superg6819

I had a boosted b16a2 in my hatch and it blew up so now im going back to na/stock b16a2 or b18c/gsr. I still have my 3" exhaust on the car and was wondering if its too much flow for a stock motor? I only plan to run a header and intake.

b20vtek

yes it is

92civiceg9gsr

No it is not.

b20vtek

It all depends where in the rpm band your making the most power at.A motor that makes it power at say 5000-6500 would benefit from a narrower exhaust them one making power at say 8500-10000.A smaller pipe diameter will produce higher exhaust velocities at a lower RPM but create unacceptably high amounts of backpressure at high rpm.The thing is you want an exhaust thats narrow enough but at the same time maintain 0 backpressure.Backpressure in its most extreme form can lead to the revesion of exhaust gases which isnt good.You must balance flow capacity with velocity. You want the exhaust gases to exit the chamber and speed along at the highest velocity possible - you want a FAST exhaust stream. If you have two exhaust pulses of equal volume, one in a 2" pipe and one in a 3" pipe, the pulse in the 2" pipe will be traveling considerably FASTER than the pulse in the 3" pipe. While it is true that the narrower the pipe, the higher the velocity of the exiting gases, you want make sure the pipe is wide enough so that there is as little backpressure as possible while maintaining suitable exhaust gas velocity.

unusual71

Everything past the collector is just a restriction anyways, no its not too big

mar778c

iTrader: (1)

No, it is not.


Your arguement is partially relevant to primary and secondary OD. It is not relevant to what happens after the collector. The exhaust provides in a generic sense resistance to flow.

As for your statement concerning the speed of a pulse, you are robbing peter to pay paul. Your "FASTER" speed comes at the expense of mass flow. While you are correct that the 2" pipe will have a higher average velocity, the mass flow (CFM) will be considerably lower at a given pressure. This will in turn reduce whp.

I have run 3" on a 1.6L and my current 1.8L.
The 1.6L trapped at 96 mph on street tires.
The 1.8L trapped at 102 mph on street tires and 108 on 22" slicks.

FST GSR 1

^^^ Concur.

Robs_B18c

iTrader: (1)

I run a 3inch on my R and it's fine.

namewasdallas

i think it will work fine, for either motor, but don't forget on how your going to connect a header to a 3inch catback.

kulo

2.5" is perfect?>

92civiceg9gsr

Put the car on the dyno. The 3" will make more power and torque.

SIred91

Bullshit. There are WAY to many other variables.

mar778c

iTrader: (1)

Wow genius, I guess this guy did not know about those "many other variables"

https://honda-tech.com/forums/all-motor-naturally-aspirated-44/who-says-3%22-too-big-k20-dyno-2341715/

88Hatchy

If it is the same engine and it is tuned then it will almost always make more power. I have never seen any other result.

superg6819

Are there any headers out there that collect to 3" or would i have to get a 2.5" to 3" test pipe?

mar778c

iTrader: (1)

A 3" collector would not be a good ideal for a motor at this level of power. However, it is easy to wield a 2.5" flange onto a 3" OD pipe. Just go to a good fabricator or exhaust shop.

36Chitownrunnin

i got a 3" exhaust with test pipe on my hatch with a gsr a noticed more gains on top end but low end is kinda questionable sometimes.. put that out there

mar778c

iTrader: (1)

Did you tune it?

92TypeR

As stated earlier in the thread, every component of the exhaust after the final merge collector is either for emissions or evacuation, and is a restriction.

Using terms like "backpressure" is funny because it makes you look like a fool. It is a non-quantifiable term given to a resistance to flow. It literally does not exist. It is unitless. It is just a word used by people who do not understand exhaust flow and exhaust dynamics. It does not exist in any index of any engineering or fluid dynamics text.

If you need further understanding, or are not satisfied with my brief explaination, buy this book: <ISBN: 1860582095>

To the OP: Yes, run the 3". The only downside to having such a large diameter pipe would be noise level.

36Chitownrunnin

No, i got the exhaust with intension to turbo my car but i wouldnt be able to pass emissions. since i would need to convert to obd1 for software. So I need to go back to drawing board figure out what i can do with car.

mar778c

iTrader: (1)

Now you have it from a real automotive engineer.

mar778c

iTrader: (1)

You may be in a condition of running very lean which would lead to a loss of power.

36Chitownrunnin

maybe, but i really hate the car right now do to not being able to turbo! even doing all motor will bite me in the ***. cause of the damn computers.