OK, I think I'll try that first... source off the manifold.

 

yeah, I should of suggested it as well.

 

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.

 

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!

 

corky posted something about it on M.net, but i couldn't find the post.

 

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.

 

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

 

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.

 

Just wondered if he'd found an easy fix. What I really need to do is get my EBC working with the link.

 

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)

 

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

Frank

 

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.

 

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, 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.

 

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.

 

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.