T10Chris

Those weren't just any sport cats, or even just good cats, that come as an option with exhausts though- they were designed for professional motorsport use and had the price tag to match. The typical cats on aftermarket exhausts out there are junk.

powdrhound

What T10 said above. The cell count is not what determines how well a catalyst will flow. It's about the cross sectional area of the catalyst. A typical 200 cell is rather restrictive and even a small 50 cell can be restrictive. A large diameter HJS/Emitec 100cpi Motorsport catalysts will flow as well as a straight pipe but said catalyst will cost upward of $1500/ea. Virtually all vendors with a tiny exception use much cheaper lower flowing cats due to the cost naturally which is why virtually everyone that goes to straight pipes seen a significant difference in flow performance. Even an HJS "Tuner" 200 cell catalyst is rather restrictive. These are what is typically used on the upper end aftermarket exhausts as it's a good street catalyst but at a much lower price point. The Motorsport offerings are what you want if you want your cake and eat it too. We did a test on this years ago...

https://hjs-motorsport.de/en/product...t/pe-catalysts

https://rennlist.com/forums/996-turb...e-settled.html

2fcknfst

Absolutely agree - I'm not sure who made the ones I used, but there was also a fellow over in the 991 forum that did a bunch of similar type testing showing a top end catylst would support over 800 to the wheels before they started seeing issues.

I just thought it was interesting that there was such an obvious difference between having them, and not.

powdrhound

What exhaust did you have? I am virtually 100% confident that the catalysts on it were substandard hence the reason you are seeing such an improvement. That is typical. Post some pics if you can.

2fcknfst

Speedtech and AP.

Not sure what ones John uses, but the ap ones are Taiwanese.

powdrhound

I know the AP is all China crap. The stock Speedtech 100 cpi catalyst is going to be restrictive too based on the very small diameter you can see in the pics in the link below. I appears they are barely 3" in diameter, about the same size as a bypass pipe. I'm pretty sure John will build an exhaust with the genuine Motorsport HJS/Emitec cats if someone is willing to pay the extra $2-3K.

http://www.speedtechexhausts.com/ast1_012.htm

This is what a 100% efficient 800wph HJS/Emitec Motorsport catalyst looks like. It's a monster sidewise but that's what it takes if you want the flow and clean air. These are bolted you your XR980s..

2fcknfst

Those are some big boys...

100 percent efficiency is impressive.

pfbz

Couldn't *agree* with you more! My second 996 Turbo came with the vaunted Europipe exhaust and 130mm 100 cell sport cats....

Absolutely love the swap to my catless titanium.

2fcknfst

I am really wishing it would stop raining so I can apply some real power.

911user

Running better than ever!

First car show of the 2023 season!

3/98 911 coupe

we are by sea level, we get 93 octane gas, 20 minutes from here we can buy 98 octane blue racing fuel. My 99 picked up power plus lost a lot of weight when I went with fabspeed catless x pipe, due to the extenders no CEL. Plus you get a bit of a smell of fuel a la aircool. Texas has had the second cheapest average gas prices in the country for the last 20 years, this is great when you are buying shell v power 93 and burning half a tank on a Saturday porsche adventure. Since gas is relatively cheap here I have leftover money for meat fest. Took my turbo this morning to Kroger to pick this up.

This was Saturday night going into Easter Sunday.

Ready to cook some more this week.

theprf

Drove it to get a state safety inspection sticker. First drive in 2023. Looks pretty good for 180k miles.

2fcknfst

It sure does; can't even tell it's not at all weathered...

3/98 911 coupe

enjoy the 23 driving season.

996dougie

What a beauty!