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Varn 09-28-2012 10:13 AM

Vacuum/boost gauge on diesel, theory?
I have had vacuum/boost gauges before on N/A gas engines and turbo engines. Have always felt that keeping the vacuum high was a key to economy.

I have a turbo VW diesel now and wonder about the usefulness of a boost gauge. I can hear the the turbo whine even with very light throttle. The diesel engine is basically at full throttle all the time and the injectors are controlled by the foot feed. Does the turbo help to push more air into the engine to keep it lean yet powerful.

If I had a boost gauge would economy be adversely affected by keeping the engine out of the boost?

UFO 09-28-2012 11:05 AM

Yes, the turbo actually helps efficiency by feeding the engine more air under a wider variety of load conditions, helping to burn the fuel more completely.

The only way that more boost is going to hurt your economy is if you are operating at high rpms and not using the available torque. Lower rpms will be better for economy providing your turbo is feeding enough air -- the VNT turbos on the ALH TDI engines are very good at this, if you are using one with a standard wastegate it may not be able to feed the engine at lighter loads.

ecomodded 09-28-2012 01:21 PM

I put the boost gauge on my diesels turbo so i could keep tabs on it and learn its behavior. I found out my turbo is working excellent,makes boost in a drop of a hat.
On steep fast hills it will make 20lbs for a a few moments then the waste gate kicks in and holds the boost at 15lbs., so it also lets me know the waste gate is working.
It does function as a driving aid as well, i find cruising with 2-3lbs of boost is more efficient then cruising with 5 lbs of boost, it acts as a load gauge in that sense.

ConnClark 09-28-2012 01:26 PM

Boost increases efficiency but its created by energy not being utilized by the pistons. If you drive in a way that keeps boost low you are putting most of your fuels energy into moving you down the road.

Do Not Try And Mod Your Car To Lower Boost. Instead do things to make it more efficient to create boost : Free flowing intake, free flowing intercooler, free flowing exhaust, ram air intake, etc...

oil pan 4 10-10-2012 10:07 PM

Also add a cold air intake for when temperatures are above freezing.

An EGT gauge is also a good measure of how hard the engine is working.

Varn 10-10-2012 10:36 PM

Thankfully the intake air comes from the right front fender. I doubt of my car has a variable intake turbine as it is an 86.

I have to plead ignorance on it even having a waste gate. Having no gauges is sometimes bliss.

gone-ot 10-11-2012 10:44 AM

A turbo charger uses "wasted" energy.

Think of it as a fart-driven propellor that's putting the fart to "good use" by 'pushing' air into the engine instead of the engine having to 'suck' the air in.

metromizer 10-11-2012 06:25 PM

Just having purchased a used E350 Powerstroke, I'm new to the whole turbo Diesel thing myself... the word among the Diesel truck guys is FE goes up if you can drive it easy enough to keep it 'off boost'.

UFO 10-11-2012 06:31 PM


Originally Posted by metromizer (Post 333430)
Just having purchased a used E350 Powerstroke, I'm new to the whole turbo Diesel thing myself... the word among the Diesel truck guys is FE goes up if you can drive it easy enough to keep it 'off boost'.

Nothing wrong with the boost, it just seems to me those big diesel trucks are usually tuned to over-fuel, so when they get on boost you see the fuel flowing out the exhaust.

Especially with something so over-powered, it is important to accelerate briskly to put the engine in it's more efficient part of the BSFC curve, just don't push it to the point of visible smoke or high rpms.

slowmover 10-11-2012 08:54 PM

In the world of Cummins TurboDiesels this is known as the 666 Rule:

1] 600F, or lower exhaust gas temperature (pyrometer)

2] 60-mph, or less (speedometer)

6] 6-psi manifold pressure, or less ("boost" gauge)

A fuel flow meter completes the trifecta of engine measurement gauges.


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