Thread: Transmision and Torque Converter Tuning discussion
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Old Wed, April 15th, 2009, 09:32 PM
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Originally Posted by JackandJanet View Post
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.
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