Open downpipe = Overboost? - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


DIY Turbo Discussion greddy on a 1.8? homebrew kit?

Reply
 
 
 
LinkBack Thread Tools
Old 05-13-2008, 11:55 PM   #1
Senior Member
Thread Starter
iTrader: (7)
 
Join Date: Aug 2007
Location: Southern Indiana
Posts: 1,371
Total Cats: -1
Default Open downpipe = Overboost?

So, a friend of mine with a mach 1 called me out (I know street racing is dumb but the road was closed) so I pulled my test pipe out. Well, my wastegate was set around 10 psi and i had an MBC set up for around 12 psi. So, we lined up and launched and i hit overboost (200kpa) hard, shifted, hit overboost again and stopped. I don't exactly understand what happened. Can someone enlighten me? Maybe i am missing how the wastegate actuator actually works.

Thanks in advance,
--Wes
wes65 is offline   Reply With Quote
Old 05-14-2008, 12:32 AM   #2
Elite Member
iTrader: (13)
 
cjernigan's Avatar
 
Join Date: Oct 2006
Location: Atlanta, GA
Posts: 8,147
Total Cats: 6
Default

That's the problem with the increased flow your regulator can't control boost well enough so you overboost badly. Go read Paul's old thread on this with his MSM kit he had on his car a while back.
You need some exhaust restriction or intake restriction to cure that. Port your wastegate and add a helper spring to the actuator if needed.
cjernigan is offline   Reply With Quote
Old 05-14-2008, 12:37 AM   #3
Senior Member
Thread Starter
iTrader: (7)
 
Join Date: Aug 2007
Location: Southern Indiana
Posts: 1,371
Total Cats: -1
Default

Hmm, sounds like i just need to get a real exhaust instead of running stock for daily driving and open DP for racing.
wes65 is offline   Reply With Quote
Old 05-14-2008, 12:38 AM   #4
Senior Member
Thread Starter
iTrader: (7)
 
Join Date: Aug 2007
Location: Southern Indiana
Posts: 1,371
Total Cats: -1
Default

The spool, however, was ridiculous with open dp.
wes65 is offline   Reply With Quote
Old 05-14-2008, 02:12 AM   #5
Supporting Vendor
iTrader: (3)
 
Join Date: Jul 2006
Location: San Diego
Posts: 2,862
Total Cats: 484
Default

Hmm.. but an open downpipe should be optimal. Maybe the problem is that your MS settings in one way or another are set up for the stock exhaust and the change to far less restriction needs to be acounted for in your settings...
I don't know enough about this stuff yet to give serious input, but it doesn't make any sense why you 'need' an exhaust vs. just unbolting the exhaust, the problem is that settings are allowing the overboost to hit, no?
-Ryan
ThePass is offline   Reply With Quote
Old 05-14-2008, 02:35 AM   #6
Supporting Vendor
iTrader: (31)
 
Savington's Avatar
 
Join Date: Nov 2006
Location: Sunnyvale, CA
Posts: 14,357
Total Cats: 1,322
Default

Quote:
Originally Posted by ThePass View Post
Hmm.. but an open downpipe should be optimal. Maybe the problem is that your MS settings in one way or another are set up for the stock exhaust and the change to far less restriction needs to be acounted for in your settings...
I don't know enough about this stuff yet to give serious input, but it doesn't make any sense why you 'need' an exhaust vs. just unbolting the exhaust, the problem is that settings are allowing the overboost to hit, no?
-Ryan
No. MS cannot account for a shitty wastegate. If you have a 10psi can, and boost control set for 12psi, no MS setting will account for a 15psi spike. You need to port your wastegate. I have the same problem on cold nights with my 3" DP and 3" catback; during the day I can scream along at 15-15.5psi, but if I try and do a highway pull at night I smack the 16.5psi overboost pretty consistently.
Savington is offline   Reply With Quote
Old 05-14-2008, 03:46 AM   #7
Elite Member
iTrader: (11)
 
Join Date: Jun 2007
Location: Overland Park, Kansas
Posts: 5,382
Total Cats: 43
Default

