wildncrazyguy

Just a useful lil FYI. I didnt know this when I just believed the mechanic who put in a higher stall converter and said there you go - free upgrade (of course its what he had available is why he did it) and than I wondered why the vehicle was slower taking off from a stop...

So this is how it works (someone correct me if Im wrong but I am an engineer in transmissions so I know a little about this stuff). The stall speed is the point at which the input shaft begins rotating with the engine at full throttle, hence driving the car. Engineers design the torque converter to match with the engine hp. This is designed so that the stall speed is the same point at which the engine is at max torque. The useable torque of an engine is when it starts dropping and you want max torque at takeoff. If you dont do any work to your engine and simply install a higher torque converter, meaning your car will take off for example at 3500 instead of 2500 engine rpm, this is at an rpm where the engine torque is less, and hence you will have worse takeoff. You also have a "looser" converter which generates more heat. If you go tighter, say 2000 rpm, you are again taking off under less hp and torque. The only reason to install a higher torque converter is if you've done a lot of work to your engine from stock. If your upgraded engine outputs higher hp and torque, now you have a converter that is too tight and you shoule get a higher stall converter and you'll notice a difference. Dont make the mistake that installing a higher converter helps with takeoff. If you havent done a lot to the engine it actually hurts it. Hopefully this helps. PS - Remember, allowing for more torque at a higher stall can risk damage to your transmission. It wasn't designed for it.

dmccain

iTrader: (2)

You wouldn't want to use a 3000 stall converter on a stock 200HP thirdgen. But.. a 2200-2400 stall on a stock engine is WAY better than the wimpy 1400-1600 stock stall converter. A lil more stall and gear even on a stock engine is a great improvement. Too much is detrimental.

wildncrazyguy

so youre saying the torque is higher at a higher rpm and the gm engineers used the wrong tc for this application. Id like to see stock engine performance curves to show that. Hard to believe theyd pick the wrong one w less performance for their application.

PaulyC

You should read through this article.

https://www.hotrod.com/articles/ccrp...ue-converters/

PaulyC

And this one.

http://www.superchevy.com/how-to/tra...ter-selection/

This info is not hard to find, just query the google machine.

dmccain

iTrader: (2)

Would you honestly want me to even start where "GM ENGINEERS" didn't use the best performance application in these cars... It starts at exhaust, induction systems that run out of breath at 4500rpm, junk 7.5in rears, etc etc. Plenty could have been improved upon, look at what they done with the Firehawk. Hell they built a V6 in 89 that was faster than any V8 they ever put out on these cars up until maybe the mid 90s. Yes, more TC would have been one of those things they could have improved on.

DynoDave43

iTrader: (11)

Makes sense with our stock L03s, dmccain. Torque peak is at 2400 rpm. You have sn S-10 4.3L TC in yours, right?

And yes, while that's "best" for acceleration, GM has a lot of variables to balance, not just max. acceleration.

dmccain

iTrader: (2)

I want to say Corvettes got a higher stall converter than the L98 F-cars though very similar in HP engines. I totally agree too much stall is very detrimental no doubt about it. I think going to a 2200-2400 stall is the same improvement all the way around as say going from a 2.73 gear to a 3.23 or 3.42 gear in these cars. But to the OP I do totally agree on the building up heat and mismatching a converter and slowing a car down and possibly damaging it yes.

wildncrazyguy

There's trade offs - Of course in other areas besides torque converters they dont just go for performance. Exhaust systems need to meet emissions and I know for a fact they had to detune and actually make slower on purpose the new cadillac - that one that was like 100k years ago - because it out performed the corvette and GM was not ok with the corvette not being the fastest car they make. Aanything is possible I guess but typically they are designed and tuned to the hp of the stock engine. All those articles shared above (which were good) all emphasize all Im trying to tell people which is just throwing on a higher stall converter likely isnt an upgrade unless you also did a lot of work to the engine as well. If you have 50 more hp than yes - you want to get a different higher stall converter to match your new torque curve from the engine but just throwing on a converter as an upgrade when you've done nothing to the rest of the car doesnt make sense.

wildncrazyguy

How about from someone THANK YOU for sharing this vs arguing with an engineer that has done this for a living.

dmccain

iTrader: (2)

I actually agree with you on many points. Thanks for sharing your knowledge on this subject.

GeneralDisorder

iTrader: (1)

Sorry but the factory converter is NOWHERE near peak torque. L98 peak torque is around 330 ft/lbs @ 3200 rpm. Factory TC stalls around 1600 rpm. There are also more considerations than just the peak torque. Fuel economy, driveability, and preventing unnecessary wheel spin..... a higher stall (than stock, within reason, and better matched to peak torque) converter WILL generally give better off the line performance. Can't say what happened in your case but I have a 3000 stall converter (and race built trans)on a basically stock engine and performance off the line is tremendously higher. Look elsewhere for your slow down. Engineering experience notwithstanding. You're flat wrong on this one.

