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Old 12-20-2010, 08:56 PM   #21
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Re: diesel exhaust

Phillip, back to back testing on several diesels showed a properly tuned n/a diesel see's no improvement with only excess air added.(turbo or supercharger) With a poorly tuned diesel, a turbo can band-aid it a bit and as you said use some of the previously unused fuel through higher cyl pressure causing higher chamber temps. But again, it was only a band aid and a proper tune up/inj replacement would of done the same thing cheaper.
Only when extra fuel is added with a turbo or supercharger does hp/torque go up. As far as milage, when the hp goes up (through the consumption of more fuel) milage drops. The only way around it is to replace a n/a 200hp engine with a smaller 200hp turbo engine. And THAT only works if you only require the max hp/tq rarely.

If you require 200hp (driving a rock crusher for example) than 200hp is 200hp. a big n/a engine will be burning x amount of fuel and the smaller turbo engine will burn almost identical amount of fuel to produce the same 200hp.
BUT...if you have a 200hp n/a engine in a crusher that only requires 100hp for regular loads, then the smaller turbo engine will be more efficient and not burn the same amount of fuel for the same 100hp.
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Old 12-21-2010, 07:59 AM   #22
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Re: diesel exhaust

since we're digging up old threads...

NA diesel exhaust requires just as much attention as NA gasser exhaust. and will benefit from good manifolds/headers and properly sized pipes. bigger=better is for turbos, gas or diesel.
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Old 12-21-2010, 10:02 AM   #23
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Re: diesel exhaust

NA diesel exhaust requires just as much attention as NA gasser exhaust. and will benefit from good manifolds/headers and properly sized pipes.
This is true.

bigger=better is for turbos, gas or diesel
This is not.
Too small gives quick response but limits flow.
Too big pronounces lag but overall flow increases.
Same as a turbo must be matched to cu.in and rpm.

Sorry about all the picky correcting, my pet peeves are old wives tales.
Another is that an engine requires backpressure to run or run correctly. This is absolutely FALSE!!!

A correctly tuned engine with restrictive exh makes "x" hp. When a free flowing dual exh is installed power drops off. Reinstall the tiny single exh and power comes back.
"see, engines require backpressure"!
Not quite, if the engine would of been retuned so it wasn't so lean (due to better flowing exh), the engine would of made more power/easier on fuel etc.
And, to add to above, replacing a 2" single exh with dual 4" pipes on a small block for example, will flow better than the restrictive single 2", but exh velocity would be so far from the ideal 300ft per second that the gain would be minimal compared to what it could be. Less restriction is better as long as the pressure wave doesn't drop too far and as long as the return wave hits the back of the exh valve during overlap to create scavenging.
(yes I build drag engines too, and am a tech inspector for Stock and SuperStock dragracing)
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