Street Torque Converter Preference

Bought a 258mm Coan Max performance 6mnths ago $902 shipped, no fancy billet or forged cover or anything,came in a brown box with nothing on it or anything to hold it from sliding around , just a kickass converter , changed my combo from what I had speced to them so it stalled 1000rpm less than the target rpm but that was on me , called and explained what I had done and that it will.be prob a year b4 new combo is ready to go and off the dyno, he said no worries he'd mark my file as "under construction" and to send it back when im ready to restall it and shipping would be all id pay, thought that was awesome that they would wait that long, most verter guys give s free restall but have a time window in which to do so.

 

Larry, if you could wire in a throttle rate sensor, you are the "wizard", after all, you could have the best of both worlds. This sensor measures the rate at which you open the throttle, and could be wired to put your converter in high stall when you hit the go pedal, as opposed to a Sally take-off (read can't spill the lady's drink or make her clutch the door handle/dash/a pillar.)

 

Larry,


"K-factor" can still be handy even though probably not for figuring out torque multiplication like Chris already mentioned. It can help someone to estimate how a given converter behind a known engine will behave behind a different engine. The kicker is you'd have to have the engine dyno sheets for both engines in hand to do the calculation. The key word is "estimate", of course. It's not transmission related though, because to measure stall the input shaft is not moving.


The formula is simple: K = RPM / √TORQUE (K equals stall rpm divided by the square root of torque input)


For example, we test a converter and find that it stalls at 3000 rpm when it sees 400 ft-lbs of torque, so we find K:


K = 3000 / √400


K = 150


Knowing K = 150 for this particular converter, we can estimate what the stall speed of this converter will be if we increase the torque to 510 by rearranging the equation to solve for RPM:


RPM = K x √TORQUE


RPM = 150 x √510


RPM = 3387


So with the increase in torque that the converter sees, we can estimate the new stall speed will be around 3300-3400 rpm. Again, that "estimate" word!


I hope that helps.


Devon

 

Its been awhile since I was in the trans business so I am a little rusty but as I recall there are to many other variables that no matter what the K factor can not account for to make it a trustworthy method.

As I recall the 450 number that the K factor was base lined off of was the TQ rating of the trans a then went from there.

I did want to say, I don't care who's converter you buy. I have had several SP trans combs some as high as 4000 stall, and I don't know how many fix pitch converters and if you are thinking any 3200-3400 high stall is going to act like your SP did when set on the low stall setting its NOT going to happen it is a different deal.

 

I think the switch pitch converter is pretty much rendered obsolete by the new 4L80E transmission with aftermarket electronic controllers. If I were to do it over again, I would absolutely use the 4L80E. They are incredibly stout stock. So, you could get one from a junkyard and buy the $800 aftermarket electronic controller and be ahead of the game. The cool thing about those new transmission with computer controlled lock up is, once you get rolling the converter locks up automatically however you program it to. So you can have the aggressive high stall and still have a good solid lock up at light throttle that is more efficient than a switch pitch could ever dream of being.

 

Did you dyno this engine at all?

 

I agree with everything folks are saying about the VP converter versus today's fixed pitch technology, it really is apples and oranges because of torque converter research and development over the last fifty or sixty years. When you bring lockup and overdrive into the picture, it's more like comparing apples to the planet Saturn, no doubt about it.

If I had a blank check for this street car, a four speed auto with a well built lockup converter would be a no-brainer!

Devon

---------- Post added at 08:41 PM ---------- Previous post was at 08:30 PM ----------

Don't worry about that at all. I haven't been 100% knee deep in automotive engineering since '08, except for some consultant work that comes in here and there. Loved some of it, loving more being away from some of it. I now have a lot more time to do stuff that's dear to me.

Devon

 

Actually, I did chassis dyno the car at the FL2K True Street race. It was a little lean at the time, but it still managed 440 Rear Wheel HP which is probably 520 or 530 crank HP I am guessing. I did not dyno the car with nitrous. Here is the sheet:

 

Larry,

I would be one that would tend to agree that if your going to get away from 1960's tech, then it makes sense to take the step into the 21st century, and go with a modern Electronic controlled OD trans with a lockup converter.

In this day and age, if your willing to invest the $$, there is no reason you can't have your cake, and eat it too, when it comes to transmissions.

Another factor is that you have a desire to go with EFI in the future, and there a some great integrated trans controllers/EFI units on the market now, and more coming every year.

As you know, even though I sell a lot of fixed pitch converters, I have not really been in favor of you changing your car to that, because while there are some great, efficient converters out there, none of them will feel like the 12" converter in low stall. Your simply not shearing enough fluid with the smaller diameter stuff, in a 4000 lbs car.

Everyone has taken great strides away from the loosy-goosy 11" converters of the 70's and 80's, but there are still limitations and physics involved here, and a torque converter is actually a very simple part. While there are certainly plenty of ways to complicate that simple part, Newton's 3 laws of motion have not changed. Only the addition of a positive locking clutch in the converter changes the game completely.

It's my opinion that while there are a lot of great fixed pitch converters out there, for a lot of different prices, for you, a lockup is the way to go.

You will improve your performance, mileage, and driving comfort, as the lockup will reduce your current rpm at speed, and will virtually eliminate any worry over transmission temperatures on long trips, in hot summer weather.

