|
I spent 10 years tuning vehicles, everything from hyundai accents up to exotics any everything in between. I only skimmed the thread but I'll add a few details in here that will hopefully correct a few things and add in a bit of info.
Diesel Dave... Try not to think of your diesel in terms of AFR then compare to gasoline engines. Stoichometric refers to the mixture that a specific fuel totally burns with a given amount of oxygen. E85, Diesel, Propane, gasoline all have different ratios. Instead if you think about it as lambda you will be talking the same numbers as the gasoline people. I've found that Diesel tuning for fuel economy is quite counter-intuitive for the gasoline guys. You actually save fuel by adding fuel. Add fuel till it smokes then back off a bit works surprisingly well. The reason for this is that more fuel produces more torque and thus gets you up to speed (and the more efficient -compared to gasoline) cruise operating range of the engine. I just finished evaluating more than 16,000km of fuel economy data for a TDI we tuned. It made 40bhp more and consumed a tiny amount LESS fuel.
Turbos do not like more backpressure. The only engine that really likes any backpressure is a supercharged one with high overlap. Too little backpressure and the mixture blows right out the open exhaust valve. Do not confuse this with the OEM tuning your car may have.
Reducing the backpressure will improve fuel economy significantly while accelerating. Steady state operation will make more gains on some vehicles - especially the EGR equipped ones. If the engine wastes less energy pushing the exhaust down a restrictive pipe through a restrictive muffler then more energy is left to turn the wheels.
I had a 1993 Civic VX with a crappy restrictive 1.25" crush bent pipe. Finally it rotted off so I bought the cheapest stainless setup I could ($150 at shop cost). With no other changes in driving habits I picked up 7% and that was with at least 5000km of test data on either side.
At the moment I have a Subaru. Originally it had pretty poorly designed factory headers and a pretty restrictive exhaust. At the time (yes 12 years ago) I picked up 11-12% doing the exhaust on that. I don't have the data anymore but it was a good 30k of driving for comparison.
Hope that helps with some real world examples.
__________________
|