How high of a converter got installed? You sure the trans isn't slipping? You sure the engine isn't having some other trouble up in the RPM where you now take off?

What exact converter did this guy put in your car? All the specs please - diameter, stall speed..... brand if you have it? You can install junk and you'll get junk results. I have a 3000 stall converter in my setup from a reputable supplier and my junk roasts tires off every light.

GD

OrangeBird

iTrader: (1)

Um , , Ok , Thank You for proving that even an "engineer in transmissions" may not have the full understanding of the subject matter that he should have ?

Dude , really ?!?!?! , you supposedly design transmissions for a living and yet had no clue of how a higher stall converter would affect the performance of your car ?

No thanks required here , Thank You very much .......

GeneralDisorder

iTrader: (1)

I get people like this in my shop occasionally. Think they know better than us "mechanics" because of some perception that we aren't educated and couldn't possibly understand....

For one thing, as a shop owner I have a ton of education just from the experience of building cars, breaking them, fixing them, and finding what works by trial and error. This is actually a much more classical engineering perspective - do the experiment - record the results - change the design - repeat. Take a look at what the Soviets did with the NK33 rocket engine in the 70's by this classical approach. In the west the technology they developed was unknown and considered impossible, or much too dangerous to even try. Why did they succeed? Because they were willing to try and fail as many times as it took. Here in the west we couldn't model it successfully on our super computers so they just gave up and deemed it an impossible problem to solve. It wasn't.

And for another thing entirely - customers are often surprised to learn that I'm a former Software Engineer and well versed in engineering concepts.

This guy doesn't seem to have a clue what the power band of his engine is. Forgot that variable in the equation I guess.

GD

Evilokc

this is interesting to me. I have a stock 305. im upgrading the suspension now and then plan to do the drive train starting in the rear. Im going to do rear end gears then I was thinking an upgraded torque converter. I was thinking 2200-2500 and then get to the motor. cam, heads, intake, exhaust, tune. I wanted to start at the rear of the car because doing al the engine upgrades without the proper support parts is silly. ive done a moderate amount of reading on torque converters and I agree with GD that a small increase in stall should make a noticeable difference in the seat of the pants feel. a mismatched converter would suck though. if I were the op I would be curious to what converter was in there.

Biledriver

GeneralDisorder

iTrader: (1)

Because it was a junk converter. Probably too large a diameter. Like I said - I have a 3000 stall converter and my stock LB9 burns tires on command.

Also - you don't call them "stall converters". ALL torque converters have a stall speed. When someone says that you instantly know they have no idea what they are talking about. The term "stall converter" is meaningless. By that terminology the stock converter is a "stall converter" too. It just stalls at 1600 rpm, not 3000 rpm.

GD

RS Chris

You don't really sound like you know what you're talking about. Some of the info above you posted was right, but most of it was just second hand B.S.

RS Chris

Does it really matter the exact term? You know what he's talking about. That's like complaining about someone calling a crescent wrench a speed wrench, or thumb wrench. It's all the same thing. If I said fluid coupler you would know what I was talking about, right?

GeneralDisorder

iTrader: (1)

It's not the same thing to the person using the term because they are under the impression that a "stall converter" is somehow different than what their car already has. It's not. The term isn't the problem - the fundamental lack of understanding is the problem. It shows *for certain* that whoever is using that term shouldn't be the one anyone listens to on the subject.

GD

FART_NUGGETS

I run the V6 S10 (Daaco) converter in my stock 305. Stalls around 2200. Huge improvement off the line, and still completely driveable including lockup.

3000R is way too high for a stock LB9 or L98.

kaos420

"ENGINEER" LOL

GeneralDisorder

iTrader: (1)

Eh I don't know about that. I have one because it came with a trans I bought off a friend. Low usage race trans because the car got wrecked. Works just fine. I did have to put in a stock vette governor because the thing wanted to shift at like 5200 and it was winding out the little LB9. But it actually does great with the 3k converter. Non locking though so had to add some additional trans cooling and the fuel economy is **** poor. But that's not important to me since my shop is 10 minutes from my house and the car is for fun and advertising. With the 3.70 gears, 1.6 rockers, headers, and custom tune I feel like it's probably getting as much off the line performance as you could ever likely see from an LB9 with only bolt on's.

GD

dmccain

iTrader: (2)

I run the same S10 torque converter behind my L03 and I figure it's around 2200-2300 stall. I think it's perfect for a street car and will run the same thing when I drop my mild 350 in. I had an 82Z28 with a 3000 stall behind a 350/ Th350 years ago but it was well over 300+ HP engine. I wouldn't want a 3000 stall on a 200-250hp engine it's just not a good match for a daily driver in my opinion.