Parasitic Drag th400 VS th350

[hi pinion]

OK, it seems since the last time i was in the garadge and actually payed attention, it was a long time ago ha ha

Its seems the new groovy deal is to run the 400/205/203 doubler setup. I have questions.Starting with the th400 transmission.Everyone swears up and down the 400 is untimatly the strongest transmission other that the 4l80e as far as slush boxes go. That may be true. But* How much parasitic Drag does the beloved th400 have vs the th350? Does it kill the power? I was told it really eats it up good. Because of how much drag it has . Is it the strength worth the HP decrease? I was told the th350 trans has waaay les drag on it, its plenty strong, and strong enough to run behind whatever setup i desire with alot less drag. So, is this like a time tested , hands down fact that you just put in a th400, expect little to no problems, and just go crazy on the drivetrain mods? I want to hear some opinions on the th400 vs the th350 trans asap. As far as power decreasing due to parasitic drag of the th400 , i would like to hear exactly right around what Percentage* of HP does it rob the motor of? I dont want to even the word manual in this conversation, because thats what i wanted originally.....the 465

How much more POWER, does the th350 GIVE to the motor? And is it worth the risk of running one in one ton applications.

Speak


Jacob

 

[big dan]

I dont know much about the power issue but as far as strength my old man has a th350 in his 1-ton with a pretty stout 350 and its not used for extreme offroading but he is pretty mean to it and I have seen him haul some massive loads of wood, big enough that his bumper almost touched the ground with a 2 inch lift and 31s, over some pretty rough terrain without any problems. He also had a 3/4 ton with a 454 and a th350 that held up just fine.

 

[hi pinion]

I dont know much about the power issue but as far as strength my old man has a th350 in his 1-ton with a pretty stout 350 and its not used for extreme offroading but he is pretty mean to it and I have seen him haul some massive loads of wood, big enough that his bumper almost touched the ground with a 2 inch lift and 31s, over some pretty rough terrain without any problems. He also had a 3/4 ton with a 454 and a th350 that held up just fine.

Thats cool, i was thinking more along the lines of a more specific answer as far as numbers go, like drag percentage, 400 vs 350 type deal, but thats cool. Also mabey if he went with big tires it would change everything? Im just kicking around ideas. Kick* kick*


Jake

 

[u2slow]

The drag racing crowd seems to think a TH400 needs an extra 50hp to get it down the track in the same time.

I can tell you a TH400 sucks really bad behind a 6.2L diesel. However, a 454/TH400 still outshines a 350/TH350 - so it can't be too inefficient.

You can still kill a TH400 though. It only takes a 454 (205hp ), crewcab, 11' camper, and 22' boat... just ask my Dad.

 

[hi pinion]

Not drag RACING maaaaan

Parasitic Drag -as in how much horsepower the transmission absorbs from the motor,, = (horsepower lost from the engine, to the trans)

Any answer is a good one i suppose. Keep them comming.

 

[sled_dog]

its the same thing maaaan. Hes telling you that drag racers feel that to get the same E/T it takes 50 more HP with a TH400. That means the parasitic drag is MORE.

I can tell you this, a TBI 350 has no place with a 4l80E behind it. My 1995 K2500 had that, it was HORRIBLE. My 97 Vortec rig with a 4l80E on the other hand has the balls to power through the transmission and still put decent power down.

 

[surpip]

depend on the motor in front of yes it will take more power to run the 400, but you gain alot in strength
for rock crawling, you wouldent really notice it
for a drivin street family fun rig, you might notice it, again depends on the power your engine is putting down.

 

[Resurrection_Joe]

You're asking me for tech? HA!

I can best sum my thought as this -

I'd sacrifice a bit of power for strength. Power is cool, but not as cool as a non explodey tranny.

 

[hi pinion]

its the same thing maaaan. Hes telling you that drag racers feel that to get the same E/T it takes 50 more HP with a TH400. That means the parasitic drag is MORE.

I can tell you this, a TBI 350 has no place with a 4l80E behind it. My 1995 K2500 had that, it was HORRIBLE. My 97 Vortec rig with a 4l80E on the other hand has the balls to power through the transmission and still put decent power down.

50 extra horsepower MORE noted after i re read it, not including the case, etc etc. So if the 400 takes up 50hp,,, how much does the th350 i wonder?


Jake

 

[dyeager535]

I know there are charts floating around that show the different power consumption of each trans, but I couldn't find any on a quick google search.

This is all I could find right now:

"If memory serves me the TH-400 takes approximately 45 HP, the TH-350 uses about 30HP, and the PowerGlide/JetAway uses about 20HP."

from http://www.442.com/oldsfaq/oftrn.htm

 

[hi pinion]

Thanks man! That pretty much sums it up right there.

