TH-400 Question
I would like to know where the numbers are coming from?
TH400 internals are not 12-15 lbs heavier than a TH350. I've weighed them.
What was the testing procedure to find out how much more power it took?
Since an object in motion tends to stay in motion, etc, etc. If both are at steady speed, there would be little or no difference in power consumption, right?
So power consumption would be mostly determined by the rate of acceleration or deceleration. Acceleration is all we are worried about...
That would mean a 9 second car would see more HP loss than a 12 second car.
I've done the swap back to back, I've weighed the parts, and I build these units everyday, so I always find this an interesting discussion.
TH400 internals are not 12-15 lbs heavier than a TH350. I've weighed them.
What was the testing procedure to find out how much more power it took?
Since an object in motion tends to stay in motion, etc, etc. If both are at steady speed, there would be little or no difference in power consumption, right?
So power consumption would be mostly determined by the rate of acceleration or deceleration. Acceleration is all we are worried about...
That would mean a 9 second car would see more HP loss than a 12 second car.
I've done the swap back to back, I've weighed the parts, and I build these units everyday, so I always find this an interesting discussion.
TECH Enthusiast
Joined: Jul 2007
Posts: 563
Likes: 0
From: Central,NJ
I would like to know where the numbers are coming from?
TH400 internals are not 12-15 lbs heavier than a TH350. I've weighed them.
What was the testing procedure to find out how much more power it took?
Since an object in motion tends to stay in motion, etc, etc. If both are at steady speed, there would be little or no difference in power consumption, right?
So power consumption would be mostly determined by the rate of acceleration or deceleration. Acceleration is all we are worried about...
That would mean a 9 second car would see more HP loss than a 12 second car.
I've done the swap back to back, I've weighed the parts, and I build these units everyday, so I always find this an interesting discussion.
TH400 internals are not 12-15 lbs heavier than a TH350. I've weighed them.
What was the testing procedure to find out how much more power it took?
Since an object in motion tends to stay in motion, etc, etc. If both are at steady speed, there would be little or no difference in power consumption, right?
So power consumption would be mostly determined by the rate of acceleration or deceleration. Acceleration is all we are worried about...
That would mean a 9 second car would see more HP loss than a 12 second car.
I've done the swap back to back, I've weighed the parts, and I build these units everyday, so I always find this an interesting discussion.
Extra weight should bring a predictable amount of loss in percent, but if the numbers are off on the weight....
Can you tell us what you KNOW to be true?
I know that swapping from a TH350 to a TH400 in the same car with the same converter in a mid 10 second combo, we saw virtually no change in ET or MPH. .04 second in the 1/4 mile loss.
On other similar combos we have actually seen ET improvement with a TH400, but again slight change in weather or tune could have caused it.
There is 10 lbs difference in the overall weight of a TH350 vs. a TH400, and this is also the difference in rotating weight.
We have gone from a TH400 to a 40+ lb heavier 4L80E and gotten faster. Obviously a different converter but built by the same vendor to match the previous converter.
I KNOW that any HP consumption would be caused by the rate of acceleration and in our experience, into the 10's we haven't seen any difference worth noting or worrying about.
IMO it's mostly mental masturbation to worry about it. If you need the strength of the TH400, you don't need to worry about HP loss.
It's also relatively easy to take out a couple of lbs in a TH400.
On other similar combos we have actually seen ET improvement with a TH400, but again slight change in weather or tune could have caused it.
There is 10 lbs difference in the overall weight of a TH350 vs. a TH400, and this is also the difference in rotating weight.
We have gone from a TH400 to a 40+ lb heavier 4L80E and gotten faster. Obviously a different converter but built by the same vendor to match the previous converter.
I KNOW that any HP consumption would be caused by the rate of acceleration and in our experience, into the 10's we haven't seen any difference worth noting or worrying about.
IMO it's mostly mental masturbation to worry about it. If you need the strength of the TH400, you don't need to worry about HP loss.
It's also relatively easy to take out a couple of lbs in a TH400.
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If you're not building a dyno queen don't worry about it. It might show a bit of loss on paper, but I know quite a few people who have TH400s and not a single one of them lost any significant amount of MPH or ET, some even gained depending on what they switched from.
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Verdad Gallardo TECH Enthusiast
Joined: Jul 2007
Posts: 563
Likes: 0
From: Central,NJ
I know that swapping from a TH350 to a TH400 in the same car with the same converter in a mid 10 second combo, we saw virtually no change in ET or MPH. .04 second in the 1/4 mile loss.
On other similar combos we have actually seen ET improvement with a TH400, but again slight change in weather or tune could have caused it.
There is 10 lbs difference in the overall weight of a TH350 vs. a TH400, and this is also the difference in rotating weight.
We have gone from a TH400 to a 40+ lb heavier 4L80E and gotten faster. Obviously a different converter but built by the same vendor to match the previous converter.
I KNOW that any HP consumption would be caused by the rate of acceleration and in our experience, into the 10's we haven't seen any difference worth noting or worrying about.
