Is the TH350 a "Good" Transmission? [Archive] - Team Camaro Tech

: Is the TH350 a "Good" Transmission?

Jul 21st, 06, 02:56 PM
I've got a 69 Camaro with a 327/TH350 combo. The 327 is toast and will be replaced with a 383 or BB chevy. My dad tells me the TH350 is junk and I need to swap in a TH400 when I change the motor.

How does a stock TH350 hold up to higher power levels? I hear the TH400 is just about bulletproof and is an ideal trans with the exception of no OD gear.

Larger Dave
Jul 21st, 06, 03:09 PM
The TH400 with an OD is called a 4L80E (E stands for electronically controlled by a remote computer). If your thinking of going this route be advised that there is now available a six speed OD tranny from Allison that is supposed to be unbreakable (I said "NEW" not the old school bus Allison, this one has a computer built into the tranny so it doesn't need an external computer).

The TH400 can be built to withstand about a thousand horse but at a price. And I'm not just talking bucks here. The TH400 is a massive tranny designed by GM to motivate all of the heavy cars in the GM stable with a lot of power (behind big blocks and High Output small blocks). It has a lot of rotating mass that has to come to dead stop and reverse it's rotational upon each shift. That consumes power; for this reason the TH400 has more parasitic drag than the TH350.

Can a TH350 live behind a 383? Sure so long as we are talking about driving on the street. As soon as we get into a "irresistible force being applied to an immovable object" then you are going to have more breakage problems with a TH350 than you will with a comparably built TH400.

Larger Dave

Jul 21st, 06, 03:42 PM
A TH400 is by far the choice of racers with heavier cars but with the right parts and I don't mean huge dollar parts you can make a TH350 last behind a 600hp BB and a shot of juice once in awhile. I did for 3 years at the track and on the street then sold it to a guy with a SB and a lighter car and it's still going strong on the the rebuild that I paid $750. Cdn for.

Jul 21st, 06, 05:58 PM
It has a lot of rotating mass that has to come to dead stop and reverse it's rotational upon each shift. That consumes power; for this reason the TH400 has more parasitic drag than the TH350.

Larger Dave

How much more rotating weight does it have?
What parts have to come to a dead stop and reverse rotation on each shift? What do they weigh individually?
How much more parasitic drag does it have?
What ET difference would the power consumption make?

Jul 21st, 06, 06:03 PM
A TH350 can reliably handle 600 hp if properly assembled with very few "fancy" parts.

Jul 21st, 06, 06:37 PM
My stock 350 lived well behind my honest 350hp 350 for a couple of years until I decided to go overdrive.:D In fact it's still sitting in my garage waiting for another project. If I ever start working on it. Don't get me wrong the TH400 is a great trans, but the TH350 is also a really good trans to that can take more abuse than some people give it credit.

Oldani Motorsports
Jul 21st, 06, 07:33 PM
I feel comfortable with the TH-350's I build living at the 650hp area with good reliability. If you use a transbrake then things get shaky. The TH-400 is a better choice once you push 700hp or use a transbrake. Only things needed in a TH-350 are a good intermediate sprag race (or step up to a 36-element sprag/drum combo) and attention paid to details when building it. I prefer to use Teflon sealing rings everywhere as well. TCI or TransGo for a valve body kit, unless you go full manual then they're all very similar.

Jul 21st, 06, 09:47 PM
Buddy of mine runs low 10's on a TH350 in a '67. With the right parts and builder it will work out just fine.

Larger Dave
Jul 22nd, 06, 11:12 AM
Parasitic drag has been estimated at 20 to 40 horse power more than the TH350 (most state at least 20; average appears to be 24hp); dependant upon how much torque is input into the system. The parasitic drag is predominately centered in the torque converter (the factory changed the angle of the blades compared to the TH350 anticipating more torque input) so which converter you choose will have a big effect upon parasitic drag.

