TH350 and TH400 build recipe

What does it take to make a TH350 and TH400 live behind an engine that makes 500, 600, 800, 1000 and 1500hp. Just bench racing but with turbos making these power levels easily attainable the rest of the combo needs to hold up too.

 

Ok how about how much horsepower do you have and what transmission and what's done to it.

 

Brandon I’ve got a bunch of high end trans and although I’m not a trans rebuilder I can give you some insight.

1. The TH-350 is a great trans especially when weight and rotating mass and HP loss matter. I’ve got a 350 here that had the case modified for room for more clutches, some billet parts, works great and it’s good to about 700 HP. The thing with these is that once you are up over 600 hp it’s less $ to build a TH-400 for the same power level. A perfect example of this is when limited to power and engine mods in a race class then every last pound and Hp loss is key. But when running a 700+ hp setup the amount of power loss becomes negligible especially when you can just turn up the boost a bit to overcome any excessive drivetrain loss.

2. The TH-400 is the lowest cost trans to build for high HP. I’ve got a Hughes TH-400 here that’s a nice unit. I got it used but it was behind a 1600 HP 5.3 LS.

http://www.hughesperformance.com/product/34-3xhd/

 

I’ve also had good luck with a nice 2004R. With the twin turbos on a 350, this trans and 4.56 gear with 32inch tall tires it turns 2000 rpm at 60 mph. It has a 3600 stall converter so it launches hard but still gives 100% lockup on the highway.

"CK Performance STAGE 2 2004R TRANSMISSION

THE STAGE 2 2004R IS BUILT FOR ENGINES PRODUCING UP TO 800 FOOT POUNDS OF TORQUE. EACH TRANSMISSION IS PROFESSIONALLY ASSEMBLED AND THEN GIVEN A THOROUGH ROAD TEST IN OUR TEST VEHICLE TO GUARANTEE FLAWLESS OPERATION PRIOR TO SHIPPING.

COMPETITION COMPONENTS
E4340 STEEL BILLET SHAFT FORWARD CLUTCH DRUM.E4340 STEEL BILLET INPUT SHAFT.E4340 STEEL BILLET OVERDRIVE PLANETARY CARRIER ASSEMBLY.E4340 STEEL BILLET OVERDRIVE RING GEAR .HEAT TREATED STATOR TUBE.HEAT TREATED SUN GEAR SHELL.OVERSIZE BILLET ALUMINUM SERVO ASSEMBLY.ROLLERIZED OVERDRIVE RING GEAR,CENTER SUPPORT,DIRECT DRUM,FORWARD DRUM,SUN GEAR SHELL,LO REVERSE CLUTCH HOUSINGAND REAR INTERNAL GEAR. THESE BEARINGS REDUCE INTERNAL FRICTION AND HORSEPOWER LOSS CREATED AND CONSUMED DURING NORMAL INTERNAL COMPONENT ROTATION.THEY ALSO INCREASE THE THRUST SURFACE AREAS BETWEEN ROTATING INTERNAL COMPONMENTS

CLUTCH AND BAND UPGRADES
OVERSIZED ALTO RED LINED 2ND GEAR BAND. CUSTOM DIRECT CLUTCH PACK WITH 6 ALTO RED LINED FRICTIONS AND 6 OVERSIZE STEEL PLATES. UPDATED OVERDRIVE CLUTCH PACK WITH 3 BORG WARNER TAN FRICTIONS. CUSTOM CNC MACHINED BILLET ALUMINUM DIRECT CLUTCH PISTON .

HYDRAULIC UPGRADES
ALL BUILDS START WITH A BRAND NEW GENERAL MOTORS FRONT PUMP ASSEMBLY.THE PUMP IS THEN REWORKED AND ASSEMBLED WITH STEEL VANE RINGS,DUAL HIGH RATE PUMP SLIDE PRIMING SPRINGS,A NEW HEAVY DUTY PRESSURE REGULATOR SPRING ,AND OVERSIZED CNC MACHINED TV AND INTERMEDIATE BOOST VALVES.THESE MODIFICATIONS IMPROVE AND INCREASE LINE AND LUBRICTION PRESSURES. ADDITIONAL PASSAGES ARE ADDED TO THE CENTER SUPPORT FOR IMPROVED THRUST SURFACE LUBRICATION. "

 

I run a 6L80 behind my 6.0 LS in a big truck and it’s great. The amazing part about this trans is the 4.0xx first gear ratio (TH-400 is 2.48!!!) plus it has two overdrive gears. With 35” tires, 3.73 gears it hauled along the highway at 2000 rpm at 80 mph, and it leaves the line hard even in a 8000 pound truck. 2800 rpm at 105 mph. I wouldn’t hesitate to use a stock 6 speed with a nice converter in any hot rod, just mod the trans tunnel, not a huge deal. I’m turbocharging the truck this summer and I expect no issues from the trans as it’s been rebuilt this year with a triple disk lockup and 3800 stall. These trans seem to handle 800+ hp stock.

Also noteworthy is that the cost goes up a lot for lockup converters in high HP applications. I paid about $900 for a lockup converter to handle 1000 hp. A non lockup can save $ but then street driving suffers due to excessive slipping and heat.... also a good thing to know is that many racers use 4L80E or other lockup type trans with Non lockup converters and mods to make that work. For racing the lockup isn’t needed.

Comparing a Th-400 to a 6L80 it would take a 4.88 gear in the rear end to get close to matching the off the line gear advantage the 6 speed has with a 3.08 rear axle. Even if a person used a 3.08 gear with a TH-400 it would still spin 3800 RPM at 100 MPH. While a 6 speed with a 4.56 gear would run the same RPM as seen below.

 

I have built many 400 for turbo LS engines making 1500hp with nothing more than aluminum direct drum and steel clutch hub. Other than occasionally rolling a intermediate sprag, they are pretty reliable.

I have yet to see someone break shafts or gearsets. To be honest, I don’t know where the limit is for stock parts.

I cringe when people complain about the cost of an aluminum drum, and spin the engine to 7k plus rpm. These same people have no problem spending 20k on a engine, but bitch about a couple grand in a transmission to handle the power. Unfortunately, the budget runs out at the flywheel.


The 350 is pretty reliable to about 550-600, after that a upgraded intermediate sprag is needed. Unfortunately, it’s far cheaper to build a 400 that will take much more abuse than building a weaker 350.


The 2004R can take some abuse, but definitely not cheap. In my opinion, the money spent upgrading a 2004R would be better spent on a trans controller for a 4L80E. If you absolutely have to have big power and overdrive, it’s hard to beat a 4L80.

I know nothing about the 6L80 transmissions. However, judging from all the lightweight stamped steel clutch retainers I’m betting they are nowhere near as strong as the 400 and 4L80.