Diesel mods and testing

[bwilson4web]

One of my favorite auto writers has a multipart series about tuning up a turbo diesel:

Powering-Up the 1.9 liter TDI, Part 1

Powering-Up the 1.9 liter TDI, Part 2

Spoiler alert:

Increasing the air intake charge of a diesel engine, unlike a gas engine, does not increase the power. In fact, it increases the overhead as more work has to be done compressing the larger mass of air.

Bob Wilson

[dcb]

it doesn't make more power until you reprogram the ecu to add more fuel anyway. There may be "smarter" ECU's on diesels out there that would respond without needing reprogramming.

[JasonG]

With modern diesels fuel is what creates HP.
The extra air is needed to control smoke by fully burning the fuel, creating more go.
I see he is next opening the exhaust. I predict there will be gains but they will be minimal.
When they change to larger injectors and adjust the idle, stand back ! I hope his tranny can handle it.
Properly fuelled they will rip their tranny apart. First the differential goes. Then after you drop $$$ on a Quaiffe or Peloquin, you'll be good to 140-150 before other things start going.

[Piwoslaw]

Crossposting:
1.9L VW/Audi/Skoda/SEAT Diesel Mod alert!

Originally Posted by JasonG

I see he is next opening the exhaust. I predict there will be gains but they will be minimal.

In a late-2007 series Julian modded a turbodiesel Peugeot 405. The first step was a new exhaust, then a new intake. It appears that latter the gave less results than the new muffler:

With the new exhaust fitted, the turbo developed boost much earlier in the rev range. With the new intake, there is a very slight improvement in the revs at which appreciable boost is achieved. However, more noticeable is the way the engine now more freely revs with power. From 3500 – 4500 rpm the power output feels noticeably sharper. (Above 4500 rpm the fuel-cutting rev limiter starts to make its presence sharply felt.)
[...]
While the on-road gain is considerably less than achieved with the new muffler, the engine feels sharper at mid/high revs.

Of course, both of these mods work best in tandem

[ConnClark]

Originally Posted by bwilson4web

Increasing the air intake charge of a diesel engine, unlike a gas engine, does not increase the power. In fact, it increases the overhead as more work has to be done compressing the larger mass of air.

Lets get this straightened out right now. Increasing the air intake charge does create more power for a given quantity of fuel burned.

One very informative paper I keep referencing is

http://aerade.cranfield.ac.uk/ara/1937/naca-tn-619.pdf

in figure 8 they show power output with boost pressure for fixed fuel increments per cycle.

In figure 10 they show what a restriction of air intake does to performance.

in both cases the more in the cylinder results in more power out and higher efficiency for a given quantity of fuel.

If you don't buy that because of the age of the report here is a more modern report abstract

Abstract

"Next, a study of the effects of varying boost pressure levels was conducted. For fixed NOx levels, with low-pressure (90 MPa) single injections, soot was found to reduce monotonically as the boost pressure increased. Interestingly, with low pressure double injections and with high pressure (>90 MPa) single injections, soot was found to decrease at first and then increase as the boost pressure was increased beyond the optimum level. This appears to be due to a reduction in the spray penetration and mixing that occurs as the engine gas density is increased. BSFC also reduced monotonically with increasing boost pressure for all cases. These results suggest that variable geometry turbochargers or other enhanced boosting methods will aid in the reduction of emissions and fuel consumption from heavy-duty truck engines. "

there was a better paper but the link is now dead

http://powerlab.mech.okayama-u.ac.jp...4/A6_1_022.pdf

[73ch13]

Originally Posted by bwilson4web

Spoiler alert:

Increasing the air intake charge of a diesel engine, unlike a gas engine, does not increase the power. In fact, it increases the overhead as more work has to be done compressing the larger mass of air.

Bob Wilson

If this was true, they wouldn't put turbos on every diesel.

Just google, How Turbos Work