all motor exhaust size info(back pressure doesn't give you power)

[dillon.ornelas]

delete

[Vvvtec]

I have a 3" exhaust on my K24, it's great. When I took my car to the exhaust shop to have it made the old fogies behind the counter literally laughed in face, following that up with 'you won't get up any hills with that'... Their opinion changed though once the exhaust was finished. Lol. Old badgers.

Pretty loud though for a daily lol

[zedries]

It's interesting that this thread comes up as I am about to arrange for a mandrel bent stainless in the coming month. It was suggested to me that a 2 1/4 would be sufficient as I will have light mods (mild cam, extractors possibly higher compression pistons). I was leaning towards a 2.5 inch and am now solidly confused... and I have done a fair bit of research!

Oh, and in case you were wandering - I have a B20A gold top engine - the original JDM B20A made for the 2nd gen prelude

[zedries]

Lol yes keeping this high revving angina quiet will be somewhat if a mission. The exhaust guy already said that even at 2.25 it will be loud and 2.5 even more so!

[JDM DC2R]

Having no exhaust and a bigger exhaust is 2 different things.

Also that 3" exhaust is on a 2.2L. try it on a B16 with just bolt on and you'll see why they say to large will loose LOW END POWER!!!!!!!!!

Not to mention the crap sound you get out of a over size exhaust!

[ALLMTR996]

Only time a bigger exhaust will make an engine lose power in any part of the torque curve is if the header you are using does not suit your engine,the only thing it will do is make noise with a bigger than needed setup for the street.I have always found after tuning more Honda's than I care to remember that as a rule of thumb these sizes work best for street cars
1600 to 1800cc 60 to 65mm exhausts noise levels can be controlled without killing power by restrictive mufflers
1800 to 2000 +cc 65 to 75mm exhausts moderate noise levels and very good power levels.

[thebob]

Having had a K swap and falling for the you need a 3inch trap. Sure it works, but you dont need it that big. Also muffler Vs straight pipe, You do not gain power by removing a muffler, the same goes if you add 4 mufflers to the system. The japanese are firm believers in 3inch (76mm?) being too big. With my current car, it come with a 3 inch system. I drove it for a while then went to a off the shelf 70mm japanese system which i think drives nicer, far more responsive and isn't any where near as loud. So having done both ends of the spectrum (3inch straight pipe k swap car, 3inch with muffler and 70mm system), i would without a doubt choose the 70mm over all of the others. Drivability is worth more to me then internet stardom.

[curtis265]

all motor exhaust size info(back pressure doesn't give you power)

just to correct you here, a smaller exhaust doesn't create backpressure, it has a better scavengeing effect (i.e. more negative backpressure than a larger exhaust from the exhaust flowing faster)

[Lukezen27]

how does exhaust back pressure effect power?

It’s actually not that complicated and it’s a proven fact..

Possible reduced power/torque not to mention potentially reducing engine longevity.

1. Exhaust systems primary function is to remove exhaust gasses from the engines combustion chambers as fast as possible!
Good systems are designed suck out gasses at the highest pressure rate possible by designing the systems to act like a vacuum based on combined heat, pipping size and bends designed for optimal air flow.

So to get the most out of your motor she needs to breath smooth and fast and why large systems can have a negative effect on your engine's performance,
Bigger not always better when it comes to flow characteristics

2. Engines are designed with back pressure in mind and are designed to rev to a selected RPM’s for that motors power band that’s based on a particular back pressure rate.

So if you change the exhaust systems size your potentially unbalancing the motors high RPM power band by changing the pressure on the exhaust side that might contribute motor longevity

[JDM DC2R]

if bigger better just run a 4". Think you could get a extra 10kws

All the dyno paper youve supplied are from bigger displacement or worked K20 putting out 155kws atws.
Get one on a stock b16/18 and watch the power loss of a 3'' over a correct sized performance exhaust.

[dillon.ornelas]

and you have yet to provide any form of evidence to show you are correct

[bennjamin]

3 inch is good for a k series , or turboed b series. 2.5 is gud for a b18 2 inch is gud for a b16 etc
The Internet knows this , what's the point of this thread ?

