Collapsed Flex Section
 

Well after working out of town for the past 20 months I'm back home. Before I left to go work out of state I was having a problem with my car not wanting to build high boost. This is the reason why I haven't been running it much since my 11.45@126mph pass on 93 pump. I've been scratching my head over why I was having this issue. My main issue was excessive high exhaust manifold pressure related to intake boost pressure.

At 20 psi of intake boost I was getting 35 psi of exhaust pressure in the manifold for a 1.5:1 pressure ratio. Not great, but could be better.

But I was hitting a boost wall of 25-27 psi. My car would not build anymore boost, period. I even mechanically jam closed my waste gate to make sure it wasn't opening under boost. When this happened I would get 25 psi of intake boost pressure and 50 psi of exhaust manifold pressure. At 2:1 pressure ratio there was a problem.

Well I'm back home now and thanks to a thread on another forum I have found my problem.

This is my 3 inch s/s flex section from my new exhaust system seen here....
http://www.mitsustyle.com/forums/sho...t=16155&page=3

Anybody see a problem??? :angryfire:
We cut the internal webbing bands and pulled it out. Still has the external webbing for support.

Re: Collapsed Flex section
 

Wow, well at least you found the problem.

Re: Collapsed Flex Section
 

Now to hammer out that 10 sec pass.

Re: Collapsed Flex Section
 

Get on it! Racing this weekend?

Re: Collapsed Flex Section
 

Not yet, still ridiculously hot here in Louisiana, but once it starts to cool off,.............. It's on.

Re: Collapsed Flex Section
 

there are nails on the ground, thus, nails are in your tires?? hahaha jk. That is one heck of a nice white 2gb you got there! so clean...so clean...

Re: Collapsed Flex Section
 

Crazy. Glad you found it, it's been forever since you've posted anything but politics haha

Re: Collapsed Flex Section
 

Wow, didn't know that could happen. With the internals out, is it going to leak? Not a big deal I suppose, maybe just a bit louder?

Re: Collapsed Flex Section
 

This is happening a lot lately.

Re: Collapsed Flex Section
 

It won't leak, the webbing is only there to support the bellows section, but it's solid, no leaks.

Now the real question is,............... how much of a problem was this when I made the 11.45@126 / 22psi pass??? Immediately after making that pass I only did three things, installed the FP4R cams, poured in some C16 and cranked up the boost. And that is when I had the problem start showing itself, the engine choked off at 25 psi.

Re: Collapsed Flex Section
 

Really? Any idea what causes this?

Re: Collapsed Flex Section
 

I would say expansion and velocity of the exhaust gasses.

Re: Collapsed Flex Section
 

That flex section seems excessively long too man, maybe put in a shorter one this time?

That really sucks though, can't wait to see what she'll do now!

Re: Collapsed Flex Section
 

It's 12 inches long and under the oil pan. I'm not changing it, just took the internal webbing out.

http://www.mitsustyle.com/photopost/...xhaust_002.JPG

I would have put a 3.5 inch diameter flex in there, but it wouldn't fit. As you can see, the 3 inch diameter is very tight.

Re: Collapsed Flex Section
 

Didn't this same exact thing happen to Hal or someone just recently?

Re: Collapsed Flex Section
 

Yes, it was his thread that made me look.

Re: Collapsed Flex Section
 

That sucks but nice that you figured it out.

I'm liking that vband placement, you wouldn't have to pull the whole exhaust to do a tranny swap. All you would have to do us undo two bolts and take the hanger off.

Re: Collapsed Flex Section
 

I'm wondering how many other people this has happened to that didn't cut the pipe apart to find out. From Hal's thread, there seems to be some correlation with running E85.

Re: Collapsed Flex Section
 

I just went and looked at mine for the heck of it. Mine doesn't have the woven mesh in the inside at all so no problem here. After seeing this I think I'll make sure to avoid flex sections with it on the inside.

Re: Collapsed Flex Section
 

Mine resulted while running 93 octane pump (or E10 as we call it down here :lol: ). As soon as I put C16 and turned up the boost for the first time the restriction was already there. I still think it has to do with heat expansion and velocity.