Quote:
Originally Posted by Savington View Post
No. MS cannot account for a shitty wastegate. If you have a 10psi can, and boost control set for 12psi, no MS setting will account for a 15psi spike. You need to port your wastegate. I have the same problem on cold nights with my 3" DP and 3" catback; during the day I can scream along at 15-15.5psi, but if I try and do a highway pull at night I smack the 16.5psi overboost pretty consistently.
Sav, Educate me: I'm unclear about correlations betweem different air temps and wastegate response.. Is the overboost problem typically from internal wastegates Only?
elesjuan is offline   Reply With Quote
Old 05-14-2008, 10:30 AM   #8
Senior Member
Thread Starter
iTrader: (7)
 
Join Date: Aug 2007
Location: Southern Indiana
Posts: 1,371
Total Cats: -1
Default

When the air is colder the charge is more dense, therefore, you create more boost. The size of the internal wastegate port is fairly small compared to the turbine outlet, therefore, when the exhaust is more dense, the exhaust has a tendency to flow through the larger turbine outlet instead of the wastegate outlet. This is alleviated by using an external wastegate because they respond faster, have a larger port, and are farther away from the turbine outlet.

I hope that makes sense, i need to take a technical writing course.
wes65 is offline   Reply With Quote
Old 05-14-2008, 11:47 AM   #9
Senior Member
iTrader: (6)
 
nester's Avatar
 
Join Date: Sep 2005
Location: Houston, TX
Posts: 812
Total Cats: 0
Default

Basically, because you've decreased the restriction on the turbine, the exhaust gas is not forced out of the wastegate.. either because the wastegate is too small, or the actuator is too slow, or both.

This is pretty common on a number of cars, DSM's and Subaru's come to mind. This is when they either go to a ported wastegate with bigger flapper (EVO3 16g with 34mm wg) or they go external.

My favorite solution to the problem is to add more fuel.
nester is offline   Reply With Quote
Old 05-14-2008, 12:14 PM   #10
Senior Member
Thread Starter
iTrader: (7)
 
Join Date: Aug 2007
Location: Southern Indiana
Posts: 1,371
Total Cats: -1
Default

My wastegate was tightened a lot to get that 10psi, so i loosened it and put my MBC back on. Hopefully i can control my boost a little bit easier now.
wes65 is offline   Reply With Quote
Old 05-14-2008, 12:41 PM   #11
Elite Member
iTrader: (30)
 
Join Date: Aug 2007
Location: Va Beach
Posts: 7,282
Total Cats: 0
Default

I had the same problem when I went from a 2.25" exhaust to my 3" exhaust. With the smaller exhaust I saw a constant 8psi. Now with the 3" my boost spikes to nearly 10psi. I've kept an eye on my wideband and it hasnt become an issue.
__________________
Best Car Insurance | Auto Protection Today | FREE Trade-In Quote
levnubhin is offline   Reply With Quote
Old 05-14-2008, 02:21 PM   #12
Antisaint
iTrader: (17)
 
Vashthestampede's Avatar
 
Join Date: Feb 2007
Location: Danbury, CT
Posts: 4,659
Total Cats: 54
Default

After reading this I'm glad I'll be going from my 2.25" exhaust to the 3" at the same I will be going to an external wastegate system.

So I take it the mach1 won?

Vash-
Vashthestampede is offline   Reply With Quote
Old 05-14-2008, 05:05 PM   #13
Senior Member
Thread Starter
iTrader: (7)
 
Join Date: Aug 2007
Location: Southern Indiana
Posts: 1,371
Total Cats: -1
Default

Quote:
Originally Posted by Vashthestampede View Post
So I take it the mach1 won?

