Thread: Boost gauge connection

Depending on your set up it can vary. You will get a very different reading if you fit it after the intercooler in the inlet manifold, as you would fitting it in the output scroll of the turbo. Up to you really .Depending on the type of engine/turbo set up it can be a couple of psi either way.

Have fun
Justin

I have tapped into the wastegate connection. After all that is the pressure that opens the gate.

Trev.

most aircraft measure the manifold pressure after the throttle plate, so you get a reading of the induction system pressure.
taking the reading from the supercharger side of the throttle will give you 'upper deck' pressure, which in a car will vary eratically with throttle opening as the upper deck manifold pressure changes with throttle opening and wastegate opening/closing, good for the doof doof boys that want to make a two horsepower starion make two and a quarter horse power with a lot of noise and show, [needle moves faster than w---ing] but you want to see what the cylinder is getting, and be able to tune or drive to your chosen power. normally aspirated vehicles also take the manifold pressure from the engine side of the throttle.
the 'manifold pressure' term is more correct than 'vacuum' as the pressure in the induction manifold is not a vacuum, but a pressure that is less than ambient [air pressure outside the engine] and in a supercharged engine will be more than ambient due to the air being pumped in, rather than being drawn in by the engine when the piston causes a reduced pressure in the cylinder that causes normal atmospheric pressure to push air in.
boost, woops, better stop here.

Originally Posted by harry

most aircraft measure the manifold pressure after the throttle plate, so you get a reading of the induction system pressure.
taking the reading from the supercharger side of the throttle will give you 'upper deck' pressure, which in a car will vary eratically with throttle opening as the upper deck manifold pressure changes with throttle opening and wastegate opening/closing, good for the doof doof boys that want to make a two horsepower starion make two and a quarter horse power with a lot of noise and show, [needle moves faster than w---ing] but you want to see what the cylinder is getting, and be able to tune or drive to your chosen power. normally aspirated vehicles also take the manifold pressure from the engine side of the throttle.
the 'manifold pressure' term is more correct than 'vacuum' as the pressure in the induction manifold is not a vacuum, but a pressure that is less than ambient [air pressure outside the engine] and in a supercharged engine will be more than ambient due to the air being pumped in, rather than being drawn in by the engine when the piston causes a reduced pressure in the cylinder that causes normal atmospheric pressure to push air in.
boost, woops, better stop here.

Sorry, but 99% of diesels don't have a "throttle". The airflow into the engine is as unrestricted as possible, only the fuel is metered.

But I agree, the best place for the gauge is as close to the inlet manifold as possible, so you know the pressure going into the engine. An alternate fitting just after the turbo would be useful too, so you can measure the pressure drop through the intercooler and piping.

Originally Posted by isuzurover

Sorry, but 99% of diesels don't have a "throttle". The airflow into the engine is as unrestricted as possible, only the fuel is metered.

But I agree, the best place for the gauge is as close to the inlet manifold as possible, so you know the pressure going into the engine. An alternate fitting just after the turbo would be useful too, so you can measure the pressure drop through the intercooler and piping.

All update Discovery TD5 (facelift model) have a Throttle body.

Tombraider

I don't know about TD5's.

With both of my 300Tdi's, I removed the inlet manifold and drilled and tapped through a cast boss on the LH side to suit a 1/8" BSP fitting.

The 300Tdi manifold has a threaded plug on the rear end (near firewall), but I haven't measured the thread - looks to be around 1/4" BSP, but could be M12 fine.

Originally Posted by Bush65

The 300Tdi manifold has a threaded plug on the rear end (near firewall), but I haven't measured the thread - looks to be around 1/4" BSP, but could be M12 fine.

On ya Bushie, being the lazy sod that I am I was waiting for someone to give me a solution rather n me sorting one myself .

Too easy!

anyone ever bothered checking the pressure drop between the turbo and manifold ?