Recently there's been quite a bit of discussion on how to power brake or power launch the auto trans G35. Other posts have addressed the relative advantages of a high performance torque converters.

While I'm not an TC expert, I do have a reasonable understanding of how they work and how a high performance unit differs from our stock torque converters. Please feel free to add your comments.

Modern torque converters (TC) are fluid couplings that also act as torque multipliers during initial acceleration.

Torque converters are comprised of four major components. A cover, turbine, stator/sprag, and impeller pump.

What we see when looking at a torque converter is an external housing which is comprised of the cover and impeller that are welded together. The cover is bolted to the engine's flex plate. The impeller is located on the transmission side of the TC housing's weld line. The TC's snout fits through the front seal and inside the transmission. It fits over, but is not connected to, the transmission’s input shaft. When the engine rotates the TC's housing (cover/impeller) turn at the same speed as the engine.

Inside the TC's housing are the two other major components. The turbine and stator/sprag assemblies.

The turbine is splined to the transmission's input shaft. When the TC’s turbine moves the transmission's output shaft moves and, if the rest of the drive train is complete, the vehicle moves.

The TC's stator is the key to torque multiplication. How it does this... F.M. Typically when an automatic transmission is in gear, but the car's not moving, the transmission is in the stall mode (no/little turbine speed vs. a higher impeller speed). Under this condition the stator relies on the sprag (a one-way mechanical clutch) to hold it in place. When the stator is held stationary, the AT fluid is routed from the impeller, through the stator, to the turbine. This redirecting of the ATF provides torque multiplication during the initial movement of the turbine (the car's drive wheels). As the car accelerates the turbine's speed will approach the impeller's speed. At that point a well designed stator would then be out of the picture, spinning with the rest of the converter.

For our discussion power braking can be defined as one foot on the brake and while reving the engine to a higher than normal rpm level. During this time the TC’s turbine and stator speed is zero and the impeller speed is high to very high.

A word of caution, stock torque converter vanes will not hold up under power braking conditions. Also, reving the engine and dropping the transmission in gear will simply destroy it. The damage from either of these actions can easily be seen when you disassemble the components. I’d be very surprised if Infiniti would honor the warranty from this type of damage.

A properly designed high performance street torque converter will typically have a customized stall speed, reduced impeller-stator-turbine fluid losses, an increased level of torque multiplication, needle bearings instead of OEM thrust washers and furnace brazed vanes for the high fluid pressures that are incurred during power braking.

Power braking with a high performance torque converter allows the engine's rpm to be set at an optimum power point. Combine this with the stator's improved torque multiplication and the high level of potential energy in the form of TC fluid pressure… come to think of it, gramp's auto trans sedan isn't so bad after all.

I'll be very interested in how Gurgen's new TC works out.


DaveO

 

Hey Dave

An excellent post, as always. I can't wait myself. THe thing will be here today (Thr) and is going into my car Sunday, along with the B&M cooler. Will post results asap.

Talkt o you soon. Gotta go to sleep. Tired.

Gurgen

 

Sounds like it will advertantly hurt the car if we use the manual mode in AT to downshift. How about upshifting, if I put the sedan in manual mode and upshift the gear manually. Would this action hurt the TC too? Thank you.

 

GGGGGGGG,

I'm real sure our AT and TC are designed to downshift and upshift in the manual mode without hurting it. Of course it's never good to downshift to too low a gear. Some AT's won't let you shift to a lower gear that would cause the engine's rpm to hit the rev limiter. I don't know if our AT's have this feature and I'm not planning to find out with my car.


DaveO

 

They do, you can't downshift unless the speed is appropriate for that particular gear. It won't let you do it until you slow down further.

Gurgen

 

Ahh . . . the old "voodoo" upgrade. At least that's what we called it back when I was learning about TCs. The advantages of performance TCs have been well known for decades, and extensive testing has been done on them (and published), including variable pitch stator TCs, which provide the best benefit for brake standing 1/4 mi runs.

What it boils down to, especially for a street car, is to choose a TC that gives you better launch torque from the kinetic energy in the brake stand (high stall TC for better torque) without excessive slipping at higher RPMS from being too "loose".

Most of the TC swaps I have been privy to made marginal gains in 0-60 time, but excessive slippage in the final 1/4mi gear often resulted in a slower gate speed. This made the overall strip time about the same. The cars that had major gains in 1/4 mi time had very loose TCs and were not freeway capable as a result. They were fun on the track though, kind of like being fired out of a slingshot.

Gurgen, choose wisely. Too high stall and you loose the top end which may occur long before you reach the 1/4mi mark, Q.E.D. Good luck and let us know what happens.


