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+--- Thread: boost readings (/showthread.php?tid=1893)
boost readings - larsalan - 10-25-2010
Just put a boost gauge on the intake manifold and I wonder if someone can help me make sense of what it's doing.
What causes vacuum to form?
I see a small dip into negative pressure from a dead stop. Then the psi will get up to like 5ish in 1st a bit higher in 2nd and in 3rd and 4th boost can go way up to 11+.
stock turbo. will have to get a close look to see who makes it.
Oh, I guess that is what's supposed to be.
http://forums.nasioc.com/forums/archive/index.php/t-252607.html
What kind of useful info can I glean from the gauge?
RE: boost readings - ConnClark - 10-25-2010
You will draw a slight vacuum at idle due to filter restriction and plumbing losses. Also the turbo doesn't spin fast enough at idle to create boost and the compressor acts as a further restriction.
It sounds like your boost numbers are pretty good for a stock turbo. If you can find a very steep hill to climb in first I'm sure you'll get boost pressures as high as the other gears.
RE: boost readings - ForcedInduction - 10-25-2010
(10-25-2010, 02:14 PM)larsalan What causes vacuum to form?Usually gauge quality. If there was a restriction high enough to form vacuum in the intake the engine's performance would be very poor.
Quote:boost can go way up to 11+.Boost on a stock engine shouldn't go higher than 9psi.
Quote:What kind of useful info can I glean from the gauge?Nothing really on a stock engine. Its just to satisfy curiosity.
RE: boost readings - larsalan - 10-25-2010
The 11psi must be from my fiddling with the wastegate. What kind of risks do I run from too much pressure?
head bolts and head gasket. Anything else? or do you mean the stock turbo shouldn't make that much?
I guess I'm thinking about the water injection too. What are required circumstances for water to be injected.
Like psi must be 5+
and the motor must be up to operating temp
and the water tank must have fluid.
RE: boost readings - ConnClark - 10-25-2010
11psi is at the top of the range of allowable boost pressures specification by the Mercedes Shop Manual. On a stock engine its just fine.
RE: boost readings - ForcedInduction - 10-25-2010
(10-25-2010, 05:38 PM)larsalan What kind of risks do I run from too much pressure?Low fuel economy. The stock engine doesn't need more than 12psi.
Quote:I guess I'm thinking about the water injection too. What are required circumstances for water to be injected.Post-turbo injection with at least 100psi water pressure and an atomizing nozzle set to turn on no earlier than 5psi boost (preferably 8psi to reduce unnecessary consumption).
RE: boost readings - ConnClark - 10-26-2010
(10-25-2010, 02:14 PM)larsalan What kind of useful info can I glean from the gauge?
I didn't see this the first time. The most obvious use of the gauge is see if you have a boost leak or turbo problem. Usually these are progressive problems that get worse. Eventually you'll notice your boost is lower than it used to be under certain driving conditions.
You can use a boost gauge to improve your fuel economy. If you drive in a way that keeps the boost gauge as low as possible your extracting the greatest percentage of combustion energy with the pistons. This does not mean that you want to modify things to keep your boost low however as it does improve efficiency.
RE: boost readings - winmutt - 10-27-2010
(10-25-2010, 02:58 PM)ForcedInduction(10-25-2010, 02:14 PM)larsalan What causes vacuum to form?Usually gauge quality. If there was a restriction high enough to form vacuum in the intake the engine's performance would be very poor.
Quote:boost can go way up to 11+.Boost on a stock engine shouldn't go higher than 9psi.
Quote:What kind of useful info can I glean from the gauge?Nothing really on a stock engine. Its just to satisfy curiosity.
Ive always seen a dip when first revving the engine on every gauge I have ever seen on every turbo om6XX engine I have ever seen.