k24a3 k swap 2.5" or 3" exhaust..

[Samm928]

headers are 2.5" flange.

should i just run with 2.5" the whole way?
or go 3" from headers back.?


would i be losing massive if running 2.5"? :S

[munkaii]

With the amount of power you'll be dealing with (considering future upgrades), 3" would be a better choice. 2.5" might be a bit restrictive. Most B series conversions would probably utilise 2.5".

[jimmeh]

ive got a K20 in my civic and i have to recommend 3" so will any shop that u speak to.

[EG5]

3 inch for sure

[xntrik]

3 Inch.

[Samm928]

ok ok.. thanks..

[kwokstaa]

has anyone even tried 2.5 inch or is that just the general go of what people say on the forums about k engines.. lol

[EG5]

has anyone even tried 2.5 inch or is that just the general go of what people say on the forums about k engines.. lol

We did tried 2.5 inch exhaust back in late 2004 on our k20a EG , 3 inch is the way on K20a , K24a

[DR HONDA]

has anyone even tried 2.5 inch or is that just the general go of what people say on the forums about k engines.. lol
3 inch 100%. I have tried 2.5 inch early days and the difference was noticeable changing over to a 3 inch in every way, good luck

[fatboyz39]

2.5 if its daily driver. 3' for all out power/race.

[DR HONDA]

2.5 if its daily driver. 3' for all out power/race.
what drugs are you smoking boy? 2.5 inch if you like breathing through a straw. if you are going to do a k swap and try to save $100 from a 2.5 inch to a 3 inch and its going to bust your budget then do it

[fatboyz39]

2.5' breathing thru a straw LOL. Might as well go 4'.

[FLICK]

3 inch...

[mitch_f1]

I have heard completely differently, when I was researching exhausts for my MX5 I was told not to go bigger than 2" otherwise you will lose power; it's all about backpressure they said. SO I have a 2.5" header into a 2" cat back

[munkaii]

For low powered vehicles, a smaller exhaust diameter should be used. Generally it's about 2-2.25" for low power NA. Any more and there's not enough backpressure. Any less and you have too much backpressure. For K swaps chasing larger power, 2.5/3inch pipes should be used.

[mitch_f1]

Fair call

[jimmeh]

2.5 if its daily driver. 3' for all out power/race.
hey bro u told me to get the 3in regardless.....if its daily driver or not......hahahahhaah

[Benson]

I have heard completely differently, when I was researching exhausts for my MX5 I was told not to go bigger than 2" otherwise you will lose power; it's all about backpressure they said. SO I have a 2.5" header into a 2" cat back

Thats because its an Mx5 engine. Different engines require different size piping for the exhaust

[Chr1s]

Fair call

Is that you Mitch!!!! BP16's are for kids :P

[bennjamin]

An otherwise standard 1.8 benefits from a 2.5 inch collector back system.
So a STD to worked 2.0-2.4l would suffice a 3 inch collector back system as others have said !

[GSi_PSi]

your comparing a 1.6 mx5 engine to 2.4 k24

[jimmeh]

can someone please explain how a car needs back pressure to make power? from my understanding...back pressure is caused by a restriction. so hw does a restriction in the exhaust system aid the car to make power?
this is not a smart as comment...i genuinely wanna know

[DLO01]

You don't want any back pressure.

[jimmeh]

here u go guys.
souce: http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm
Some say that "an engine needs backpressure to work correctly." Is this true?
No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning.
The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below.
The other reason why people say "backpressure is good" is because they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of backpressure.
The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.
Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.
Getting back to the discussion, the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before. Earlier cars (and motorcycles) with carburetion often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.

[Killa From Manila]

was researching exhausts for my h22 setup, many back to back dyno runs from ppl on hondatech found gains all throughout the rev range when upgrading from a 2.5 to 3" exhaust

[Samm928]

would a 2.5" inlet. muffler be ok? or recommended go 3" muffler inlet.?

so..

2.5" header. 3" header back to muffler then muffler back 2.5"/3"?

thanks.

[EG5]

would a 2.5" inlet. muffler be ok? or recommended go 3" muffler inlet.?

so..

2.5" header. 3" header back to muffler then muffler back 2.5"/3"?

thanks.

No problem at all man with that set up