turbo 350 vs turbo 400

[Guest Indy]

Any differences / preferances between the 2 trannies?

[Lason]

Turbo 350 is the lighter duty of the two and takes a lot less power to turn. Has a cable for the detent cable where as the th400 uses a switch. The TH400 will take a lot more power but weighs more, takes more power to turn, etc. Basically if you run a built th350 and break it then maybe you need to think about a th400.

[jnjdragracing]

The turbo 400 is more heavy duty than the turbo 350. Also if my memory serves me right the turbo 350 and the powerglide are the same length, the turbo 400 is longer. I also think the input of the drive shaft is different for the 400. I personaly like the two speed powerglide for racing. If it is for the dtreet then I would invest in a 200r4 or 700r4 to get the overdrive, but they will need to be buily up some in any horsepower / torque was put to them.

 

John

 

PS: you can search the site for this information as well.

[Pyro]

I don't like the downshift cable on the TH350. It messes with the throttle feel.

 

The TH400 is bigger and stronger. The size may be an issue when installing into a Z. I like the electronic downshift switch setup.

[jakeshoe]

Turbo 350 is the lighter duty of the two and takes a lot less power to turn. Has a cable for the detent cable where as the th400 uses a switch. The TH400 will take a lot more power but weighs more, takes more power to turn, etc. Basically if you run a built th350 and break it then maybe you need to think about a th400.

Please explain to me how a TH350 takes less power to turn...

Keep in mind Newton's First Law of Motion...

[280zwitha383]

Please explain to me how a TH350 takes less power to turn...

Keep in mind Newton's First Law of Motion...

 

hmm, maybe you should educate us and tell us why it shouldn't take more power...

[Lason]

Please explain to me how a TH350 takes less power to turn...

Keep in mind Newton's First Law of Motion...

 

I couldnt tell you for sure but I would assume it has something to do with the smaller firctions and steels which is also why it will handle less power. Kind of like the 'glide I just built for my Z. I used 5 frictions in the high gear and 6 in the low/reverse gear. I COULD have put 8 thin frictions in the high gear but I didnt need to and it would have cause more resistance and in turn taken more power to turn the assembly.

[jakeshoe]

It takes no more power to "turn" a TH350 than a TH400.

Most people relate the slightly heavier internals of a TH400 as consuming more energy just because they are heavier and this is not the case.

 

It DOES take more power to accelerate or decelerate a heavier mass, but not to "turn" it, as in steady rpm.

 

Quick explanation..

At idle not engaged in gear, the only portion of the trans that consumes power is the trans pump, as it is pumping fluid at idle to lube the trans and maintain pressure for gear engagement.

A TH350 and TH400 use the same gearset. If trans mainline pressure is setup the same, the pumps would consume pretty much exactly the same HP. Very minimal anyway.

 

Some of the parts that make a TH400 heavier (a total of about 15 lbs heavier) are not rotating, the center support for example in a TH400 is probably 2 lbs of this difference and one of the reasons a TH400 is more durable. It is better at keeping the parts running true and centered in the trans, remember this for later.

 

The direct drum in a Th400 weighs ~14 lbs fully loaded and filled with oil.

A Th350 weighs 12..

2 lbs difference.

I would theorize that the direct drum is the most power consuming portion of the transmission during acceleration, particularly in 3rd gear, on a shift from 2nd to 3rd gear the direct drum must go from ZERO rpm to engine rpm pretty much instantaneously. THIS is what consumes power. Accelerating the mass...

We're talking about 2 lbs difference on the direct drum...The diameter and weight of the torque converter has a larger effect.

Most sportsman racers think nothing of adding a couple of lbs for anti-ballooning plates.

 

The amount of HP used doesn't change if the drum is in steady motion, or constant RPM. If it takes 3HP to operate the pump, and 2 HP to overcome frictional losses, that would be all it takes to operate either transmission at steady RPM.

If you accelerate the parts (or decel) then the greater mass would require more HP, but the amount of HP required is dependent on how quickly you accelerate it.

 

A 14 second 1/4 mile car will never accelerate the parts quickly enough to realize any measurable HP difference.

A 10 second car MIGHT see .05 seconds difference in ET due to the rotating mass difference of a TH400

An 8 second car might have a noticeable difference in ET, but it also wouldn't likely be using stock weight parts. I can take 1 lb off of a stock TH400 direct drum fairly easily.

 

When someone states that a TH400 require ALOT more HP to "turn", "run", etc. they usually do not even know why they are saying it, just repeating what they have heard.

 

This is also why stating a TH400 takes "15 hp" more to operate than a TH350 is incorrect, there is no set number for this, as it would absolutely depend on how fast the parts where accelerated during testing.