 

[k20]

yeh, thats about what Ive heard as far as power useage goes. And yes, you can break a th400, Im on lucky #4

 

[6.2Blazer]

I would call BS on the 50 hp more idea, but a TH400 taking about 15 hp more than a TH350 at leasts sounds reasonable. If you had a stock 200 hp smallblock you might be able to notice a small difference between a TH350 and TH400 trans, but not like somebody put the parking brake half-way on or anything. As the engine output increased, the difference should become less noticable. With a 200 hp engine you would theoretically have a 7.5% decrease in power with a TH400........but with a 350 hp engine it would only be 4% difference, etc...

 

[BARRAZA]

This topic has been debated for almost 40 years. Stock class drag racers discovered that a turbo 350 was marginally quicker than a 400 not long after the 350 came out. If I remember correctly, the only back to back test had the difference in the order of a tenth of a second on a 11-12 second car. But remember the difference is in max power acceleration over a quarter mile, that doesnt necessarily mean a 400 is less efficient, it is probably just because the 400 has a much larger internal rotating weight, ie it won't accelerate as fast but at a steady rpm it transmits just as much torque. The difference in internal rotating weight of a transmission is meaningless compared to the weight of the heavy parts we all rotate - namely four 100 plus pound tires. Compared stock to stock, a t400 is much stronger, it was factory installed in 500 ft lb cars. Given the choice, I would always go 400 in a truck. Anybody else remember that when a t350 came out it was regarded as junk and suitable only for small blocks and light cars?

 

[79k20350]

The 400 also has a higher first gear than a 350. this means if they ran them back to back and that the differant first gear could have changed the outcome entirely. Also 350's can be known to have weak cases. ive seens quite a few broken, one with a 205 behind it, all original brackets, torque rods, etc installed and a 6 bolt cast cover. i wouldnt be worried about the internals of a built 350 over 400, its the case id be worried about. but then again if your going doubler and you make a nice crossmemeber to really hold up the doubler tan there may be no weight on the case and it wont be a problem... but hey, what do i know im a carpenter...

 

[71 Blazer]

I was told along time ago that a th350 takes away about 18% of HP, where a th400 removes 30%. Not sure on how true this is just what I was told.

 

[rjfguitar]

Jake,

I think I know what you are up to. If the truck already has a th350 in it than leave it. If it does actually blow up take it to our buddy Kevin that did our Th700R4's. Have him mod it just like he did to our 700's.

You don't need a th400, it's not just a bolt in thing exactly and I doubt you will run the HP, gearing and tires, and hard wheeling that will even harm the stock trans.

As far as your question, A 400 doesn't take that much more power than a th350 does, not enough for it to really matter much at all.

 

[jekbrown]

i run a mild 350 and am going to a th400 (have a 700 now). Not especially worried about parasitic drag. I doubt its that big a deal. I guess we'll see.

IMO the strength of a 400 is well worth whatever single-digit-percent hp loss there is more than a th350. If you don't have enough torque at the wheels (only place it ever matters) just add more gearing (axles, t-case or both) and call it good.

j

 

[hi pinion]

Jake,

I think I know what you are up to. If the truck already has a th350 in it than leave it. If it does actually blow up take it to our buddy Kevin that did our Th700R4's. Have him mod it just like he did to our 700's.

You don't need a th400, it's not just a bolt in thing exactly and I doubt you will run the HP, gearing and tires, and hard wheeling that will even harm the stock trans.

As far as your question, A 400 doesn't take that much more power than a th350 does, not enough for it to really matter much at all.

Thank You Mr Frobose, You Do Rock , see you sometime soon. For sure.

Jake

 

[Lonnie P]

The amount of HP consumed depends on the rate of acceleration.

At highway cruise, the hp required to turn a th-400 is essentially no different than a th-350. Maybe 2 hp tops. Meaning your mileage should not change. Mine didn't.....

Now when you try to accelerate a vehicle, it will take more power to accelerate the heavier internal components. On a chassis dyno testing performance cars (400-450rwhp range), I have seen 15hp difference between the 2.

A strict % of hp is loss is hard to state. Most cars lose 15-20% from the entire driveline, not just the tranny. Manual trans 15-17% & autos 17-20% on average that I have tested. Trucks are generally 5-10% higher due to the heavier axles, driveshafts & obviously the larger tires which also has a large effect. These all take HP to accelerate.

The statement of 50hp difference is very possible on a very fast car (something running in the low 10's) because everything must accelerate at a much higher rate. This does not apply to a pickup or street car though. This is the reason that the Powerglide trans is a favorite with the racers of very high hp cars. (they do not need the gear multiplication due to the high hpto wt. ratio & it also has the lowest rotating mass of all automatics)

You may notice a slight loss of acceleration in low gear with a th-400 due to the 2.48 low gear instead of a 2.52 in the th-350.... only about 2% though. Most will never notice.

This is factual data based on real world testing, not internet heresay... I build performance cars & trucks & have paid for the dyno time to get these results.

Hope this sheds some light on the situation.