how much power will i really lose running a 400 compared to the lighter,"more efficient" 350? transmissions thet is, not motors. thanks

just wondering why you want to run a 400 over a 350, if you really have too much power for a 350, then its worth using a 400, no one likes to blow a tranny, but if you can get away with the 350, why not?


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383: protopline heads, eagle rotating assembly, rpm intake, msd pro-billet hei, harland sharp 1.6 roller rockers,comp XE268H,headers,3" flowmaster exhaust,TH-350 S/S package, 3.73 gears.

Greg,
In reality the amount of difference is pretty negligble.
The approximation that I've read, and seems to be pretty accurate as far as a HP approx would be about 35hp for a TH350 and about 45HP for a 400.

I do not believe this is a hard number.
It would vary by the amount of total power you are putting out.
Basically it should be a percentage and not a difinite HP number.

Say if the test was done on a 350 hp engine, and the TH350 uses 35hp, then it uses 10%, but the 400 uses about 13%.

Some of this is also based on a stock converter, running a smaller, lighter, converter may make them use less HP.
Or any lighter rotating weight, like an aluminum drum, etc..

What it really comes down to is that a TH350 is a pretty stout trans, very underrated.
If you currently have a Th350 I would probably recommend having it properly built to handle any additonal abuse you plan to feed it.
If you are worried about that last .005 ET drag racing it is a better trans also, but isn't going to make a huge difference in ET, no more than a couple of hundreths.

As far as pure strength the 400 is hard to match but it also has to be properly built.
it has some of the same weakness as a Th350 and if these aren't addressed it will break as easy as a Th350.
I've broken more TH400's than Th350's http://www.nastyz28.com/ubb/smile.gif
Sprag failure and burned clutches doing stupid stuff...

Totally annihlated a TH350 once though, http://www.nastyz28.com/ubb/smile.gif
Neutral drop behind a 400 SBC at about 4000 rpm in a '78 chevy pickup
Couldn't even take the innards out...

Also had to replace a driveshaft and harmonic balancer LOL

Now we all know why Jake builds his own trannys...

I agree with jakeshoe on everything except the strength of a stock th400.I went to a 400 because I kept breaking well built 350's.I'm running a 400 right now that has a stage 2 shift kit nothing else and it hasn't given me any trouble yet.
The clutches are going away by the look of my fluid but I had to change them every year in the 350 as well and I have almost 200 passes at the track and some street miles on it.For the $300.Cdn that I paid I got my money's worth.

If you were breaking "well built" 350's then something wasn't right unless you are making in excess of 800 hp.

What shift kit or valve body was used on the TH350's?
This is KEY to the survival of it.

The reason you are NOT breaking the 400 is because the TransGo kit is keeping your 1-2 shift timing in check and it is dual feeding the directs.
Takes care of the common causes of failure in a hi-po application.

I have a couple of Th350's in ~600 hp applications as well as one of my own behind a ~550 lb ft 454 with no problems.
I had to warranty one due to a assembly error that happened because of a broken pump bolt and having to pull the pump out multiple times causes a fracture on a cast iron sealign ring.
I have since permanently corrected this on my builds by using Teflon.

No power related failures.

A TH350 will NEVER have the sheer strength of a 400, just due to the beefy parts a 400 has, but up to 800 hp or so, it can work fine.

Operater error in the burnout box can break sprags, as well as decel downshifting.

Both trannies have the same shift kits and both trannies came from the same guy who builds around half the trannies at our track.So I have confidence in him.
I'm making around the 600hp n/a and have broke hardened spragues in the 350.In my opinion from my exprience it's the torque of the bb that is killing the 350 along with the fact the car is a pig.
I now have the same 350 in my Vega that has a sb and is quite a bit lighter and it works great.
Some may last over the 600hp level and behind a bb but I think you're on the edge at 600hp.

