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Old 11-22-2010, 03:18 PM
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T56 practical torque limits

I have a TNET1247 viper T56 sitting on the shelf. It has been modified with a bored-out GM tailhousing and a GM input shaft and front plate. I have seen T56s rated anywhere from 350 lb-ft up to 750 lb-ft based on very superficial differences. D&D often rates their TNET1247s at 650 lb-ft, but the only real difference is upgraded synchros and shift forks.

I also know that manual tranny torque ratings are 2 parts SWAG (stupid wild-*** guess), 1 part engineering guess, 5 parts based on the rest of the vehicle combo, and 9 parts CYA (cover your ***) from the person who writes the warranties.

Anyone with more practical knowledge? One of the engine's I'm considering is a real monster... like nearly 700 lb-ft monster.

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Old 11-23-2010, 08:55 AM
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Most OEM transmissions are rated by the motor they put in front of it. There arent very many differences in the internals of a T56, aside from the Viper conversions for the GM guys. Triple cone and compressed carbon blocker rings dont add much in the way of ability to handle abuse. A lot of places will put a trans behind a godzilla engine that makes ludicrous power and as long as they put the trans in 4th (direct drive) and dont shift it...no problem.

Bronze fork pads and billet keys just are band-aids to allow you to over shift the transmissions. I know the bronze pads wear faster than the plastic ones. These modern units have ALL the gears turning constantly, thats a lot of inertia to slow down. They shift smooth, but not FAST.

Anyway, you'll need to build up a T56 to reliably hold that kind of power, assuming you can get it to stick to the road. Wheel spin saves transmissions.

I can personally recommend The Gear Box in Michigan (734-793-0727 Ask for Kevin); RPM in Daleville Indiana (800-406-1109 ask for 'Guffey') and Finishline in Wood Dale Illinois (630-350-7776 ask for Chuck), Rockland Standard in NY and D&D Perf.

If you have any questions, let me know. I'll look up your tag number for you

Last edited by AutoGear; 11-23-2010 at 09:06 AM.
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Old 11-23-2010, 09:04 AM
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You do have a Viper T56.
Here is an exploded view and parts list
http://autogear.net/pdf/T56Catalog/T...er_92_2004.pdf
compliments of Auto Gear

If you want to compare it to other T56s, here is a link to my other T56 and TR6060 catalogs
http://autogear.net/T56Catalog1.html

The places listed previously use Tremec parts (aside from upgrades). There are other great builders like Tick; but I dont have personal experience with them
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Old 11-23-2010, 10:44 AM
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My conversion is basically an exact copy of what D&D does with their Fbody conversion. Viper output shaft, bored GM tailhousing, GM front plate and input. Its been sitting on the shelf for a couple years waiting to go into my 96 Impala SS, but now that I have my 67 LeMans I think it would be better suited in the 67.

The plan is going to take shape slowly, I have the engine choices narrowed down to an LS-based engine in the 550hp range, or (for about the same money) I can use my long experience with Caddy 500s and build a 700/700 hp/tq engine for about $6000. But all that torque won't do me any good if I turn my T56 into shrapnel.
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Old 11-23-2010, 11:35 AM
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Youre good for 600-650 reliably. If you have the iron shift fork, its going to be able to last longer. Your goals are right on the edge of the viper mainshaft; you may want to talk to someone knowledgeable about perhaps the SSR mainshaft. We don't build T56s so I dont know all the tricks but I think if you didnt wail; on it, you might find you can keep it alive. What is your rear axle ratio?
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Old 11-23-2010, 11:51 AM
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Quote:
Originally Posted by AutoGear
What is your rear axle ratio?
Truthfully, it will depend on the engine and the final torque peak. With the caddy, probably 4.10 to 4.56. LS-based motor probably 4.56 or lower. Sounds like a lot, but this T56 is the 2.66/0.50 gearset
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Old 11-23-2010, 12:53 PM
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And, of course final tire size. I am mini-tubbing the rear to fit 285 or 305 rubber, and I'm guessing 305/40-18?
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Old 11-24-2010, 07:44 AM
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woof...this is serious.

