My brother just picked up an ISF
I have been reading many posts about the primary cat delete. I have the sikky headers installed.

He just purchased a set of used manifolds and will be gutting the primary cats on the manifolds.

Who here has had this done? How did you like the mod?

Thanks

 

Check this thread: https://www.clublexus.com/forums/is-...come-soon.html

As for gains, it's still debatable. Some might appreciate it if you could do some before and after dyno runs if you do install headers with gutted cats.

 

Your gutting factory cat which will make like 30 wheel just to install after market ones and take 10 horse off... Sounds like a lot of time and work when a borla exhaust will get you 20 wheel for 800 bucks used off the forum

 

The purpose of removing the cats is because they are so close to the engine which causes a bottleneck.

 

Do what you want, it's your car. I'm not saying you will lose 10hp. Completely removing primary isf cats makes about 30hp. Ppe cats cut about 10 hp off ppe's race headers. So you might end up with a 20hp gain if your lucky on gutting factory manifolds. Plus it will serious decrease your cat reliability and exhaust fitment over oem. Whole process will take anyone one or good shop 10 hour min. Absolutely not worth it IMO. If you before and after dyno your car, your going to be disgusted with your results . Not trying to down your idea, just help you out. I'm without doubt a veteran isf modder on CL, have been on about half dozen dynos and done some serious testing on mult bolt on parts.

 

I appreciate everyone's input. This is why I posed the question on here. I was looking for advice from the veterans.
He would not be removing the stock manifolds. We would gut the primary cats on the car. The whole process should take about 2 hours. He purchased a second set of stock manifolds to go back to stock when he wanted.

 

One of our Isf guys in the family gutted the cats and has JoeZ exhaust and intake
Picked up 1mph on the 1/4 and few tenth also installed the sikky o2 modulator
From 12.45 @114 to 12.42 @115

 

Going through all the trouble to R & R the manifolds and install high flow cats you might as well put headers on. It's about the same amount of work, with better gains.

 

I wouldn't be removing the manifolds

 

No need to remove manifolds to gut the cats lol

But I still think it's not the same gains as on headers . The stock manifolds have kinks and bootle necks

On the same track we had a ppe header Isf ran 12.37@116 then there was a gutted cats Isf 12.42@115 his previous best runs with cats were 12.45@113-114 I managed 12.55@114 now there was some weight differences between drivers and me and the ppe equipped having mechanical diff .

 

I daily drove my ISF with no cats at all for over two years, the smell was not that bad, noticeable at the begining but either I got used to it or it went away over time. I'd say forget about hi-flow cats, just gut the manifolds.

I don't understand why people keep placing a question mark on gutted manifolds and their performance compared to full exhaust + headers. I was at the Miami ISF meet early this year where we had CJ (MrSlay) with gutted manifolds racing Danny (dcoolbeans) with PPE headers + ISS Forged DES. From a roll going to triple digits Danny took the lead but not by much, definitely not what I expected, especially because I had the same setup as Danny and spent over $3.5k between headers, exhaust, and installation. For that performance, gutting manifolds is a steal!

 

I'd be curious to see the results of a gutted header with a tube installed inside where the cat bulges out to minimize the slow down created by the cat's large diameter. It think it would really minimize the difference between gutted and headers.

 

I had the same thoughts but it be hard to accomplish as now your further reducing diamater ,it be nice to cut of the cats and weld in a straight section but that would require removing the stock headers and at that point might aswell go with headers. I doubt there is room to weld all the way around lol

 

I don't think the tiny diameter difference in a tube would be as big an issue as the bulge for the cat is. I agree, cutting off the cat and replacing with the same diameter tube is ideal, but as you said, at that point you might as well just drop the manifolds and put on a header.

 

I took some pics of my spare manifolds also measured the inside diamater going out to the exhaust which is surprisingly small at 2 inches

I was also dissapointed to see the welds not being all the same in the stock manifold
I realize it's mass production but here is some pics I wonder if they all are the same or it just happened to be an issue on the line when these were welded. I know things like this happen since I worked at a shop that built landing gears for truck trailer and sometimes things would not align and yet nothing was done about it because that operator in that robotic welding cell didn't care to fix the problem. It's just a matter of shifting coordinates and reprogramming the robot.

This is the runner I'm talking about


This one isn't too bad



This is what it should look like




Cat section now here you will see that there is another piece of metal already inside which would further reduce the 2" inside diamater I would say it's about .02" thick per wall so take off another .04" total you're at 1.96"
If you were to put another tube that's .04" total you're now at 1.920"



To modify the cat and properly install a tube your better off to cut into the bottom half section of the cat and work your magic from there .