Convertor loose or tight

[slo-joe55]

What is ment by a convertor being loose or tight? On a street car does it make a differece? I hope I am asking this question correctly.

 

[Dabigguy]

Good question. A converter allows the transmission to slip at idle so you can sit at a stop light without taking it out of gear like you would have to with a manual transmission. When you push the accelerator the engine revs and the car moves. Most cars you can hold your foot on the brake and the engine will rev to about 1800-2000 rpm before the engine torque overcomes the holding power of the brakes. The looser the converter is, the higher the rpm is before the car moves.

High performance engines are built to operate in a specific rpm range, turbo Buicks make the best power from 1800-5000 rpm and needs a converter that slips up to 1800 rpm and you want to keep the engine operating within that rpm range for max. power. Race engines may make the most power from 4500-8500 rpm so you want a converter that slips until it gets to 4500 rpms so it is in that powerband.

So, a loose converter slips up to a higher rpm than a tighter converter.

The term stall comes from the point what if your wheels did not turn, the engine would stall.

 

[slo-joe55]

Dibigguy,

Thanks for that explanation, I am currently running a 3800 NL 9inch convertor I am considering new school 71Hpqh turbo to complete my setup. I was told to tighten up my convertor, and that where the original question came from. This 3800 was the size convetor recommended from the engine builder. So what does non-lockup mean? and is this a good thing for a street car?

 

[Dusty Bradford]

Dibigguy,

Thanks for that explanation, I am currently running a 3800 NL 9inch convertor I am considering new school 71Hpqh turbo to complete my setup. I was told to tighten up my convertor, and that where the original question came from. This 3800 was the size convetor recommended from the engine builder. So what does non-lockup mean? and is this a good thing for a street car?

I'd stick with a non lock, especially with a turbo as large as a 71mm. You will need to install the turbo and see how you like it's spool characteristics before you decide on a stall change. Run a good external trans cooler if you drive the car alot on the street. Some of the 9" converters are pretty loose when driving so the cooler will help with the heat generated.

The non lock means the converter does not have a lock-up clutch like a stock converter does. The stock lock-up clutch is used to lock the converter up 1:1 just like a clutch in a stick shift car. This keeps the slippage lower so there is less heat generated and better fuel mileage. The problem with some of the old non locks is the stall rpm is too high which made them feel sloppy for street driving. Non locks got a bad rap from some users but I personally prefer a non lock converter in almost every application. I drove my car on interstate trips and all with one of my own converters and never had any issues with heat.

The other thing for you to consider if this is a street car. Unless your trying to run 9's, you don't need a 71mm turbo. For a street car, you want to run as small of a turbo as you can to meet your et goals. This allows you to run a tighter converter which will have better street manners.

 

[slo-joe55]

Dusty,

Thanks for the explanation, to make a long story short I originally had the engine built to compete in the TSM class, but by the time it was completed the times were just to fast. I still would like to get the car to run low 10s/ high 9s, while keeping the boost as low as possible,this is the reason for the 71mm, and then see if any adjustment can be made at that point to give it street manners, if that makes sense. Once the new turbo is installed then I will see if any adjustments need to be made.

Thanks again
slo-joe