I encourage you to seriously look into the 4L80E options, and I would also advertise your current complete VP trans/Gear vendor/Driveshaft/controller setup on the board... You have a proven combo there, and many guys would love to have it, especially if they can get it for a price less than new stuff costs.

I believe that you would be as informed as possible for all the different options available at that point.

My .02c

JW

 

Like I said, once you go with a lockup converter it is TOUGH to go back to a regular converter... The extra slippage, loss of fuel mileage, extra heat, etc are all a result using a non lockup converter on the highway.

I am using steering wheel mounted paddle shifters, a computer that I had custom made for $220, and I will be able to bang through the gears without taking my hands off the wheel. On the highway I can flick the switch and go to 100% lockup.

My 4L80E was built to handle 1000 HP and it was not that expensive really... The custom converter came from Hughes and list price was $999 but I got it for $750 due to a discount for "the turbo forums" members. Hughes advises to only lockup the converter when putting under 600 HP through the trans. At highway cruising it is fine to lockup just not under full throttle blasts.

 

What Jim said,except keep the gear vendors and install it on the 4L80E make it an 8 speed and overdrive the overdrive on the highway! That engine should have enough torque to do that at cruising speeds.:TU:

But if you're going the fixed pitch for the current setup,you need to to a couple of runs with the current setup before you swap it out. Because the last time you ran you didn't have a tach at that time(if I recall correctly) and your shifts were probably low on the RPM and I think you were in 3rd instead of 2nd O/D. By just optimizing your shifts probably would be enough to get kicked off the track.:Brow:


Derek

 

What I have been saying since the other thread. Find out why the mph is low, stall speed or what ever, the mph should still be in the zone. If the car makes in the 500hp range @ 5000rpm and you shift it there isn't it going to run like a 500hp+ engine until it hits 3rd gear?

This is real important for anyone that is et hunting Not only is it real important to retest with the current set up so to have a base line but It is also very important to know the rpm as you cross the finish line so you can figure out torque converter slip %.

 

I got my 4L80E out of a 2 wheel drive 92 GMC 3500, and had it rebuilt with all the good stuff. A bellhousing adapter is needed unless a person goes to a LS engine LOL. The spedo is a hassle to setup but otherwise it is pretty straight forward deal. The 4L80E is a great setup for heavy duty applications.

 

There is a retrofit tail housing now that accepts a mechanical speedo drive.

JW

 

I have been in favor of the 4L80E for a long time here, I guess I was about 10 years ahead of my time on this one:laugh:
This is from 2004, post #19 http://www.v8buick.com/showthread.p...-Gear-Vendors-Overdirve!&highlight=compushift

http://www.v8buick.com/showthread.php?166567-4L80E-Info&highlight=compushift

Anyone thinking about using a 4L80E Chris at CKPerformance is real good and the prices look good also, here are some options and prices http://www.ckperformance.com/resources/GM4L80ETRANSMISSIONS.html

I still think the Compushift II is the way to go.http://www.hgmelectronics.com/products-compushift-controllers/compushiftii

As far as the best years for 4l80e cores, I would look for a unit built from 1991 part way through 1997 before they went to the center lube and change a few hard parts etc late 1997. I seen lots of 1998 and later 4l80e's with blown up gear trains.

When looking at the early 4l80e's these units came with the bolt together wiring harness so if you see one with the snap together harness chances are its been gone through at some point.

 

Thanks for chiming in Bob, I knew there was a couple other guys with the same Coan converter, and I remember you and I getting ours around the same time. Wow time flies!

Larry, looking over some of your posts and looking at your build, you and I share a fairly similar combo. Our motors dyno'd roughly the same hp numbers, I think I run a little more compression, but your head flow #'s are better than mine and I hun the 290-08 TA flat tappet as apposed to a roller.
So power wise were pretty close. My car weighs over 4000 with me in it and I trap 121mph. You run the same 3:73 gear as I do, so something must be a little off if your trapping in the 115 range, and it could very well be the trans/converter. Again, I'm just comparing our combos and I understand there are alot of variables in the equation.
Just curious, have you ever calculated your converter slip? Just a thought.

 

Honestly the converter is prob definitely hindering Larry but there's so much other tuning the car needs, the converter should be last on his list of improvements. He swapped from a quadrajet to the holley hp1000 at the track and the car didn't pickup?? Hello??? Some things not tuned efficiently?? We knew the year before the car wasn't shifting at 6000 but did nothing to change it in a year?? Larry doesn't remotely beat on his car the least bit on the street. That's his perogotive..sometimes doing too much research is not a good thing, you get 20 people giving 15 different opinions and have to sort through all of it.. find one person that you trust and go with his knowledge and experiance.Your happy with Jim's engine, go with one of his converters, if he says it will work great with your application. BUT get your car to 100% as it is now. You can change your converter pick up little bit but the rest of your combination is still off
Again going to the track once a year isn't going to get a car tuned, it takes time and proper knowledge of what direction to go in
Work on that then think about converters.if that's what you want?? If your totally happy and content how it drives on the street and runs cool then leave it alone since that's what you do 99% of the time. And all talk about mpg... really who cares I doubt these are our everyday drivers, were talking about making power not mileage. Let's be serious here just my .02