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Discussion Starter · #1 ·
Hey all,

I've been looking online at the differences between running high flow cat with downpipe vs just catless and was wondering regarding our specific car is there a huge noticeable difference in power gain in going with one or the other?

What are the benefits of running one vs the other?
 

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I was pushing over 240 at the wheels with a HFC.
There is a difference, but it's like 5%.
The biggest disadvantage of catless is the damage you are doing to the environment. That and the check engine lights. You can put in spacers and mess with that but you will be on the edge of throwing a light all day.
As for the HFCs, some people have had great luck never throwing a single code (myself included) while others throw a code every once in a while.
My personal opinion is that it is irresponsible to run a catless on the street. It does not provide enough of a gain in performance vs a modern HFC.
 

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Yeah, I don't buy the 240HP thing. In the 2016 and newer VT's you can gut the 2nd cat because it's downwind of any sensors but the primary cat is the one in question. I wouldn't run catless. I know about the performance gains but I know I can't stand driving behind someone with no cats because it stinks. I don't want to be that guy. The stock cat has no problem with a stage 1 but it does begin overheating if you don't monitor it.
I've debated getting a DP with high flow but installation is a bitch and I don't want to do it twice when I sell the car.

I think the 240 thing may be valid with older cars because with them it's all or none. The 2 cats are together in the older cars along with the 02 sensors. You can't just gut one of the cats because you'll throw codes (unless you use cheaters). The new cars can at least get half way there.
 

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I can see 240whp depending on the dyno and tune. The biggest difference between the two is the price. Everything else is personal preference and of you like polar bears. I don't, they bite.

If you go catless; you have to live with constant worry about a code (unless you get a tune), pollute more, have you live with the smell when the wind is blowing right and it makes it tough to find a quiet exhaust setup. However, you get the most performance gain for the least amount of money.

If you go Catted; you only kind of have to live with the code popping up rearly, it smells better, it won't scare away polar bears (so good luck with that) and it's a little bit quieter. However, it's going to cost at least $100 more and you'll be out some potential power.
 

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Also, keep in mind the 2016's are more sensitive. I can't remove the CEL with the catted tork downpipe. I haven't spent the time to elbow yet but have them available if needed. The tune I have just turns it off currently. Keep that in mind if they do checks of emissions where you are.
 

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CDninATL dyno'd ~246wHP/265wTq with stock downpipe on his 2013 manual, while I have a catless downpipe, and only cleared ~211wHP/270wTq because of my larger than stock tires. Every car is different, and will get more or less out of various components. For instance, manual 2013s typically dyno higher wHP than a manual 2014+ with the same hardware (they also like to explode). Model year, auto or manual, mileage, height above sea-level, barometric pressure, humidity, and temperature all have a say.

So, while it could be true that at the time of his testing, on his dyno, at his shop, Tork found that downpipes limit to 240wHP. That doesn't mean that someone on a different dyno won't see significantly more HP. Keep in mind that Tork is here to sell parts. If people know they can hit 250/270 with an intake and exhaust, he won't sell any more downpipes. That's bad for business.

Also note: Any number quoted by Tork is relative to the part he sells. It could very well be that his downpipe limits to 240wHP.
 

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Yeah, wtf? Also 211whp and 270wtq means something is choking things at higher rpm. As for 246whp vs 240whp, that is arguably within margin of error at 2.5% when you consider variance in dyno's and environmental adjusters.
 

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Yeah, wtf? Also 211whp and 270wtq means something is choking things at higher rpm. As for 246whp vs 240whp, that is arguably within margin of error at 2.5% when you consider variance in dyno's and environmental adjusters.
I was surprised when I first saw the numbers, for sure. However after a bunch of research done mostly on truck forums where they are used to changing out different size tires, it's a rule of thumb that you lose about 8-12% wHP per inch of increase in tire height (depending on gearing). The trick is that you only usually see the drop when run on a load-based dyno, like the Mustang dyno we used for the tune (numbers quoted already account for the 10% drop mustang to dynojet). The tires I have on the car are an inch higher at rest, and as much as 2" higher at 4000+ RPM due to the contraction of the sidewall at speed. So take the 211 wHP, and add 20%, and you get 253 wHP, which is about what you'd expect with my mods.

