Are cutouts really helping you. Look inside.
 

Here is a problem I have been considering. Everyone that has dynoed with their cut out open and shut haven't dynoed without a cutout installed. How much power is being lost because the cutout messes up the flow of the pipe? Think about the design. When its open there is no problem but when its closed the exhaust gases are bouncing off the closed pipe and coming back to distrupt the flow. This has to be considered. If you have a stock exhaust it should help a lot but if you have a good flowing exhaust like mine I think it may do nothing for you. Also, in both cases it will hurt performance when its closed. What do you think?

Well, if you have a cutout, why would it be closed if you want to go fast and need the power? :)


Post #700 :D

Sound for one! I would like to see a before cut out and after cut out dyno sheet. I have a feeling that you will get very little if any gains from a cut with a good 3" exhaust. Then again someone may have the proof and my hunch will be put to rest.

I would think that once the void is pressurized, airflow will continue its course to the path of least resistance (down the rest of the catback).

On my car I ran a Corsa with no cutout and made 430hp.Installed a SLP dual dual and made 395hp.Then installed a cutout and went back to 430hp with it open.
Hope this answers your question.There are 3" exhausts out there that flow just as good as the cutout,but us people that want a quiet exhaust for the street run a electric cutout for the most power gain in a race :)

I think the usual setup (the Flowtech Y dump with
cutout on the end) is going to make a lot of dog-
whistle turbulence, and this would hurt flow.

For mine, my plan is to put it at the axle arch bend with
the flange directly MIG'd to the pipe (cut w/ 3" hole saw)
and then the cutout gets a straight shot out, while the
muffler bend might be just a little more bumpy with the
1/4" divot for the flange.

Since I think my muffler & back pipes are pretty much
the same as the dual-dual (except for tips) this 35HP
gain looks pretty good to me. Though the stuff before
the muffler isn't quite up to this example....

You nailed it. :thumb: The air in the closed part of the cuttout acts as a wall to guide the exhaust gasses along their merry way. There is no measurable power loss from installing a cuttout. Open it up and there's certianly a measurable power increase! I picked up 28 RWHP with my cuttout open! At the track I found an additional 3.5 MPH.

Before any mods (cutout only) I gained about .10 et and 1/2 mph.

i love my cut-out

i have not dynoed my q-tec cutout yet,but at the track i gained NOTHING at all. lots of noise but no performance gain.

mike c. what kinda exhuast you runnin'? sounds pretty free flowing.

Stock exh with edelbrock muffler...11.95 @ 113.2 Opened cutout on very next pass....11.74 @ 115.07.. I'm not a big fan of noise so i think i will go true duals with an x pipe and edelbrok muffs.

Phil

i have a loudmouth, if i added a cutout to my exuast system would i see a gain in performance or do u think it isnt worth it because the LM flows so well?

I haven't really noticed a big difference on motor, about .05, and but I usually see a little more gain on nitrous b/c I usually gain 1 mph and I haven't really gotten much of a time difference mainly b/c I can't spray it out of the whole where I would like so that I could get a definate baseline.

Josh S.

I posted this in the other thread, too. Closed to open gained 17 RWHP on an otherwise stock engine.

I went 11.46 at 118.50 threw a flowmaster rear half and i know it's nothing to brag about. And threw the cutout i went 11.31 121.50 so the cutout works for me.

I am with South.FL.02.Ss and Colonel on this. My reasoning may be different but we all arrive at the same conclusion.

Here's my take on it:

The area off to the side that you think would cause a restriction is filled with pressurized gas.It requires more effort to make a turn and displace that existing gas than it does to shoot right by and head toward the exhaust tips(where there is low pressure).The gas will do nothing but travel in a somewhat straight line unless it is acted upon by something else(that's a law I looked it up ;) ).Since the exhaust piping is pressurized to some extent almost immediately you have no outside force working on turning your current exhaust stream into the y. So unless that cut-out is on a curve or a bend in the piping or there is a leak in your cut-out it should continue right by the y with no ill-effects.

By opening the cut-out you have introduced a pressure differential. This pressure difference between the piping and outside atmosphere will draw the hot, higher pressure (than the atmosphere anyway) exhaust out at the cutout.There is your outside force acting on the gas.

Yes, the path of least resistance... :thumb:

Most of the guys showing gains are comparing an innstalled cutout open or closed. I would like to see a test where an exhaust like mine or a LM is tested before a cutout is installed and then after. My concern is the exhaust bouncing off the closed cutout.

I like all the theories and they seem valid but I am a Thomas. I need to see to believe. Proof would be greatly appreciated so I can bury this hunch. Thanks

Bowtie, You do not have a cut out correct? They are $30 and $20 to install. Why not dyno, put one in the same day and Dyno again. If you loose HP with it in being closed then take it out and patch a straight pipe in. At most your looking at $100.

If you don't loose HP from putting it in, then uncap it and see what you gain. Then you'll have a cut out :)