befor

i had a catback on running stock cat and down pipe. i would spike to about 22 1/2 23 psi and then hold 21 psi and about 19 to 20 psi by redline. im using a forge unos mbc.

after

i installed a 3 inch down pipe and cat delete pipe. as i knew i hit 24 psi tapering to about 20 psi by redline. i had to lower my boost. so i lowered the boost to where it seems best becasue i was hitting boost cut i guess. well now im spiking 23psi and then droping to 20psi and 19 by redline.

if i let the car spike to 22psi well then it just spikes 22 and drops to 19psi and holds.

the spike is much more agressive then it used to be. plus most of the time i spike and then taper and the boost seems to move between 22 and 20 psi. the boost just easly moves back and forth. then to about 6300rpm it just holds 19psi.

do you think an ebc will help. do they spike like mbc's? are they as dead on as a mbc. i would be getting an apex-i avc-r if i went ebc.

or what do you think i can do to fix this problem if i even got one.

 

It doesn't sound like you have a problem...what is the problem? So it spikes to 22-23psi. What's wrong with that? That's normal.

When you did the DP/TP, that reduced the backpressure, thus allowing the turbo to spool more violently without restriction. We consider that a good thing, not a problem...

 

ok but what about the boost bouncing from 20 to 22 psi. its not fast but it does move between 20 and 22psi. just easly moves. like 20 21 22 21 20 21 22 21 20 21 22 21 20 i would say from 3800rpm to about 6500 then holds 20 19psi at redline.

 

I have seen a lot of IXs do the double spike thing but not many VIIIs. A MBC is a great mod and you might be able to get rid of it with a EBC, but their expensive and might not be the best route to go.

Oh, you have the Forge......It might just need to be cleaned. Warr can help you out with that.

 

Are you still running the original unported 9.8 HS?

 

yes i am. but i have a ported 10.5 hotside, works o2 housing, forge w/g/a, and ported e/manifold waiting for install

the mbc is new and has ben cleaned 2 times already. this all just started after the d/p and custom test pipe went on.

 

not to hijack but...

i just finished installing my DP & TP, and i hit boost cut. so i lowered it now i spike 20 and hold 16. befor i would spike 20 and hold 18. and reasons should i reset the ECU? i havent yet.

 

its sounds like the same problem i got. im just running higher bost then you. i dont have boost leaks you may want to check if your only hiting 16 and 18 psi.

 

Are you saying thay it'll spike to 23# no matter what you set the boost to? For example, if you set boost to 17#, what happens, will it still spike to 23# and eventually settle down to 17#? Or, are you unable to lower it that low?

 

i cant get it lower then say 18psi. because i got the stiff spring in my forge mbc.

what im saying is i cant run 21 22psi without a boost cut or whatever it is now that i put the 2 parts on. i spike to high. plus my boost fluckuates between 20 and 22 psi. like i said above. it gos 20 21 22 21 20 21 22 21 20 then at about 6500rpm its holding 19psi.

befor my test pipe and down pipe install i was hiting 22 psi holding 21 and then at redline like 20 19 psi. no boost cut

now with the parts on i hit boost cut so i lowerd boost but now i cant run 21psi with out a boost cut cause it will spike to high.

better. man this sucks. plus my check enjine light came on. i got to install my o2 sim i guess.

 

I think part of your problem may be the fact that you've increased flow though the exhaust housing via your DP and testpipe mods and that your turbine wheel is spinning up a lot faster within the tight confines of the 9.8 hsg. and the small unported WG bypass port can't vent enough exhaust flow to control boost levels. So you've got boost creep.

If you put on the freer flowing O2 hsg. it will only get worse. What you've gotta do is port your new 10.5 and install it. When you port it. Scribe the OD of your flapper valve onto its seat with dye then port the bypass port out to just where the valve still seals. Then on the inside of the hotside grind down the transition radius into the WG bypass port.

I had the same creep problem with my JDM TiAl RS turbo that came equipped with a 9.8 HS. It didn't go away until I installed a fully ported 10.5 onto it. I had made all the same exhaust side mods that you had made and I couldn't control boost either.

 

i have a ported 10.5 hotside. just not installed yet.

 

Sounds normal, I wouldnt worry about it. Im spiking 25-26 and holding 23.... then 19.5-20 by redline.