Transmision and Torque Converter Tuning discussion

[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!

[cleatus12r]

DJ,

How about you use that fancy AE package you have and put it to use!

Here's what you do.

1. Drive in 3rd gear at 45 MPH; no load, not accelerating. Check the Mass Fuel Desired by what the datastream says.

2. Same test...only in 4th gear.


3. Use the MFD data and calculate over time and engine speed.

4. It's not the most accurate, but it may give you an idea.

I have a Genisys sitting here, but it's cold and snowing out.

[Jackpine]

That's actually a very good explanation of the difference between horsepower and torque, southpaw!

So, at low speeds (lugging) we need more torque to produce equivalent horsepower. Sure - and some engines like my old 427 cu in Police Interceptor were designed to produce high torque in the low RPM band so it was easy to move off from a standing start. I know diesels are weak in this regard.

But, why is a diesel so different from a gasser? Is it because the compression is so high that it "works against" the output at low rpm?

Naturally, we can only really continue to accelerate as long as the torque output of the engine exceeds the torque demand needed to maintain the current speed. And, at cruise, the torque/fuel demand is reduced, since we're no longer accelerating, but have to supply just enough to counter the force of wind resistance, friction, and other losses that try to slow us down.

The whole horsepower thing is kind of a "fiction", isn't it?

And, does the EGT go up in lugging because the fuel is "afterburning" as it leaves the cylinders? (Hasn't completed the burn during the power stroke)? Or, did it finish the burn too early, since the piston is moving too slowly? (Creating a "hot spot" effect in the cylinders that is not countered soon enough by the cooling exhaust and intake cycles)? In either case, wouldn't a gasser have the same problem?

And, getting back to the "lugging" proposition, what, specifically, is wrong with this strategy? Does it work in a gasser but not in a diesel due to the low RPM power characteristic?

I did not mean to hijack this thread and if I have, I'll start a different discussion of it elsewhere.

I'm honestly just trying to gain a better understanding of the two technologies. I'm already a diesel convert, just don't have one yet!

- Jack

[Jackpine]

Originally Posted by cleatus12r

DJ,

How about you use that fancy AE package you have and put it to use!

Here's what you do.

1. Drive in 3rd gear at 45 MPH; no load, not accelerating. Check the Mass Fuel Desired by what the datastream says.

2. Same test...only in 4th gear.


3. Use the MFD data and calculate over time and engine speed.

4. It's not the most accurate, but it may give you an idea.

I have a Genisys sitting here, but it's cold and snowing out.

Yes! that's a good approach Cody! (Your new avatar really creeps me out, you know - how does a guy with the friendly screen names of "cleatus" and a real name of "Cody" come up with such a sinister looking guy)?

Anyway, your approach is clearly the right one. At the "lugging" speed of 45 mph, which gear uses more gas? And, if the tune locked you into the "higher gas use" gear at that constant speed, then it's not the right one.

But, if you are accelerating, and lugging momentarily, do you get out of the high gas use region faster and with less fuel than if you downshift, then upshift again?

- Jack

[cleatus12r]

Originally Posted by JackandJanet

But, why is a diesel so different from a gasser? Is it because the compression is so high that it "works against" the output at low rpm? Because the air/fuel ratio of a gasoline engine remains constant at all operating conditions. 13:1 (loaded or idle) up to 15.5:1 (light cruise). A diesel engine operates at anywhere from 70:1 (idle) down to 18:1 (smoke haze). Diesel fuel burns a lot slower than gasoline causing a longer duration "push" on the top of the piston on the power stroke.


The whole horsepower thing is kind of a "fiction", isn't it?Yep, it is only a mathematical solution derived from torque and time.

And, does the EGT go up in lugging because the fuel is "afterburning" as it leaves the cylinders? (Hasn't completed the burn during the power stroke)? Or, did it finish the burn too early, since the piston is moving too slowly? Nope, it's just a function of fuel available to burn. A diesel's EGT will range from 250 degrees at an idle to 1400+ degrees under load with excess fuel. A gasoline engine will run at 900-1000 degrees at an idle and 1800-1900 under cruise conditions. Once the fuel mixture goes rich again under load, the EGT will drop. Rich diesel=HOT....Lean gasser=HOT.

And, getting back to the "lugging" proposition, what, specifically, is wrong with this strategy? Does it work in a gasser but not in a diesel due to the low RPM power characteristic?Again, we run into the required air/fuel ratio. Anytime you can run a gasoline engine slower under light load, you'll use less fuel. For any given amount of air, you'll use 14.7 times less fuel. A diesel always has the same amount of air available (for all intents and purposes) so anytime you require more power for lugging, you will add more fuel. Granted, the amount of airflow goes up with RPM, therefore more fuel is used albeit at a lower injection rate for a leaner burn.

I did not mean to hijack this thread and if I have, I'll start a different discussion of it elsewhere.

I'm honestly just trying to gain a better understanding of the two technologies. I'm already a diesel convert, just don't have one yet!

- Jack

Jack, I'll try to explain to the best of my ability about all of your questions.

[cleatus12r]

Originally Posted by JackandJanet

Yes! that's a good approach Cody! (Your new avatar really creeps me out, you know - how does a guy with the friendly screen names of "cleatus" and a real name of "Cody" come up with such a sinister looking guy)?Vigo the Carpathian from Ghostbusters 2

Anyway, your approach is clearly the right one. At the "lugging" speed of 45 mph, which gear uses more gas? And, if the tune locked you into the "higher gas use" gear at that constant speed, then it's not the right one.

But, if you are accelerating, and lugging momentarily, do you get out of the high gas use region faster and with less fuel than if you downshift, then upshift again?Only controlled experimentation will tell. In my position, driveability reins over economy....mostly because people in my neck of the woods USE their trucks.

- Jack

Here's the second part.