9 psi max boost
 

Is that on the low side? What is the max boost I should shoot for with the stock IP fueling for best performance /economy?

Is this on your 300D? I have the same question...

Don't quote me on this, but I'm thinking 12-15

12-15 sounds like the right area. we have a 300sd running around with 20 and a bit more fuel and it seems pretty happy. but... you have to watch out for overboost protection at about 16 psi

The boost air pipe is provided with a pressure switch (3) At a boost pressure above 1.1 ±0.15 bar gauge pressure, the pressure switch will close and will connect minus (negative) to changeover valve (2), which is connected to plus (positive) via terminal 15. The changeover valve interrupts the connection boost air pipe to ALDA aneroid capsule on injection pump. The aneroid capsule is connected to atmosphere and the injection fuel quantity is thereby reduced. If the pressure drops to below 1.1 ±0.15 bar gauge pressure, the pressure switch will again interrupt the minus (negative) connection and will connect the ALDA aneroid capsule again to boost air pipe

http://sphotos.ak.fbcdn.net/hphotos-..._5133570_n.jpg

Hope that worked, last time i tried to post a pic it went very wrong...

:o oh no... you mean ive been wasting energy this whole time?

... unless you have added fuel.

:D sarcasim is hard to get across it text.

Only to those of us who aren't paying attention (me).

If you've removed the Full load fuel limiter then the max boost you should run is about 15. If you have a intercooler then up to 18 or so- after that the air is still heated quite a bit. You need a egt placed properly as well as a good boost gauge. If you have a IC and both gauges with the stock turbo then no more than 17-20 and make sure you keep the temp under 1200 on a regular basis, and 1350 for no more than 20 seconds, never above 1550. Better safe than sorry and these figures are very liberal- go on the conservative side and drop them all a hundred degrees really. I run up to 25 psi boost with my myna pump and get to 1400 for perhaps 15 seconds after a hard pull ending in 90 mph- but my exhaust manifold is coated with a jet hot type process and I have a IC. I also have some of the best junkyards in the USA to pull spare parts from. I have 1978 300SD intake and exhaust manifolds- pre EGR stuff with larger tubing.

Thanks for the helpful replies. This is the second boost gauge I tried with the same reading so it is unlikely a gauge issue. I am gonna check and make sure I have no leaks in the boost lines. What other things should I check? What are the usual causes of low boost in a 28 year old 300D turbo?

I vote wastegate spring. If it was a fuel issue it should still climb above 9 under full load. If it reaches 9 early and levels off it is your wastegate. Just to be sure though let me check my crystal ball ;)

"Less boost is needed with an intercooler"

More boost is possiable with a intercooler

Boost is air.
Fuel is fuel

More fuel without more boost is more energy, but without more air it has diminishing returns.
More boost allows more fuel.

More fuel and boost creates more heat, an intercooler/aftercooler allows more fuel and boost than is possible without by keeping the charge temperature down. The intercooler also creates a more dense charge (cooler) so that more gasses are introduced into the combustion chamber for more power.

It is generally accepted that an intercooler added to an engine that does not need it, wastes energy through more intake restriction. The three are best designed in together.

agreed.