Car falling on its face at 4500rpm, only with cutout closed?!?!?

I have been running with my cutout open for quite a while now, and it has been running great. Well yesterday I went ahead and capped the cutout, and now the car falls flat on its face around 4500rpm while under boost. It feels almost exactly like when the orange dryer hose used to collapse on me. I have the hard plastic piece from ATI now so I know its not that. I checked to see if the air filter was collapsing, and it wasn't.. Was a little dirty though.
Fuel pressure seems fine. Plugs are Autolite 104's gapped at 35.

I have searched through all the posts I could find with similar problems, and it doesn't seem like its the same thing.


Any ideas?

Maybe you have too much back pressure now..

Maybe... I was starting to wonder if its possible that my muffler is clogged or something.

Could be, or your CAT if you have one .. Probably should upgrade your headers to long tubes to support the amount of power you have .. They'll flow a bit better, people have been known to pick up 20-40 RWHP just from long tubes in high HP applications.

Probably should upgrade your headers to long tubes to support the amount of power you have .. They'll flow a bit better, people have been known to pick up 20-40 RWHP just from long tubes in high HP applications.

This certainly isn't the issue, and I don't know where people keep coming up with this info. Assuming the same size primaries and collector size and design, longtubes are going to shift the powerband, not make more power. George Baxter's car didn't see any difference between AS&M 1.75" primary shorties and Hooker 1.75" longtubes until he was making over 700 to the tire. I did a cam and all the bolt-ons on an LS1 TA. After it was done, tuned and dynoed the owner swapped out his Macs for a set of Hookers and saw a 1 peak horsepower difference on the same dyno, and this was on a car that made 401 to the tire with the shorties.

Didn't mean to get off topic. Just wanted to assure you the shorties are NOT your problem. This is especilly common sense since they are UPSTREAM of the cutout.

-Chris

The CAT is only about 3 months old, put it on to replace my gutted one for smog.

But anyways, I figured out what it was. When I capped the cutout the other day, I also zip tied up one of the fuel lines on the inline pump. It kinked just a touch. So I rerouted the line today and bingo, no bog/stumble or anything. Pulls real hard up to redline. Don't know why I didn't notice any differense on the fuel pressure though.

Thanks for the suggestions =]