I am interested in getting a TH400 with a Vigilante 2600-2800 stall converter. Someone told me not to go with this set up because I will loose HP. Is this true? Will I still see gains at the track? Thanx for any helpful imput!!

 

I would estimate that the TH400 is going to increase your drive line losses by up to 2 to 3% over what you would have with a 4L60E. Depends on how loose the converter is and whether it has lockup or not.

I lost up to 70rwHP going from a T56 to a TH400:

T56 - Steel FW Street Twin - 3" chrome moly DS - 3.73 12-bolt:

NA: 486flywheelHP/425rwHP = 12.6% loss
1 stage N2O: 633 flywheelHP/555rwHP = 12.3% loss
2 stage N2O: 762 flywheelHP/670rwHP = 12.1% loss

(these are direct comparisons of the engine on an engine dyno with full intake and exhaust, and on a chassis dyno)

TH400 - non-locking convertor/5,000 flash at 800 lb-ft (everything else the same ):

NA 486fw/390rw = 19.8% loss
1 stage: 633fw/505rw = 20.2% loss
2 stage: 762fw/600rw = 21.3% loss

Performance was not changed all that much, at least not with NA and 1-stage nitrous... ET's/MPH were not that much different. Haven't run it on the track with full N2O.

I've seen the TH400 losses go as high as 24% on a setup with 1,325fwHP/1,007rwHP, using a 3.50:1 9-inch rear with spool.

 

THM 400 is a VERY strong 3-speed (no OD) transmission. The OD version is the 4L80E.

Down sides to changing your 4L60 (700R4) to a 400:

-because the 400 has bigger and heavier parts, it has more inertia and more friction, so, yes it will eat a few more horses at the rear wheels, but that won't be the biggest downside.

-you lose about 20% of your first geat torque multiplication because the 400 has 2.48 first gear and the 4L60 has a 3.06

-your cruise rpm increases from say 2000 to about 2900 because of no overdrive, plus it won't be a lockup so revs will be hgher yet. That's probably 4-5 mpg worse in cruise fuel economy.

-the 400 is quite a few pounds heavier

-it will cost a significant amount to do the change

Upside:

-the higher stall will get back some of your losses at initial launch, but probably not all

-the 400 can be built to handle many hundreds of hp more than your car makes. So when you upgrade the engine to the 700+ hp level, all you'll need to do is rebuild the 400 to take it

If your tires can handle more launch, consider a replacement lockup converter for your current transmission.

See Fred's detailed comments also.

Bottom line: with a relatively stock engine in your car, changing is a bad idea.

My $.02

 

The previous two posts summed it up pretty well. If you aren't making too much hp for the 4L60E than there is certainly no reason to change and a lot of reasons not too.

Rich Krause

 

If you could "lockup" the torque converter (obvious you can not) on the TH400 you would find that it does not eat as much horsepower as you see with the loose torque converter on the dyno. Years ago there was a test to determine how much horsepower different transmisions "eat". The TH400 was using about - 38, the TH350 - 35, the Powerglide - 18, Mopar TF727 - 32, Ford C-6 - 45. The torque converter will show a "higher" loss than a stick and depending on the STR, stall, and diameter of the TC will contribute to how good or bad the losses will be on the dyno. Remember the automatic transmission will "see" more total rpm's than the stick in the quarter mile (due to the slippage of the torque converter) and can run just as fast and as quick as the stick because of seeing more available horsepower, and the multiplication of torque. This should give you an idea of why you do not see the stick running away with the race. The TH400 weighs about 15-17 pounds more than the 4L60E.

 

At first I was going to question you on the transmission input shaft and beyond seeing more engine rpm for a given driveshaft rpm, but I think you meant higher engine and converter input or "pump" rpm which could mean more engine hp. The trans "sees" only converter turbine rpm but all the hp that gets thru, right?

Thanks for the good numbers.