32 replies to this topic

[tyrone]

why is it that a smaller size muffler is better that a bigger size one

[orangecrx]

dont think that is true. i went from 1 inch piping to 2.25 piping and my car is alot faster now. where did you hear that?

[tyrone]

people on the board where telling me to change my 4inch exhaust when i asked them for performance enhancements on my ZC rex.

[NNBD]

If you've got a 4" straight pipe to the end...indeed it is too big. It has got to do something with de flow, i don't know exactly but I asked a proffessor in unstable combustions at my university some things about no muffer at all etc....He also told me that also a normal 4 stroke engine need some kind of resistance because of the flow. I think that 4" is something as NO resistance

Edited by NNBD, 25 August 2004 - 04:47 PM.

[tyrone]

could this be the reason that it makes a hissing noise and feels like its losing power when it reaches 3000 revs then stops

[Kain]

just lose the fart can, man.

[kamikaze_fish]

the way I've always thought of it is like straws. If you take a coffee stir stick and drink of it, it's really hard and takes more effort than needed, we'll call this stock exhaust. Then take a normal straw and drink from it, much less effort and you get much more drink from it, much better choice, we'll call this performance exhaust. Then, take a straw that is 2 inches wide, barely big enough to fit your mouth and try to drink from that, you'll get a great start but you run out of lungs before you actaully get the drink to your mouth, we'll call this way too big oversize exhaust.

[taphonomist]

I think that the idea is that the backpressure generated by a smaller ehaust keeps more of the intake charge in the cylinder while both the intake and exhaust valves are open simultaneously. It's a balancing act, however, because too much backpressure will cause more exhaust to back up into the cylinder.

Oh, and I second the vote to lose the fartcan. Just because something is loud doesn't mean that it's fast, and just because something is loud doesn't mean it sounds good.

taphonomist

[female four]

Easy. Its a 4 stroke engine and there is a firing pattern to it. 1-3-4-2 is the order in which it fires. When cylinder one fires, and stops, 3 fires and stops and so on. What happens in the exhaust manifold (in other words, header) is that it takes those pulses one by one and collects them at the collector creating an even flow going out your exhaust.

Too little of a size and you will have too much back pressure. Too big of a exhaust size and well... you lose velocity and it kinda loses itself somewhere.

Think of a smoker. I know its not the best analogy, but bare with me. If he blows smoke out mouth with his lips closed into a small orifice, then the smoke rushes out. At some point it'll just fade into the air.

Now just have him open his mouth. The smoke just flows everywhere with no direction. We don't want that to happen in a motor engine and that is why you should run your engine without a header because the air will just puff out the exhaust ports.

What you want for performance is ZERO backpressure. Its hard to believe, but yes that is what you want. But the important part here is to not just go out and buy the largest system there is. You want the smallest setup with the least amount (as close to zero as possible) of back pressure because you don't want to lose that exhaust velocity out to nowhere.

Normally, the 60mm (2.36") or 2.25" exhaust should be good enough for any setup because the stock system is most likely restricting flow (which most factory setups are btw). So opening them up slightly helps.

Once you have more flow entering and exiting the motor (ie boost), then stepping up to a larger 2.5" or 3" exhaust is very benificial because you have more flow therefore you will not lose the exhaust velocity in the larger sized exhaust.


And I also motion to lose the fart can.

[1stGenRex]

people on the board where telling me to change my 4inch exhaust when i asked them for performance enhancements on my ZC rex.

i've only seen a 4" exhaust on a 454!!!! 2.25" is perfect...just enough backpressure...usually 3" is used in turbo apps.

[Cramo]

yes there is such thing as to big.. because if you lose your backpressure you have absolutly no torque. honda's already have like no torque why would you want to lose more.. 2.25 is like perfect for a N/A motor. you look at 2.75-3.00 for turbo applications. You really want to keep as much torque as possible and still bring up your HP. exhaust it a major part to making a nice car.. and im not talking about poopy fart cans that cause loud trumpet effects, lol.. get some balls and buy a borla. lol

[female four]

Guys, having back pressure is just as bad. You want a free flowing exhaust, but at the same time not lose exhaust velocity. So its something thats in between. Not too small and not too big.

[zAd -]

didn't really read the thread but i dunno if it was stated but backpressure is a myth the reason why people lose hp with such a big exhaust is due to the decrease of veloctiy. it has been seen smaller exhasut mroe torque less hp. bigger exhaust more hp less torque from the dyno's ive seen from other honda's but the goal is to find the ideal sizing it really dpeends on how much to whp you plan on putting out ill tell you what a good size. the header design really helps also with the velocity.

[orangecrx]

i would have to sayt that four inches was alot. i htought you were talking about a 1inch pipe. whne i got my exhaust the guy said i should not have more thatn 2.25inches because i would lose back presure then lose horespower.

[tyrone]

i see what your saying so ideally a dtm exhaust or a bike can would be perfect or am i wrong.

Edited by tyrone, 26 August 2004 - 07:59 AM.