Why do Diesel's smoke and not gas engines?
Why do older engines smoke more than modern ones (12-valve vs. 24-valve)?

 

Because they can!
A properly tuned and warmed up diesel shouldn't smoke much. Smoke is just unburnt fuel. A diesel depends on the heat of compression to ignite the fuel, a cold engine will smoke till warm. Low boost combined with too much fuel such as when accelerating from a stop will cause smoke due to not enough air for combustion. Injection pumps are adjusted from the factory to prevent this but folks often readjust looking for more power. As to stock 12 vs. 24 valve smoke, neither should visibly smoke more but the 24 is under tighter smog laws that took effect in '98.
The whole reason for the electronic 24 valve fuel system was a stop gap measure to meet emissions requirements without major changes from the 12 valve until the newer common rail engine was ready.

 

A gas engine runs completley different than a diesel. One thing to keep in mind about the two is their air to fuel ratios. A gas enging has to have a 14:1 air to fuel mix. To much or too little will make the gas engine run rough or not at all. Also a rich gas engine will moke a little but not like a diesel can.

A diesel is compression ignition engine. It is totally fuel controlled. There is no set air to fuel ratio, its part of the reason why diesels are more efficient than gas engines.) The intake is usually an open intake with NO throttle plate, throttle body, etc. On the modern diesels there is usually a turbocharger with the engine. The smoke is caused by not enough air in the cylinders for the amount of fuel being injected. (ex. stomping on the accelerator from a stand still). The old diesels without turbochargers smoke more than a diesel with a turbo. The turbos job is to ram more air into the cylinders. This helps the diesel produce more power, and burn cleaner, as the black smoke is unburned fuel.

Hope this explains it for ya.

 

The new younger generation of diesels has more will power to not smoke than they used to but they are eventually broken down by AST boxes and 11 second ET's and begin smoking.

The older diesels have been smoking for too long and are addicted. Combined with their mechanical injector pumps and lack of emission controls they will never change. Since smoking is no longer socially acceptable you'll usually find the 1st and 2nd gens clumped together at the burn-out pit smoking and telling fish stories about their ET's...

Gassers never did appreciate a good smoke. They're always too busy zipping from here to there to enjoy a full bodied smoke.

Diesels are just prone to fine smoking......more like a conniseaur than a recreational smoker.

Hope this answers your questions


Couldn't resist - probably gonna get banned

 

Thats great man. Got a good laugh outta reading that.
DM01

 

MikeyB