what stall convertar, and tranny should i use? - Page 2 - Hot Rod Forum : Hotrodders Bulletin Board
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  #16 (permalink)  
Old 02-04-2011, 05:28 PM
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Quote:
Originally Posted by F-BIRD'88
No I`m not kidding. High stall converters `cruise `very well on the hiway when matched to the right rear gears.

The converter coupling at part throttle while `cruising`is quite good in fact.

One of the biggest mistakes many people make is not picking a converter and gear combo to match the engines power band and assuming that a high stall or gear will be evil.



If you want to get the power of a `thumpr cam`and go fast you need to the correct gears and converter to use the power.

When tuned correctly this type of setup is actually quite good on gas.

many people combine a high stall with the wrong gear and then complain about slippage or....
Well your info seems to contradict yourself. You say a high stall is good, but then too high will cause slippage. That was exactly my reason for questioning a 3500 stall. That converter will only be locked up fully and not cause slippage when he's on the freeway unless he constantly keeps it above 3500 rpm around town. Having a converter with a stall speed that's higher than what you will normally use driving around town will only create excess heat, and gas mileage will be grossly affected by hainv to use lower range in the tranny to keep it above 3500 to lock it up all the time.

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Old 02-04-2011, 09:36 PM
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Quote:
Originally Posted by 1971BB427
Well your info seems to contradict yourself. You say a high stall is good, but then too high will cause slippage. That was exactly my reason for questioning a 3500 stall. That converter will only be locked up fully and not cause slippage when he's on the freeway unless he constantly keeps it above 3500 rpm around town. Having a converter with a stall speed that's higher than what you will normally use driving around town will only create excess heat, and gas mileage will be grossly affected by hainv to use lower range in the tranny to keep it above 3500 to lock it up all the time.
Mistake is thinking it is like a slipper clutch in a go kart, that it has to rev at least 3500 to do anything or lock up. They don't work like that. A 3500rpm stall converter is only 3500 stall under WOT, at lower throttle openings the converter will couple up at a much lower rpm. They do not slip like crazy at cruise speeds, that is a myth perpetuated by the car magazine idiots.

I've cruised a 4500 and 5200 stall converters around on the street with absolutely no problems, and so have 1000's of others. Doesn't slip badly or make a ton of heat in town at all...unless you are leaving every single intersection like it was the final round at the US Nationals.

I agree F-Bird is exactly right, I feel the same way. 95% of all rodders buy too low a stall based on this false fear of it "slipping like crazy if my rpm is too low". This is one of the most common performance mistakes I see.
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Old 02-04-2011, 10:37 PM
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I'm not mistaking a torque converter for a clutch. What a torque converter does was thorughly covered way back in 1969 when I was in GM training school. I do understand what a torque converter is, and it's name truly explains what it does. It transfers engine torque to the drive components.
If the torque converter has too high a stall speed it is inefficeient, and never "catches up" up to engine speed. The stall speed of the torque converter is the speed when 100% of the engine's torque is transferred tothe transmission, and the engine and torque converter are going the same speed. Prior to that time the two are going at different speeds and the torque converter doesn't fully transfer torque, and it builds excess heat, which is cooled through an external cooler.
I'm sure you know some of this, but hopefully some will get a clearer picture of what a torque converter is and does.
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Old 02-04-2011, 10:46 PM
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Regardless, the amount of slip is not excessive at light throttle and/or cruise speeds w/a 3500 RPM stall speed TC- and that's where you are mistaken.
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Old 02-04-2011, 10:54 PM
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You are confusing stall speed(stator sprag locked, stator fins redirecting fluid at maximum efficiency, multiplying torque at the converter designs maximum rate(usually between 1.7 and 2.2 to 1 in most performance converters) with the speed at which the converter "couples"(stator sprag is no longer locked and converters driven turbine has matched (or nearly matched, never is 100% unless it is a lock-up clutch equipped converter) the drive turbine speed at lower than peak loads and power inputs.
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Old 02-05-2011, 12:17 PM
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Quote:
Originally Posted by 1971BB427
I'm not mistaking a torque converter for a clutch. What a torque converter does was thorughly covered way back in 1969 when I was in GM training school. I do understand what a torque converter is, and it's name truly explains what it does. It transfers engine torque to the drive components.
If the torque converter has too high a stall speed it is inefficeient, and never "catches up" up to engine speed. The stall speed of the torque converter is the speed when 100% of the engine's torque is transferred tothe transmission, and the engine and torque converter are going the same speed. Prior to that time the two are going at different speeds and the torque converter doesn't fully transfer torque, and it builds excess heat, which is cooled through an external cooler.
I'm sure you know some of this, but hopefully some will get a clearer picture of what a torque converter is and does.
Back in 1969 GM did not have any good high stall converters.
All GM at the time had was a modified 12" for the L-88 corvette and a 11" for the power glide for straight sixes. They both stunk.
In 1970 thye came out with a 10" converter for the vega. it gave a high stall but also slipped a lot in anything else but the stock vega 4cylinder.
This is where high stall converters got their bad rep.

