[Sirrotica]

A lot of talk about parasitic drag on a T 400 as compared to a T 350, unless you're running a 10 second or quicker combo drag car, the parasitic drag is negligible between the two. That thought is a quote from Jake himself on his website talking about 4L80E parasitic drag as compared to lighter duty OD transmissions used for performance rebuilds. A 4L80E uses 75% of the same internals as a T 400 has so the comparison is a valid one.

A street car is never going to need the lighter internals to see any difference, lighter internals also have less strength for the same materials used.

Does anyone find it strange that Cliff Ruggles runs a T 400 in his own street car as opposed to a T 350, even though he has written a book about the T 350?

My money is on a T 400 or a 4L80E (basically T 400 internals with overdrive capability) for longevity. The extra beef will have no noticeable effect on performance, but will withstand abuse over the long haul more effectively.

One more point is, to get the lighter duty transmissions to live in a performance environment the hard parts in most cases, need to be replaced with better materials. The stock factory hard parts in a T 400, 4L80E, will live just fine to 750 HP, giving your project room to grow as far as future improvements in your engine program.

There is a reason that the T400 and 4L80E transmissions weigh more to begin with, they have more mass to take abuse from the initial design. They don't need the band aids that the aftermarket has designed to try to make them live in an abusive environment.

I like to do a job one time and not keep re-doing it because the original design was deficient, and the weak link in the chain was uncovered. Spending my adult life in vehicle, stock car racing, and shop maintenance areas, has taught me to remove as many weak links in a mechanical device as possible, and never have to revisit it for breakage. JMO............

Other than a slight weight penalty, a stronger transmission platform has no drawbacks that are evident to me.........

That said, the OP seems 99% committed to the T350, but he has asked for opinions, and I have stated mine, FWIW.

[ponyakr]

"...The stock factory hard parts in a T 400, 4L80E, will live just fine to 750 HP..."


Not for the sake of argument, but just to present my differing opinion, I don't think the factory int sprag or roller clutch that came in most Pontiac TH400's will live with that much power. I broke 2 of the stock 16 element sprags, with only about 400hp/500 torque.

My trans guy, at the time, installed what he called a 500 Cadillac sprag, in all my bracket TH400's, and I never broke one. I assume those sprags were about equal to the 34 element sprags used today, for HP TH400 builds.

[Sirrotica]

Originally Posted by ponyakr

"...The stock factory hard parts in a T 400, 4L80E, will live just fine to 750 HP..."


Not for the sake of argument, but just to present my differing opinion, I don't think the factory int sprag or roller clutch that came in most Pontiac TH400's will live with that much power. I broke 2 of the stock 16 element sprags, with only about 400hp/500 torque.

My trans guy, at the time, installed what he called a 500 Cadillac sprag, in all my bracket TH400's, and I never broke one. I assume those sprags were about equal to the 34 element sprags used today, for HP TH400 builds.

Also from Jakes Performance:

A totally stock unit or rebuild will typically live well with up to 450 flywheel HP/TQ. Above this point the direct clutches will not live long without some hydraulic improvements.
Using our modifications or some valve body kits, the direct clutch issues are resolved and the 4L80E will generally be reliable up to the 750 HP/TQ range unless it’s a very heavy combination (over 4500 lbs) or using nitrous.

The weak point above this power level becomes the OEM input shaft. An upgraded input shaft becomes mandatory. We like to upgrade the forward hub at the same time.

The next real weakness is the stock 34 element sprag. This part is actually capable on a well built unit of living at over 1000 HP/TQ BUT it requires care and knowledge by the end-user. Knowledge of proper burnout procedures is critical. It will also be a maintenance item at the 1000 HP level. It will need to be inspected/replaced occasionally depending on how the unit is used.

We recommend upgrading to a “Super Drum” style sprag that requires a modified or custom made drum and race. It has 36 elements that are wider, a larger race, and uses more intermediate frictions. If it fits in your budget, this is always an excellent upgrade above the 750 HP/TQ range. Combined with the input shaft and forward hub upgrade, it makes the 4L80E almost bulletproof.

Jake is probably in the top echelon of aftermarket performance transmission shops in the country. He does acknowledge that a sprag unit can break. The shafts, pumps, drums, and other hard parts will be reliable under 750 HP according to Jakes website. He cites proper burnout procedures as a longevity extender in either T 400 or 4L80E transmissions.