Help me settle an argument
 

Hi, so I know there are probably going to be alot of different opinions on this subject but here it goes. So first the vehicle is an 86 Toyota pickup that I swapped a Mercedes om617 in, for those of you not familiar with the engine its a 3.0L 5cyl mechanical turbo diesel. Anyway I said to my friend that I was going to turn up the boost with a manual boost controller and see how much boost it could take before the injectors/pump maxed out, and he said NO WAY! don't do that because it'll lean out and ruin the pistons, to which I responded you cant run a diesel too lean, the leaner the better until it gets too the point of so much air and not enough fuel that it just doesn't ignite. So my question is, am I correct in saying that you couldn't actually hurt a diesel by turning up the boost without any supporting mods because it would just lose combustion before it would hurt any of the internals?

it is just the opposite for diesels

diesels are not run on a lean to rich condition.

there is a theoretical "stoichiometry" for diesels but non of the engines are tuned for it. diesels are best run with just the amount of diesel needed to maintain the desired speed or acceleration

the more air added the cleaner it burns. there is a point that of no-return where putting in more air will not make it burn any better.

when you remove fuel to lean out a diesel all it does is goes down in HP. the leaner it is the cooler it will run till it cant make enough power to turn itself over and stalls

turning up the boost will usually allow it to burn more of the fuel so there will be some HP increases. increasing boost usually allows for more fuel to be injected for even more HP.

have fun playing with turning up your boost. the only things to keep in mind are your turbo maps. operating above the efficiency range can cause the turbo to make more heat then air flow and reduce its life. most stock turbos can be safely increased a few pounds with out noticeably reducing life.

we should add this one to: https://www.dieselbombers.com/genera...dos-donts.html

Oh man I'm so glad you actually know what your talking about. I've been reading on here and seeing all the horrible misconceptions some of these guys have about diesels I expected to be called a retard lol.

You can't just "turn boost up", you need heat/fuel to get the turbo to spin. Typically adding a little more fuel/timing will get you more boost.

There are a lot of misconceptions about boost too. Everyone thinks the higher the boost number, the better it is, but in reality, boost is a measurement of restriction. What we want is volume of air.

If you're pushing the limits of the turbo, you may want to consider measuring backpressure as well. Backpressure is a ratio of pressure it takes to drive the turbo, vs. what the turbo is making on the other side. We want this to stay as close to 1:1 as possible. If you're running 100psi of drive pressure and only creating 50psi of boost, you're going to have lots of problems.

Its already maxed out. More boost beyond the stock 11psi will not make ANY more power without internal pump adjustments.

Here is a guide for getting more power from your engine: Injection Pump fuel adjustment for the MW and M pumps, pyrometer install - Mercedes Forum - Mercedes Benz Enthusiast Forums

The injectors on IDI engines are not a restriction, the stock ones are good up to 100hp/cylinder.

Wow thats some great info, I will be doing the rack limiter removal and I have an intercooler that I haven't gotten around to installing yet, I guess we're going to find out how much torque a Toyota 5spd will take lol :up:

wow thats an nice stuff it would help me a lot thanks for the post.

I think David Lott of diesel innovations burned up an engine in his race truck because he leaned it out.

Its not common and not easy to do but it can happen.

You actually can run too much boost on that engine. Compression ratio is gonna be somewhere in the range of 18-1 to 23-1. Any more past 20 lbs of boost, and your looking at a blown head gasket.

As mentioned already, more air than fuel, major turbo lag.

The only thing running a diesel excessively lean will do is cause high turbo drive pressures. Same idea as using an exhaust brake, you're choking exhaust flow out of the engine which will make the hot combustion gasses stay in contact with the pistons and cylinder walls longer. That will also make the engine work harder which means more wasted combustion heat.

Not quite true. Mercedes engines are much better built than the International or Detroit IDI engines, they can take much higher boost with the stock 21.5:1 compression without any damage. People in Finland regularly run MB's 3.0L IDI diesels up to 300hp and 30psi boost with stock internals.