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Wastegate operation on a Mercedes 300D Turbodiesel

Can someone help me to understand just how the wastegate operates on my

83 W123 Benz I5 Turbodiesel.

I assume the following: (correct me if I'm wrong)

The hose going from the intake (high pressure) side of the turbo goes to the wastegate on the exhaust side of the turbo. I think this wastegate operates like a pop valve... The turbo boosts to a high threshold pressure causing the wastegate to open. This allows excess pressure to escape into the exhaust. Then the turbo slows and the boost pressure drops to a low threshold causing the wastegate to close.

I did an experiment today to see if my analysis of the system was correct. I unhooked the hose to the wastegate and held my finger over it with the engine running. Then I revved it very gently... Just enough to get the turbo to spool very slightly. I felt a little pressure indicating boost.

Next I wanted to see just how much power I would lose by unhooking this hose and driving the car. To my surprise, the engine performance did not change drastically. I did notice that I had the acceleration was much more linear. That makes sense because there was no wastegate to stay closed until the high threshold pressure was reached. Unhooking the hose simulated having the wastegate open all the time.

I actually liked the performance without the wastegate. That "power surge" form 1st to 2nd gear was greatly softened. This also feels like it is not as hard on the transmission during the 1st to 2nd shift. There is not as much torque at that instant.

I also enjoyed the "psssssh" sound since the hose was venting under the hood and not into the exhaust anymore.

I am really thinking about getting a boost gauge hooked up to the intake so I can tweak the boost. I am planning on installing a valve on this hose and venting the hose into the engine compartment. This way I can adjust the max boost to about 12 PSI. The smaller the leak, the more boost and vice versa. I also like a more linear power distribution and the noise :)

Any input is welcome. I would like to know if anyone else has done something similar.

Reply to
bcc304
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You're close.

There are two components to the power surge: Turbo boost which is limited by the wastegate to about 10 or 11 psi and, fuel enrichment based on the turbo's boost. (It takes fuel to make power.)

The hose to the wastegate delivers the turbo's boost pressure, not air volume, against a spring loaded piston. As the boost overcomes the spring's load the wastegate valve opens a passage for the exhaust gases to bypass the turbocharger and be dumped directly into the exhaust. Some owners have cranked the adjustment to increase the turbo's boost pressure to about 12 or 13 psi - some turbochargers are easily adjusted, others easy to adjust but nearly impossible to get back together again. So don't. Now to fuel.

Look at the very aft end of the motor's intake manifold. You'll find a "banjo" fitting attached there by a hollow bolt. It's designed to transmit the turbo's boost pressure over to the injection pump's sensor. As the boost rises the injection pump adds fuel - beyond the throttle setting - to give the car better acceleration. To see the difference, simply remove (and pocket) the hollow bolt and drive the car without the line to the injection pump connected - that's flat acceleration! And it's not due to some air escaping, its lack of additional fuel.

That's how it works.

Reply to
T.G. Lambach

Stu Ritter once drove a car with a welded shut wastegate and disabled the ovrboost protection. He said it pulled like a 300SEL 6.3 but only drive it two blocks cause he figured the engine would melt down pretty quickly.

The wastegate is supposed to open at 1.1 bar, most of them come out of the factory at 0.9 bar so there is a bit of tweaking there while still keeping it in spec. Clean out the banjo fitting too, it gets clogged easily and frequently and robs power.

Reply to
Richard Sexton

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