So I am going to the track in a week with a bunch of guys from my work, should be a great time. I am only worried about a couple of cars...03 Cobra with some mods and a 5.0 Mustang with a Vortech. I don't have time to do much to my car but I was thinking I could uncap my exhaust after the cats. My exhaust is currently SLP shorties (single cat style) going into dual cats and then into 3" catback with a Dynomax muffler. So uncapped it would be through the headers and though the cats and thats it. Do you think it would be worth my time? I have flanges after both cats so it would take all of about 10 minutes to open it up. My only chance with these to cars is to get them out of the hole and I will need all the power I can get to hold them off on the top end! What do you think?

 

may pick up 10hp or so...if it is really that easy...why not test it out?

couple runs with and couple without...and let us know how it goes.

 

We dyno'd my Dad's '73, and by un-capping the cutouts on it (we have 1 per pipe, right off the header collector) it picked up 18 RWHP . At the track, the open headers also gained us ~4 - 5 mph .

 

picked up 9rwhp on the dyno with cutout open, but thats when i had cats. it was mounted after the y.

 

Might as well uncap it, but the cats are still going to rob some flow.

 

It wouldn't hurt to uncap the exhaust, most dyno sheets I've see show a nice, modest gain involved.

 

Why not just get a cut out welded in. They're only about $30, $45 if you decide to go with stainless steel.

 

Well, from my experience i have often seen .1 off a 1/4 time.

 

Well survey says to upcap it, so I will and let you know what happens. I thought about running it both ways and might depending on how the day goes.

 

Overall upcaping will get your more hp. I am always switching between the my cutoff on or off. I can feel a slight torque loss when taking off from a stop light in normal driving (the amount of gas needed to get on the clutch) is a little more. But the cutout definitely helps in the High RPM when you need to get that exhaust out fast.

 

You shouldn't see any torque loss unless your cutout is ungodly close to the exhaust ports, in which case you are probably risking a burnt valve.

 

Mine cuts 2/10 off when it's uncapped.

Frank
CPT

 

Mines right before the axel, I also have a magnaflow catback and gutted cats tho. There is a small torque loss. Try moving you car by just letting the clutch out (no gas) with and without the cutout open. You will see what I mean.

I had the same cutout on a 93' lt1 as well but it was an A4 and I could feel the torque loss as well.

Its very logical that you will loss the torque: open cutout = less backpressure = less low low end torque.

For racing it doesnt matter Ive always seens gains with it open, Im just saying that daily driving I notice it, More so on an M6.

The gains from a cutout also, I belive depend on how heavily modded your engine is. A full bolt on, cammed car is going to get more gains then a stock car w/ a cutout.

 

Ok, so here is what happened. I uncapped it as soon as I got there. I raced 5 times, best being 12.44 at 114.7 MPH. This was on Nitto drag radials. So for the last run I capped it up and ran 12.48 at 113.2. So MPH was down, but I had also ran 113 on two of the uncapped runs. All in all, not worth the effort to uncap it. I am fairly supprised that my exhaust is not slowing me down. Maybe the resistriction is the cats?? BTW, the 03 Cobra bairly beat me...he ran a best of 12.39 one time with alll his other runs 12.68 or higher. the 5.0 was no contest with his best of 12.78. Not too bad for a heads/cam LT1 with more than 100K miles.