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Old 03-08-2009, 10:12 PM   #1
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Default Boost pressure and boost cut

I wanted to get some input from you guys on where you have your boost cut set. I would like to run 12 pounds (~183kpa) of boost. I felt like I had that set pretty well, tuned at ambient temperatures around 75 degrees. When I datalogged I saw a spike to 189kpa but pressures seemed to hold right around 180-185kpa. I set boost cut to 200kpa, which I figured would give me a little leeway but still be safe enough if I did jump that high. The trouble is when it's cooler out, even 65 degrees out, I'm getting a little boost cut at higher rpms. Conversely, when it gets up to 85 degrees I'm loosing a little boost.

Also, should I be seeing this much variance in pressure when the temperature fluctuates (talking about the difference in 11.5 and 14.5psi w/ a 20 degree ambient fluctuation)?

Finally, if that much fluctuation in manifold pressure is common, what do you consider "the boost you're running" to be? For example, hypothetically on a very cold day I peak 15psi and I consistently hold 14psi, on a normal day I peak 13psi and consistently hold 12psi, then on a hot day I peak 11psi and consistently hold 10psi. What would you personally consider boost I'm running to be? I realize this may sound like a stupid question, but I think most would agree here that 10psi on a stock motor is fairly safe, while 15psi on a stock motor is pushing the limits, I'd just like to clarify how "xx psi" is being defined. So I can tune accordingly.

Thanks for the help. I appreciate you guys baring with my stupid questions.

*Mods, if this isn't the right forum, I apologize and feel free to move it, I wasn't sure where it should go*
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Old 03-08-2009, 10:16 PM   #2
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u yeah thats simple physics man cold air is denser. 1-2 psi is perfectly fine.
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Old 03-08-2009, 10:25 PM   #3
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Get rid of your MS-controlled EBC and get a simple MBC. It brings the temp variances to like 1psi, instead of 3-4. Open-loop EBC is crap.

I used to aim for 15psi, overshoots to 16.5, had the overboost cut at 17.5psi.
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Old 03-08-2009, 11:14 PM   #4
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on my vw's I loved EBC because it was a highway car. Its nice to have the slower response with the MBC, its more predictable and easier to drive on the track. If you're just a streetracer though, it you'll probably like the EBC.
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Old 03-09-2009, 04:07 PM   #5
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I gave up on the EBC and went back to the MBC. I have the MBC set for 189 and I have boost cut set at 198, but it is tuned up there. I don't want to go higher than 14psi. I retarded the timing and added fuel to the cells from 198 to 212. In case the MBC and the boost cut fails, unlikely, then I am covered. 16psi is ridiculous, and I don't need a DD street car with that much power. There is no place in the city to exploit its potential.
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Old 03-09-2009, 09:17 PM   #6
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Guess I should have mentioned I'm running a MBC.
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