10 hours ago, D.FYLAKTOS said:

We are waiting

Ok lets clear some things up.

Do you remember the post with the air filter box, restriction = higher air velocity = better low speed performance.

Well a car exhaust is tuned in a similar manner, that meaning that the length of the exhaust manifold as well as the diameter and the curvature are all calculated in order to create an effect called scavenging (similar to what 2strokes use).

Lets get down to the felly example, our cars have a 2+2 to common collector exhaust, after the collector lies the catalytic converter, when a pulse from a firing cylinder is generated this pulse travels down the exhaust hits the catalyst and goes back. Thus, this pressure wave is timed to arrive and start bouncing back again when another valve is opening. Helping the engine scavenge get more air and fuel in and more exhaust out.
A sport(metallic) catalytic converter by being more free flowing messes with the exhaust pulses weakening them, pretty much killing scavenging. That pretty much is the myth of backpressure, cars DONT need back pressure they just need a properly tuned exhaust to which backpressure is a byproduct of its tuning.

The freer-flowing nature of the cat though allows the car to breathe better at higher rpm (because at that point its already off its resonance tuning), while a stock cat would not do that.

The same principle applies to velocity stack tuning you honestly DO NOT gain power you are just SHIFTING the power band in a region that ITS NOT tuned for.
Naturally aspirated cars need scavenging, and it is possible to get that effect without any cat whatsoever just equal length runners terminating to a single collector.

Take a look at this F1 V10 no cat no nothing just properly tuned exhaust runners.

 

Edited 1 July, 20214 yr by Thefeliciahacker

But I honestly think this cat is better he is very efficient better that both ceramic and metallic 

13 hours ago, Thefeliciahacker said:

 

Do you remember the post with the air filter box, restriction = higher air velocity = better low speed performance.

 

Oh yes and it works fine !

 

13 hours ago, Thefeliciahacker said:

A sport(metallic) catalytic converter by being more free flowing messes with the exhaust pulses weakening them, pretty much killing scavenging.

 

That pretty much is the myth of backpressure, cars DONT need back pressure they just need a properly tuned exhaust to which backpressure is a byproduct of its tuning.

The freer-flowing nature of the cat though allows the car to breathe better at higher rpm (because at that point its already off its resonance tuning), while a stock cat would not do that.

 

One day a mechanic drove my Felicia for a while and when returner back he said ''Your car wan not the proper torque on the low rpm, what you have done? "

I told him that i have changed the stock Catalytic with a Metallic one because (yes i have to admit it) i believed the car tuning magazines of that era and now that i have returned back to the Ceramic (and 45mm muffler) i noticed that the noise is lower plus i there is no need to downshift so often as before in mountain roads.

Turning back to the factory way or air incoming plus the Ceramic Cat i feel my Felicia much better on the low-medium rpm no matter if it's city driving or national road

There is a slightly change on the high rpm but nothing significant, after all i haven't a Honda to turn on 9000 rpm.

 

13 hours ago, Thefeliciahacker said:

 

The same principle applies to velocity stack tuning you honestly DO NOT gain power you are just SHIFTING the power band in a region that ITS NOT tuned for.
Naturally aspirated cars need scavenging, and it is possible to get that effect without any cat whatsoever just equal length runners terminating to a single collector.

 

 

Another myth is the "custom exhaust manifold" which ''will raise your horsepower"

i have seen videos with guys with expensive cars which paid almost a thousand dollars for a custom exhaust manifold and the gain was 4 HP only.