Transmision and Torque Converter Tuning discussion

[cleatus12r]

Don't look over the fact that a lower RPM for any given road speed is going to put more load on the engine.....in some instances, it is counter-intuitive to lower the operating RPM. I wouldn't try (if it were possible) a 40 MPH overdrive shift.

Case in point:

At 55 MPH in 3rd gear on level surfaces, I will see a very low EGT reading. However, in 4th gear just to maintain 55 MPH will result in higher EGT. I'm not saying that it's burning more fuel in 4th. However, I just lost ALL of my boost-building and low-smoke moderate acceleration abilities since all of a sudden I'm running a lot less RPM. Less fuel at a faster rate or more fuel at a slower rate....it's your call I guess.

If you could find a way to run a 40 MPH 4th gear setup, it would probably be wise to tune in a 4-3 downshift that occurs at a decent speed/APP as well (like anything less than 10% APP). If your low boost fueling is too high and the transmission won't downshift until you're running a decent amount of APP, you'll get a ton of smoke, no acceleration, and a really hard downshift when it does occur.

[soutthpaw]

thanks for the suggestion.. I think it was doing a 3-2 downshift not a 4-3 so i just need to fix the 3-2 downshift setting probably bring the 4-3 down around 43 or 42 mph at low throttle. need to make a log of my throttle position s though
I came up with an idea on how to get really low OD shift at a low mph. Talking with Bill a couple of days ago I mentioned I corrected my tire size setting and he told me that does not fix the RPM, only affects the shift points for the transmission... Sooooo you could put a different number in the tire Revs per mile and then you actually fool the tranny into thinking the vehicle is going faster than it really is so it would shift earlier
what ya think??

[cleatus12r]

That would work. Of course, you're clever enough to realize that it will affect ALL aspects of shift scheduling.

[soutthpaw]

yeah I would have to practically change all the shift points and throttle positon setting and lots of trial and error...

[cleatus12r]

Here's a question for everyone...feel free to throw anything into the pot.

Do you feel that lugging the engine constantly (as such in a fuel economy-minded program) is the best way to gain increases in mileage?


I'll start. No.

[soutthpaw]

I agree lugging is always bad. But these engines make so much low end torque that it seems in theory you could drive empty at much lower rpms than stock and still drive around fine. The followup to that is finding the right balance. And will it yield better, worse, or no change in fuel economy.
Hope Bill gets caught up soon so we can get him back on the forum and get his take on it.

[Jackpine]

Originally Posted by cleatus12r

Here's a question for everyone...feel free to throw anything into the pot.

Do you feel that lugging the engine constantly (as such in a fuel economy-minded program) is the best way to gain increases in mileage?


I'll start. No.

But, Cody, isn't the effect different for diesels vs gas engines? (And I'm sorry I didn't qualify my original post with that caveat - I know next to nothing about diesels). My post probably seemed kind of stupid. And, I was trying to open the discussion up to diesel AND gas - but maybe that was too ambitious.

Now, I'm really NOT suggesting lugging any engine constantly, because it seems to me that you're not getting a clean, efficient burn and you're going to see maybe fouled plugs at a minimum in gas engines and possibly valve damage? But, my experience "lugging" my old stick shifters, was for a pretty minimal amount of time, maybe about 5 seconds before the engine speed would increase enough to stop the lugging.

It always seemed to me that I had to be using less fuel that way than with a downshift, followed by an upshift a short time later.

Am I out to lunch on this one? (Wouldn't be the first time)!

- Jack

[soutthpaw]

well Gas and Diesel are sooo different it is hard to talk about both other than in general terms.... That's what makes Diesels so awesome Maybe we will convince Jack to get a diesel

Lugging means you are trying to move too much weight with too little power...

as RPM increases even past the peak torque you still need less HP to move the weight because of the formula
here is a good example I found on the web
example 1: How much TORQUE is required to produce 300 HP at 2700 RPM?

since HP = TORQUE x RPM ÷ 5252
then by rearranging the equation:
TORQUE = HP x 5252 ÷ RPM
Answer: TORQUE = 300 x 5252 ÷ 2700 = 584 lb-ft.

Example 2: How much TORQUE is required to produce 300 HP at 4600 RPM?
Answer: TORQUE = 300 x 5252 ÷ 4600 = 343 lb-ft.

Example 3: How much TORQUE is required to produce 300 HP at 8000 RPM?
Answer: TORQUE = 300 x 5252 ÷ 8000 = 197 lb-ft.

Example 4: How much TORQUE does the 41,000 RPM turbine section of a 300 HP gas turbine engine produce?
Answer: TORQUE = 300 x 5252 ÷ 41,000 = 38.4 lb-ft

read it a few times and see if it makes sense... this is really the key to finding the best combination of RPM and Torque to get the best result..... you have to then look at how much torque the vehicle makes at various RPM then figure out what speeds the vehicle is traveling at using those figures
Remember Torque is an actual directly measurable value, whereas HP is a calculated figure...

Lets say my engine is in OD at 50 mph at 1600 RPM and making 500ftlb of torque (stock peak torque is at 1600)
500x1600/5252=152.3 hp
now at 2600 rpm lets say we get 450 ftlb torque
450x2600/5252=137.1hp

so even though we are making less torque we also need less power due to the higher engine speed......

sounds simple right...
except for a couple of things... we are not using Wide Open Throttle WOT most of the time when driveing... so now you look at how much throttle and hence fuel u need to get the power to move the vehicle ; so you will need less throttle to get the same amount of torque at peak torque rpm than you will at higher RPM and as the engine is spinning less times a minute you are injecting less fuel per minute at the slower speeds

Confused yet
so in the real world it comes down to trial and error!