how much hp to run th400 - Chevelle Tech
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post #1 of 14 (permalink) Old Mar 19th, 10, 11:40 PM Thread Starter
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john
 
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how much hp to run th400

Well as some of y7ou may know I tore up my torque converter last fall,which sent metal fragments through my th350 I was running.To get to tjhe point I need to get my car up and running as spring is in the air.I really need to keep expenses to a minimum.I have a good th400 that I could throw a converter in and of course driveshaft and kick down mods.Or should I have my th350 gone through.Another option is a th350 from a friend which was rebuilt aq couple years ago but never ran.I keep shying away from the th400 I have because I have heard many times it would rob some hp to run it.What do you think I should do??

70 chevelle 468 2 bolt mains,steel crank,srp 14cc
pistons .049 heads 2.19/1.88 manley/116cc,harland sharp roller rockers,Cam 501/527,214/224 at .050.air gap 750 double pump .3.73 posi.9.6:1 compression Th400-Hughes 3,000 stall speed bm holeshot converter. Best time 12.2
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post #2 of 14 (permalink) Old Mar 19th, 10, 11:47 PM
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Brian Gooding
 
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Re: how much hp to run th400

Put your buddies TH350 in and run it until you need a th400.
Cheapest and easiest.
As far as TH400 HP, unless you are chasing hundreths on a timeslip you won't notice it.
Does it use more power yes. But a negative change in weather will cost you more hp than a TH400.

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post #3 of 14 (permalink) Old Mar 20th, 10, 10:46 AM
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Re: how much hp to run th400

John.....Search TCI's web site, they used to have HP figures. I don't think there's enough difference worry with. You'll have to deal with diveshaft length to change also. Break in your friend's TH for him.....

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post #4 of 14 (permalink) Old Mar 20th, 10, 12:02 PM
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Re: how much hp to run th400

I have been running a TH400 for 10 years. This year I am building a pump gas 400 in the 700Hp range in search of some sub 9.99 slips. I bought a Coan TH350. Art estimated that over my TH400 the XLT was worth .3-.4 in the quarter mile at my 3600lb raceweight. We will find out. All just a pipe dream right now, but should have the facts soon.

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post #5 of 14 (permalink) Old Mar 20th, 10, 8:02 PM
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Re: how much hp to run th400

TH400 is great, but if you dont want to mod your DS ...... just throw the 350 in it

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post #6 of 14 (permalink) Old Mar 20th, 10, 11:07 PM
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Re: how much hp to run th400

Watching this thread to see if someone that's already done back to back testing will chime in, TTT
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post #7 of 14 (permalink) Old Mar 21st, 10, 2:31 AM
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Jake
 
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Re: how much hp to run th400

I've been involved in back to back testing with several customers.
The problem with good testing is you first need a fairly consistent car and secondly, most people change the converter, so rarely do we get a good test.

The couple of times we have, there has never been more than .04 change and in one case the TH400 was faster.

We've even installed a 40 lb heavier 4L80E in a car, with a couple of lbs heavier converter (lockup) and the car got faster.

A TH400 has some advantages over the TH350 even though the TH350 theoretically would have less HP loss due to rotating mass.

The rate of acceleration has the greatest effect. A 8 second car will see a greater HP loss at the wheels than a 12 second car. Rear gear ratio has a play here as well.

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post #8 of 14 (permalink) Old Mar 21st, 10, 12:05 PM
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Re: how much hp to run th400

John if you have a good 400 put it in. Some guys like the "challenge" of making smaller parts work (like going 9's with a 10 bolt) and that's cool if that's what floats your boat.

For guys like you and I the horsepower loss thing isn't really worth discussing (if there really is any of significance). I think you said there was economics involved so if you've got a good 400 and it's cheaper to go that way it's a no brainer to me....put it back together ASAP so you can start having some fun again....Dave

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post #9 of 14 (permalink) Old Mar 21st, 10, 3:04 PM
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Ken
 
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Re: how much hp to run th400

A TH400, in stock form, is one of the strongest transmissions made. Using mostly stock parts, they will hold up well to about 750 Ft Lbs of torque. I had a friend with a BBC Caprice convertible who raced it every weekend. For launch, he would rev the engine to 6000 RPM, and pull the column shift lever into "Low". He did that for a year and a half before something broke. Literally hundreds of times. That's when I became a believer in TH 400's. Yes, he did break other things, axles and yokes, etc.

I considered using a TH350 until I talked to Arnie Beswick at a Nostalgia race. He went with one because of the supposed better efficiency, but after blowing up a few of them, switched to a 400 like everyone else was using. No more problems.

