Supercharged boost loss question

[tenxal]

Can a supercharged engine show a significant loss of boost if the engine has excessive blow by/leakage?

Thanks!

[PackardV8]

"Boost" or inlet manifold pressure is the measure of work done by the supercharger/turbocharger which could not be utilized by the intake valve/cylinder, thus remains in the intake manifold. I.E, it's measured in the intake system, before the cylinder, so worn rings/poor ring seal/blowby should not, in theory, affect inlet manifold pressure, true?

[Keith Morganstein]

You would see a major increase in blow-by / crankcase pressure if the rings are that worn.

It actually a way to check ring seal on turbo Diesel engines. Compare no load blow-by to full load. A very worn engine may show 6X as much.

[user-23911]

When you start playing with boost, it's pretty "normal" to end up with broken ringlands.

Then you get increased crankcase pressure which shows up as oil leaks.

Like leaks at the filler cap and the dipstick blowing out.

[tenxal]

"Boost" or inlet manifold pressure is the measure of work done by the supercharger/turbocharger which could not be utilized by the intake valve/cylinder, thus remains in the intake manifold. I.E, it's measured in the intake system, before the cylinder, so worn rings/poor ring seal/blowby should not, in theory, affect inlet manifold pressure, true?

Jack, that is my understanding, also. This one is a puzzler, for sure. Lots more to check out. It's down on power and the data shows about a 25-30 percent lost of boost relative to what was recorded previously.

[MadBill]

No. Boost pressurizes the cylinders; that's the whole point, BUT it would take huge blow by (like the top missing from a piston) to show up on a boost gauge. Burned valves would be a different story..

[CharlieB53]

Increased clearances between rotors and case will reduce boost. Sloppy rotor end clearances possibly caused by overheating will reduce boost.

[MadBill]

A blown out intake or SC base gasket would also drop the boost some...

[user-23911]

An IAT gauge will give an idea as to what's going on.

Loss of efficiency = higher intake temps.

Pulling and inspecting sparkplugs never fails either.

[tenxal]

All the basics seem to be fine. The boost actuator valve may be the culprit.

[ptuomov]

I don’t know what kind of supercharger drive you have, but would slipping belt be the most common explanation for low boost and low power?