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Статья про выхлоп. blinx's OFFICIAL EXHUAST THREAD
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СообщениеДобавлено: 18 мар 2009, 08:57
Аватара пользователяСообщения: 5929Откуда: УфаЗарегистрирован: 16 дек 2005, 07:38
o far I’ve seen A LOT of exhaust questions and A LOT of misconceptions, so im typing this up to clear those up and hopefully some people will learn the truth about exhaust systems back pressure and velocity, I will try to keep this as brief as possible,

But first let me say I don’t care what your friend said or what the exhaust shop says or what the v8 drag racer said to you, trust me on this one:

First I will address back pressure:
its simple, back pressure is BAD always BAD! Forget the idea of some engines need back pressure it’s a LIE!! Back pressure means the engine has the waste its HP to push the exhaust out of the system (also known as pumping loss) so you will ALWAYS lose power with back pressure!

Now I will address velocity:
exhaust velocity is what’s important, increase in exhaust velocity is what will free up extra power. now if your wondering how then read on:

Why does velocity free up more power: exhaust velocity is when the exhaust flow is so smooth that each exhaust pulse leaves a vacuum behind to suck out the next pulse so instead of the engine pushing the exhaust out the exhaust itself is sucking out exhaust hence taking the load off the engine and reducing pumping losses. This is where exhaust piping is important, different size piping will give you ideal exhaust velocity at different RPM points. You can’t have perfect velocity throughout your entire rpm range. a smaller piping will give you better velocity down low but too small and your sacrificing top end power because your restricting flow, a large exhaust will give you that ideal velocity higher up in the power band but you may loose some power down low.

Why do you loose power down low with large exhaust: when I say large I mean like having a 3" piping on a stock low revving na 1.6 sohc, what this does is it takes longer for the exhaust to exit the tail pipe because it takes longer to fill up the system, so the engine has to constantly push the exhaust through the system until it gets to the tail pipe. Basically there are more pumping losses. Basically the exhaust has more space to fill before it exits the tailpipe and the engine has to work harder to do that.

So now you know BACK PRESSURE IS BAD! And VELOCITY IS GOOD. but your wondering why so many people think back pressure is good, ill explain that too:

Why people think back pressure is good: in the 1960's racers would put larger pipes on there cars but there cars felt slower sometimes because they where shifting there ideal velocity to a higher rpm, V8's most redlined at 4500-5000rpm in those days so they shifted the point past there engine operating range, then they put much smaller pipes on which gave them a great deal of velocity down low so they had a jump in hp and tq say from 1500-3000 rpm and they thought it was because of back pressure, but it was actually velocity that had increased. Basically it was all a misunderstanding.

How do I know what size to choose to have ideal velocity:
well it’s really complicated it depends on a lot of stuff like your driving style and mods you have etc... So I don’t feel like getting into it, plus everybody has there own preference so I can’t decide what is good for YOU, only you can. And I don’t want to start an argument here.

But blinx I really wanna know your opinion on piping size, I promise not to argue I know it’s just your opinion:
ok fine this is my opinion and preference only. first your exhaust piping size should match the size of your collector on your header (or larger) in most cases, the header collector can always be modded to be larger to match the exhaust size you need, don’t limit yourself to a 2" just cause your collector is 2" that just means you need to cut it off and have a larger collector welded on.

-I think most vtec engines 1.6-1.8 stock or mildly moded (stock internals) are good with 2.5" with a high flow cat or no cat at all, you can get away with a 2.25 if you have NO cat but i just don't see why you would choose such a small exhaust.

-for 1.6-1.8 vtecs with internal work like cams, raised compression, higher redline, port work etc.. I prefer a minimum of 2.5 to 2.75". You can try to step up to 3" if your heavily modded, you might see some gains.

-for 1.9-2.1+ vtecs 3" all the way! B-series 1.9+, H22, K20, or K24 setups should all use 3" for max power, even if the internals are OEM, you will in most cases see gains across the whole power band.

-for turbo Honda’s making 400whp and less 3" if your making under 300whp you could do a 2.5" with no cat but you will make more power with a 3". You can make a lot more than 400whp on a 3" but some people chose to step up to 3.5 or 4" at this point its really preference as ground clearance is heavily sacrificed at this point...

There now next time someone tries to tell you back pressure is good you can educate them

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