What percentage drivetrain loss would I experience with a 700R4 and a TCS 3200 stall converter?

Regular 700R4s are 18% correct?

What would it be with a 3200 stall?

 

Depends on the car and your driving conditions. When a converter is operating below it's stall speed it slips. Operating higher than the stall speed the converter is acting 1:1. There is a small amount of slippage but not enough to consider.

If you have a 3200 stall converter and drive around in a high enough gear to keep the rpms around 2500 then there's going to be a lot of slippage and heat created. If you keep it in a lower gear so that the rpms stay above the stall speed then you'll have less slipping and better fuel mileage however the higher rpms will eat up that extra fuel mileage.

I don't know about a street number but at the dragstrip I think anything that slips more than 12% is too loose. My converter stalls, with a transbrake, at 5700 rpm. From a 1/4 mile pass I have a calculated slip of only 10.2%. I wish it was a little bit tighter, closer to 8%.

To calculate converter slip you need to know the diameter of the tire (height), finish line rpm, finish line mph and diff gear ratio.

 

Ok so if I jumped on a dyno, how much lower would my horsepower numbers be than someone with the exact same mods but a stock converter in a 700R4?

 

Depends on the engine. You haven't changed anything in the drivetrain so the drivetrain loss doesn't change. A torque converter transfers torque. Depending on where the engine produces torque will determine if changing the converter increases or decreases the amount of power reaching the wheels. A stock converter is around 1200 rpm. By changing nothing except the converter, you'll probably lose power since it's higher than where the engine will make torque. If the engine is built up and produces torque at a higher rpm then using a stock converter is restricting the engine from transmitting torque in the best powerband. Swapping the converter will be a big improvement.

As to how much it will gain or lose will only be known by putting it on a dyno. No 2 cars or engines are exactly alike.

HP numbers will not change since you did nothing to the engine to change the HP. HP is a calculated number from the amount of torque the engine produces. By swapping the converter, you change the torque rpm range going through it. It's up to the engine to determine where the best torque range is. The converter must be matched to the engine to produce the best power.

Theoretically if you did a converter swap at the dragstrip, the MPH will stay the same since it's calculated from HP. ET will change because it's affected by torque and a converter swap will change the torque rpm range.

A higher stall converter will allow the engine rpms to climb faster to get the engine into it's power band. If the engine's rpm is in the power band quicker then it can use it's available power quicker.

Think of it as using a manual transmission with only high gear. If you can get the car moving, it will take a long time for the engine to get up to speed since it has to work so hard at low rpms. Using lower gears, the engine can operate at higher rpms where it makes more power.

 

Thanx for the info.

Right now I have a 3200 stall and the motor makes its peak torque at 3500rpm according to my engine builder.

 

I've heard as a general guestamate... 20% auto, 25% with a real loose convertor.

 

I posted my actual numbers for him on the LT1 Tech board. I have a fairly loose convertor that stalls to 5K under 800 ft-lb of input, non-locking obviously (11% slip), TH400, 3" CM DS, 3.73 12-bolt. Got 19.8% loss at 486HP NA, and 21.3% loss at 784HP N2O.

 

Nice I never knew this, always wondering what the numbers were, thanx

 

A torque converter multiplies torque (when it's not locked up) but it does that by slipping and generating heat. Horsepower is never increased by a TC, only decreased. The hp which is used to heat up the oil is lost to the driveline. The higher the stall, the more heat generated and the more hp lost. I consider TC loss to be driveline loss, so max. hp should be less at the wheels at engine power peak.

Of course, torque at the wheels is what accelerates a vehicle, so multiplying the torque, or allowing the engine to run near it's torque peak during launch will improve acceleration.

Trap speed relates directly to hp/weight ratio. If you are not losing mph in the traps with a higher stall TC, even though there is a hp loss, it's probably because the engine is running closer to it's hp peak because of the slippage. If you were geared for hp peak rpm in the traps, and added a higher stall converter which allowed the engine to go say 500 past it's power peak, you might lose a little mph, but maybe have a lower ET because of the multiplied torque at low speeds.

There's no free lunch. The closest thing might be a high stall TC with a lockup clutch which could hold full engine power.