 

I would also venture to guess that a TH400 actually has LESS frictional loss than a TH350...

[jakeshoe]

I couldnt tell you for sure but I would assume it has something to do with the smaller firctions and steels which is also why it will handle less power. Kind of like the 'glide I just built for my Z. I used 5 frictions in the high gear and 6 in the low/reverse gear. I COULD have put 8 thin frictions in the high gear but I didnt need to and it would have cause more resistance and in turn taken more power to turn the assembly.

 

A TH350 has larger intermediate frictions and steels than a TH400, much greater surface area. The forward and direct clutches are of similar size between the two units.

A TH400 uses a low band, a TH350 uses clutches.

5 or 8 clutch pack makes little difference in the amount of drag, why would it be of huge concern in a 'glide in the high drum?

The clutches would be applied in high gear anyway, the only drag created would be in 1st gear and this would be more affected by clutch pack clearance than count.

I would reduce the clutch count in the reverse clutches before I would in the high drum.

You can also do other things to reduce clutch drag.

[Lason]

Two things. First Im a drag racer and there is no such thing as "constant motion" in drag racing. So in my world it DOES take more power to turn the TH400 because of either constant acceleration or decelleration.

 

Second you never rebutted my original statement of more clutch surface area on the TH400 than the TH350 causing more parasitic drag at constant speed, or otherwise.

 

Yeah I have heard it and always gone by it but if everyone has said it for years there must be something to it right?

[Lason]

A TH350 has larger intermediate frictions and steels than a TH400' date=' much greater surface area. The forward and direct clutches are of similar size between the two units.

A TH400 uses a low band, a TH350 uses clutches.

5 or 8 clutch pack makes little difference in the amount of drag, why would it be of huge concern in a 'glide in the high drum?

The clutches would be applied in high gear anyway, the only drag created would be in 1st gear and this would be more affected by clutch pack clearance than count.

I would reduce the clutch count in the reverse clutches before I would in the high drum.

You can also do other things to reduce clutch drag.[/quote']

 

They may not be engaged but there is still only a fraction of play in between the frictions and steels. That is also the reason they make smooth and grooved faced frictions. I mean seriously. Why would they make all these different type of frictions and thickness (so you can run more) and all that if it made no difference? I think Ill trust Alto over anythign I hear here.

[jakeshoe]

Two things. First Im a drag racer and there is no such thing as "constant motion" in drag racing. So in my world it DOES take more power to turn the TH400 because of either constant acceleration or decelleration.

 

Second you never rebutted my original statement of more clutch surface area on the TH400 than the TH350 causing more parasitic drag at constant speed' date=' or otherwise.

 

Yeah I have heard it and always gone by it but if everyone has said it for years there must be something to it right?[/quote']

 

I drag race too, and I know from experience and as a performance transmission builder, that the ET difference between the two transmission is usually ZERO in a mid 10 second or slower car. I have seen instances of .04 difference in ET in a swap that consisted of no other changes, but this slight difference could be weather, tune, etc.

 

So I understand no constant motion in drag racing, but I also know what the actual effects are.

[jakeshoe]

They may not be engaged but there is still only a fraction of play in between the frictions and steels. That is also the reason they make smooth and grooved faced frictions. I mean seriously. Why would they make all these different type of frictions and thickness (so you can run more) and all that if it made no difference? I think Ill trust Alto over anythign I hear here.

 

I never said that there was no difference, just that there are other factors in play that have an effect.

A TH350 has a greater friction area overall, if you figured it in 1st gear, where it would be driving through all the frictions except the forwards which are always engaged in any forward gear, and the low/reverse which would be engage in 1st.

The direct clutches would be driven through and the surface area is slightly smaller than a TH400, but the intermediates on a TH350 are much bigger and are also driven through.

 

Once it shifts to 2nd, they are on even turf.

Once it shifts to third, it depends it the best answer I could give.

"I" believe the Th400 would have a bit less frictinal loss due to it using a band, than a Th350 which uses clutches. However it would depend mostly on the band clearance or the clutch clearance.

 

If you set up the clearances looser, you reduce friction. I would recommend a MINIMUM of .008' per friction clearance on the directs of eith unit. I prefer to see about .010-.012.

On a TH350 the intermediates need to be a bit loose, because they fairly large in diameter.

Having .080" or more clearance on this stack of 3 clutches is perfectly acceptable.

 

I would leave low/reverse on the loose side on a racing TH350. It may cause a harsher reverse engagement, but we aren't too worried about it in a performance application.

I have built TH350's for use in a Bonneville Salt Flats racer (240+ mph) and I totally eliminate the low/reverse clutch pack, apply piston and related parts for reduced friction and safety.