Have you driven a street car ( or any car) without an exhaust ? No power at all.

[thebob]

no, im not stupid enough to drive a car in Australia without an exhaust lol, the whole point of this thread is to attempt to answer the question, will back pressure from an exhaust give you more power, from the evidence i can gather, the exhaust back pressure loses you power, back pressure in the headers is important for scavenging and can utilized to gain power.

sorry if i have stepped on people toes or people have lost the point im trying to make

is a giant exhaust good for the street? only if we lived in a world where we were all deaf
will a giant exhaust loose you power? only if you motor doesn't have a well designed header/extractor.

i honestly WANT to see a dyno that proves back pressure will show a gain somewhere on some motor

Numbers aren't everything. My experience was the car felt much better going from 3inch to 70mm. Sure, 3 inch probably makes more numbers, but i enjoy driving my car and value the driving experience more then the print out from the rollers.

I find it funny reading interviews with Japanese tuners and reading interviews with american tuners and how they both have conflicting ideas/methods.

http://www.hybrid-racing.com/blog/japan-day-five-part-one-k-tech-engine-service/

Long read, but you will understand what I'm saying when you get to the end.

[curtis265]

Its not really about empirical evidene here... Go study some basic fluid dynamics.

You dont see us harping on about backpressure here...

Cos theres no such thing as backpressure.

[curtis265]

Okay, Then why is the principle seemingly hard to apply?

According to bernoulli, faster exhaust gas = lower presure in the pipe (and therefore less backpressure)

So for a given flowrate (Q), there will be an ideal velocity which is directly related exhaust size. As Q is related to engine speed, a a givenexhaust size will not favour all engine speeds. This is why bigger exhausts produce more power on a dyno (producing torque at high rpm gives more power which isnt always useable)

You also seem to be correlating backpressure to exhaust size, this isnt necessarily correct

[curtis265]

it raised more questions than it answered
to start the fluid we are dealing with isn't ideal (one which is in-compressible and has no viscosity) then we have to deal with the fact that flow is unsteady and at times not laminar (it comes out in pulses)
then we have to deal with head losses, losses from fluctuating temperature, expansion and contraction, friction and turbulence from bends, surface imperfections and viscosity. (there is probably more that im forgetting).
hence why f1 designs headers with trial and error (the people who make them are very experienced) and why every year they look completely different.
You were asking specifically about sizing, not about head loss due to bends and temperature loss

these cant be avoided with the design of a streetcar

[PHO]

OoOoOoOoOoOoOoOoOoOoOoOo!!!!!!!!

[curtis265]

Yes thats correct but still does not necessarily quantify a larger vs smaller exhaust, that comes down to rigorous lab testing i suppose.... Which is whst you seem to be alluding to :)

I thougbt u were being the usual backpressure potato

[curtis265]

Its ok we're not all potatoes on here

[curtis265]

I know what laminar/turbulent means...

[lolmclol]

this thread makes me

http://www.ozhonda.com/forum/customavatars/avatar24136_23.gif

[ALLMTR996]

lol "backpressure potato" when ever someone calls someone else a potato i giggle like a school girl. (its sad, im telling the truth)
i know its not real. the term back pressure has never come up in fluid dynamics text books ONCE. NEVER. i honestly never thought i would have to get so technical on an online forum.

So are you giving this knowledge/advice on your own research and YOUR REAL WORLD TESTING or just crap you have read in text books and the web ?

[bennjamin]

So are you giving this knowledge/advice on your own research and YOUR REAL WORLD TESTING or just crap you have read in text books and the web ?

He (the thread starter) sounds like a disgruntled 1st year student - all book smart and no real world knowledge. No offence OP - but you sound like you are directly quoting wikis / other net resources with info but you clearly do not understand yourself.

[ALLMTR996]

No wiki's or net info here just many years of dyno knowledge on what works best on Honda setups.

