Has anyone done a before and after dyno w/ the stock cats and gutted stock cats?

Does the large chamber where the cat material used to be hurt flow or velocity at all and cause a loss in power or torque anywhere in the RPM band?

VQ35HR experiences are preferred, but any information is appreciated.

 

gutting oem cat's are stupid when you can get tp's at a very reasonable price.

HR cat's have also been shown to flow better than previous years. I'd think twice before hacking into your expensive oem cats (that might come in handy if you have to pass smog).

 

Yeah no ****. The cheap mod crowd is becoming larger by the day. I wonder if this guy has PVC pipe anywhere under his hood? haha.

 

I've got a spare set sitting around, so going back to stock is no problem. It's also not a matter of price. If I were going to buy an 'aftermarket' part I'd just get a set of HFC's.

I want the car to look as stock as possible for when I have it serviced at the dealer.

There is also no smog or any kind of inspection in my state.

Test pipes have showed gains of 10+whp on the HR motor, so I know there is power to be had. I just was curious if the bulbous shape of the catalytic converter pipe would result in lower gains (or no gains) when compared to a 2.5" straight pipe.

Thanks for the replies though.

 

it should work well, if anything a gutted cat probly will never crack unlike the aftermarket shlt. Only thing is that a testpipe would have a smoother exhaust flow, try it out man. A friend of mine gutted his on a 06 Z and his car is freaking loud, so it must be flowing haha

 

just get test pipes, they'll probably flow better than a gutted cat.

 

look up how much a OEM cat cost that might make you think twice if you ever have to make the car stock again. Waste of an expensive part if you ask me testpipes were made for a reason.

 

do it if you want. its your car. i did mine and noticed a nice gain on my vq35de

 

gutting cats on this car would be an utter waste of time...

have you seen the cats on this car?

you might as well buy some used test pipes off someone for $50 rather than waste hours of time destroying $3200 worth of cats...

 

I don't want the missing cats to be obvious.

 

as stated above, these are extras I have laying around. My car is still stock and the stock cats that I remove will be saved while the modified gutted ones are installed.

 

Why would it be a waste of time? I've seen the cats, held them in my hands, and inspected the amount of material that would need to be removed.

They also cost me under $200 used w/ low mileage.

 

Lets stop worrying about the cost/work/ect. Will the design of the stock cats cause velocity to slow down and lose power? Any real documented gains/losses from running gutted cats? I'd be curious to see the before/after curves.

 

my car put down 246rwhp with gutted cat's and a pop charger. Everything else was stock. That was on a dynojet.

 

Get to it man! come on. BTW those oem cats are HUGE.. so i'm sure if you gutted them out they would do no harm. Dyno before and after, I guarantee something gained.. and besides.. you do have a extra set.

 

thats about a car with just a cat back...

My Z did 244RWHP with just nismo cat back...

 

You need to understand exhaust velocity to know why gutting cats isn't a good idea, especially when the cats are located so close to the heads. The fact is most people don't understand that exhaust velocity and heat retention is the key to an optimally flowing NA exhaust. Bigger pipes may or may not help as well as mandrel or non-mandrel bends. I am 98 3/4% certain that gutting the cats will cause soft low/mid rpm performance along with a super nasty noise since the gutted cat will have such an odd shape. Power will be lost in the low to mid rpms because the exhaust velocity will be slower because the exhaust gases to enter a big chamber just after the header. This is will cause turbulence, will effect exhaust flow from the heads, and the exhaust gases will cool in the chamber. All of these things will kill throttle response and power. How bad, I don't really know, but I'd guess it would be pretty significant. There may be a slight gain above 5500rpms, but I highly doubt it will be enough to offset the losses in the low/mid range.

 

+1.

As used Z's become older & less expensive, the younger ricer crowd grows in numbers, desecrating our precious Z. I wonder if the OP has an x02 anywhere on his Z to compliment his gutted cats? FTL.

 

I have an '08 G35.

Thanks for the ignorant response and not reading a single one of my comments about why i'm considering this route.

dumb flaming trolls are worse than ricers IMO.

 

It just seems like the cat material and expansion into the cat filled chamber would slow down velocity more than having the large open space. At least you understand my primary concern... I should have just stayed on KCSR and debated this between the 2 of us