Boost Spike - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


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

Reply
 
 
 
LinkBack Thread Tools Search this Thread
Old 05-12-2010, 11:28 PM   #1
Junior Member
Thread Starter
 
Join Date: Oct 2009
Location: Mesa, AZ
Posts: 169
Total Cats: 0
Default Boost Spike

I've always had this boost spike, at first I thought it was because I had my actuator line coming from the intake manifold, today I moved it to the turbo outlet and I've still got the same 2psi boost spike to 9 psi then it goes back down to 7 psi.

I've got a sr20 t25 on my 1.6 engine. The WG has not been ported yet, didn't know if it would need it or not being that it's off a nissan and I'm sure they don't make their cars with boost spikes. The nissan it came off of normally runs 7psi stock. At the time that was my goal. I also tried to up the boost a little to 8 psi, same result of a 2 psi spike to 10 psi. I have a slight preload on my actuator, it's not adjustable, however I would think that releasing some pressure off the rod would only lower my boost and still have the spike.

I can't think of anything else that would be causing it right now, I do have 3" straight through exhaust, I've read on here that free flowing exhaust makes boost spike worse but I don't have anything to restrict it right now. If I could make a baffle to stick in there to restrict the flow to see if the spike goes away it would pin point that it is indeed the waste gate being too small right?

I'd like to fix this asap so I can boost 10 psi this weekend weeeee!
Cookie Monster is offline   Reply With Quote
Old 05-12-2010, 11:31 PM   #2
Elite Member
 
Join Date: Feb 2008
Location: Victoria, BC
Posts: 2,322
Total Cats: 12
Default

Not much you can do. You can try porting the wastegate, or just accept the fact that it's boost spiking. My 300ZX T25 would boost spike to 18psi, and then settle in at 14. I wouldn't worry about it going to 12psi for a short time then settling at 10.
dustinb is offline   Reply With Quote
Old 05-13-2010, 02:06 AM   #3
Elite Member
iTrader: (10)
 
Join Date: Oct 2008
Location: Seattle, Wa
Posts: 1,780
Total Cats: 30
Default

With 430cc injectors you could run that little turbo to 14 or 15psi without issue, just raise up the boost and ball hard.
Jeff_Ciesielski is offline   Reply With Quote
Old 05-13-2010, 08:07 PM   #4
Junior Member
Thread Starter
 
Join Date: Oct 2009
Location: Mesa, AZ
Posts: 169
Total Cats: 0
Default

The injectors are only running 46% duty cycle so your right there. I'm more worried about the motor, it's completely stock except for the turbo stuff. How much can that engine take anyway? I've heard more than 220hp is risky but I don't know how much boost I would need to be at that level.
Cookie Monster is offline   Reply With Quote
Old 05-13-2010, 08:14 PM   #5
Elite Member
iTrader: (10)
 
Join Date: Oct 2008
Location: Seattle, Wa
Posts: 1,780
Total Cats: 30
Default

Quote:
Originally Posted by Cookie Monster View Post
The injectors are only running 46% duty cycle so your right there. I'm more worried about the motor, it's completely stock except for the turbo stuff. How much can that engine take anyway? I've heard more than 220hp is risky but I don't know how much boost I would need to be at that level.
On a good tune, 250hp is easily doable on a stock block. I would guess that 14-16psi would put you at 230whp+. Show some mechanical empathy and the motor will be fine.
Jeff_Ciesielski is offline   Reply With Quote
Old 05-13-2010, 08:37 PM   #6
Elite Member
 
Join Date: Feb 2008
Location: Victoria, BC
Posts: 2,322
Total Cats: 12
Default

Quote:
Originally Posted by Jeff_Ciesielski View Post
On a good tune, 250hp is easily doable on a stock block. I would guess that 14-16psi would put you at 230whp+. Show some mechanical empathy and the motor will be fine.
On a sr20t25 14-16psi would probably be about 200hp.
dustinb is offline   Reply With Quote
Old 05-13-2010, 08:41 PM   #7
Elite Member
iTrader: (10)
 
Join Date: Oct 2008
Location: Seattle, Wa
Posts: 1,780
Total Cats: 30
Default

Quote:
Originally Posted by dustinb View Post
On a sr20t25 14-16psi would probably be about 200hp.
...

That's sad. I guess I've been giving those too much credit.

Edit: To be fair though, from the dyno sheets I've seen, it looks like 16psi on an sr20 t25 + 1.8 would get you close to ~220-230whp. 1.6....not so much.
Jeff_Ciesielski is offline   Reply With Quote
Old 05-13-2010, 10:46 PM   #8
Tour de Franzia
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

hustler is offline   Reply With Quote
Old 05-14-2010, 12:22 AM   #9
Junior Member
 
Join Date: Dec 2009
Posts: 63
Total Cats: 0
Default

T25 s love to spike. Fairly normal to get a 2-5psi spike.

Most just live with it because it doesn't really hurt anything with T25 on the SR20. External gates get rid of the spike and gain some power. 38mm works great for that.
wnwright is offline   Reply With Quote
Old 05-14-2010, 10:26 PM   #10
Junior Member
Thread Starter
 
Join Date: Oct 2009
Location: Mesa, AZ
Posts: 169
Total Cats: 0
Default

I guess I'll deal with it for now. It's not a massive spike anyways, just very annoying to watch. I'll port out the waste gate later.
Cookie Monster is offline   Reply With Quote
Old 05-14-2010, 10:33 PM   #11
Junior Member
Thread Starter
 
Join Date: Oct 2009
Location: Mesa, AZ
Posts: 169
Total Cats: 0
Default

Quote:
Originally Posted by Jeff_Ciesielski View Post
...

That's sad. I guess I've been giving those too much credit.

Edit: To be fair though, from the dyno sheets I've seen, it looks like 16psi on an sr20 t25 + 1.8 would get you close to ~220-230whp. 1.6....not so much.
I got 156hp at 6.5 psi without an intercoooler. I installed the intercooler and changed nothing else and I gained a very very nice amount of power, how much is unknown. It did drop the IAT's 40-50* or about 3* above ambient. Time for a redyno for sure.
Cookie Monster 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
LucaCarMods's Boosted Dutch Miata Build! LucaCarMods Build Threads 11 02-14-2016 07:13 AM
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 08:41 PM.