Thread: 300tdi boost question.

nope thats normal...

you dont need full boost to make full rpm so the white man magic in the fuel injector pump limits the fuel flow when max rpm is reached. without max fuel you cant get max boost.

if you leave the boost gauge on and push it up a hill you'll get full boost without full speed.

Petrols work the same.

for comparison

Big red will sit on 17psi boost in top cog at 100 on the hills from about 80kph right up to as fast as my wallet will let me go.

put her in angel gear and im lucky to hit 5psi before the instinct that the engines going to have a hearty and I should ease up off the limiter kicks in.

how ever my mates turbod 351 would not read any boost with out load. and later after replaceing the turbo with a super charger centrfical no screw type would get one psi with no load so why does this not happen with the diesel?

Vacuum operated boost control I would think but Im not entirly sure of that.

Originally Posted by 460cixy

how ever my mates turbod 351 would not read any boost with out load. and later after replaceing the turbo with a super charger centrfical no screw type would get one psi with no load so why does this not happen with the diesel?

as the super charger is shaft driven and not exhaust gas driven then boost pressure is directly related to crankshaft speed (and limited by the safety valves and a few other factors)

Turbo charges run on exhaust gas so engine RPM is no longer the sole consideration as you will pump out more exhaust gas when your dumping more fuel in. A diesel cuts the fuel back when the govenor says that its going faster than wanted so the exhaust gas generation is limited.


A fun fact..

A turbo can be made to run with just a pipe, fuel and a source of ignition on exactly the same theory of a jet turbine engine.

theres a bloke in NZ whose got one setup running on bottled gas and he uses the cooling effect of the gas going from liquid to gas to run the turbo to cool his beer. the reason he needs to cool the beer is cause some idiot runs a jet engine up in his shed....

My kinda guy I'll dig up his site

edit Link found

disclaimer first

What follows is my story about a shed, a warm beer and a home made jet engine. It is being presented for entertainment purposes only and no-one should attempt to emulate what I have done here. The risks should be obvious but it is worth pointing out that beer is a very dangerous substance when used without due care.

http://www.asciimation.co.nz/beer/

endedit

Originally Posted by 460cixy

how ever my mates turbod 351 would not read any boost with out load. and later after replaceing the turbo with a super charger centrfical no screw type would get one psi with no load so why does this not happen with the diesel?

This is interesting and not really something that I have thought about.

My guess is that it is a result of the fact that the diesel doesn't have a throttle to restict the mass of air drawn into the engine. Hence even at low speed with little load, there is sufficient exhaust flow to generate some (quite significant it seems) boost.

I'm interested to see what others think.