[Tim]

I’ve just had a B and M Superholeshot Converter installed in my 727 (and very pleased with the results I am too!).
I understand the basic principles of how a performance converter allows higher stall speeds, letting you bring the revs up into your torque curve on the line, and providing a ‘slipping clutch’ effect letting the engine rev quicky up the rpm range on each shift, but my question is (finally): are the internals (stator, etc) of a hi- po converter more mechanically efficient than a stock unit, thus letting more horsepower through to your rear wheels?

[dave-r]

It is a matter of clearence I think. I only have a VERY basic grasp of how a converter really works.

My understanding is that the two sets of blades in a stock converter (one set driven by the engine and the other fixed to the trans input) are very close together. As engine speed picks up the oil trapped in the driven blades forces the blades fixed to the trans to rotate with them.

Building in more distance between the sets of blades means that the engine has to go faster to drive the system. In fact I think in the early days of performance the guys used to just cut open a stock converter and hammer the blades a bit to increase stall.

Now i can see how engine speed will effect this system. what I do not understand is how torque effects the stall speed. I think i have a book with an explanation in. Maybe I ought to read it?

All converters are slightly inefficient. ie they slip a bit unless you have the 'lock-up' type. A well made converter slipps less than a cheap one (they say). Slippage can be anywhere between 5% and 10% in general. Of course it is always slipping below the stall speed.

Where is our trans expert???

[transman]

Tim.
email me at home.
gshortre@telus.net

I can help you.
Graham

[transman]

Ok, guys, I've got some time this morning, so let's see if I can help you.
Dave has part of the question answered, ie the blade issues.
In the converter industry, to increase stall, you modify the vane angle on the pump (hub part of the converter) and also on the turbine of the converter. We also modify the stator to allow more oil to pass through it, by machining the openings in the stator. The clearances are very strict, and we do not increase stall speed by increasing these clearances. Industry standards dictate the following general rules.
A modified 12" diameter converter will give you 400 to 800 rpm stall over a stock converter, with MOST stock converters stalling at 1400 to 1600 rpm.
A modified 11" converter will stall approximately from 2200 to 2700 rpm.
A modified 10" converter will stall aprroximately from 2800 rpm to 3500 rpm.
A modified 9" converter will stall from 3500 rpm to 4500 rpm.
A modified 8" converter will stall from 4500 rpm to 65-6600 rpm.
A modified 7.5" converter will stall from 6500-7500 rpm.
You notice that the smaller the diameter, the higher the stall.
There are many things that must be taken into consideration in building a high stall converter, the engine, the rear axle ratio, tire size etc. weight of the car. etc., because improperly applied, a high stall converter can be the worst investment you will ever make.
I always ask my customer who is looking for a high stall converter, what he is using his car for, is it a daily driver, weekend cruiser, or is it mainly going to be for racing. This helps me determine what converter is best for his application. When you are looking to buy a converter, please consider the application. My Challenger for example, cruising down the highway at 70MPH, has the engine turning over only at about 2800 rpm, therefore, if I do a lot of highway/street driving, a converter with a stall speed over that rpm would be a poor choice.
If anyone on this board needs a recommendation or my help in choosing a converter (and I don't care what brand) drop me a note. What I'll want from you is, engine size, transmission type, rear axle ratio, rear tire size, cam specifications, horsepower/torque figures, car weight, and what you are going to mainly use your Challenger for.
Cheers
Graham
Transman

[dave-r]

You're a good man Graham.

[Tim]

Dave/ Graham,

Thank you for posting this information. I’ve heard it said that converters cause more confusion and disappointment than any other performance upgrade. I got lucky, mine goes like a bugger!

Is a performance converter mechanically more efficient than a stock factory unit? In other words if you put a car with a stock converter on a rolling road and measured the torque at the rear wheels, and then swapped in a hi-po converter and re- measured it, would the second reading be higher? Would it also make any difference to where the peak output was at the rear wheels?

As I’ve said earlier, I’m more than happy with my converter, I’m just interested in gaining a better understanding of how they work.

[transman]

At low speeds (below its' rated stall speed), a high stall converter is not very effecient. Once it is past its rated stall speed and if it has been carefully constructed, a high stall converter acts just like the factory converter, approximately 95%+ effecient.
At work tommorrow, I'll get the stall speed ratings on Mopar high stall converters and post them here.
Graham

[transman]

HERE ARE THE STALL CHARTS WE USE AT WORK FOR A BASE LINE FOR MOPARS.
318 CU IN. 11" 2400 RPM
10" 3000
340/360/383 11" 2600
10" 3600
413/426/440 11" 3000
10" 3500
HEMI 11" 3000
10" 3500

Remember these are the base lines. Depending on what you are doing with the car or what you intend to do with the car, these stall ratings will vary. Something else I'd like to point out, is a RACE converter is typically a unit custom built for YOUR particular application.
Graham