Need a TH400 convertor suggestion

[jpwalt1987]

I am finally getting around to figuring this car out after getting the engine fixed at DLS. I stall tested my convertor thats in my th400 and it goes to 2700rpm at zero boost and 3000 rpm at 3psi. I havent really leaned on this combo since getting it back either. Here are the specs:
235 cid 109 block
ported GN1 heads (249cfm/200cfm)
8.6:1 compression
218/218 hyd roller DLS cam
PTE front mount
Old school PT70 with .63 a/r
and supporting stuff too.
The convertor is an ATI unit that stalled 3200 behind a 274ci motor and 76 turbo.
Not sure if I should get it restalled or just get a new unit all together. I have a transbrake, so spooling at the track should be no problem but it is a turd on the street. I am going to get it from PTC but am unsure on what it should stall and how it will act. thanks for any suggestions.

 

[Dusty Bradford]

I'm guessing your converter is a tight 9" or a loose 10". My 9.5 would go 3000-3200 at 0-1# of boost. How quickly it comes up from a roll on the street will depend on your power and et goals. The faster you want to go, the tighter it needs to be to couple the power.

Someone with a 70mm that only wants to run 10.60's can get away with a looser converter if they prefer quick spooling.

 

[buickboy]

Mine is at 3800 stall right now. 1.5 60 ft, and 126 MPH in 1/4. That is the same turbo, Etc.
Mitch

 

[buickboy]

TH400 Fluid Capacity

What is the total fluid capacity with a 9-1/2 convertor, and a 2-1/2 in ch deep pan? I have 9 quarts in it right now after a new rebuild and 1 quart in the convertor?
Mitch

 

[jasjamz]

Are there converters out there that offer 3800 stall speeds and slippage under 6% in any of the buicks you have done? The old school jb turbos need stall speeds of 3600 or better to feel nice on the street. But the top end slip is 20% or more at times. Why is it so difficult to resolve that?

 

[Dusty Bradford]

What is the total fluid capacity with a 9-1/2 convertor, and a 2-1/2 in ch deep pan? I have 9 quarts in it right now after a new rebuild and 1 quart in the convertor?
Mitch

I'd say your pretty close to being full, but it's been a while since I topped off a T-400. I usually put 8 quarts in a trans then start the engine before topping it off.

 

[Dusty Bradford]

Are there converters out there that offer 3800 stall speeds and slippage under 6% in any of the buicks you have done? The old school jb turbos need stall speeds of 3600 or better to feel nice on the street. But the top end slip is 20% or more at times. Why is it so difficult to resolve that?

Combo, combo, combo

Yes you can have a converter stall 3600 at 0-1# of boost and slip 6% but you may have to turn the engine 6800 rpm.

The issue with the Buick is the rpm range. They make good power but most street cars won't turn over 6000 rpm. If you have a large turbo that requires 3600 stall but the engine has to shift at 6000 rpm, your flash stall is too close to the shift rpm and the converter can't couple. For example a 70mm turbo on a 231. Once the boost comes up the car makes good power. A 3600 stall may flash to 5600 rpm but the engine shifts at 6000. This isn't enough of a difference to let the converter "catch up" to the engine. It may have 17% slip, turn the engine 6800 and it may only have 6%

This is why the turbo size and camshaft really needs to match the operating range of the engine. If someone wants great spool-up and wants to run 10.50's, they don't need a 70mm. Something smaller like a 6262 will run the et and greatly improve response time.

 

[jasjamz]

I hear ya on that Dusty. I just was hoping with technology advancements that things would get better in that deparment. The new billet units are nice!

 

[Dusty Bradford]

Stall speeds are also very misleading. I try to stress 0-1# stall speeds to get everyone on a level field.

A converter stall speed depends on the torque the engine applies to it. A converter that stalls 3000 rpm in n/a V6 may stall 4200 rpm behind a big block. Same is true with a turbo converter except the stall changes on the same engine as boost is produced.

A turbo converter really doesn't have a true stall speed. It may stall 2800 at 0-1# of boost, 3300 at 5# of boost, 4200 at 10# of boost and it just keeps going. The flash stall can be found on a data log which is what the rpm drops to on the gear change. For example, your running 24# of boost, you shift at 6000 rpm and it drops to 5200 rpm, your flash stall is 5200 rpm. Now raise the boost to 30#, the engine makes more power and it may only drop to 5400 rpm. You have made enough power to raise the flash stall speed 200 rpm but your 0-1# stall speed has not changed. The converter will always drop to 5400 rpm at 30# of boost whether you shift at 5800 or 6400. The car that shifts at 6400 will have better efficiency.

 

[Dusty Bradford]

I hear ya on that Dusty. I just was hoping with technology advancements that things would get better in that deparment. The new billet units are nice!

There are things that can help. Things like sprag's and mechanical diode's are designed to help increase efficiency without loosing spool-up. But in my testing with these I have found my 9.5 couples so well for it's given rpm range the sprag or diode doesn't offer much if anything. The only cases I use them is if the turbo is on the large side for the combo, I will spec it on the loose side to help spool-up then use the diode to help a little up top....but the help is minimal.

