Demystify Torque Converters in a Road Racing application.

Ok, new tangent. I feel that I understand how a torque converter works.  But is better fluid the only modification for them in this application?

What say you?

Temperature.  A higher stall converter might get you up in the power curve quicker, but it will create all the heat.  Stock converter will keep the heat lower, but all the cooling is still critical.  You might be able to trick the converter clutch into locking up quicker, but I doubt it would last very long in an angry situation.

Coolers, and a trans temp gauge, along with good synthetic fluid.

I ran a T-350 behind a 400 Pontiac V8 in my Firebird with stock convertor on tracks for years with no problems. NASA 20 min HPDE sessions.  Trans had a shift kit, ran Amsoil synthetic fluid, B&M plate type cooler in addition to radiator. I'm kind of a minimalist when it comes to track cars so no temp gauge because that just adds possible places for leaks. 

Ideally, you'd want a converter with a good, strong lockup clutch and good programming.  Outside of when the trans is shifting, it should be locked most of the time (for less heat and better feel) except for when you go WOT or dip into the throttle quickly in a higher gear.  Then it should unlock to snap you into the powerband faster. 

For cooling, just run the biggest cooler you can fit (with a thermostat if over-cooling is a concern) and a temp gauge in the pan so you know if you're pushing it too hard. 

I’m in no way trying to thread-jack.  Just need a simple answer from NOT A TA and I’ll go on my way.  I’ve had this question burning for a while now and the internet gives mixed answers.  Here’s a golden opportunity while we’re on the subject. 

Did any second generation TA come from the factory with a TH-350?  My know it all cousin, member of PHS - bla bla bla, belittled his brother in law for buying a ‘76 with a TH350.  He said the car was a fake since no TA ever had “just” a TH350.  But then I read somewhere else that starting in ‘75 they couldn’t squeeze the cat in there with a TH400 so they switched to a 350.  What’s the story?

BarryNorman said:

Ok, new tangent. I feel that I understand how a torque converter works.  But is better fluid the only modification for them in this application?

What say you?

Fluid should not really affect how a torque converter works.

Additionally, my gut feeling, and remember that one's gut is full of E36 M3, is that the torque converter should never really come into play in a road racing situation.  When you're below the stall speed, yes the converter is multiplying torque like a hydraulic CVT (which is kind of is), but it is also generating a lot of heat, which has to be rejected.  This is not a big deal when you are on the drag strip riding the converter for half of every upshift, not good at all when you're balls to the wall for 20 minutes plus.

I have a 3700rpm stall converter in my S60R.  Yes, it's a bit excessive, but it's fun and there is no such thing as turbo lag anymore.  However, when I have a scan tool plugged in and I am watching trans fluid temps, they skyrocket any time I am accelerating and the TCC is not locked up.  And this is on the street.

I keep thinking about/keep getting goaded into a LS swap in one of teh RX-7s that I have.  What I would want, for maximum throttle response, is the SMALLEST converter possible that could still contain a clutch.  Flexplates weigh practically nothing but converters are heavy and contain a lot of fluid.  Smaller converters weigh less, and that means better response.  New problem:  A decent converter will cost more than the whole rest of the LS swap.

Depends on the car. In say, 95%, of the cars out there, stone stock is your only option anyway.

If you're racing something with a drag racing aftermarket (PG, TH350/400, 727TF, 4R70W, 4L65/80, etc) there's a E36 M3 ton of options.

Javelin said:

Depends on the car. In say, 95%, of the cars out there, stone stock is your only option anyway.

You may be surprised.

Our trans guy has a very interesting converter book.  There is a lot of reuse in the OEM world.  Five billion cars used the TH125, for instance.  And there are thirty or fifty different converters for them, with different stall speeds.  We had a somewhat unusual build that required a really loose, yet lockup, converter for a '125.  We went through this Great Big Converter Book and chose one, I think it was from a 1.8 SOHC Cavalier or something.  Worked great for the big cammed 2.5l Fiero that was commissioned.

A converter for a 1.9l Volvo S40 would be hi-larious in a 5 cylinder car with the same transmission, for another example.  Maybe it'd work in a SAAB that used that trans, as well.

Alternatively, there are converter shops that can modify your existing converters.  This is what I did for my S60R, since the converter had to be gone through anyway.  While they had it cut open to clean out all the debris from the pump failure, I had them do a little work inside, and the expense was susprisingly not all that much.

In reply to Knurled. :

When I left parts 2 years ago the big book existed but none of the parts did, they were predominantly NLA or OOP. A lot of the manufacturers were bought up or closed up shop.

A competent trans shop can certainly do what you had done, but try finding one these days. Same problem.

