. I have a good hookup for converters. A guy named Chris at Continental has built me some custom diesel converters in the past and I've been happy with them. He built me a converter for a TH400 that stalled at 800

Everyone keeps telling me to use an Allison, but this is going in a car... there is no hammer big enough to make an allison fit in a 66 Pontiac tunnel.
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Old 11-02-2007, 02:43 PM
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The hard parts (gears, carriers, clutches) used in first, second, and third gears of the 4L80E are exactly the same parts used on the TH400. The aftermarket beefed parts for the TH400 fit the 4L80E as well.
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Old 11-03-2007, 01:18 PM
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Ok, so based on that, I assume that the 1-3 section of the 4L80E can be made to take as much as a TH400 can be made to take. I'm sure there are modest upgrades for the OD, but I shouldn't have to worry about it... it will drop out of OD long before any massive torque hits it.

So, how much would a heavily beefed TH400 take?
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Old 11-03-2007, 01:44 PM
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Quote:
Originally Posted by curtis73
Ok, so based on that, I assume that the 1-3 section of the 4L80E can be made to take as much as a TH400 can be made to take. I'm sure there are modest upgrades for the OD, but I shouldn't have to worry about it... it will drop out of OD long before any massive torque hits it.

So, how much would a heavily beefed TH400 take?
How much money ya got? TH400 transmissions can be built to take in excess of 1,200 hp. You are correct to note that the OD in the 4L80E is the weak link. I trashed the OD in my stock Chevy crewcab dually just by towing. Yes, I now know that I should not be towing in OD...
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Old 11-03-2007, 02:20 PM
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Most of the heavy duty after market t-400 gear train parts fit a 4L80E.... you must watch the L80E lube circuit depending on what year L80E you have .... early or later design oil lube.

Also need to watch the input shaft splines. Splines will rip off cleanly as the photo indicates. At the right side of the shaft, there should be splines and another set of sealing rings. The end snapped off

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Old 11-03-2007, 05:06 PM
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Quote:
Originally Posted by joe_padavano
How much money ya got?
Well, I'm not rich, but this is a big project that already has big money in it. I truly love this car and would sell my first born to complete it the way I want it, so I think money is no object if it can be done RIGHT.

I have about $15,000 wrapped up in a car that hasn't even touched body work. I have a 14-bolt full floater in the rear that has been modified to bolt in with trailing arms. I have modified 3/4 ton front spindles on custom control arms that mount 8-lug truck brakes up front. I have a heavily modified Caddy 500 that was a good idea when I started the project but now its no longer what I want.

When I started the project in 1999, I was looking at all kinds of diesels, but none were suitable. The 5.9 cummins is just a huge engine that is too heavy, too long, and too tall. The 7.3 powerstroke was a full 10 inches too tall to fit under the hood at the heads, let alone the turbo and intake plumbing. The 6.5 chevy is just not an option. Now with Dmaxes having proven themselves and becoming more common in the salvage arena, it poses a serious possibility. Its not as bulky and heavy as what was available in 1999 which is why I originally fitted the Caddy 500.

Now that I've found a viable diesel, I gotta get the power to the ground. I'm also looking into the new 6L90. It might take some serious abuse, but its geared a little low. The highest gears i can get for the 14-bolt are 3.21s and that 4.xx first in the L90 makes for a really low first.
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Old 11-03-2007, 07:46 PM
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I have been told they will handle 1000 lb/ft, but with that input shaft pic I am skeptical. You can get a new hard input for around $600 which might be money well spent. I am having one done right now for a 5.9 cummins that is around 600 lb/ft. The TH475 is holding up now with no complaints, but I want OD. I am not doing the input shaft, but everything else is being upgraded that can be including extra clutches in direct and OD.
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Old 11-03-2007, 07:57 PM
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check out www.ckperformance.com th 400 stage 3, 2000 hp and 2000 lbft of torque. heck it might be cheaper to buy one of these things and a gear vendors, they take like 1500 plus torque too.
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Old 11-03-2007, 08:09 PM
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Speaking of GVODs, at the SEMA show this week I saw a "top fuel" diesel dragster with a 2000 lb-ft cummins running through a GVOD. it was funny to see this massive diesel backed up by a transmission the size of a coffee can.

I've been very happy with my GVOD, but I really (for some reason) don't like the non-lockup.
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Old 11-03-2007, 08:37 PM
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i agree with the lock up issue. but if you are having the converter built for you, its low stall and very tight, why not go with the more reliable route? or if its of interest, have you hear of switch pitch converters? you might be able to have one built that just about locks up, i dont know the specifics on them but it is another route.

let us know what you go with and good luck!
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Old 11-04-2007, 10:15 PM
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Curtis.., nice project. Nice to see someone doing a modern diesel hot rod. Even if it is a Duramax. Keep the info coming on it. The GVOD is getting my attention too. There is a lot of mis-information on these units. I'm also looking at one for my Willys when the blower comes along. This Cummins guy is hoping you have a good one.
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Old 11-05-2007, 01:50 PM
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Thanks! and thanks for all the advice and help.
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Old 11-06-2007, 07:29 PM
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Quote:
Originally Posted by 1drwgn
check out www.ckperformance.com th 400 stage 3, 2000 hp and 2000 lbft of torque. heck it might be cheaper to buy one of these things and a gear vendors, they take like 1500 plus torque too.
I got a price for a gear vendors to go behind my bbc/th400, $2500 to my door. But I hear that is worth every penny.
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