I am toying with the notion of having a TC installed in my car with a corvette servo and shift kit. I will need to have it installed because I know nothing about transmissions.

My question is am I really going to get any worth while performance change out of all the money???

I am not going to race the car at the track but it is nice knowing that you have the torque and HP there if you meet someone in a mustang!!

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1989 Pontiac Formula L98 Ported Plenum, Edelbrock 6085 Heads, Edelbrock HI-FLO Intake, BBK 52MM TB, Edelbrock TES, FlowMaster 3" Exhaust, Dual Cats, 3.27 Gear, CompuCam 2032 Cam, 1.5 Rollers, Ed Wright FastChip, Accel Super Coil, MSD 8mm Wires

 

Yes. When my tranny **** the bed, I bought a 2000 stall TC (forget the brand, it was a no-name heavy duty TC) because I had to replace the TC anyways. I figured it made the most sense to go with something better than stock. This one has 400 RPM more stall than the stock unit did. To tell you the truth, it only feels a little different from stock. The car creeps a little less than it did with the stock TC. Punching it from a stop feels a little better than the stock TC did... it 'jumps' to a higher RPM than the stock unit did. Many will tell you that a TC will soften your shifts. This may be the case with a TC with 2500+ stall, but my shifts are as hard as I ever would want them to be... hard enough to make the car get squirrely on the 1-2 shift and lose traction. When it comes to aftermarket TCs, you usually get what you pay for. The Vigilante TC that everyone loves so much is the best example of this. The price is $600+, but it puts out a ton of torque multiplication. This is like having better gears. Some models of the Vigilante automatically lock the torque converter clutch at wide open throttle in 2nd through 4th gear, eliminating slippage. Pretty cool, isn't it? If you're looking for a good TC on a budget, I recommend the Turbine Technologies 2400 stall converter. It's 12", same as stock, and will feel a whole lot better than the stock TC does. Plus the price is awesome, $160 shipped I believe. 'ws6transam' can hook you up with one.

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91 Trans Am WS6
Bright White
5.0 TPI auto
Flowmaster 3" 2 chamber catback
Trans Go shiftkit
2000 stall converter

Built on Wednesday

 

From your sig, it looks like a bunch of modifications have already been done. Chances are you've moved the power curve up in the engine. A higher stall converter will allow the engine to build rpm up quicker to where the the power curve is. This way the engine isn't slowly building up to that rpm.

I have a 3800 stall converter in my race car and with the new BBC it might be too low. The camshaft I had in my 383 started building power around 3500 rpm. When I launch, the rpms quickly come up with little car movement until the stall speed cuts in. This allows the car to be in the engine's power range faster.

Now in a street car you operate more in the idle to 4000 range. A stock converter can be around 800 rpm so the car will actually creep forward at an idle. Lets say your power range is now 2000-6000. That stock converter will start lugging the engine below where it wants to make power. The converter is actually holding the car back since the engine isn't making as much power at the low rpm. If you install a 2500 stall converter, the car won't creep at an idle. The rpms would have to be brought up before the car would start moving. Normal driving would still be the same. The rpms may be a little higher at very low speeds because the converter is slipping when under the stall speeds. However when you floor it, the converter will allow the engine to quickly rev up to the stall and the power of the engine will give you faster accelleration and ET.

The proper way to chose the stall speed is to have the engine dynoed. Not a chassis dyno. Then you pick a converter that stalls a couple of hundred rpm under the peak torque. This isn't a good option for a street car since you need to pull the engine. All you can do is guess what stall speed will work best. Call the torque converter manufactures and ask. They'll want to know cam specs, car weight, rear end gearing etc since those all will determine what stall speed will work best.

When installing any higher stall converter you should also install an external cooler. High stall converters generate more heat because of how much heat they generate when slipping under the stall speed.