I guess I'm jut a lot more conservative. The truck wouldn't top 500 horse on a good winters day, the TH350 did fine, but it was so well wrung out when it went,, sheeze you should see the list of new items tht Hughes put in what was a well built, long lived TH350. The poor little trans was just thrashed. That's my limit. 500 horse in a 3200-3500 pound chassis that will hook and pull a fair 60' time. Sure the TH350 'can' survive more HP and torque, but when it's used up,, I mean its USED up! Simply because of the support for the internals of a 400 it has a better 'service life' of thrust surfaces and bushings. I think you really need to consider 'maintenance costs' when you put a power limit on something. Now Jake before you jump all over me on that,, I'm talking about the guys who don't have the luxury of building their own, but Joe Schmoe who is paying the shop to resurrect his trashed TH350. The 400 will be more forgiving to the 500HP level over the years. That's all I'm getting at. Hell there are guys in stock classes that are making th200's survive those 'stock' 10 second passes. But they are pulling the thing down between races too!

<font face="Arial,Verdana" size="2">Originally posted by jakeshoe:

Operater error in the burnout box can break sprags,
</font>


How?

i know my basic rebuilt(transgo shift kit) th350 with 4500 stall in my 10 sec bbc 468 ci 81 3600 pound pig for a camaro has lived a very long life and yet to break........even with nitrous off the line............


but then again i wonder why my stock th350 in my daily driver 80 z28 with a B&M shift kit broke the damn input shaft off the forward drum and it only makes and honest 300 hp to the rear tires in a 4000 lbs car.

i think it depends on what day of the week your tranny parts were made on ....lol........

craggar,
If you were using a transGo kit in a 350 and breaking sprags, something else was going on. You may still break one even with a TG kit (WAY less likely) but if it was built using a cushion plate in the intermediates (no reason not to), and you were doing burnouts properly, the direct drum bushing was in good shape and the sprag race was properly prepped, it shouldn't be an issue.

I'm not totally convinced a hardened sprag race is necessary or even beneficial. i do install them on these types of builds because I haven't seen a sprag failure on a Th350 I've built (yet).
I do however ALWAYS install a new sprag and race.
My theory is that the race will fatigue under abuse eventually so start with a new one (similar to running new rods though a recon one will do...).
Also the roller clutch (sprag) is spring loaded so one with new springs can only help, also should be nice new round rollers. No uneven stress placed on the outer race.
I also prep the race to let ATF move so the sprag can apply quicker, not hydro-plane over the ATF...
Little things...

I ALWAYS install a new wide direct drum bushing. This way the drum is riding centered on the pump.
Even sprag apply...

I always install a wavy in the intermediates.

So far so good....

Craggar,
Your guy probably builds a good trans, the BB torque will kill parts, but how are you doing your burnouts?

You answer that and I'll answer why operator error can kill a sprag on burnouts for camdoc.
http://www.nastyz28.com/ubb/wink.gif

Marv,
You will NEVER get me to say a Th350 is as stout as a 400.
I'm a TH400 fanatic.
I think they are the single greatest drivetrain component GM EVER made.
The best automatic transmission EVER designed IMO.

Rolls Royce apparantly thought so too, as well as Jag, Ferrari, and others.

I have however over time learned the TH350 is not as bad as some believe and is really a VERY stout piece when done right.

At one time I would NEVER have put a Th350 behind a BBC, partly due to the fact GM never did.
when it came time to pull the 6 speed and put an auto back in the '72...
Jake had both cores sitting in storage, costs me the same to rebuild one.
I put a 350 in behind the pretty torquey 454.
Mostly due to the ease of finding a driveshaaft and crossmember.
My dad asked "Will the TH350 be OK behind the 454?"
I asked him if he thought it would be lifting the tires like Michael's (Old School) Camaro does http://www.nastyz28.com/ubb/smile.gif

Like Marv said as far as long term heavy hitter reliability the 400 will easily beat the TH350.

