As I have read, my 01 5.4l puts out roughly 260 at the flywheel and about 200 to the road. This is a pretty significant drop.

So, here is my question: Where does it go? Are there a few components that are primarliy responsible or is it a function of the overall complexity of the tranny?

Can a performance transmission kit with higher grade bands, springs, gaskets, TC, lines, etc. etc. reduce the % loss in the system? We are looking at a stock drop of 25+% from flywheel to rubber. Is it possible to get that down to 15%? If so, that's a big chunk of ponies to get. Every additional mod over stock that increased HP would net out 10% more in the above scenario. It's kind of the gift that keeps on giving.

Can anyone share their thoughts on this issue?

Thanks in advance.

Ken

 

I believe all that wasted HP goes to heat. As things rotate, the oil/ATF/grease gets pushed around and the friction causes heat. I don't think you can reduce it much, except to use thin, synthetic oils.

 

I think heat plays a role. I think the biggest loss is basically the result of using a fluid coupling rather than a mechanical coupling like in a manual. Essentially an automatic transmission is always slipping a little, unless it's up to a higher speed where the lockup can happen. With a manual, once your in gear, no energy is being wasted.

I also think maybe because our trucks our basically low-end torque vehicles (and thus low-end HP vehicles), that also contributes to the problem. If an auto trans loses HP before it can get to a higher RPM for lockup, what do you think happens when your peak torque and peak HP occur at lower RPMs? I presume you'll lose a large amount of that torque and HP...
If your 5.4 put out 260HP at 7000 RPM, I'd think you'd have less of a drop from flywheel to driven wheel...But then of course that means your peak torque would be around 5000 RPM, which isn't the low-end torque needed by people that tow, haul, etc.

 

Then a really "tight" torque converter that was designed to minimize "fluid slip" could theoretically decrease the % loss to the rear wheels. I also assume a tranny cooler with synthetic fluid would provide some increase as well. Given the above, what kind of improvement? 2% 5% 10%?

Ken

 

ken800

I'm not really knowledgeable enough to give you a %, someone else will have to do that. From a theoretical standpoint, yes I believe a "tight" torque converter will do that. But then I think you might get less low-end torque. The impeller to the turbine to stator to impleller fluid flow actually helps the impeller turn and creates a torque multiplication of about 2:1. If you lockup the impeller and turbine, you'll get a 1:1, before you get to your planetary gearset torque multiplication. What you might find is that you no longer have the HP loss from flywheel to driven wheel, but you also don't have the torque you need to get up and go (accelerate).