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post #10 of 14 (permalink) Old Mar 21st, 10, 4:08 PM
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Re: how much hp to run th400

Quote:
Originally Posted by lun40119 View Post
I have been running a TH400 for 10 years. This year I am building a pump gas 400 in the 700Hp range in search of some sub 9.99 slips. I bought a Coan TH350. Art estimated that over my TH400 the XLT was worth .3-.4 in the quarter mile at my 3600lb raceweight. We will find out. All just a pipe dream right now, but should have the facts soon.
I think he was smoking some good stuff that day if he really thinks you will gain .4 going to a 350 from a 400!
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post #11 of 14 (permalink) Old Mar 21st, 10, 9:12 PM
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Re: how much hp to run th400

Quote:
Originally Posted by job68327 View Post
I keep shying away from the th400 I have because I have heard many times it would rob some hp to run it.What do you think I should do??
Quote:
Originally Posted by blue66 View Post
As far as TH400 HP, unless you are chasing hundreths on a timeslip you won't notice it.
.
Quote:
Originally Posted by jakeshoe View Post
The couple of times we have, there has never been more than .04 change and in one case the TH400 was faster.

We've even installed a 40 lb heavier 4L80E in a car, with a couple of lbs heavier converter (lockup) and the car got faster.

A TH400 has some advantages over the TH350 even though the TH350 theoretically would have less HP loss due to rotating mass.

The rate of acceleration has the greatest effect. A 8 second car will see a greater HP loss at the wheels than a 12 second car. Rear gear ratio has a play here as well.
Some Good and well thought out points here^ above. My first reaction to your question in the first post of this thread was that if your vehicle specs in your post signature are up to date, and apply to the vehicle in question here, then I'd have to say that a guy using such a mild camshaft in his engine shouldn't be concerned about the miniscule wheel HP loss that will occur by switching to the TH400. So if it were me, I'd take the opportunity to get that TH400 trans in there, as long as you know that the internals are healthy, or if you'll be rebuilding it anyway. In other words, given the choice, i for one would much rather put money into a TH400 than put it into a TH350

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post #12 of 14 (permalink) Old Mar 21st, 10, 9:46 PM Thread Starter
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Re: how much hp to run th400

Thanks for the replies.Not sure what i am going to do but it will be soon.I was real happy to get into the 12's last year and I didnt want to go backwards.The reality is I have a million other things going on and will be happy to just get it up and going again.Thanks for the opinions.I will keep you updated!

70 chevelle 468 2 bolt mains,steel crank,srp 14cc
pistons .049 heads 2.19/1.88 manley/116cc,harland sharp roller rockers,Cam 501/527,214/224 at .050.air gap 750 double pump .3.73 posi.9.6:1 compression Th400-Hughes 3,000 stall speed bm holeshot converter. Best time 12.2
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post #13 of 14 (permalink) Old Mar 22nd, 10, 1:18 AM
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Re: how much hp to run th400

Quote:
Originally Posted by job68327 View Post
Thanks for the replies.Not sure what i am going to do but it will be soon.I was real happy to get into the 12's last year and I didnt want to go backwards.The reality is I have a million other things going on and will be happy to just get it up and going again.Thanks for the opinions.I will keep you updated!
I'd get the 350 fixed and put some good parts in it so it will live. You'll need a different driveshaft if you change over to a T-400 from the present T-350. In my son's car the 350 was .11 hundreths quicker than the T-400 although the mph was almost identical. Changing the converter will make more difference than the type transmission. Every time we got a better torque converter the car got quicker and faster. Most of the time the sprag breaks from improper burnout procedures. If the burnout is continued until the tires "chirp" it is likely you'll break the intermediate sprag in the transmission, ask Jakeshoe to explain that problem.
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post #14 of 14 (permalink) Old Mar 22nd, 10, 7:33 AM Thread Starter
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john
 
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Re: how much hp to run th400

Quote:
Originally Posted by Harold Sutton View Post
I'd get the 350 fixed and put some good parts in it so it will live. You'll need a different driveshaft if you change over to a T-400 from the present T-350. In my son's car the 350 was .11 hundreths quicker than the T-400 although the mph was almost identical. Changing the converter will make more difference than the type transmission. Every time we got a better torque converter the car got quicker and faster. Most of the time the sprag breaks from improper burnout procedures. If the burnout is continued until the tires "chirp" it is likely you'll break the intermediate sprag in the transmission, ask Jakeshoe to explain that problem.
"improper burnout procedure"I love it!!Thats actually how I killed mine.Also they were repeated one after another after another.

70 chevelle 468 2 bolt mains,steel crank,srp 14cc
pistons .049 heads 2.19/1.88 manley/116cc,harland sharp roller rockers,Cam 501/527,214/224 at .050.air gap 750 double pump .3.73 posi.9.6:1 compression Th400-Hughes 3,000 stall speed bm holeshot converter. Best time 12.2
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