As far as CDNinATL's numbers, they are definitely within a margin of error for a hi-flow cat, sure, but his car had stock downpipe. You'd think stock would score much lower than catted or catless aftermarket, but it didn't. That's all I was trying to toss out there.
 

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I dont think tires would effect the HP rating that much.... at least not a 30HP difference.
Yeah, I was surprised as hell when I saw the dyno numbers as well. After a bunch of research, and running the math, it made a lot more sense. Only really shows up on load based dynos, and can knock off as much as ~10% per inch of tire height, and you have to take into account tire expansion. So with my tires, it's a 2" gain in height at speed, which kills the HP numbers on the dyno.

My big question is how it affects real world track times, 0-60, 0-100, 1/4, etc.
 

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Discussion Starter · #13 ·
Thanks guys! Any recommendations for high flow cats? I know there are threads about the Solo, are there any others? Any experiences with Tork's?
 

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Yeah, I was surprised as hell when I saw the dyno numbers as well. After a bunch of research, and running the math, it made a lot more sense. Only really shows up on load based dynos, and can knock off as much as ~10% per inch of tire height, and you have to take into account tire expansion. So with my tires, it's a 2" gain in height at speed, which kills the HP numbers on the dyno.

My big question is how it affects real world track times, 0-60, 0-100, 1/4, etc.
I know my car feels a little slower with my current tires at higher speeds. They are almost a half inch taller than my stock ones. And they weigh almost the same.
 

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I know my car feels a little slower with my current tires at higher speeds. They are almost a half inch taller than my stock ones. And they weigh almost the same.
Larger tires effect track times as well, and not because of weight. When you change the size of a tire your essentially changing the gear ratio because the tire is a spinning part of the drive train. A larger tire reduces the gear ratio.

In a nutshell, for your engine to turn that wheel the same amount as the smaller wheel it has to use more energy to move the larger mass. That's wasted energy or HP. On the plus side you'll have a higher top speed.
 

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Exactly as the Swordfish said.
I have a Pierce Motorsport single cat down pipe on mine currently doing 225w/Hp on an auto.
I also have a catless down pipe Henderson exhaust made up for me that I had on the car while waiting for the Pierce down pipe to arrive .
When using it was always worried that I was going to be pulled up by Police and have to be tested by the EPA as the fine in Australia for tampering with, or removing a catalytic converter $22,000..
As by the HP figures you have guessed we have done a lot of work on the tune. However, every how and then the car would still through up a code on the catless down pipe.
The difference in power of the Pierce Motorsport single cat down pipe against the catless down pipe was only 6 Hp which I feel is negligible considering the car runs better, smells cleaner, and doesn't pop a code anymore.
Not to mention the piece of mind of doing the right thing.
Zapp
 

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I have the Pierce catless and the biggest issue is the noise. It is much louder at higher RPMs or cruising at 80 mph so if that bothers you get one with a CAT. The Catted downpipes can still throw codes and i think you won't be able to tell the difference in MPG or butt dyno so for me just comes down to the noise.
 

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Larger tires effect track times as well, and not because of weight. When you change the size of a tire your essentially changing the gear ratio because the tire is a spinning part of the drive train. A larger tire reduces the gear ratio.

In a nutshell, for your engine to turn that wheel the same amount as the smaller wheel it has to use more energy to move the larger mass. That's wasted energy or HP. On the plus side you'll have a higher top speed.
This, I'm aware of. I'm just confirming that its enough to feel with only a half inch difference.
 

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I dynoed 233hp and 240tq with a high flow cat and tork canned tune. Catless and tork dyno tune i got 255hp and 265tq. Im going for max performance and Utahs laws aren't too strict so it works for me. I can tell you that my catless setup with the cnt exhaust is WAYYY quiter than the high flow cat and a muffler delete were.
 
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