Good aftermarket made 10" high stalls cannot be compared to the old stuff.
Event thou the full throttle max stall is approx the same, the internal modification so the converter components and clearances between them makes a huge difference in overall efficiently (power transfer, ET/MPH) and over all feel (driveability).
My 10" B&M super hole shot converter is way better in all respects than the stock GM 10" Vega converter which is what they start with.

There is a big difference between the stock converter core they start with and the finished product.

Too much 1969 era "school" and not enough practical real world experience.
Torque converters never "lock up" 100%. ever. even stock converters.

Torque converters are torque (input) sensitive and load sensitive.
When the gear ratio is correctly chosen for the application, the torque converter has only a small load and input on it under hiway cruise conditions.
like a 10" converter with 4.10's.
There is very little slippage or heat buildup.

If you wimp out and match the converter up with a 3.42 gear, then you may have issues. The car won;t go good either cause you got no gear.

If you want to win a light to light race you need to leave the line hard.
You need to launch the car way up on the engines torque curve. ( within 500rpm of peak torque.)
The bigger the cam the higher the torque curve.

Driveability:

The only time you really notice the converter "dynamo effect" or "slippage"
is at very low vehicle speeds and/or going up steep hills (high vehicle load) and small throttle inputs. Takes about a week of driving to get used to it compared to a "stock converter".

Short of towing a trailer up long steep hills these converters perform very well overall in street machine applications. Don;t wimp on the converter and don;t wimp on the gears.

Last edited by F-BIRD'88; 02-05-2011 at 12:37 PM.
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Old 02-05-2011, 01:09 PM
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If your initial or "old school" experience with high stall torque converters was with a 10" GM vega converter swapped in a th350 or th400 , yes you will have a justified poor opinion of high stalls on the street. Particulairly if you don't put gears in the car too. A lot of people tried this vega converter swap with 3.42's or 3.55's and as expected were very disapointed.
The vega converters used to slip a lot and heat up behind a V8.

Modern custom built converters even 8" race converters are much more efficient. A bud here runs a full race 8" ATI treemaster converter. It is actually very "driveable" And goes like hell...!
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Old 02-05-2011, 03:03 PM
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I guess from your replies that you assume I've not been around cars or trannies since 1969. I give up, you're way too smart for me.
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Old 02-05-2011, 03:35 PM
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Quote:
Originally Posted by 1971BB427
I guess from your replies that you assume I've not been around cars or trannies since 1969. I give up, you're way too smart for me.....You say a high stall is good, but then too high will cause slippage.
No I did not say that. I said a high stall should not be matched to a numericily low gear or its a mismatch.

You are recomending based on what you have in your 427 Camaro.
This not a 427 in a tank Camaro or 4X4 truck. It's a cammed up 350 SBC that has no torque below 3000 rpm in a light weight Malibu w/ 4.11's.
And the poster wants to go fast with it.