Vash-
Haha, yeah, technically he did, he is up for a rematch though! His car is basically stock with intake and exhaust.
wes65 is offline   Reply With Quote
Old 05-14-2008, 05:31 PM   #14
Elite Member
iTrader: (11)
 
Join Date: Jun 2007
Location: Overland Park, Kansas
Posts: 5,382
Total Cats: 43
Default

Quote:
Originally Posted by wes65 View Post
When the air is colder the charge is more dense, therefore, you create more boost. The size of the internal wastegate port is fairly small compared to the turbine outlet, therefore, when the exhaust is more dense, the exhaust has a tendency to flow through the larger turbine outlet instead of the wastegate outlet. This is alleviated by using an external wastegate because they respond faster, have a larger port, and are farther away from the turbine outlet.

I hope that makes sense, i need to take a technical writing course.
That makes perfect sense. I guess it didn't really occur to me that more air in = more air out.


Quote:
Originally Posted by wes65 View Post
Haha, yeah, technically he did, he is up for a rematch though! His car is basically stock with intake and exhaust.


Get that **** fixed and walk his ***, Son!
elesjuan is offline   Reply With Quote
Old 05-14-2008, 05:41 PM   #15
Senior Member
Thread Starter
iTrader: (7)
 
Join Date: Aug 2007
Location: Southern Indiana
Posts: 1,371
Total Cats: -1
Default

Quote:
Originally Posted by elesjuan View Post
Get that **** fixed and walk his ***, Son!
One of the main reasons i am building this car, to smoke all the guys with stock mustangs/TA's/camaros/corvettes that think they are tough ****.
wes65 is offline   Reply With Quote
Old 05-14-2008, 09:04 PM   #16
Elite Member
iTrader: (11)
 
Join Date: Jun 2007
Location: Overland Park, Kansas
Posts: 5,382
Total Cats: 43
Default

Quote:
Originally Posted by wes65 View Post
One of the main reasons i am building this car, to smoke all the guys with stock mustangs/TA's/camaros/corvettes that think they are tough ****.
Haha. I can't wait myself!

Its a lose / lose situation for anyone that ever runs against a miata. Nobody will brag they beat a miata, and nobody will ever tell anyone they got beat by a miata.
elesjuan is offline   Reply With Quote
Old 05-14-2008, 09:16 PM   #17
Junior Member
 
Join Date: Oct 2007
Location: AC, NJ
Posts: 346
Total Cats: 0
Default

Quote:
Originally Posted by wes65 View Post
Haha, yeah, technically he did, he is up for a rematch though! His car is basically stock with intake and exhaust.

Look out, Cobras can get over 50HP from a K&N intake. Now thats poor design.
compy is offline   Reply With Quote
Old 05-14-2008, 09:24 PM   #18
Elite Member
iTrader: (11)
 
Join Date: Jun 2007
Location: Overland Park, Kansas
Posts: 5,382
Total Cats: 43
Default

Quote:
Originally Posted by compy View Post
Look out, Cobras can get over 50HP from a K&N intake. Now thats poor design.
I hope you're talking about the 03/04 Cobra..
elesjuan is offline   Reply With Quote
Old 05-14-2008, 11:44 PM   #19
Senior Member
iTrader: (4)
 
Join Date: Aug 2007
Location: Guam (U.S Terr.)
Posts: 786
Total Cats: -2
Default

I hear you on the stock exhaust. I do the same. DD with it on and race with it off.
mike_671 is offline   Reply With Quote
Old 05-15-2008, 12:17 AM   #20
Murderator
iTrader: (76)
 
18psi's Avatar
 
Join Date: Apr 2008
Posts: 36,174
Total Cats: 2,575
Default

Quote:
Originally Posted by elesjuan View Post
Haha. I can't wait myself!

Its a lose / lose situation for anyone that ever runs against a miata. Nobody will brag they beat a miata, and nobody will ever tell anyone they got beat by a miata.
omg so true
18psi is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Project Gemini - Turbo Civic on the Cheap Full_Tilt_Boogie Build Threads 57 07-19-2017 05:11 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
1996 Turbo Build Goldwar DIY Turbo Discussion 2 09-29-2015 10:20 AM
WTB; na6 Miata things (Canada) Jared Rowe WTB 0 09-23-2015 12:57 PM


Thread Tools

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 02:58 AM.