Boost pressure and boost cut - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to   Members

Engine Performance This section is for discussion on all engine building related questions.
Sponsored by:
Sponsored by:

LinkBack Thread Tools Search this Thread
Old 03-08-2009, 11:12 PM   #1
Elite Member
Thread Starter
iTrader: (17)
Join Date: Aug 2007
Location: Fort Myers, FL
Posts: 2,791
Total Cats: 130
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*
pdexta is offline   Reply With Quote
Old 03-08-2009, 11:16 PM   #2
iTrader: (7)
Join Date: Jul 2006
Location: nowhere
Posts: 8,281
Total Cats: 2

u yeah thats simple physics man cold air is denser. 1-2 psi is perfectly fine.
magnamx-5 is offline   Reply With Quote
Old 03-08-2009, 11:25 PM   #3
Supporting Vendor
iTrader: (31)
Savington's Avatar
Join Date: Nov 2006
Location: Sunnyvale, CA
Posts: 14,370
Total Cats: 1,332

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.
Savington is offline   Reply With Quote
Old 03-09-2009, 12:14 AM   #4
Tour de Franzia
iTrader: (6)
hustler's Avatar
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351

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.
hustler is offline   Reply With Quote
Old 03-09-2009, 05:07 PM   #5
Senior Member
iTrader: (4)
Join Date: Oct 2006
Location: Tampa
Posts: 780
Total Cats: 0

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.
96rdstr is offline   Reply With Quote
Old 03-09-2009, 10:17 PM   #6
Elite Member
Thread Starter
iTrader: (17)
Join Date: Aug 2007
Location: Fort Myers, FL
Posts: 2,791
Total Cats: 130

Guess I should have mentioned I'm running a MBC.
pdexta is offline   Reply With Quote

Related Topics
Thread Thread Starter Forum Replies Last Post
Project Gemini - Turbo Civic on the Cheap Full_Tilt_Boogie Build Threads 59 12-15-2017 09:00 PM
OTS Bilstein to motorsports ASN conversion stoves Suspension, Brakes, Drivetrain 5 04-21-2016 04:00 PM
Back to Stock Part Out!! Turbo Parts, MS2 Enhanced 01-05, Suspension, and MOAR! StratoBlue1109 Miata parts for sale/trade 16 10-02-2015 10:39 AM
Going back to stock. Need some 1.6 parts. Trent WTB 2 10-01-2015 01:15 PM
Bad head gasket or ? shooterschmidty Engine Performance 8 09-30-2015 11:28 PM

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

All times are GMT -4. The time now is 06:34 AM.