So i swapped my wastegate to the conventional style with parts listed on thread fro gsxr. I have been running this way for maybe 3 months. I normally drive around 25 miles each way to work ranging between 70 and 80 with cruise control on. Last night I had some free time and hooked up the 30 psi boost gauge I bought some time ago. I noticed today on the drive in, at 78 indicated I was holding 9ish psi. I do not have an EGT but plan to get one. Does this seem about right?

I also took so video of the gauge. Seems in the beginning there was a pressure spike to 17. Perhaps bleeding of the gauge. Normal seems to hold at 14.5 psi

https://www.youtube.com/watch?v=JRJqVFKmOUQ

my sd hit 23 psi, but i'd keep it to 16 psi taking off

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

how about on the highway?

hill about 12,cruising 9 10

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

Boost pressure will depend on engine load, not RPM or cruising speed. Since you're testing your wastegate setup, go find a long hill and give it a bootful going up the hill. If you're after a stock pressure (and you should be unless you've modified your engine) you should see the gauge max out somewhere around 13-14PSI.

Unless you've turned the fuel up on your injection pump, any higher boost is just wasted.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

I don't care about max boost. I wanted to verify boost level on the highway. At some point rpm and boost cross paths no matter what. I sit at 5 psi with cruise at 70. 9psi at 78-80.

As I said before, boost is a function of LOAD, not RPM. Don't believe me? Go find a hill. Go the same speed up and go back down the same hill at the same speed. You'll have higher boost going up the hill than coming back down. Neither will be the same boost level as on flat ground doing the exact same speed.

The wastegate only comes into play to limit the maximum boost to a given level. At no other time is the wastegate open, any boost you generate is due to the exhaust gasses expanding through the turbine side of the turbocharger.

You set the wastegate for the maximum boost level you want to see in your intake manifold.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

congrats on clarifying something i'm well aware of. You keep sidestepping my question, meaning you likely don't know what your car does on flat land at 70 on cruise. All i wanted to know is what people are seeing boost wise on the highway with cruise control on. I know it will be slightly different car to car and location to location. Not sure why you are getting so worked up.

Thanks i missed this response earlier.

Because you're asking a question that is specific to your car, in your climate, on your terrain, with your tires, running the fuel (and any additives you may run), and of course weather conditions.

If you run 9PSI today, you may run 10 PSI tomorrow depending on if it's cooler, more humid, etc. Your car doesn't have an intercooler so your power production will vary with the weather conditions and fuel quality. I'm not getting worked up BTW, I'm trying to explain how the turbocharger works. You won't get "XPSI at X000 RPM" It just doesn't work that way.

FWIW, my car runs 10-12PSI at 70. There are no flat roads here, so the best I can do is a slight gradient up or down (as a result, no I DON'T know what my car does on level ground since I can't test it where I live). It varies with the weather conditions as well. It can be as low at 9 or as high as 13 depending on weather and which grade I'm on. Going up a hill at 70 pegs at 13.5PSI where my wastegate operates. Going back down runs somewhere around 4-5PSI.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Hey you the man.