Calling automatic transmission experts

My 240 sx mini stock has a gearing issue. We are required to run 13 inch wheels with Hoosier short track tires. So I cannot change the gearing with tire size. Trouble is that changing the gearing on this car is not easy. Without going into the details, I am considering an automatic transmission because second gear will work on paper, plus I can pick any number of them up for almost free. What I am wondering is how much rpm would I loose through a stock torque convertor. If the transmission was a manual, I would hit the corner at about 6800 rpm, which is just fine. But because a slush box is not 100 per cent efficient, I suppose I will be doing something less than that. Because it is slipping and I am accelerating slower. Or am I spinning higher rpms because the convertor is acting like a slipping clutch? Or because I am now at the corner and pretty much done accelerating, and the torque requirement is reduced, has the inefficient transmission now caught up, at the expense of some earlier acceleration when I was first putting my boot in it after the previous corner?

As you can see, I am not sure what is going on in the transmission under a load. For the record, there are high stall TC's available, but I am not sure that is what I need either. Seems like I want it to engage at a lower rpm rather than higher.

Any thoughts?

You don't want high stall you want lower stall or a dumby converter. I'm sure someone wih more info will reply soon. I'd point you to Burt Brown racing transmissions as Burt builds some great stuff at an honest price.

At high RPM the convertor is almost solid.

44Dwarf wrote: You don't want high stall you want lower stall or a dumby converter. I'm sure someone wih more info will reply soon. I'd point you to Burt Brown racing transmissions as Burt builds some great stuff at an honest price.

I looked up dummy convertors, which sound ideal. But it sounds like they only work on a gear type automatic like a Torqueflite.

How are you going to control the Trans? it has its own electronic controller.

This is real life, adapt, adapt, adapt!

I would call one of the multitudes of converter companies and see what they have to say and for how much.

At high RPM the convertor is almost solid.

That is not true, and the extent to which it is not true is different for different converters in different situations. A stock, tight, low-rpm stalling converter may only slip by a hundred or two rpm at redline, but a higher stall unit, especially depending on how high it stalls and how it is built, can slip a LOT at high rpm. Ive put a cheap high stall converter in a car and lost high rpm power (to the ground) in my own experience which is not super vast with converters.

I agree that you need to talk to people who build converters to get GOOD info on this because your run of the mill enthusiast knows very little about torque converters. If you are running a relatively low-torque engine (non turbo 4 cyl) you can probably get away with having the converter clutch engaged full time in 2nd gear if it is mechanically/hydraulically possible to do so with that trans. You would probably have to rig some external controls onto the transmission to do this, but it could be fairly simple.

I am proceeding with this idea on the basis that it is a very cheap experiment. And in for a penny, in for a pound as they say. I picked up an automatic tranny for some spare change, and I want to eliminate the torque convertor. This is what 44Dwarf suggested. The idea is that you tap into the pressure side of the hydraulic pump and run the fluid through a line with a ball valve, and thence back to the pan. So you are driving the pump as soon as you fire the motor up, but the car does not move because as long as the ball valve is open the pressure is returned to the sump. When you want to move, you slowly close the valve and the car begins to move. From there I can select gears manually using the manual shifter that I just picked up. So I get a mechanically driven manually shifted automatic that weighs the same as a standard.

The question is, where do I tie into the high pressure system? I am going to pull the pump out sometime this week and look at it, but perhaps someone has already looked at one. Its an RE4R01A Nissan 4 speed.

I'd probably be pulling the high pressure out of one of the testing ports. But with that being said, just look at what the powerglides being used already are doing.

Don't there exist "clutch pedals" for what you want to do? I seems to remember reading hat was SOP for circle track powerglides.

Give Burt a call. He is a real nice guy if he tells you what to do, do it it will work. He can also sell you part you might need for a honest price. He's in OH but many local guys from out here in MA use his tranys cause he stands by his work. http://www.burtbrownracingtrans.com/

oh no intrest or gain for me. other then he's help others i know.

Ranger50 wrote: I'd probably be pulling the high pressure out of one of the testing ports. But with that being said, just look at what the powerglides being used already are doing.

Well the powerglides are mostly found in the street stock class and the no convertor trick has been outlawed. So no joy there, and I don't know of one to look at. But I thought I might be able to power the transmission up on the floor of the shop using a 1 inch electric drill that I have. Then I will take a look at the test port, although that seems too easy. Either way I will just pull things apart and spray oil everywhere until I figure it out.

Kenny_McCormic wrote: Don't there exist "clutch pedals" for what you want to do? I seems to remember reading hat was SOP for circle track powerglides.

There do exist clutch pedals. But they are for powerglides and turbo400's. And making one work would pretty much blow my tiny budget.

bearmtnmartin wrote:

Ranger50 wrote: I'd probably be pulling the high pressure out of one of the testing ports. But with that being said, just look at what the powerglides being used already are doing.

Well the powerglides are mostly found in the street stock class and the no convertor trick has been outlawed. So no joy there, and I don't know of one to look at. But I thought I might be able to power the transmission up on the floor of the shop using a 1 inch electric drill that I have. Then I will take a look at the test port, although that seems too easy. Either way I will just pull things apart and spray oil everywhere until I figure it out.

That is why you have the dummy converters for classes that don't allow direct drive....

That is why you have the dummy converters for classes that don't allow direct drive....

Yes, there are probably a few out there, but they are not talking.....

I might have missed this... but what slushboxes are we discussing? There are a few thousand possible answers based on what we have to work with.

A stock converter in (for instance) a Powerglide or many other stock transmissions will usually give 200-300 rpm depending on load, RPM, and weight. That is to say, if you put identical transmissions and converters in a 240sx and in a pickup towing 10,000 lbs going uphill, the converter is seeing vastly different torque bias. The amount of torque coming in from the crankshaft vs the resistance offered by the load has a large effect.

It also has a lot to do with the design of the converter. Lots of hot rodders choose the cheapest 3000-stall converter to match their cam and then complain about street manners because the car won't move until you rev it to 2000 rpms. Others who spend good money on a 3000-stall TC notice the same street manners as a stock TC, but it just flash-stalls at 3000.

I'm not that familiar with your particular ride... care to enlighten me and maybe I can chip in some more concrete info?

Sounds like a diff change might be more reliable for racing.

I think getting rid of the converter is goofy. Why not just keep the converter and let it operate like a perfectly normal trans other than you having manual control of converter clutch lockup?