I have just been thinking about what percentage of exhaust would flow through the open side of a cutout vs through the rest of the catback?

True there is less resistance by going out the open side of the cutout vs the restriction of the rest of the exhaust including the muffler... but the open side of the cutout is an offshoot to the side whereas the main catback is straight in the exhaust path.

Hmmm just had me thinking.

 

i'm sure it could be done. just take those things that spin that weather guys use and put 2 on the cutouts and 2 in the back

 

Good question. Exhaust flow will follow the path of least resistance except turning a corner at that velocity is a lot of resistance. Anything that can't go thru the muffler will bypass thru the cutout. That's not a very elegant arrangement, IMO.

My take on cutouts is to design the y-pipe or header extensions with a straight shot just past the 90 degree turn toward the center of the car, and put the 2 cutouts in the straight area AFTER the 90s. IOW, the closed cutout is in the "runoff" area of the turns. Maybe a little less efficient thru the mufflers, but virtually no restriction when open. You could even put turndowns after the cutouts.

My .02.

 

Thanks for the input Jon. I dont really see how you meant using the cutouts. I was going to use an electric plate(s)... so from what your saying this is what i got-
Pic(Have to love MS Paint LOL)
Or did i miss what you meant?

 

Nope, you didn't miss it. I'd try to put the cutouts as close to the 90 as I could just to make the closed-cutout system a little more efficient.

 

That picture is the exact set up I'm planning on doing when I buy my Jet-Hot long tubes and y-pip... what y-pipe and headers are those btw?

Trevor

 

Trevor, those are Jet Hot Long Tubes with a custom fabbed y-pipe.

Jon, thanks for the design suggestion!

I'd still be interested in knowing if there was some software, or formula that could be used to get some kind of idea what percentage of exhaust goes where in a open cutout.

 

I suppose if you plumbed pressure gages to both pipes (the cutout extension and the cat back) and recorded the pressures you could calculate it. IMO, it would vary with each installation, and probably be much more trouble than it's worth. In this case, measuring hp output or strip times with various systems is probably easier and more accurate. Heck, you could just hook up your exhaust system to a couple of large blowers on the garage floor, mock up different systems and measure the pressures, and calculate the flows. Better yet, measure the flows directly. It would give one something to do during the long cold winter here in the north.

Visualize yourself as the exhaust flow: look at the system and intuitively you'll see where it's easier to go. That's my shade-tree approach.

CFD is finally reaching the point, if you have the computer power of Ferrari or GM, that full vehicle airflow prediction is possible. 24-7 in the Ferrrari wind tunnel still hasn't stopped, however, AFAIK.

My $.02

 

Kmook,
If you go the cutout route, do yourself a favor and get the Electric Cutouts from www.dmhperformance.com

They are FULLY covered with a 4 year Warranty. They are made with the tightest clearances and nicest materials I have seen.
You can check out my link below. I did a write up on the install on my Borla with pics, open/close time, Sound etc...
I have heard many guys here at Z28.com that went this same exact route picked up 6-15RWHP when open vs closed (from 400RWHP Levels to 650RWHP levels). I am sure if you had your cutout closer to the headers it should give more of a gain. I really like my set up because it really quiets down the car when closed and is more pleasureable to drive everyday. I drive my car everyday (600 Miles weekly) so its good to have it quiet most of the time and then Mean sounding with a few more HP when I 'need' it or just want to terrorize the import in the next lane.

http://camaroz28.cardomain.com/memberpage/342629/5

Just this morning, I Humbled a 2002 WS6 car that came up next to me and threw a few revs at me. My car was so quiet that he thought he must have had easy pickens on my Lt1....I then open the cutout and we went thru 3/4 of first gear with him and had to let off cuz of traffic (he started falling back quickly)...But that WS6 did not want anything to do with me after that even though the road opened up later, he still would not even look my way afterwards (no matter how much I tried to entice him for a full out run).

Thx,
Claude

 

Sounds like something for you and UB to get together on to test... remember we dont have winter down here
Thanks for the suggestion though, that sounds like an easy way to test it.

 

Ken:

Not sure I understand the purpose of your question. The flow split will depend on the exact configuration, orientation of the cutout relative to the main flow, and the magnitude of the restrictions on the full exhaust system..... as people have explained above.

You could just assume everything comes out the cutout, if you are trying to size the cutout. Then any flow that happens to continue through the full system will just be "gravy" because the cutout is already sized correctly. I would think the largest portion of the flow is going to take the path of least resistance, and an open cutout (assuming its the same size as the pipe its in) will certainly have significantly less flow resistance than a full exhaust.

Maybe you could clarify what you are trying to do with the info.

Fred

 

Hey Fred,

Not really trying to "DO" anything per say with this, just curious about it.

I know a decent amount will flow through the open side of a cutout as people see gaines on the dyno with it uncapped. But im just woundering how much exahust actually flows out of the offshute vs straight through. (I know it will vary with every setup of course).

But to gank a pic from Stevil It is clear to see that a lot will flow out of the open side but it is still at a good angle to the side.

In thinking about it id like to see a cutout designed like the borla catback. Where the straight through section has the cap and the side shoot is for the restricted exhaust system.