Id try to keep it 4.10 or numerically lower. With the 2.60 1st you could go to a 3.73 and STILL have a better launch than a 4.11/2.20 (M21 or M22) vintage muscle car.

I think the trans will hold it. How long is something entirely different. Don't faceplate it, unless you can drive one 1st and see how you like it.
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Old 11-24-2010, 03:07 PM
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Quote:
Originally Posted by AutoGear
woof...this is serious.

Id try to keep it 4.10 or numerically lower. With the 2.60 1st you could go to a 3.73 and STILL have a better launch than a 4.11/2.20 (M21 or M22) vintage muscle car.

I think the trans will hold it. How long is something entirely different. Don't faceplate it, unless you can drive one 1st and see how you like it.
Serious doesn't start to describe this one. It might take me forever, but my favorite car of all time is the 67 GTO. This is a LeMans but its the look I'm after, not the high-dollar nameplate. I also don't feel like hacking up a real GTO for my project.

For starters, its getting a full road-race chassis. It will be basically a purpose-built road racer that happens to have carpet, four seats, and A/C. My goal is to have a rip-roaring car that can be driven every day if I choose, but I'm also very interested in getting into amateur road racing for fun.

As far as 1st gear final drive ratio, I'll have to get all the final numbers together - tire size, torque peak, etc and we can hash that out when the time comes.

I had been leaning hard towards an LS1, but A) everybody does an LS1 swap, and 2) getting to 550 hp plus the initial purchase of the engine itself would cost almost as much if I just built a 700 hp big block something.
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Old 11-24-2010, 04:12 PM
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Just for conversation's sake...

Here's a build up of a 6L LQ4 that made 550 hp for around $4900. The 550 HP was made w/a cam that has 228 duration @ 0.050" and ~0.570" lift on a 112 LSA. The real story is the L92 heads that were used.

CC this month put a set of Pro-Filer heads on a 454 they're working with- the engine had earlier made 455 HP/552 TQ w/PP heads, a Holley 750HP and a Comp XE268H cam.

Swapping to the Pro-Filer heads, a Holley 950HP and a stouter Comp XE284H cam added about 120 HP to the peak, 564 HP/542 TQ. Both combinations used the same 9.4:1 CR.

The original engine w/the PP heads came w/o a carb and no front dress, but everything else- including a DP aluminum intake and a HEI distributor, all for $2650. The addition of the Pro-Filer heads and et cetera brought the cost up to about $5650.

Trick Flow has a $3450 top end kit to make 550 HP from a LS2 engine.

Last edited by cobalt327; 11-24-2010 at 04:35 PM. Reason: Add link.
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Old 11-24-2010, 11:14 PM
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Quote:
Originally Posted by cobalt327
Here's a build up of a 6L LQ4 that made 550 hp for around $4900. The 550 HP was made w/a cam that has 228 duration @ 0.050" and ~0.570" lift on a 112 LSA. The real story is the L92 heads that were used.

CC this month put a set of Pro-Filer heads on a 454 they're working with- the engine had earlier made 455 HP/552 TQ w/PP heads, a Holley 750HP and a Comp XE268H cam.

Swapping to the Pro-Filer heads, a Holley 950HP and a stouter Comp XE284H cam added about 120 HP to the peak, 564 HP/542 TQ. Both combinations used the same 9.4:1 CR.

The original engine w/the PP heads came w/o a carb and no front dress, but everything else- including a DP aluminum intake and a HEI distributor, all for $2650. The addition of the Pro-Filer heads and et cetera brought the cost up to about $5650.

Trick Flow has a $3450 top end kit to make 550 HP from a LS2 engine.
Excellent info. I'm looking for exactly this... engine recipes that I can use.

That LS1 top end kit is attractive, but Potter makes a top end kit for Caddy 500s for $3900 that has made 775 hp and 750 tq... but to be truthful, it did have about $800 worth of rods and pistons in it.

But, when it comes down to it I have a lot of research to do on HP vs weight, torque vs RPM, yadda yadda. The LS engine is attractive, but I'm trying to decide between lightweight EFI and middleweight monster. A caddy 500 with aluminum heads weighs in at about the same as an iron-headed SBC with aluminum intake.

Fortunately I'm early in the decision process.

Keep the ideas coming.
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