No converter will be able to fix or make up for a combo that is not ideal. Billet is nice but in reality it's like shiny wrapping paper. Looks nice on the outside but on the inside is the same internals.

 

[norbs]

Dusty my converter you spec'd gives me about 2500 rpm ability to cruise on the highway and average 23 mpg with the GV, however with a 231 and the 76 turbo, as you pointed out its a turd on the street. I guess i have no choice to reduce turbo size correct?I am thinking maybe a billet 70? Whats your opinion?

 

[John Wilde]

Dusty my converter you spec'd gives me about 2500 rpm ability to cruise on the highway and average 23 mpg with the GV, however with a 231 and the 76 turbo, as you pointed out its a turd on the street. I guess i have no choice to reduce turbo size correct?I am thinking maybe a billet 70? Whats your opinion?

Norbs,

How fast do you want to go?
The Billet 62 is enough for 90% of the street cars.
PT6265 CEA 700HP
Considering the rest of your combination a 67 might be up your alley:
PT6765 CEA 900HP

I would keep the 65/P trim turbine wheel to help spool.
I don't think the 68/GTQ wheel is the most street friendly on a driven 231.

 

[norbs]

Thanks John for your ideas, I just want to run anywhere in the 9s is fine.

 

[Dusty Bradford]

Dusty my converter you spec'd gives me about 2500 rpm ability to cruise on the highway and average 23 mpg with the GV, however with a 231 and the 76 turbo, as you pointed out its a turd on the street. I guess i have no choice to reduce turbo size correct?I am thinking maybe a billet 70? Whats your opinion?

That's basically it. A 76 is overkill on anything short of a larger stroker unless it's a high winding engine. I'd look into the 6765 or a 70mm DBB

 

[jpwalt1987]

Dusty, That pt70 turbo that I have is rated for 775 hp. I am guessing that is flywheel hp. The convertor is a 10inch ATI. THe convertor went a 9.21@148 behind a 274 GN1 headed car that wieghed 3450. This was with a 76mm.
I have no problem turning the motor 6500rpm if it makes power up to there. I want the car to run around the 10.0 mark on a conservitive tune. I have contemplated changing turbos but I already have this one even though it is very old school technology. I think it would probably be best to get this setup running to its full potential before changing anything. What kind of info on the way this convertor acts under full load would you need to determine what needs to changed? Thanks for the help. Jeremy

 

[Dusty Bradford]

Dusty, That pt70 turbo that I have is rated for 775 hp. I am guessing that is flywheel hp. The convertor is a 10inch ATI. THe convertor went a 9.21@148 behind a 274 GN1 headed car that wieghed 3450. This was with a 76mm.
I have no problem turning the motor 6500rpm if it makes power up to there. I want the car to run around the 10.0 mark on a conservitive tune. I have contemplated changing turbos but I already have this one even though it is very old school technology. I think it would probably be best to get this setup running to its full potential before changing anything. What kind of info on the way this convertor acts under full load would you need to determine what needs to changed? Thanks for the help. Jeremy

The motor will make power to 6500 rpm as long as the valve springs are up to the task.

The turbo will work for your goals so I see no need to change it unless you want the new technology. The newer smaller turbos from Precision can support more power so you get much better throttle response without giving up any hp.

Your converter is a nice piece but the 10" converter is just tighter down low and looser up top. You can swap to a 9.5 and gain spool-up while also gaining a little efficiency. The 10" stuff from ATI and Chance work well with the right combo but you have to have plenty of engine for a given turbo. Such as a 274 with a smaller turbo or a TSM car with a stroker and 70mm. Combo's where spooling is generally easy.

 

[jetmech]

Hey Dusty, can i pick your brain too. I think im going to send my coan converter back for some rework. Its rpm on gear changes is 5000 and i shift at or slightly above 6000. My car traps around 116-119 at between 5375 and 5425 rpm and on the tci calculator im at 13.8 % slip with entering a 28 inch tire not considering tire growth(get worse if i add .5 inch on tire growth) Its been restalled once because they missed it bad on initial purchase but now its around 3200 stall. I would like it a little looser down low and more efficient up top. Any suggestions besides filling out their spec card i can give them. Thanks.
ps it is behind a th350 trans pt61 turbo, 218/218 flat tappet cam with ported irons.

 

[Dusty Bradford]

It is possible to loosen a converter down low and tighten it up top by changing stator and pump designs. Without knowing what they use for internals it's hard to say if it's possible with the converter you have but they should be able to do it.

The bad thing about these types of changes is it's a real guessing game. If they use a cast stator where the change may result in loosening it 400 rpm, there has to be enough room for adjustment in the rest of the converter to make up for that 400 rpm plus try and make it even tighter up top.

Is it a 10" converter? If it's a 9" it should not need to be looser down low considering it's still slipping over 13%. The 10" converters tend to be tight down low and loose up top in the Buicks. The 9" converters are loose down low and usually work well if your shifting as high as you are at your power level.

 

[jetmech]

Thanks Dusty. Im not 100% sure its a 10 inch. I need to get the serial number to them so they can make a decision on what can be done. Thanks