Gear vendors states that they have measured parasitic drag before and after on a Spintron and their overdrive units contribute only one additional horse power (way better than the 4L80E numbers).

To begin with, there is an incredible amount of inertia produced inside an automatic transmission. The Turbo 400 had to handle the torque of a big-block powerhouse as well as deliver a comfortable and reliable drive. This is the reasoning behind having heavy internal parts. Keep in mind, when General Motors designed the TH400, it was for an entirely different purpose than racing.

For example, shifting from first gear to second gear, will mean instantly stopping the 14-pound direct drum, which is turning at 84 percent of engine speed, while the 8-pound front reaction carrier starts turning at 50 percent engine speed. All of this happens in the short time it takes to shift gears (less than a second if using a shift kit). Additionally, there is an equal amount of force generated when shifting in and out of all three gears.

Luckily just like Camaros there are more people than GM making parts for the tranny. I'm surprised no one caught my typo the TH400 properly preped can handle nearly 2,000 hp not the 1,000 as I said (I was thinking of the 4L80E which can only handle about 1,200 horse when built to the max). Anyway there are companies that make ultra light-weight parts out of expensive aerospace materials like titanium that can reduce the rotating weight by up to thirty pounds and are stronger by far than the stock parts. A further added benefit of lightening the parts and going billet is that more clutch discs can be added to spread the load out over a greater area to hold better.

Finally you asked how heavy is it? Well the TH400 is 60 pounds less than the 4L60E and it weights 166 pounds less than a 4L80E; however it does weigh 8 pounds more than the TH350 (all weights are for transmissions only without the filled torque converter). So there isn't that great a penalty there as most people think because the difference in the two is mostly in the torque converter which most people swap for a smaller one to raise their stall RPM.

Larger Dave

Jul 22nd, 06, 11:24 AM
I built my T-350 in my garage with just a couple of aftermarket parts (HD sprag, 700R4 Low and Reverse sprag, new pump, TCI rebuild kit, ETC) and I have been beating on it for over 2 years of Street and Strip driving with a manual valve body.
It will hold up behind all but the nastiest 383's without a problem as long as it is put together by someone who know's how and pays attention to the details and has a sterile work area.

Jul 22nd, 06, 12:11 PM
Someone that knows how to build trasnmissions for abuse can easily make a TH350 live behind 700 horse, the large factor here that hasn't been brought up is weight, however. 700 horse in a 4000 pound car is different than in a 3000 pound car as far as the trans is concerned. This shouldn't be an issue for you however.
We have a guy locally that builds bulletproof trannys, he's the only guy around that can make the automatic transmissions live behind the pro street cars we race, usually powerglides, but quite a few TH350's in the slower lighter cars, by slower I mean 9's and slower. There is one other place at least on the west coast I know that builds killer transmissions, Mike's in california. The guy we have builds them in his home garage on the side, so you have to Know him to get it done, I'm sure there are others, and no doubt there are some guys on the east coast too, I just don't know that area.
For an example my buddy has a 62 nova that weighs about 3000 pounds, and has gone 9.80 with a 406 and a liitle nitrous, and races a lot, running a TH350 and with 100% reliabilty. he recently switched to a powerglide just to see if he could pick up some ET, but has not yet.
But, getting to the original question, it depends on wahat you build, a smallblock I would go with a well built TH350, if you go big block, you may consider a TH400, depending on how much power you will be making. There is a larger potential for lots o' torque with a big block.

Jul 22nd, 06, 12:25 PM
Well Jake, it sure looks like Dave knows his stuff. lol

Jul 22nd, 06, 03:06 PM
He has corrected his mis-statement in the first post and actually posted some weights.
Looks like he got his information from John Kilgore's site here:

Which is good information and John Kilgore is one fo the innovators on the Th400, however I'm looking for some actual data that Dave has, not what he can find online.

He still hasn't answered what the ET difference would be or the total rotating weight.