However at the 500-600 hp level I would expect a TH350 to live 2 seasons without ANY maintenance.
I would however pull it down every 2-3 seasons and install a NEW sprag and race, new direct drum bushing and pump bushing, and check frictions and thrust surfaces.

On a TH400 I would run it 4-5 seasons before doing the same.

BUT,
A Th400 WILL break a sprag as easy as a TH350 IF it isn't setup right (prep and shift kit) and if a burnout is done improperly or a manual deceleration downshift from 3rd to 2nd above stall speed.

ddeennis,
Your Th350 sounded like a freak of nature deal.
The input shaft to forward drum is not a common failure. Actually fairly rare.
Even in high HP applications.
I'm guessing the pump was not square or the shaft/drum was weakened or possibly a faulty part.

I'm NOT a fan of B&M stuff as it is too harsh and causes ALOT of the sprag failures.

Some have had decent luck with it (Marv...) and my only guess here is that they went with a mellower calibration when selecting shift firmness, or got lucky...

Marv,
Speaking of 200's in the 10's...
I'm building one (unless I can sell it) for my chevelle.
200-4R with all the bells and whistles.
I have the GN core and all the stuff to beef it up to stand the power except a couple of more billet pieces I need to order.

I kinda like the 200-4R for this because of the parts available (but not cheap) the fact I can retain normal auto features, then also have a t'brake, and good gear ratios. Also a lock-up converter...

However if I could sell it all off and break even, I would just do a Gear vendors in my Chevelle because reliability would NEVER be an issue.

However if I wanted a 'brake, I would have to give up auto shifts on a TH400.

Trade-offs....

Wonder if the 2.75 low gear on a 200 would be too mch torque multiplication behind my 396 http://www.nastyz28.com/ubb/wink.gif

I always do a 1,2 then out of the burnout box Jake.
I ran both cars this weekend and got the Vega in the 12.1's leaving at 3500rpm off the brake and the 350 worked perfect.
I plan on bumping up the hp on the Vega this winter enough to put it in the mid 11's on motor then I'm putting a cheater kit on to have fun with so will see how the 350 works then.If it doesn't break I would have to say it was the weight of my Camaro along with the torque of the bb that was killing it.
If it does break then maybe it's the builder or like you said I'm doing something wrong in the b/o box.
So what should a guy do in the b/o box?

i know when i do burn outs it depends on which car i got out there and how much i want to play.....he he heehheh


in my drag car 81 camaro i roll out of the box to get out of the water(our boys like to stop you right in it,,,,lol) then i bring on the gas easy up against the stall until the tires break loose then i run it up to 6000 rpms in first then 6000 rpms in second then release the brake and ride it out to the start line.........i hit the brakes and shift in neutral at the same time while i rev up the motor a few times to keep it from dying since im hard on the brakes.....


on my daily driver i just roll thru the water do a power brake burn out to 6000 rpms in first and ride it out to the line......throwing into neutral while on the brakes clearing it out..........i dont do dry hops find it be waste of motion and heat on the parts..........


and if this is wrong damn.....guess ive been doing it wrong since 92 when i first started racing......back then i use to do dry hops but why i thought i need it to stick at the line not behind it lol.......so i cut that part out years ago....

TH350 plus: it weighs less than at TH400 and usually more available. Never do a complete burnout in 1st, always start in 2nd and shift to 3rd (especially if you can over rev engine if you have 4 series or bigger rear gears). Spragues take a beating otherwise. The trans should have the five clutch pack elements (not 4 or less V6/4 banger version).

TH350 minus: weak bell housings (crack ear to ear if any torque thrust is put on them. Not for over 600 HP (though you can find highly modified TH350's in use).

TH400 plus: one tough transmission from the get go. Not much to do to them to handle big HP.

TH400 minus: Heavier than TH350 or aluminum Powerglide. Does take 10%+ to turn it over a TH350 or PG.

