Hp difference With or without cat.
01-27-2019, 07:23 PM
#3
Water Foul
Right around 2% at most. Not worth doing. Your butt dyno will not feel the difference, and it is within the margin of error for a real dyno.
Take a look at this article and maybe multiply the tiny gains by 2 for the RX-8. As they found, you may realize a small gain in some RPM band, but you often lose a few HP in another RPM band. The most common scenario is gaining power at high RPM, thanks to increased flow, but losing power at lower RPM, where flow is less important. I'd rather have the lower end power--especially with this car. I spend a lot more time at 4500 RPM than I do at 7500 RPM.
I do extensive data logging at the track. Between running cat-less and cat-ted under the same conditions, my lap times are exactly the same. Because of this, I choose to run a cat. The only downside, is the car doesn't fart flames with the cat on.
Take a look at this article and maybe multiply the tiny gains by 2 for the RX-8. As they found, you may realize a small gain in some RPM band, but you often lose a few HP in another RPM band. The most common scenario is gaining power at high RPM, thanks to increased flow, but losing power at lower RPM, where flow is less important. I'd rather have the lower end power--especially with this car. I spend a lot more time at 4500 RPM than I do at 7500 RPM.
I do extensive data logging at the track. Between running cat-less and cat-ted under the same conditions, my lap times are exactly the same. Because of this, I choose to run a cat. The only downside, is the car doesn't fart flames with the cat on.
01-27-2019, 10:29 PM
#4
Smoking turbo yay
Here is a video of an STi on a dyno with and without cat:
Bottom line: if you like to spit fire, go catless; if you don't like smelling gas fume, go catted.
Bottom line: if you like to spit fire, go catless; if you don't like smelling gas fume, go catted.
01-28-2019, 06:47 AM
#6
The Blue Blur
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01-28-2019, 09:01 AM
#8
Water Foul
Also, he is claiming removing the cat gained him 50HP, but they also removed the muffler, increased the boost, and were actively tuning the engine. In short, he's an idiot.
Do some searching on this forum. There are a lot of before and after dynos. Many members have optimized intake and exhaust with all the best bolt-ons, and spent a lot of $$ doing it, only to LOSE power. You can expect +/- 5HP.
The most legitimate reason to remove the cat is to prevent a clogged cat from killing your engine.
01-28-2019, 09:12 AM
#9
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01-28-2019, 09:41 AM
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Not at all comparable to this engine. The exhaust systems are completely different. Flow rates and pulse frequencies are completely different.
Also, he is claiming removing the cat gained him 50HP, but they also removed the muffler, increased the boost, and were actively tuning the engine. In short, he's an idiot.
Do some searching on this forum. There are a lot of before and after dynos. Many members have optimized intake and exhaust with all the best bolt-ons, and spent a lot of $$ doing it, only to LOSE power. You can expect +/- 5HP.
The most legitimate reason to remove the cat is to prevent a clogged cat from killing your engine.
Also, he is claiming removing the cat gained him 50HP, but they also removed the muffler, increased the boost, and were actively tuning the engine. In short, he's an idiot.
Do some searching on this forum. There are a lot of before and after dynos. Many members have optimized intake and exhaust with all the best bolt-ons, and spent a lot of $$ doing it, only to LOSE power. You can expect +/- 5HP.
The most legitimate reason to remove the cat is to prevent a clogged cat from killing your engine.
Last edited by Onlyoneromeo; 01-28-2019 at 09:45 AM.
01-28-2019, 03:52 PM
#13
Water Foul
I think in the truck video all he did was remove the cats and muffler in the second pull. I can't imagine a muffler making much of a difference . But either way you're right about the engines and setups being different. The same goes for the first video posted. That engine had cylinders and a turbo right ? I'd like to see before and after on a n/a rotary.
Think about this logically, though. Do you really think cat design is so poor in 2019, that simply removing one is good for a 10% power gain? This isn't 1980. The factory cat flows more than a normally aspirated Renny can pump. There is little to no restriction in the cat. Mazda squeezed nearly every last HP out of this engine from the factory. As stated before, even if you gain some power up top, it is very likely you are losing it somewhere else, and the result is often a poor trade.
But you don't have to take my word for it. Search this site for dyno plots. The truth is out there.
01-28-2019, 04:16 PM
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In the video, the guy said they increased boost and worked on the tune before the 2nd pull.
Think about this logically, though. Do you really think cat design is so poor in 2019, that simply removing one is good for a 10% power gain? This isn't 1980. The factory cat flows more than a normally aspirated Renny can pump. There is little to no restriction in the cat. Mazda squeezed nearly every last HP out of this engine from the factory. As stated before, even if you gain some power up top, it is very likely you are losing it somewhere else, and the result is often a poor trade.
But you don't have to take my word for it. Search this site for dyno plots. The truth is out there.
Think about this logically, though. Do you really think cat design is so poor in 2019, that simply removing one is good for a 10% power gain? This isn't 1980. The factory cat flows more than a normally aspirated Renny can pump. There is little to no restriction in the cat. Mazda squeezed nearly every last HP out of this engine from the factory. As stated before, even if you gain some power up top, it is very likely you are losing it somewhere else, and the result is often a poor trade.
But you don't have to take my word for it. Search this site for dyno plots. The truth is out there.
In the video at 1:04 he said he only took cats and exhaust off and ran an open exhaust. He did not say anything about making any other changes. Watch it again.
01-28-2019, 04:55 PM
#15
Water Foul
Watch it all the way through at least 1:47. He says at 1:36 they were still tuning, and at 1:46 they increased boost to 17psi for that pull.
Let me condense his nonsense for you... "All we did was remove the cat and muffler and did nothing else and gained like 50 hundred HP. Also, we increased the boost to 17psi and were still tuning, but only removed the cat and muffler. So next time someone tells you cats don't kill HP, show them this lame video in which I contradict myself and otherwise say idiotic things."
Yep. Trust that guy!
01-29-2019, 12:13 PM
#16
Registered
Keep in mind, going catless on something with a Turbo has a completely different effect then doing it on some thing naturally aspirated, especially a typical OEM Cat on something like a truck.
Not to mention per the video, this is being done on a vehicle with a cat designed around much less power and flow then originally intended..
It is not uncommon for NA engines to pick up a small amount of torque with a High Flow Cat over no Cat at all...
I drank the coolaid and gutted my OEM Cat the same week I got my RX-8. virtually felt zero difference even at redline, and was left with a car that constantly made my clothes smell like I had been using a 2 Stroke Lawn Mower all day, and a check engine light that feels like staring into the sun when driving down a dark road at night.
Not to mention per the video, this is being done on a vehicle with a cat designed around much less power and flow then originally intended..
It is not uncommon for NA engines to pick up a small amount of torque with a High Flow Cat over no Cat at all...
I drank the coolaid and gutted my OEM Cat the same week I got my RX-8. virtually felt zero difference even at redline, and was left with a car that constantly made my clothes smell like I had been using a 2 Stroke Lawn Mower all day, and a check engine light that feels like staring into the sun when driving down a dark road at night.
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