In reply to Javelin :

Yes.  I do remember that finding the right converter for that Fiero involved finding something that looked good, then finding out that it was not available, then trying again.  Fortunately there were MANY options to choose from.

As per your second point, maybe I am spoiled living in the land of Mr. Gasket's Empire (grew up a mile from their headquarters) and Summit.  There are a lot of shops around here that do stuff like that.  We stopped going to mass-market converters when we can get them made semi-locally (on the far south-east side of Cleveland, but we are far north-west, teh horror!) and for much less than, say, TCI.  Or Level 10, which by inference from online searching, mostly just goes through the Big Converter Book and paints the parts their own color.

Fluid should not really affect how a torque converter works.

Fluid viscosity does have an effect on stall speed but most people are even less willing to experiment with fluid than they are with converters. In the turbo dodge world some people were mixing straight hydraulic fluid with a little motor oil in the old fwd 3spd and seeing lower stall speed, firmer shifts, etc. But that only becomes an advantage when you are making more power than you planned to and you don't want to redo your converter.  

In reply to A 401 CJ :

Lots of 70's F-bodys came with TH350's. Its no big deal. My friends 76 400 T/A has one, my '79 Camaro had one...

We've got 10000+ race miles with a non-lockup auto. The cars get high quality fluid and use the factory coolers. I'm a big fan of leaving well enough alone.

In reply to Knurled. :

Would that model converter be readily available? I ask because evey time I see an 850 IT estate I wonder how to clone the BTCC version. With a similar converter the next problem to overcome would be resurfacing the head to achieve 12degrees intake valve to piston on a challangesque budget.

In reply to BarryNorman :

I have a TF80, which is the mongo 6 speed that is used behind V8s, late model sixes, and the last two years of S60R.  An 850 probably has a AW55-40(?) and converters are readily available for that.

Heck the 2.5t S80 (5 speed, so AW55-51) that I have been driving has a 3200rpm stall speed, stock.

BarryNorman said:

In reply to Knurled. :

Would that model converter be readily available? I ask because evey time I see an 850 IT estate I wonder how to clone the BTCC version. With a similar converter the next problem to overcome would be resurfacing the head to achieve 12degrees intake valve to piston on a challangesque budget.

Tricky part is finding the head bolts with the universal joints in the middle of them.

In reply to Streetwiseguy :

II know VW played with changing the head angle, because the stock 16v head (really, all 16v/20v geometry on the old belt engines) has the exhaust valves almost vertical.  Nothing you can't do with a milling machine, although they had to go through many cores to get ones with shift in the right direction, and the heads tended to only last one or two races anyway.  But you don't need U joints in the head bolts, you just need to spot face the tops and maybe clean up the holes a bit.  Angle milling is something hotrodders have been doing since the 60s and maybe 50s, turning those 23 degree SBC heads into 20 or 18 degree.

TWR, as far as I know, did not play with altering valve angles.  They did damn near everything else, though.  They milled off the whole top of the head so they could fabricate new cam boxes that would accomodate higher lift.  The rules said the intake port opening must be the same height from the deck as stock, but they didn't say the face had to be the same distance from the block centerline, so they milled the intke face in a whole lot so they could make the ports steeper.  Stuff like that.  (Kind of surprising since the stock whiteblock ports, at least in the '00s era fours and fives, have some of the straightest-entry ports I ever see.

It just occurred to me that we're the wrong group to be asking. You should be asking on a LeMons forum. 

A 401 CJ said:

I’m in no way trying to thread-jack.  Just need a simple answer from NOT A TA and I’ll go on my way.  I’ve had this question burning for a while now and the internet gives mixed answers.  Here’s a golden opportunity while we’re on the subject. 

Did any second generation TA come from the factory with a TH-350?  My know it all cousin, member of PHS - bla bla bla, belittled his brother in law for buying a ‘76 with a TH350.  He said the car was a fake since no TA ever had “just” a TH350.  But then I read somewhere else that starting in ‘75 they couldn’t squeeze the cat in there with a TH400 so they switched to a 350.  What’s the story?

There were 2nd gen TA's with T-350's. Off the top of my head, I'm sure the 79-81 301 engine Trans Am's  came with them and IIRC the turbo versions came with the T-350C with the lockup convertor. Up to '74 I believe all automatic TA's and Formulas came with the T-400 after that I'm not positive which versions came with which auto trans options. They were down to 185 HP by the late 70's so didn't really need a T-400.

While typing the above and thinking about where to get proof. So I pulled up a link for ya to send to your cousin. https://en.wikipedia.org/wiki/Pontiac_301_Turbo