Myvi 1.3 Auto 4-1 or 4-2-1?

[brandylau]

Oh! I thought you meant fc compared to stock, because most do, as they always say want extractor and straight thru' but also want better fc....

If compared between the 2 probably S-flow better as have slightly more restriction against straight thru'....

Hahaha we can't compare back to stock cause we have already modify the exhaust system. Well power means fuel and fuel means high fc haha. So basically s flow has better fc compared to straight flow? Thanks for the advice bro.

Well does the extractor play apart of fc also? Like 4-2-1 and 4-1?

 

[vr2turbo]

Hahaha we can't compare back to stock cause we have already modify the exhaust system. Well power means fuel and fuel means high fc haha. So basically s flow has better fc compared to straight flow? Thanks for the advice bro.

Well does the extractor play apart of fc also? Like 4-2-1 and 4-1?

Between the two not sure but against stock will have because stock still have cat con....

 

[Izso]

Hahaha we can't compare back to stock cause we have already modify the exhaust system. Well power means fuel and fuel means high fc haha. So basically s flow has better fc compared to straight flow? Thanks for the advice bro.

Well does the extractor play apart of fc also? Like 4-2-1 and 4-1?

I just noticed your name is "Brandy Lau". If you're a girl I'm flabberghasted and welcome you since your knowledge is not at the average / typical girl level. Interest wise is impressive too as you seem to be asking the 'right' questions, so much so no one yet is irritated.

Anyway, the differences between 4-2-1 and 4-1 is how the exhaust gases are pushed out. Read up on the scavenging effect within exhaust systems as well. In very generic layman terms : the easier it is for the exhaust to go out, the less effort engine needs to push it out, the faster the exhaust gas flow, less energy lost trying to "exhale". To some extent it means you have lower power in the lower rev ranges since a certain velocity is required to force the exhaust gases out. But it also means mid-range to high rev range the power is better since lesser restriction when the gas velocity is higher.

Generally the exhaust gases are "exhaled" in pulses and whether you use 4-1 or 4-2-1 dictates how those gases travel to the atmosphere. Which is why you need a proper tuned length extractor otherwise it's a waste of time changing to either one if the car is too short or small to use a proper length runner/extractor. Having had a "tuned" length 4-2-1 for my old Wira, I personally feel the Myvi is too short/small to have a properly tuned length one which is why just stick with the stock 4-1 la.

Mind you, this info isn't 100% accurate, there's a lot of other things that contribute to how the exhaust works. It's just a general explanation of how it sort of works.