IMO it's mostly mental masturbation to worry about it. If you need the strength of the TH400, you don't need to worry about HP loss.
It's also relatively easy to take out a couple of lbs in a TH400.
On other similar combos we have actually seen ET improvement with a TH400, but again slight change in weather or tune could have caused it.
There is 10 lbs difference in the overall weight of a TH350 vs. a TH400, and this is also the difference in rotating weight.
We have gone from a TH400 to a 40+ lb heavier 4L80E and gotten faster. Obviously a different converter but built by the same vendor to match the previous converter.
I KNOW that any HP consumption would be caused by the rate of acceleration and in our experience, into the 10's we haven't seen any difference worth noting or worrying about.
IMO it's mostly mental masturbation to worry about it. If you need the strength of the TH400, you don't need to worry about HP loss.
It's also relatively easy to take out a couple of lbs in a TH400.
Do you have any experience with the 2.75/1.57 gear swap for the 400. Is this something worth looking at for a lower power drag car? I've read claims of it increasing efficiency but I don't know what they mean by that.
The steeper ratio in a 400 should make a nice reliable trans for a 450HP bracket car, is what I'm thinking at the moment and may take my build in this direction.
Jakeshoe, thank you for this, very informative.
Do you have any experience with the 2.75/1.57 gear swap for the 400. Is this something worth looking at for a lower power drag car? I've read claims of it increasing efficiency but I don't know what they mean by that.
The steeper ratio in a 400 should make a nice reliable trans for a 450HP bracket car, is what I'm thinking at the moment and may take my build in this direction.
Do you have any experience with the 2.75/1.57 gear swap for the 400. Is this something worth looking at for a lower power drag car? I've read claims of it increasing efficiency but I don't know what they mean by that.
The steeper ratio in a 400 should make a nice reliable trans for a 450HP bracket car, is what I'm thinking at the moment and may take my build in this direction.
I have done the low gear sets in the TH400. They work good in a "underpowered" combo that has decent traction. Lots of Stock Eliminator guys run the low ratio TH350's and the 200's for this reason.
Everybody likes to state this but I've never seen anybody who could post the test information to prove it was true.
Launching!
Joined: Nov 2009
Posts: 245
Likes: 1
From: Illinois
I don't think GM ever put out that information. I know a couple of former Hydramatic engineers and we've discussed this.
I know this is frequently passed along.
IMO it is blindly believed and regurgitated but is just another myth.
Anybody that has had basic science classes in high school should be able realize that there is no way those numbers can be accurate as a "hard" figure if at all.
Launching!
Joined: Nov 2009
Posts: 245
Likes: 1
From: Illinois
Jakeshoe, I guess the only way to truly quantify how much power a TH400 or TH350 uses up is to put a car on the dyno and use both transmissions for a test. Assuming that the drivetrain remains the same (rear end and engine), this is the only way to find out the information.
I've never measured the hp loss through a TH400 or TH350, but a tricked out PG with alum drum and fully rollerized throughout measured 7 hp consumption at 6000 rpm at 300 rpm/sec acceleration. If I get bored sometime, I'll check the TH350 and 400.
A Powerglide is an efficient trans.
They use a Ravigneaux type gearset that is more efficient than the Simpson type used in the TH350 and TH400.
The best way to test them would be on a dyno specifically to measure the power loss.
Under very calibrated conditions.
A car on a chassis dyno leaves too many other variables.
Engine temp, tune and air supply, rear diff fluid temp, tire pressure,etc.
If we are going to test them that way, my dragstrip testing should be as valid, and like I said we have never seen a significant difference either way on any car we've been able to keep the same converter (which unfortunately doesn't happen often).
I've actually seen ET improvement going to a TH400 more times than I've seen loss.
Another factor that many guys aren't taking into account is rear gearing.
Your HP losses in the drivetrain will theoretically go up with steeper gearing.
They use a Ravigneaux type gearset that is more efficient than the Simpson type used in the TH350 and TH400.
The best way to test them would be on a dyno specifically to measure the power loss.
Under very calibrated conditions.
A car on a chassis dyno leaves too many other variables.
Engine temp, tune and air supply, rear diff fluid temp, tire pressure,etc.
If we are going to test them that way, my dragstrip testing should be as valid, and like I said we have never seen a significant difference either way on any car we've been able to keep the same converter (which unfortunately doesn't happen often).
I've actually seen ET improvement going to a TH400 more times than I've seen loss.
Another factor that many guys aren't taking into account is rear gearing.
Your HP losses in the drivetrain will theoretically go up with steeper gearing.
Very interesting stuff Jake. I have had discussions about this as well and from the "tests" I have heard of and seen, I think you are correct. The object in motion theory means that there is no HP loss, only acceleration rate. I have been looking for somebody who knows how to calculate this. I strive to have the lightest possible converter and still be durable, but how much does this help? Would love to know the real answer to this.
Chris
Chris