[bennjamin]

No wiki's or net info here just many years of dyno knowledge on what works best on Honda setups.

Not you - the thread starter lol. I know you know your shit ;)

[dougie_504]

I use a 60mm on my B16A CRX. Perfect size IMO.

I wouldn't use a 2" on a B16A though. On a D16 sure, but B16 I'd go 2.25" up to 60mm.

B18C 60mm-63mm.

K-series has long been proven to make more power with the 3" than a 2.5-2.75".

[ALLMTR996]

I use a 60mm on my B16A CRX. Perfect size IMO.

I wouldn't use a 2" on a B16A though. On a D16 sure, but B16 I'd go 2.25" up to 60mm.

B18C 60mm-63mm.

K-series has long been proven to make more power with the 3" than a 2.5-2.75".

Some nice advice right there and your opinion is very good when you cam up a B16a bigger than a ITR style cam 65mm exhaust works very good with a very well designed header.

[DreadAngel]

I'll try and find those dyno printouts you want as evidence to show where you might be wrong. From an AE111 dyno day, iirc most of us like me used 2.38"/60.5mm [FGK PG] while another guy got a HKS Super Dragger off a Supra iirc which was 3.34"/85mm and you want to know the result, loud noise =/= good curve or peak output... Drove the car later confirmed it was a pig compared to mine...

FYI 4AGE 20V is a 1.6L...


if bigger better just run a 4". Think you could get a extra 10kws

All the dyno paper youve supplied are from bigger displacement or worked K20 putting out 155kws atws.
Get one on a stock b16/18 and watch the power loss of a 3'' over a correct sized performance exhaust.

This...

When you're working with Force Induction, Large Capacity or Built engine, the parameters of what constitutes as the ideal sizing is far different to that of a small capacity NA engine.

For example even with NA 2L, there are very few stock engines that will benefit from 2.75" [F20C and K20A w/ 215/220PS]. These engines benefit from that because of the aggressive factory specs they have, try this on say a stock SR20DE [165PS] or a F20B [155PS?] and see the results... I can't remember their camshaft specs to show how 'mild' they are in comparison to the F20C/K20A or your examples but you get the point...

The sizing people above and on the internet usually go with are for stock to mild bolt-ons...

[dougie_504]

Some nice advice right there and your opinion is very good when you cam up a B16a bigger than a ITR style cam 65mm exhaust works very good with a very well designed header.

Well I'm using Skunk2 Pro stage 1 cams atm, not yet tuned, as well accompanying adjustable gears, Supertech springs/titanium retainers, Jun oversized valved, ITR TB/IM, re-welded combustion chambers, enlarged ports etc. RS*R header which is port matched to my head, and the 60mm catback setup with a 100CEL Metal cat.

Do you think I should consider a larger exhaust? Bought my Kakimoto R brand new :(

[ALLMTR996]

Well I'm using Skunk2 Pro stage 1 cams atm, not yet tuned, as well accompanying adjustable gears, Supertech springs/titanium retainers, Jun oversized valved, ITR TB/IM, re-welded combustion chambers, enlarged ports etc. RS*R header which is port matched to my head, and the 60mm catback setup with a 100CEL Metal cat.

Do you think I should consider a larger exhaust? Bought my Kakimoto R brand new :(

I think your setup is on the money I would not change it at all.

[ALLMTR996]

What alot of people do not understand is Honda engines are different to most 4cyl setups you need to look at alot of things when it comes to choosing the right exhaust for your car with its given engine size.There are so many papers written by text book tradesmen about exhaust size + header design and so on but not one of them has ever tested there idea's but yes it works on paper and in a engine simulation computer program but in the real world its a fail,the sizes I posted before are a general idea of what I have always found to work on Honda engines and in no way am I saying I am 100% correct it just comes from years of dynoing and testing and racing these Honda engines that we all own.

[zropts]

For a k series all motor ill probly go 3inch

[DreadAngel]

K-series light tune to moderate [NA] better with 70mm/2.75" than 3"... 3" a bit too big for bolt-ons and/or drop in cams + tune.