Mopar Muscle Association UK

Can anyone explain how a high stall converter differs from a standard converter? I'm assuming they are for uprated engines and improve acceleration. I've always wondered but never asked.

They keep your revs at or near peak power/torque. IE a really loose convertor (hi-stall speed) will say let you launch at 5000rpm and it'll more or less do that for the entire run. (5000-redline in each gear.) Andy had a great vid of Tweety on the street and it just stays up on the revs whilst accelerating madly!

There is also another reason to use a higher stall converter. The same reason small blocks have smaller converters than big blocks.

Your actual stall speed has just as much to do with the torque of the engine as it has the stall speed rating of the converter.

If you fit a longer duration camshaft in your engine it moves the torque curve higher up the rpm scale right? This is to make more horsepower because horsepower is torque multiplied by rpm.

The downside to this is that the engine (with no other changes) will then make less torque at lower rpm. In particular at and just above idle. The bigger the cam the less torque at idle the engine will make.

Now this effects stall speed a lot. The more torque you have the higher the rpm any given converter will stall. Less torque and the converter stalls at a lower rpm.

So in an engine with a bigger cam you will suddenly find that you have less stall speed from your stock converter.

Typical symtom of this is when you shift the car from neutral into Drive you will get an rpm drop as the converter drags the engine speed down.

Fitting a higher (just a couple of hundred rpm) stall converter in this case will simply put the engine back to normal.

I currently use a 10" converter with around a 3300rpm stall speed rating. However because of my long duration camshaft it drives the car in a way not much different to stock.

The big difference comes when you fit a converter with a MUCH higher stall speed than you need for street driving. THEN the car gets up on the torque curve when you hit the throttle. It is the same effect as revving the engine and then dumping the clutch on a manual trans.

Hope that explains it.

I have always wondered about Hi-Stall torque convertors n all.

Explained it very well (once again) Dave.


CHEERS

Well explained Dave, makes more sense to me too now ta!
but...whats the story with dual speed converters?

PaulThompson wrote:but...whats the story with dual speed converters?

No idea. Never heard of them. I'm just a simple man and I like the simple things.

Don't put Diana down like that!

Oooh! Wait 'till I show her that Kev. Yours eyes/ears really will be like your avitar after she has finished with you!

Nice explanation Dave!

PaulThompson wrote:.whats the story with dual speed converters?

Paul, I wonder if you are talking about lockup convertors? Torque converters are not the most efficient devices and there is always some slippage internally even under normal conditions (a few % at best IIRC). (One of the reasons why Autos are less fuel efficent than manuals). Later models feature lockup converters, where under certain conditions the engine computer will electrically activate an internal lockup in the convertor so that it becomes a straight through drive - 1:1, with no slippage. It is possible to retrofit these in some cases, with a switch wired to either manually activate the lockup or have it rpm-activated. They've never found much favour in perfomrance applications since a) until recently you couldn't get hi-perf versions (I think you can now?), b) there's more to go wrong, and c) most people with a Mopar don't have fuel economy at the top of their list!!

Thanks Dave and Kev.

Hmm... dunno where i got that idea from now
The lockup sounds a nice idea tho, i'll investigate....

I'd never heard of dual speed convertors but i've found out that Dynamic do a dual stall

Haven't a clue how it works

Opinions on lockups vary....

http://www.carcraft.com/techarticles/85019/index4.html

Still can't find ANY evidence of the existence of 'dual convertors'

Dynamic do a dual pattern convertor as i've got one coming over for Wildman.

I haven't a clue how these things work but the stall on this particular one is
2800 nice and steady on the gas and 3600 if you nail it, and anything in between the two figures depending on how it's driven.

Wildman check out Daves post on this thread for a better explaination of why your car won't tick over in gear.
236 @0.50, 8.2:1 comp and a stock convertor