 

You can use special steels for less drag and quicker application. Many performance builders have gotten away from using grooved clutches at all.

 

You mention Alto. Alto's frictions do not have any grooves. Smooth red paper based friction elements. I use Alto products extensively.

[Lason]

I never said that there was no difference' date=' just that there are other factors in play that have an effect.

A TH350 has a greater friction area overall, if you figured it in 1st gear, where it would be driving through all the frictions except the forwards which are always engaged in any forward gear, and the low/reverse which would be engage in 1st.

The direct clutches would be driven through and the surface area is slightly smaller than a TH400, but the intermediates on a TH350 are much bigger and are also driven through.

 

Once it shifts to 2nd, they are on even turf.

Once it shifts to third, it depends it the best answer I could give.

"I" believe the Th400 would have a bit less frictinal loss due to it using a band, than a Th350 which uses clutches. However it would depend mostly on the band clearance or the clutch clearance.

 

If you set up the clearances looser, you reduce friction. I would recommend a MINIMUM of .008' per friction clearance on the directs of eith unit. I prefer to see about .010-.012.

On a TH350 the intermediates need to be a bit loose, because they fairly large in diameter.

Having .080" or more clearance on this stack of 3 clutches is perfectly acceptable.

 

I would leave low/reverse on the loose side on a racing TH350. It may cause a harsher reverse engagement, but we aren't too worried about it in a performance application.

I have built TH350's for use in a Bonneville Salt Flats racer (240+ mph) and I totally eliminate the low/reverse clutch pack, apply piston and related parts for reduced friction and safety.

 

You can use special steels for less drag and quicker application. Many performance builders have gotten away from using grooved clutches at all.

 

You mention Alto. Alto's frictions do not have any grooves. Smooth red paper based friction elements. I use Alto products extensively.[/quote']

 

Alto does still make grooved clutches. Check out their blue clutches with waffle face. Heres a link for ya... http://www.tsr-racing.com/catalog/pg_frictions.html

 

**EDIT** you may be right, those arent Alto brand, they are raybestos.

 

And I pulled out grooved Alto red clutches out of my 'glide when I tore it down but have yet to see any for sale new so their may be some truth to them not making the red grooved frictions anymore. Of course there is no way to tell if they were Alto's but that is just what I was told. I went with standard thickness smooth frictions when I built it.

 

It doesnt really matter. You have already said that the TH400 will rob power through acceleration and decelleration and that is the debate here. Power isnt measured by "constant speed". A 40hp VW bug will cruise at 60mph just as easily as a 305hp f-body. Getting to 60mph is another story and the dyno will show a drop in power since it measures power through acceleration. Also if you were to swap out a TH-350 for a TH-400 and use the same converter and everything you SHOULD see a drop in ET no matter if your running 4's or 14's. The sheer weight of the 400 vs. the 350 alone is enough to cause a drop not counting the rotaional weight of the compnents etc.

[jakeshoe]

Alto does still make grooved clutches. Check out their blue clutches with waffle face. Heres a link for ya... http://www.tsr-racing.com/catalog/pg_frictions.html

 

**EDIT** you may be right' date=' those arent Alto brand, they are raybestos.

 

And I pulled out grooved Alto red clutches out of my 'glide when I tore it down but have yet to see any for sale new so their may be some truth to them not making the red grooved frictions anymore. Of course there is no way to tell if they were Alto's but that is just what I was told. I went with standard thickness smooth frictions when I built it.

 

It doesnt really matter. You have already said that the TH400 will rob power through acceleration and decelleration and that is the debate here. Power isnt measured by "constant speed". A 40hp VW bug will cruise at 60mph just as easily as a 305hp f-body. Getting to 60mph is another story and the dyno will show a drop in power since it measures power through acceleration. Also if you were to swap out a TH-350 for a TH-400 and use the same converter and everything you SHOULD see a drop in ET no matter if your running 4's or 14's. The sheer weight of the 400 vs. the 350 alone is enough to cause a drop not counting the rotaional weight of the compnents etc.[/quote']

 

The grooved red plates you pulle dout of your glide were Raybestos too Not Alto...

 

How much power do you think 5 or 6 lbs is going to rob? That's essentially what we are talking about here. in rotating weight.

I actually have two complete TH400's torn down right now and a TH350, if I had a good scale I would do an exact and accurate comparison of the rotating weights.

The total difference in weight is supposedly around 15 lbs. That sounds about right.

As I've stated and you can confirm this through other sources, there is usually ZERO measurable difference in ET between the two. Some of the faster cars will see a bit of difference.