His quoted weights are wrong, the Th400 does not weigh 166 lbs less than a 4L80E..., The 4L80E is not THAT heavy...

The difference in total rotating weight between a TH350 and 400 is 10.4 lbs.
The difference in the direct drum is less than 2 lbs.

There is no set HP consumption number for the difference, yes a Th400 will consume more HP under acceleration or decel of the parts, but not at steady speed...
The amount consumed is not going to be "24 HP" it will vary by the rate of acceleration, not the torque input.

You cannot compare two transmission based off of a different torque converter, they both use interchangeable torque converters but for the purposes of this comparison, the converter has no effect.
Notice in his original post:

Originally Posted by Larger Dave
It has a lot of rotating mass that has to come to dead stop and reverse it's rotational upon each shift. That consumes power; for this reason the TH400 has more parasitic drag than the TH350.

Larger Dave

he did not mention the parasitic drag as being the converter but the larger mass of the TH400, so which is it, the converter or the transmission.

If we back to back tested a Th350 vs. a 400 using the same converter, or a hub drive to eliminate converter variables, what would the ET difference be..?

I can say this much,
on all the cars I've dealt with, I've never seen any difference in ET (usually an "upgrade" to a Th400, that according to all the internet experts would result in an ET loss because of gearing, rotating mass, overall weight, there has never been any real measurable loss.

Jul 22nd, 06, 03:07 PM

Just a point of reference...

Jul 22nd, 06, 08:32 PM
the planetary gear sets normal direction of rotation cause the compounded sun gear(shared by both planets)to run opposite output rotation .this consequently drives the sun gear shell and the direct clutch drum opposite the turbine shaft in first gear .this is part of the design characteristics.this causes power loss by increases the amount of energy subracted from final output due to "driving losses".tooth contact frequency in a given ratio and planetary gear set also increases the amount of energy subtracted from final output due to "driving losses".other things such as tooth load verses length of contact,specific sliding verses verses diametrical pitch,stifness verses diametrical pitch etc .are engineered in to reduce gear noise and result in additional driving losses.inertia forces on the sprag when overrunning increase driving losses as well.the point trying to show itself here is there are many consequent driving losses inherent in the design of an automatic transmission that must be at work in order to sucessfully "transmit" input engine torque from the turbine shaft into output torque for the output shaft to drive the vehicle against vehicle weight,differential/final drive ,road friction and atmospheric conditions.with properly selected internal componets the th350 can live at 700 foot pounds in a 3000 lb. car with specific attention paid to hydraulic calibration ie: proper clutch pack accumulation during friction element application.HOWEVER going back to tooth contact frequency pattern theory and applied loads to the gear set high numerical final drive ratios and heavier vehicle weights will quickly destroy the under engineered planetary gear set of this gm 3 speed.hydraulically the transmission can probably handle 1500 horsepower and 1500 foot pounds of torque,but not mechanically.if you want to view what we use at what power lever for either a th350 or th400 visit

Jul 23rd, 06, 10:48 PM
cs can be added to spread the load out over a greater area to hold better.

Finally you asked how heavy is it? Well the TH400 is 60 pounds less than the 4L60E and it weights 166 pounds less than a 4L80E; however it does weigh 8 pounds more than the TH350 (all weights are for transmissions only without the filled torque converter).

Larger Dave

According to Dave's information, a TH400 would only weigh 12 lbs...
I took the time to weigh a TH350 short shaft complete, a TH400 short shaft, and a 4L80-E today while I was building a couple of units.

TH350 was almost exactly 125 lbs.
TH400 was right at 135 lbs.
4L80-E was 178 lbs.

Larger Dave
Jul 23rd, 06, 11:05 PM
My error sorry for any misinformation. I was getting the weight of the 4L80 off the web as I have never actually weighed one. Though it seemed to weigh a ton when I put it in while lying on my back the figure they quoted seemed very probable.

Once again my appologies.

Larger Dave