MBC overshoot - Page 2 - 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 12-14-2006, 12:08 PM   #21
Elite Member
Thread Starter
iTrader: (7)
 
samnavy's Avatar
 
Join Date: Apr 2006
Location: VIRGINIA BEACH, VA
Posts: 6,020
Total Cats: 175
Default

OK, I think I'll try that first... source off the manifold.
samnavy is offline   Reply With Quote
Old 12-14-2006, 12:18 PM   #22
Boost Czar
iTrader: (61)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 72,846
Total Cats: 1,787
Default

yeah, I should of suggested it as well.
Braineack is online now   Reply With Quote
Old 12-15-2006, 01:42 PM   #23
Senior Member
 
Join Date: Jan 2005
Posts: 737
Total Cats: 0
Default

Quote:
Originally Posted by AndyFloyd View Post
the internal wastegate is going to do that, no matter what.
The T25 wastegate port is too small to stop a small spike...unless you can somehow get an EBC to open before full boost is hit the wastegate cannot divert exhaust fast enough to stop a spike. You could port the wastegate hole to see if that helps.
F20turbo is offline   Reply With Quote
Old 12-15-2006, 09:35 PM   #24
Elite Member
Thread Starter
iTrader: (7)
 
samnavy's Avatar
 
Join Date: Apr 2006
Location: VIRGINIA BEACH, VA
Posts: 6,020
Total Cats: 175
Default

Quote:
Originally Posted by AndyFloyd View Post
The T25 wastegate port is too small to stop a small spike...
NO ****!? How come I never heard about that before... I did a search and there doesn't seem to be any issues w/the DSM or SR20 guys.
samnavy is offline   Reply With Quote
Old 12-15-2006, 09:46 PM   #25
Elite Member
iTrader: (1)
 
Join Date: Jun 2005
Location: Charleston, SC
Posts: 2,980
Total Cats: 14
Default

Quote:
Originally Posted by samnavy View Post
NO ****!? How come I never heard about that before... I did a search and there doesn't seem to be any issues w/the DSM or SR20 guys.
Find us some DIY porting instructions. I'd love to take care of my spike issues!
rmcelwee is offline   Reply With Quote
Old 12-15-2006, 09:56 PM   #26
Boost Czar
iTrader: (61)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 72,846
Total Cats: 1,787
Default

corky posted something about it on M.net, but i couldn't find the post.
Braineack is online now   Reply With Quote
Old 12-17-2006, 06:49 PM   #27
Elite Member
Thread Starter
iTrader: (7)
 
samnavy's Avatar
 
Join Date: Apr 2006
Location: VIRGINIA BEACH, VA
Posts: 6,020
Total Cats: 175
Default

Plugges the compressor nipple and tapped off the front of the mani... used 5feet of hose from the source. So far, absolutely no difference. It will still spool all the way up to wherever I've got the MBC set by about 3500rpms, and then decrease about 3psi until 4500 where it holds to redline.

Tomorrow, I'm going to engineer a helper spring... but I'd love some pics first. What kind of stiffness am I looking for? Are we talking valve-spring stiffness or Slinky stiffness?

I'm also probably going to drill an extra hole in the WG rod, straighten it out a little, and give it a slight amount of preload... but one test at a time.
samnavy is offline   Reply With Quote
Old 12-30-2006, 12:06 AM   #28
Elite Member
iTrader: (5)
 
m2cupcar's Avatar
 
Join Date: Jan 2005
Location: Atlanta
Posts: 7,236
Total Cats: 288
Default

Sam whatever happened to this? My setup with internal gate does exactly the same thing- peaks just over 13 and then falls to 12. I'm using a mbc like the one in the faq but with a bleeder hole. - rob
m2cupcar is offline   Reply With Quote
Old 12-30-2006, 12:31 AM   #29
Ben
Supporting Vendor
iTrader: (33)
 
Ben's Avatar
 
Join Date: Jul 2006
Location: atlanta-ish
Posts: 12,689
Total Cats: 99
Default

I had that problem as well with my home depot boost controller. I ditched it in favor of a FM mbc and no longer overshoot. I believe that it has to do with the mass of the ball.
Ben is offline   Reply With Quote
Old 12-30-2006, 01:27 AM   #30
Elite Member
iTrader: (5)
 
m2cupcar's Avatar
 
Join Date: Jan 2005
Location: Atlanta
Posts: 7,236
Total Cats: 288
Default

Just wondered if he'd found an easy fix. What I really need to do is get my EBC working with the link.
m2cupcar is offline   Reply With Quote
Old 12-30-2006, 10:40 AM   #31
Elite Member
Thread Starter
iTrader: (7)
 
samnavy's Avatar
 
Join Date: Apr 2006
Location: VIRGINIA BEACH, VA
Posts: 6,020
Total Cats: 175
Default

I ran out of time to really run this to ground as my fuel injector problem began simultaneously. I get the injectors back (Wed I hope) and will be able to see if the helper spring I'm working on will fix the overshoot. I'll post pics and a writeup later today about the HS.

With just 1psi of problem, you're way ahead of me... I still had a solid 3psi last time she ran.

Solutions tried:
1.Tapping boost source off the manifold vice compressor housing.