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Follow my racing progress on Stephen's racing page
and check out the race car

87 IROC-Z Pro ET Bracket Race Car
383 stroker (carbed) with double hump cast iron heads and pump gas
454 Big Block almost ready for the 2001 racing season

Best results before the 383 blew up
Best ET on a time slip: 11.857 altitude corrected to 11.163
Best MPH on a time slip: 117.87 altitude corrected to 126.10
Altitude corrected rear wheel HP based on power to weight ratio: 476.5
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

[This message has been edited by Stephen 87 IROC (edited January 17, 2001).]

 

Stephen; Is it difficult to install a TC and what manufacturers do you suggest? My car only has 29,000 miles on it so the trans is in pretty good shape I would think. Any suggestions??

 

Everyone has their own favorite manufacturer. I guess it all depends on previous experience. I use a JW converter. If you search in the archives for other topics on torque converters, you'll see that "you get what you pay for" is the best way to describe converters. A cheap bargain basement converter is usually just that. The one I have is a 10" 3800 stall. Designed for up to 500hp. No nitrous or transbrake use. If I exceed the limits of the converter I can't really go complain to the dealer that it was their defective part. I may need a better converter with this new engine. A 8 or 9 inch one with anti-balloning plates that can take more power. However the cost will be double or more than what I paid for this one.

Installing it is simple. Drop the tranny as per instructions in a Haynes or Chilton manual. Pull off the old converter, install the new one and reinstall the tranny. Recheck the fluid level after you start it up and add on an external cooler.

 

With the right stall speed, you should see a noticeable difference, especially from a stop. I have an 87 IROC L98, the only thing not stock being the torque converter. I don't know the manufacturer, the stall is supposedly 2250 rpm. The difference could be felt almost in direct proportion to how hard and fast I punched the accellerator. After driving with it for a few months, I came to believe the stock converter would probably suit me better. The reason for this is, like you, I do not race at the track, and I don't often (from a standing start) race on the street.

When you're driving aroung town at low rpm, the higher stall speed means most of the time the converter is not locked up and less efficient than if it were locked up. To some degree this reduces fuel economy, but this is not why I think the stock TC would be better for me. I'll try to explain as briefly as I can.

On the occasions when I do want to go fast I am usually already in motion. Let's say I'm cruising along at 1700 rpm and a Mustang passes me and I decide to chase him. I accellerate hard, lockup occurs, revs drop, the transmission downshifts and the converter is slipping. While its slipping and until it reaches lockup, I am going almost nowhere. This may be because I have a poor quality converter, I don't know. It just seems to take too long for the power to get to the ground. This may be what people mean when they say their shifts are softer. With the stock converter in the same situation lockup occurred alot quicker, and even though I was lower in the torque curve when it locked, response was better.

I've thought about putting in the TransGo shift kit and I'm sure it would make my shifts harder, but not sure it would make a big difference in the situation I described above. MrJ and Stephen, what do you think about this?

fast89, Back to your question. Since I noticed the difference in my stock L98, and you have quite a few mods, I would expect you would notice a big difference in the way your car performs.

 

I'm not sure what you mean about lockup. Unless you rigged up a torque converter clutch lockup switch, the tranny shouldn't be locking at wide open throttle. The TransGo shiftkit wouldn't change the problem you describe. Is your car 100% stock besides the converter?

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91 Trans Am WS6
Bright White
5.0 TPI auto
Flowmaster 3" 2 chamber catback
Trans Go shiftkit
2000 stall converter

Built on Wednesday

 

MrJ,

The engine has been rebuilt (.030 over) and I have foam air filters instead of paper, and the converter. That's it. In the scenario I described above, I'm not necessarily at WOT, though sometimes I may be. By lockup I mean the point at which the converter is no longer slipping.

 

To understand converter lockup, you need to understand how a converter works. When the converter input is turning the same speed as the output, it's considered locked up 1:1. Read these web pages.
http://www.calgarydragracing.ab.ca/s...converter.html http://www.calgarydragracing.ab.ca/t...onverters.html

 

If you get a "locking type" convertor (and you should), you can compensate for a higher stall by adjusting the TC Lock speed in the eprom. You have a variety of controls right in the eprom which can allow you to have your cake and eat it too.

