What effect does a larger or smaller diamter have?

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Valvebounce

Valvebounce

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I'm a bit of a newbie at the whole Hi stall thing. I've started buying up parts for a low buck build I have planned, and as much as I cant really afford one, I'm gonna have to get a hi stall for it. I've used one of my dads cars on the strip which has a nasty engine with a stock converter, and it really doesn't go like it should. Since we have some parts being shipped down here in the next few months, I'm thinking I best get a converter sent at the same time. (air freight would be HORRENDUS!)

So I took a browse of a well known parts website, and I see along with each converter, they list it's diameter. What effect does the diameter have on how the converter performs/behaves?

I've read on here somewhere that having a standard converter made into a hi-stall is nowhere near as good as buying one that was hi stall by design.
I don't want a converter than will be a piece of crap to try and drive below the stall speed. And it'l definately be getting a decent sized tras cooler.
 
Disclaimer: the following is based primarily on my own deranged reasoning

I believe the diameter to mostly influence inertia. A smaller diameter presents a lower moment of inertia (rev quicker, less torque) while a larger diameter presents a greater moment of inertia (rev slower, more torque). The speed at which a given converter stalls is a function of input power and the angle/shape of the stator elements as they interact with the thing** that I can't think of the name of at present.

Then again, I should've been asleep an hour ago.

** turbine, perhaps
 
Thanks.
from my limited look at one sites selection, I noticed that the smaller diameter ones were more expensive. As much as I don't want to buy a cheap unit, my budget dictates thats what I'm limited too.
 
how dynamic explained it to me was the smaller diameter gives it the higher stahl, and the positive pitch on the veins makes it lock up and be efficient.
 
Good write DJV
doktor_x said:
Disclaimer: the following is based primarily on my own deranged reasoning

I believe the diameter to mostly influence inertia. A smaller diameter presents a lower moment of inertia (rev quicker, less torque) while a larger diameter presents a greater moment of inertia (rev slower, more torque). The speed at which a given converter stalls is a function of input power and the angle/shape of the stator elements as they interact with the thing** that I can't think of the name of at present.

** turbine, perhaps
Click to expand...

Inertia and the amount of fluid it use's and force's out of the converter into the tranny to operate.

abodyjoe said:
how dynamic explained it to me was the smaller diameter gives it the higher stahl, and the positive pitch on the veins makes it lock up and be efficient.
Click to expand...

I beileve that is also due to the converter being a custom make/design for the application. Of course, having less fluid for power transfer is adding to the combo and action of this all.


Valvebounce, I think the above is on the right track. I don't have much to add since I'm really a manual trans owner and have not been down the road with high stalll auto trans cars. Though, I have been in several high and very high stall set ups, alot depends on the build of the engine and how and where it is making power and how you want to use it.

High stall converters do not automaticly mean you can not drive it on the street due to having nothing below the advertised stall speed. There just less efficent and sometimes terribly so below the stall speed. Alot depends on design of the inside of the converter as well as size and intended purpose for it.

From what I am told, (*In general since there are alot of variables to contend with) that a stall converter of approx. 2600 - 2800 will still act reasonable if not close to a stock converter unless you hit the gas pedal hard.

Having a converter stall @ 3200 - 3600 will have a soft feeling down low and etc... and on up the RPM range for each converter stalling higher and higher. The above recomendation for Dynamic is about the best you can do since if I was to list the top 5 converter makers for performance applications, they would be in it.

You can also contact PTC (Performance Torque Converters)
They come with a very good rep as well Do a search on this for more info and the forum members favorites on this topic. I'm sure you'll find some very very good info on it.

It can't be easy living across the Pacific ocean and getting these parts. I can see why you wuld be very careful and slow to get anything. Theres a few areas of building a car that some will jump up and shout, this is an area where you just do not skimp. This would be one of them if your getting serious about racing the car. Purchasing a "Econo" C-verter could be OK for a dual purpose machine or a lightly raced car where the racer isn't so serious about chasing the money with victories.
 
From what I am told, (*In general since there are alot of variables to contend with) that a stall converter of approx. 2600 - 2800 will still act reasonable if not close to a stock converter unless you hit the gas pedal hard.

Having a converter stall @ 3200 - 3600 will have a soft feeling down low and etc... and on up the RPM range for each converter stalling higher and higher. The above recomendation for Dynamic is about the best you can do since if I was to list the top 5 converter makers for performance applications, they would be in it.
Click to expand...


i can tell ya my dynamic 9 1/2" converter that is a 3800 stahl acted stock on the street. when ya mashed the loud pedal look out and hold the hell on... :). like ya said its all about how well its matched to your combination. i ordered mine for my combo. had 3.91 gears in the car at the time and it worked great. now if i took that exact same converter and put 3.23 gears in my car then it would have slipped down low. the new converter technology is awesome. in the old days anything over a 3k would suck on the street. no now. its awesome. ya get the best of both worlds.

i would call:

dynamic
ptc
ultimate

get opinions from all three and go with the one you feel most comfortable with... a converter can make or break your combo.
 
Thanks for those links. Very imformative! The auto trans/TQ has been a bit of a mystery to me thus far. There is some great info for me to chew over.

rumblefish360 said:
It can't be easy living across the Pacific ocean and getting these parts. I can see why you wuld be very careful and slow to get anything. Theres a few areas of building a car that some will jump up and shout, this is an area where you just do not skimp. This would be one of them if your getting serious about racing the car. Purchasing a "Econo" C-verter could be OK for a dual purpose machine or a lightly raced car where the racer isn't so serious about chasing the money with victories.
Click to expand...

There isn't much in the way of prize money round these parts. (hell, we're lucky if we get one meeting a month here) I just do it for fun. Hence not having a monster budget.
Since I don't have a monster cam, I don't think I'll be needing a big dollar converter. But (as I said in my 1st post) after driving my dads car with a big stick and no hi-stall I'm sold on the idea. The really frustrating part is our dollar only being worth around 67c US at the moment. Thats a real hinderence. That plus freight makes what I pay for a "cheap" unit where you are the same cost as you guys buying a decent unit.

Getting a little off my original topic, but ae there any brands to avoid like the plague?
 
TCI has a bad wrap around here. Joe's recomendations are sound choices.
 
I'd avoid anything cheaper than about $290, or made by TCI. I've had older TCIs that were great. But they changed after the business was sold. If this is a race car and you're interested in going fast repeatedly, the best convertor you can afford is the way to go. Contingency or not. As for size... I was told once that as the stall and lockup characteristics need to be at higher rpms, the diameter had to be reduced because of the way the oil had to react. Which was why in past years smaller meant looser. With better understanding of fluid dynamics and better control over the assembly process, a modern convertor can be slippry when neeeded and tight (within reason) when needed. Again, better convertor=$$$.
 
Thanks again for the input guys. The wealth of experience and wisdom here is fantastic. I hate to think what a god awful lemon I would have bolted together if not for the things I've learned on this site.
You guys rule! :thumblef:
 
HEY! We try and serve it up well. This is what it is all about.
 
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