You will aos find that you can rollerize every part of the internals of abotu any auto trans and not find any ET in most cases.

I have a friend who holds several records in NHRA Super Stock and uses TH350's in his Oldsmobiles, he has done ALOT of tweaks to them to get every ounce of ET, and the only noticeable difference was a 2.75 gearset...

Yes there SHOULD be an ET difference with the gear ratio difference, overall weight difference, and rotating mass difference, but I nor any of my customers have ever experienced it, and if you research it you will find similar experiences with others.

Many racers use lighter internals in an auto trans to reduce the load on the parts, particularly the direct drum on a TH400/TH350. Not for ET, but for reliability.

 

This is one reason why I believe the TH400 has less frictional loss.

I think it has less loss because of 1. the int clutches I already mentioned, 2. the low band I already mentioned, and 3. the parts ride more on center due to a much better support.

A Th350 is rough on bushings and thrust washers, a Th400 isn't.

[dr_hunt]

I've gone by this GM internet information for years. It's on several GM related websites. Not sure where it came from but it would be nice to see some dyno charts that could verify the following.

 

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

 

What they are talking about is acceleration. If you could shave 2 lbs off your engines rotational weight, it should show similar gains. Also the th350 has lower gears than the th400.

[jap tin]

My Z with a TH350 went 10.90's. My Z with a TH400 went 9.40's. My Z with a glide went 8.40's. However they were 3 diffrent Z's with 3 diffrent engines and 3 diffrent chassis, but you get the idea.

[jakeshoe]

Dr Hunt,

In your profile it states you are an engineer...

what type?

 

You should understand exactly what I'm speaking of. It is not as simple as saying it takes X amount of HP, it all depends on how much difference there is and the rate of acceleration.

Very similar to figuring HP for a particular car based on the weight, and ET or MPH.

IF a car weighs 3000 lbs, and can accelerate to 120 mph in the 1/4 mile, it has X amount of HP.

We are figuring the rate of acceleration over a defined distance, by the end result.

We know the weight, and we can calculate the HP.

If the weight remains the same, but the rate of accelation changes, we know it required a different amount of HP.

 

I'm pretty sure GM never published those specs...They were written in a transmission manual some years ago and I can check but I believe they were approxmations made by a builder at that time.

[dr_hunt]

Dr Hunt' date='

In your profile it states you are an engineer...

what type?

 

You should understand exactly what I'm speaking of. It is not as simple as saying it takes X amount of HP, it all depends on how much difference there is and the rate of acceleration.

Very similar to figuring HP for a particular car based on the weight, and ET or MPH.

IF a car weighs 3000 lbs, and can accelerate to 120 mph in the 1/4 mile, it has X amount of HP.

We are figuring the rate of acceleration over a defined distance, by the end result.

We know the weight, and we can calculate the HP.

If the weight remains the same, but the rate of accelation changes, we know it required a different amount of HP.

 

I'm pretty sure GM never published those specs...They were written in a transmission manual some years ago and I can check but I believe they were approxmations made by a builder at that time.[/quote']

 

HP is work, or force times distance so it's relating to getting the thing rotating, going through the gears and the comparison is directly related to rotational mass otherwise there isn't any work being done. THe trannies don't just eat HP, it's gets used doing work.

 

Pretty simple.

 

BS Electrical minor math, MS environmental, 16 years PE. Taught college for 3 years.

[jakeshoe]

I know they don't eat HP,

and this is what I'm trying to explain here.

 

You understand that the hp numbers aren't constant because they would change with the rate of acceleration right?

 

Also the other part that would have to be factored in is the rotating mass in question, doesn't have to accelerate at the same rpm as the engine in 1st gear, most of the weight is out of play in 2nd gear because it isn't rotating, and by the time a vehicle gets into 3rd gear the rate of acceleration has usually slowed because of the lack of gear reduction helping the engine to accelerate as quickly.

 

In a TH400, the direct drum is being driven by the planetaries (reverse rotation) at 84% of engine rpm. On a shift to 2nd gear it comes to a complete stop. On the shift to 3rd it has to spin up to engine rpm from a complete stop.

The difference between a TH350 and TH400 direct drum is 2 lbs.

A Th400 has heavier planets but they are already in rotation, 2 seperate pieces here, but one is already at engine rpm (and wouldn't require any HP on a shift because it is already in motion, but would use a small amount to continue to accel afte rthe shift), the other must be accelerated, but the weight isn't the total weight of the particular planet, only a portion of it because of the design of a planetary gearset. Sun, pinions, ring.

It would get somewhat complicated to calculate because you would have to disassemble a planetary set to get the weight of the ring gear portion.