Cardinal

Craggar,
Sounds like your burnout technique was killing sprags...

As Cardinal posted, you need to get the tires spinning in the water in 1st, shift to 2nd and then roll out of the water and throttle up. Shift from 2nd to 3rd or stay in 2nd.

Don't do a 1-2 shift under throttle in the burnout box.

Probably not your builder...

<font face="Arial,Verdana" size="2">Originally posted by jakeshoe:
Craggar,
Sounds like your burnout technique was killing sprags...

As Cardinal posted, you need to get the tires spinning in the water in 1st, shift to 2nd and then roll out of the water and throttle up. Shift from 2nd to 3rd or stay in 2nd.

Don't do a 1-2 shift under throttle in the burnout box.

Probably not your builder...

</font>

So does this apply to both or just the 350?
It's new to new but so is everything else before I hear of it. http://www.nastyz28.com/ubb/smile.gif
With my 400 I have no choice since it isn't a full manual valve body.

Sorry GREG'S if it looks like we are taking over.

craggar,
You do not need a full manual VB to shift into 2nd .
Once the tires are wet they will spin easily so you roll out of the box, spin up tire rpm under light throttle, shift to 2nd then hammer it.
The ideal is to keep the 1-2 shift at as low of a torque output as possible.

Yes it applies to TH350's and 400's.

I've been told to never use 3rd gear for a burnout with a TH350....any truth to that?

The local "expert" also says not to drive it out of the box under power. I know you can shear off cheap wheel studs this way, but what about the trans?

When I shift into 2nd there is not much of a load since the tires are just starting to heat up in the box.All the load is when you launch then shift into 2nd and that's when they have broken on me.
Are you saying that the burnout causes it to do this when you shift into 2nd after the launch?

Yep,
Your breaking the sprag in the box, then not knowing until you get under a load and traction.

It will not hurt anything to shift into 3rd while doing a burnout.
If your trans is built to handle the torque in 3rd gear at the end of the track, it won't hurt in the box.
Basically if the direct clutches (3rd) are dual fed, they will be fine.

The shift from 1st to 2nd, is the killer.
First of all there are more things happening so it is harder to time it all correctly (shift timing) to prevent breaking parts, or undue harshness.

2nd of all it affects the weakest link the most.

On a 1-2 shift in a TH350 or 400 manually,
The low reverse apply device (clutches on a 350, band on a Th400) have to release.
The intermediate sprag and cltuches have to apply.
Also on the manual shift the intermediate band has to apply.

The sprag MUST lock before the clutches.
If it doesn't it will get hurt.
The band takes some of the hit off the sprag, by slowing down the direct drum.
You need to keep the intermediate cluthc apply ever so slightly slow, so that the sprag can lock, then the clutches apply.
The BEST way to do this is to use a cushion plate in the intermediates.
Also to not overdo the 2nd apply orifice in the seperator plate.
There are other things you can do but these are the two most important.

Shifting from 1-2 in the burnout box, there isn't an accelerating load on the planetaries, so they are not "pushing" the sprag to lock.
So the clutches will apply faster than the sprag.
Under acceleration, the planetaries are "driving" the sprag towards the locked position, so it will lock after the L/R releases and before the intermediates apply.

The shift from 2nd to 3rd is very simple.
The directs apply...
If it is a manual shift the intermediate band has to release but it is still a simple shift. No sprag is in play.

The direct clutches apply, the sprag freewheels, the intermediates stay applied.

Only problem here is on a 3-2 downshift. That weak sprag has to relock and the intermediate band will slow the drum but on a deceleration downshift, it is harsh on the sprag.

Once under the converter stall speed, it is OK though.

So shift to 2nd under light throttle, low rpm. Just as you come out of the water so there is a little load on the trans. The NO load, high throttle hurts it.

You learn something new everyday,tks Jake.

Interesting post Jake, does a reverse shift pattern have any affect on that too?