The controls available are: 4th and non-4th, minimum speed to lock/unlock, min/max MAP at various rpms AND the minimum highway speed to cause it to remain lock.

By getting a higher stall speed AND controlling those settings you can make it so when you are at part throttle, it locks up just like the stock covertor but when you stomp on it, it unlocks. And by setting the highway speed (stock eprom is 75 mph), you can keep it lock to maximize your gas mileage. Just play with it to the settings you like; you can even burn a setting for the drags and a different setting for the city or highway.

 

I am confusing lockup and stall speed. But looking at Phil Parson's articles, it is easy to confuse lockup and 'the engine RPM level at which the torque converter "locks"'

This is what he says in Torque Converters Explained:

'One traditional problem with automatic transmissions is that the converter never achieved a true coupling; that is, there was always a small difference in speed between the impeller and turbine. This was due to the fact that the converter uses fluid for power transfer, rather than a direct mechanical coupling. Thus, the high speed efficiency of automatics suffered, because some of the engine's power was always lost as heat from slippage in the converter. This problem was alleviated somewhat by the development of the lockup torque converter. This type of converter uses a clutch (similar to the type used in stick shift transmissions) to create the needed direct mechanical coupling, which eliminates slippage at highway speeds. The clutch is usually engaged at steady cruising speeds by an electrical solenoid in the transmission. Some drag racers use a switch to manually engage the clutch during runs, shaving some time off of the 1/4 mile.'

Then in Selecting the Right Torque Converter, he says:

'So what is stall speed? This is another widely misunderstood term. In the simplest of definitions, stall speed is the engine RPM level at which the torque converter "locks" and overcomes whatever resistance is present to turn the wheels. This resistance is the weight of the vehicle, combined with any other factors (i.e. if you have the brakes on). The old definition of stall speed used to be the engine RPM at which the brakes can no longer hold the wheels still at full throttle. This is not exactly accurate, due to the variations in brake holding power from vehicle to vehicle. In other words, in two cars that are exactly the same weight, horsepower, etc., the one with weaker brakes will display a lower stall speed, even if it really isn't, because the brakes will lose their grip at a lower RPM. The most accurate method for determining actual stall speed on your vehicle is to launch the vehicle at full throttle, and note the rpm at which the car actually takes off (this generally requires a partner watching the tach). This will be quite low on stock vehicles - around 1500-1800 RPM, slightly higher if the engine has been modified.'

In my description in the previous post of how my car performed under specific conditions, I was using the term lockup in the same sense he uses it when he says 'RPM level at which the torque converter "locks"' in Selecting the Right Torque Converter. Thanks for the input.

[This message has been edited by 87kevroc (edited January 21, 2001).]

 

There are two types of TCs; locking and non-locking. The locking type as the article says "physically locks" so there is no slippage whatsoever. This ensures all the power gets to from the engine to the rear wheels; thus giving full power and maximum fuel economy.

All TCs slip. That's their basic concept of how they transmit power. The higher the stall, the more they slip until that rpm is attained; thus multiplying the power and acting like a "slipping clutch". This is what you want for launch.

Once stall has been attained and you are moving, then if you have a non-locking type, it will still slip slightly inspite of attaining the "stall speed". With a locking type, it will not slip once the locking mechanism is engaged.

The best I can do in translating into "common everday English".

 

Made sense to me and that's about the best way I could have described it also. A typical torque converter will still slip about 10% when above the stall speed. When using a lockup type converter, there is no slipping.

On a further note, years ago someone designed a special racing transmission. It used a 2 speed powerglide tranny but also used a clutch. You could rev the engine to any rpm and drop the clutch. After that it was just an automatic transmission however you had to step on the clutch when you came to a stop. This would allow you to have an infinite launching speed (clutch) and no slippage of a converter.

[This message has been edited by Stephen 87 IROC (edited January 21, 2001).]