03.5 Coupe - Black/Willow, 6MT, Premium, Navi, Aero, Sat

 

DaveO, Re "come to think of it, gramp's auto trans sedan isn't so bad after all". Ah, yes. In the '60s it was not uncommon to see 426 Hemis power braked to the point where the rear tires (8"-10" street slicks) would be slowly creeping around.

<font color=blue>Dan</font color=blue>

 

The manumatic is very different in the Sedan than in the Coupe. You have much more control to downshift with the coupe.

Luv My G

 

Shader,

They set my stall speed at 3000rpm. They could go as high 4000, but that of course would mean affecting drivability drammatically. What do yout think about this? Am I really in danger of changing the character of the car to the point of giving up day-to-day drivability?

Gurgen

<P ID="edit"><FONT class="small"><EM>Edited by gurgenpb on 11/06/03 10:51 PM.</EM></FONT></P>

 

"The manumatic is very different in the Sedan than in the Coupe. You have much more control to downshift with the coupe."

Yes! totally for me the sedan manual mode is pretty much useless. You guys should look into swithing the controller chip to whats in the coupe. Its most likely the same exact tranny just the chip programming is different.

Crawford Plenum / Z tube + Stillen Hi-Flow / Borla Dual Exhaust / Stillen Xdrilled+Stotted Rotors
Best 1/4 mile 14.371 @ 100.29, 60ft 2.347

 

Can you explain the difference or share some examples or comparisons of the coupe vs. sedans downshifting? I've had no problems whatsoever with downshifting in my sedan. It's very responsive and I get really good engine braking. Not exactly sure what you're basing your theory on.

'03 AT Sedan | Brilliant Silver | Willow Leather | Sport | Premium | Aerokit w/Spoiler | Nav

 

I have driven the sedan a couple of times as a loaner when I had my coupe in the shop. What I am talkign about it that in the coupe when you have lets say 3 showing on the dash you are in 3rd gear not 1 or 2 or 3. In the sedan its a top gear select in the coupe its the actual gear you are in. For example you might wanna stay in 4th but the sedan migh thave you in 3rd because at that point 4th is the maximum the sadan can use. Say you are in 4th in the sedan and you come to a stop you will still have 4th displaying on the dash, on the other had you will have 1st in the coupe. As you accelerate at that point you will have to manually shift on the coupe whereas on the sedan its like the regular auto mode just limited to the 4th gear. I dont have a clue why they did that in the sedan, I like the coupe MM mode much better .... just my opinion though.

Crawford Plenum / Z tube + Stillen Hi-Flow / Borla Dual Exhaust / Stillen Xdrilled+Stotted Rotors
Best 1/4 mile 14.371 @ 100.29, 60ft 2.347

 

Gurgen,

In my experience, it was nearly impossible to predict the behavior of the car when swapping out the TC without prior data on the same (or similar) car. It depends a lot on the mass of the car, but there are so many other variables that it's just easier to do it and see what happens. Once we got that data though, we could usually tune the TC right where wanted it in one more iteration. I've never done the G, nor have I seen any data on it. You are possibly the first public Lewis or Clark for this work.

TC swaps aren't that popular for several reasons. Possibly the unknown (voodoo) nature of them keeps people away. Also, lots of data for modern cars shows that stock TCs are pretty darn good. Another reason is that such modifications often adversely affect day-to-day drivability.

Anyway, It's good that you didn't max it out from the get go. Certainly 3K will be better at high rpms than 4K. Do you have data on the stock stall speed? How much of a change will going to 3K be?

In the end, you need to be comfortable with the engine rpm at whatever top speed you will likely want; that is where the looser TC trade-off is. Once the TC locks to the flywheel you're fine, and I'm certain the G's tranny/TC is a locking type, or the mpg would stink. Until it gets to that point though you will lose performance as it slips more and more with increasing rpm.

Let me know how it goes. My favorite TC swap was putting a super loose kit into a '72 Grand Prix. It was a 455 with a 400A/T. On launch, it pressed me back into the seat so hard sometimes that my head and helmet turned to the side a bit. Pretty funny, it was street legal, but we had to tow it to the track (PIR) when that TC was in it because it slipped so much on the freeway. It was doing low 12s though, killing everyone off the line as they slowly caught up after halfway down the track. We won some, lost some; in the end I put a tighter TC back in and didn't lose any 1/4mi time, and I could drive it to the track.


03.5 Coupe - Black/Willow, 6MT, Premium, Navi, Aero, Sat

 

How did the swap go Gurgen?


03.5 Coupe - Black/Willow, 6MT, Premium, Navi, Aero, Sat