1. the factory gm 12" "2200 stall" will give you 2500 stall behind a 427.
A typical 11" "high stall will give you 3400-3500 real stall behind a 427BBC.
A typical "10" "3500 stall" will give you a 4100-4200 rpm real stall behind a 427. (with traction)

A mild moderate cammed 427BBC has so much available low end torque you don't need much converter or gear. (especially on typical street tires) so you can get away with a stock or near stock converter stall.

Try to transfer your setup to this little "thumpr" cammed up SBC Malibu and you will have a slow slug. But if the poster goes with a real deal 3500stall 10" 4.10's and the good tires and rear suspension traction mods for his Malibu he will leave you standing at a stop light like you 427 engine just shut off.
And pass all the gas stations you have to pull into.
And cruise on the hiway very very well.

Chassis load: your BBC Camaro weights 3860# w/driver.
His little SBC Malibu Weights 3350# w driver if he's lucky.
Big difference in how the converter is going to work and feel when driving.

You just don;t want to get your doors blown off by another lil SBC Malibu, that all.

Peace brother

Last edited by F-BIRD'88; 02-05-2011 at 03:50 PM.
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Old 02-05-2011, 03:50 PM
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Quote:
Originally Posted by jeffery wells
o.k. im in the process of building a 400hp 350 to put in my 1980 chevy malibu, it has a thumper cam, performer intake manifold, 650cfm carb, and i just had the stock vortec heads machined out.
i have a turbo 350 transmition and i dont know if i should have a shift kit instaled or get a beefier tranny all together, and my other problem is i dont know what stall converter i should use, i have access to a tci 2400, but i dont know if it will give me the launch im going for, im really building this as an every day driver, but, there are so many imports around here that i cant help but run em from light to light, anyone with any sugestions would help.
I would question why you want to use a thumper cam- there are far better cams that make more power than those "bark w/o much bite" cams.

I know- you want the "sound", right?

AFA a "Performer" intake, if you add "RPM" to that, you'll have something worthy of your time and trouble.

Choose the torque converter to compliment the cam/engine's powerband. Often a "tight 10 inch" TC works well w/a performance SBC build, but this is a generalization- the exact TC will depend on other things besides the engine, like weight, use, traction, chassis set-up, etc. Use a tranny cooler.

A TH350 w/a solid rebuild- with a shift kit- will suffice- it will break the 7-1/2" diff way before the transmission breaks.
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Old 02-05-2011, 04:08 PM
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The key to stock 7.5" GM rear axles is
1. eliminate all wheel hop. (see my Malibu G body traction mods)
wheel hop is a crank, converter, transmission, U joint and rear axle killer.
(launching with full traction on slicks at the drags is easier on the rear end than any wheel hop) $$$Wheel hop$$$ will cost you money even with a Ford 9".
(the small diameter high stall 10" converter actually acts to reduce drivetrain shock if you do get some wheel hop. Acts much like a shock absorber.
It's your friend)

2. proper ring and pinion gear setup. (pay a drivetrain pro to install if you don;t know how or can;t be bothered to spend the time.)
If the gears make noise, they are telling you something.
The set up is not right.

3. stable pinion gear bearing preload spacer (crush sleeve) Eliminate with a spacer and precision shimming if possible. Otherwise make sure the crush sleeve "crushes" correctly and holds the bearing preload.

4. ring gear back lash. just a matter of setup patience.
recheck the gear back lash and pinion nut torque after a few 1000 miles.

5. replace worn axle bearings. Old worn high mileage bearings an seals will let you down.

6. the factory GM Dana differential is weak. The Coo coo clock GM Gov lock posi is a time bomb. If someone gives you either one, give it back.
Get a NEW aftermarket Auburn Gear posi differential or a NEW Eatons Posi.
Never buy a used posi from any one. its like putting use oil in your pan.
(no body removes and sells a differential unless its fubared)
Buy new. And install correctly.

Keep an eye on the pinion yoke nut. (some times they come loose, simply maintenance)

The 7.5" rear is plenty strong if you take car of it.
Get a drive shaft safely loop and rebuild the old U joiints.

Last edited by F-BIRD'88; 02-05-2011 at 04:30 PM.
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