I have an original article from 1982 Car and Driver magazing on a 300CDT which states that the turbo not only improves the car's performance, it also improves its fuel economy.......sounds implausable doesn't it.

The explanation they gave is that a turbo diesel engine's combustion process is actually improved over normally aspirated engine because the delay between initial fuel injection and the onset of compustion is reduced as the compressed-air temperature is higher (due to the turbo's compression). This allows more effecient injection timing and improves overall efficiency by about 5%. They also stated that the turbo diesel had better "detonation" behavior than the non-turbo diesel.

The article noted that EPA milage city rating went from 24 to 27 when the turbo was introduced to the 300CD, and highway milage rating went from 28 to 33.

I'm not an engineer but thought this an interesting addition to this particular discussion topic.

Nic
'85 300CD @ 148k miles

Bill:

Just what have you "bypassed" on your SD? You DO NOT have an air bypass, just boost controller and overboost protection valve. Bypassing either one can cause serious engine damage from overboost -- if the overboost valve is bypassed and the turbo runs away, you risk a blow head gasket or bent rods.

NIC:

A turbo on a diesel increases both volumetric effciency and combustion efficiency by increasing the "effective" compression ratio -- the turbo stuffs more air into the engine than would get in from plain atmospheric pressure. This effect is larger at high rpm, where one normally expericences "pumping losses" -- the air simply "stretches" and you get vacuum when the pressure isn't high enough to force it into the cylinder in the short time the valves are open.

More compression gives more heat, better ignition and combustion (up the the point where there is too much fuel to burn!), and greater expansion potential for the hot gasses. Since diesels don't require a fixed mixture of fuel and air, increasing the combustion pressure and air flow increases the expansion effiecency, gives better fuel economy, and more power, enhanced by the ability to burn more fuel.

The only real drawback is the collasal amounts of air that goes through a turbodiesel. Explains the huge air cleaners.

Pretty cheap way to get better power -- an MB 220D like mine is rated at 65 hp/95 ftlbs torque, while my Volvo TD (2.4L engine) is rated at 105 hp/145 ft/lbs torque. Fuel consumption is similar!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

NIC,

Thanks for the information of what the turbo does for diesels. I like to hear the the turbo gives better performance and fuel economy.