Solutions Remaining:
1.Helper Spring (in progress)
2.Preload wastegate actuator by straightening and drilling arm (maybe today)
samnavy is offline   Reply With Quote
Old 12-30-2006, 10:59 AM   #32
Elite Member
iTrader: (8)
 
Join Date: Sep 2006
Location: Severn, MD
Posts: 1,927
Total Cats: 5
Default

I wouldn't worry too much about a 1 psi overshoot. Pretty standard on an internal gate as Andy said.

Frank
fmowry is offline   Reply With Quote
Old 12-30-2006, 02:35 PM   #33
Elite Member
iTrader: (5)
 
m2cupcar's Avatar
 
Join Date: Jan 2005
Location: Atlanta
Posts: 7,236
Total Cats: 288
Default

It actually peaks at 13.8 and falls to 12 even. I've got an EBC which needs to be set up, as soon as I figure out a problem with it. I went with the MBC temporarily because I was sick of driving around at 8psi. It's a lot more fun tuning 12psi than troubleshooting electrical.
m2cupcar is offline   Reply With Quote
Old 12-30-2006, 08:06 PM   #34
Junior Member
 
Join Date: Nov 2006
Location: Goshen, IN
Posts: 58
Total Cats: 0
Default Fwiw...

I posted this when I first joined in it's own dedicated thread but didn't get much response.

My IHI RHB5 (said to be comparable to a T25 in size) started overboosting after the addition of the FMII intake pipe and the BEGi sep-gas DP. Before, with the small Cartech intake pipe and as-delivered downpipe, the car would make 12 psi at 4500 rpm and hold it to redline with a Hallman MBC. Now, with upgrades, I get a peak of 15 psi near redline (steadily builds from 12 psi after 4000 rpm). Car has an Enthuza 2.5-in turbo exhaust choked by the 1.6 stock cat. Wastegate actuates, tried hooking actuator to compressor housing after wastegate pushrod and MBC adjustments, no difference seen.

After discussion with Corky, he suggested porting. He referred to the wastegate as wimpy and not able to compensate for higher boost levels. The RHB5 internal wastegate measures 21mm in diameter and was enlarged to this when these kits were delivered (meant for 8 psi with an AFPR and J&S Dual Monitor). Apparently, with the recent upgrades, the turbo is not able to bypass enough exhaust flow through the wastegate to control boost.

I actually found porting info on a DSM forum. http://www.dsmtuners.com/forums/show...t=183108&pp=25 This is one of the better threads I found, guy had boost creep after some mods and fixed it by porting the turbine inlet and wastegate. I'm planning on doing the same with my IHI, though not removing the amount of material he did.

The avenue for a fix with this problem is not so simple, so I hope your overshoot is not related to exhaust flow.
mkrazit is offline   Reply With Quote
Old 12-30-2006, 10:00 PM   #35
Elite Member
Thread Starter
iTrader: (7)
 
samnavy's Avatar
 
Join Date: Apr 2006
Location: VIRGINIA BEACH, VA
Posts: 6,020
Total Cats: 175
Default

Mkrazit, the problem you are talking about is boost creep... we have an entirely different problem... boost overshoot. I have an initial spike, and then a steady DECLINE in boost, not the other way around. I'm pretty sure that a helper spring is the answer to my problem. The MBC is only doing so much after it's open... then the stock DSM wastegate actuator just won't hold the 10-12psi I'm asking it to do.

We'll see next Tues/Wed when I get my injectors back.
samnavy is offline   Reply With Quote
Old 12-31-2006, 04:11 PM   #36
Junior Member
 
Join Date: Nov 2006
Location: Goshen, IN
Posts: 58
Total Cats: 0
Default

My bad Thinking a little bit more about this, porting would only solve a flow problem. It would make more sense that the problem lies in the actuation of the wastegate (duh!).

I know you said your car is undrivable at the moment, but do you have much preload on the wastegate pushrod? Adding preload would seem like a more permanent solution after experimenting with the helper spring. As it was mentioned, it does seem like the flapper is flying open then finding a steady-state position after your initial spike.
mkrazit is offline   Reply With Quote
Old 12-31-2006, 04:56 PM   #37
Senior Member
 
Join Date: Jan 2005
Posts: 737
Total Cats: 0
Default

Quote:
Originally Posted by samnavy View Post
Mkrazit, the problem you are talking about is boost creep... we have an entirely different problem... boost overshoot. I have an initial spike, and then a steady DECLINE in boost, not the other way around. I'm pretty sure that a helper spring is the answer to my problem. The MBC is only doing so much after it's open... then the stock DSM wastegate actuator just won't hold the 10-12psi I'm asking it to do.

We'll see next Tues/Wed when I get my injectors back.
actually if you ported it your overshoot problem would also get a lot better. Think about it....making the hole bigger w/ porting makes it easier for the wastegate to bypass exhaust quicker thus not only will it never creep it but wont overshoot as badly either.
F20turbo is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
FS/FT: 03.5 Mazdaspeed Protege leatherface24 Cars for sale/trade 15 10-16-2015 12:35 PM
How high with a Greddy? tritium Prefabbed Turbo Kits 11 07-14-2007 01:21 PM
New turbo installed, YIPPEEE!!! samnavy DIY Turbo Discussion 21 03-06-2007 03:53 PM
SamNavy Dyno Results samnavy Dynos and timesheets 29 01-20-2007 03:29 PM
Building a MBC Braineack Useful Saved Posts 0 10-30-2006 09:14 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 06:07 PM.