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I was talking to a guy who ran a 460/C6/205 in his 79 Bronco for mud bog racing. He said the C6 was a "power robber", taking away a lot of horsepower, meaning that if the engine put out 400hp, if you run a C6 it would put out ~360hp in the end. Anybody experience this, know what he might be talking about?

There is a lot of parasitic drag in a C6. All transmissions and drive lines loose some power, the C6 just uses a lot in exchange for the strength it has.

Same goes for 9" vs 8.8 due to the hypoid offset.

yep, but that c6 will probably use more than 40hp. i have heard that they usually take about 60hp to turn. but again its super strong so its still worth it.

Power loss is a percentage, not a set number. Put a 20 horse motor on a C6 and it will still turn.

60hp is actually what he said too. I guess there are trade offs for everything.

philofab wrote:Power loss is a percentage, not a set number. Put a 20 horse motor on a C6 and it will still turn.

oh definitely, i was referring more to a stock bronco motor. i have just heard that 60hp number pop up several times when referring to broncos. generally about 10-15% loss for manuals and 15-20% for autos. a c6 is up around 25%. so that 60hp loss equates to about a 240hp motor.

But what are the options?
C4 less drag but not gonna live.
E40d not any less drag probably more
Rollerized C6 a little less drag (higher stall converter=way more loss though)
T400 I dont know about drag but run a scatter shield
Manual of some sort less drag but not popular for(v8) off road trucks (xcpt Philo)

I wouldnt say the C6 has a lot of power loss, its actually a lot of inertial weight internally in the gear train. The C6 was primarily designed for the old FE series of engines, in the days of real factory horsepower, so the gear train is very robust to handle the massive torque of the bigger FE's. Strong heavy gears, planetaries, etc. mean a lot of weight that needs to be spun up and down all the time. Using a C6 on a small block engine, it has a high parasitic power drain. Thats the main disadvantage, the advantage being that, properly prepared, they will last a long time in a hi-performance environment. Rollerizing a C6 will help a lot, cutting down wear and heat and reducing friction, but with few reliable or better alternatives to swap straight in, the simple, rugged old war horse is still a viable option. Apart from the AOD (when properly built can handle a lot of power), I cant see a drop-in alternative. Just my 2 cents worth.

Basics: Automatics are power robbers. Fact
All automatics eat more power than manual. It’s impossible to change that. The C4/6s have an open torque converter which converts HP to heat since they have no lockup feature. Starting with the E4OD all Ford trannys have TC lockup that can be modified to be manually controlled.
A newly rebuilt auto is about as efficient as can be done. Thus the slippage is reduced. The auto can use shift kits to help with efficiency as well.
The AOD sucks and has an open TC in 1-3 and locks in 4th = no improvement in efficiency.
The 700R4 is also possible. It works like an AOD and I was told it is possible to manually lock the TRC. It has a deep 1st gear.
The C4/6/AOD/700R4 all have the advantage of not needing an electronic controller
So for off road the TC seems to be the way to reduce the shock damage from all the hard hits. Now days we are seeing manual trannys with open TC to reduce shock load damage.

Bottom line is use fresh auto and a stronger motor. Add power to the motor to compensate for drivetrain losses and be happy with less damage to the drivetrain.
PaulW

MOSS2 wrote: Manual of some sort less drag but not popular for(v8) off road trucks (xcpt Philo)

Haha! That's what I was thinking. Honestly the only transmission I would swap out for my C6 is a manual M5R2 (I think) like the one Philo has in his Bronco. He can break the tires loose with just a 302 even though he's running 37s.

The 400 had less then 160 HP in the '79 Bronco and the 351M had 150 HP??? on a good day so maybe that's why they said the C6 sucked in that but I love the C6 in my '89 with the 351W. I overheated the crap out of it and lost almost 5 quarts of oil (105 degrees + half the radiator covered in mud + 35's + stock gears + L.A. traffic for 3.5 hours = lots of heat build up) but all I did was add more oil and wash off the radiator and I got home fine. Got the transmission serviced and everything was fine. I put a Trans Go shift kit in it and its way nicer to drive now and the shifts are firm and quick without tearing up mounts. I'm very happy with it.

I also have a C6 behind my 460 in my '79 Bronco and I like it. If there's a parasitic power loss at all I really can't feel the difference since the truck still has enough power to take off hard even in 2nd gear. I'm sure I loose way more power with larger tires, an NP205 T-case and a 9-Inch rear especially with the Bronco weighing over 6500 pounds.

I have c6s and e4ods. the c6 sucks on the hiway if you gear the truck so it works good offroad. The no od really sucks. the hp loss though the e4od and the c6 are probally pretty close. The e4od is great eccept that the coverter lockup destoys rearend parts. and if you unlock it it gets super hot. And e4od parts are geting realllly expensive. Front pumps have tripled in price and some of the hard parts are getting hard to find. C6s are worse because they stoped making alot of the race parts in the late 90s. A built 4l80e is probally the best chioce of an od because of all the parts for them. I know Culhane can built a non electonic, non lock up overdrive and for a resoneable price too.