Exhuast pipes, best size according to the pros

[jugbugz]

Ok, from reading that HONDA builders book I've gathered so much damn good specific info that It's A MUST HAVE for all honda owners...

recommended sizes below;

1.6L = 2.25inch
1.8L-2.0L = 2.50inch
2.2L-2.4L = 2.75innch

I'll be posting the theory and physics of why soon. But the main reason is maintaining VELOCITY.

 

[Dino-Spumoni]

When talking to John at Hytech exhaust, I asked him things like " if I had a b series with 250 hp on the engine dyno, would a 2.5" exhuast be good?" He said that 2.5" is pretty much the limit for that setup until you need to go bigger. I asked him what Larry Wildmer of Endyn uses on his 300hp b20/vtec cars, and he said 3" exhaust.

 

[jugbugz]

yup, just wait till I post up the reasons why from HONDA builders book. The capacity has velocity limits. Going bigger than your capacity suggests would affect the low and mid range power, becasue there is not much air velocity. It's more complicated than Hp figures suggests.

 

[Dino-Spumoni]

I know, I have both those honda builders books.
I realize that an exhaust made to breath at 9000+ rpms on a built motor will not be optimized in the lower and mid rpms, I was just giving a quick example of a conversation I had with an expert in the field.

 

[blinx9900]

i will accept jugbugz reccomenddations as a GENERAL rule, which maybe helpful to people with mild set ups and are new to fixing up cars, but there is no way you can say that 2.25" is perfect for any 1.6 b-series, believe me shifting at 9000rpm a 2.25" becomes very restrictive, and the whole idea of maintaing exhuast velocity is for street cars and lower rpm power gains. jugbugs keep in mind when you read something it is just that side of the coin.

 

[rvm]

thanks for the information, I run a 2.25" one

 

[blinx9900]

rvm dont you have the mugen twin loop? i though most japanese exhuasts were 60mm which is 2.37 inches. or were you referring to the comptech you used to run?

 

[jugbugz]

i will accept jugbugz reccomenddations as a GENERAL rule, which maybe helpful to people with mild set ups and are new to fixing up cars, but there is no way you can say that 2.25" is perfect for any 1.6 b-series, believe me shifting at 9000rpm a 2.25" becomes very restrictive, and the whole idea of maintaing exhuast velocity is for street cars and lower rpm power gains. jugbugs keep in mind when you read something it is just that side of the coin.

Yup, thats a street mod advice... if it was a track car then you wouldn't worry too much about anything but the top end.

 

[rvm]

rvm dont you have the mugen twin loop? i though most japanese exhuasts were 60mm which is 2.37 inches. or were you referring to the comptech you used to run?

Mugen one, I didn't know that information sorry I learned something new today

 

[jugbugz]

hmmm since stock redline is 8600rpm and I already have headers and exhaust then I'd like to keep my bottom and mid range torque and sacrifice 400rpms if it would affect or not.

 

[jugbugz]

Ok, sorry I have to correct what was stated in HONDA BUILDERS..

Cat back exhaust system with free flowing muffler:
Suggested diameters:
1.6L : 2.00 inches
1.7-1.8L : 2.25 inches
2.0-2.2L : 2.50 inches
2.3-2.4L : 2.75 inches(for nitrous, turbo, and supercharger applications, add at least 0.5 inches to the diameter.)

The principles and the tuning observations can be generalized to other combination. To dail in an exhuast system, you must flow test each cylinder and have a specific end use in mind, such as DRAG RACING, ROAD RACING or SLALOM. Then you need to take into account gear ratios, vehicle weight, and the cam, head and intake combination just to name a few.

Tom Ballantyne owns a test car, it's 1992 1.6 SOHC VTEC civic with DC header flowing into 2.25inch exhuast pipe from the cat back to a sebring muffler. The only other mod is an MSD ignition, which shouldn't influence these results. The car comes stock with 125hp. Before getting into the test, Oscar mentioned that a 2.00 inch exhuast pipe seems to work better for these 1.6L SOHC motors. This one has 2.25inch, so it may lose some velocity and flow on the high end. This is a good time to bring up that fact that the exhuast pipes, after the header, are a part of the system. As long as you don't squeeze the diameter down drastically or start doing rollor coaster bends with it, it won't cause you to loose power. In fact, you can find a spot under the car, or on the side for that matter, where a low pressure bubble forms with the car moving, you'll really help the exhaust system efficiency.

Header designs have only 2 main tools with which to work, diameter and length. Generally, engines are most sensitive to changes in primary diameter. The primary diameter seems to establish horsepower peak, while the length of the primary tube tends to shift the RPM range where the peak occurs. In general, a longer primary shifts the power peak to a lower RPM and vice versa.

Of course this relationship doesn't always hold true for every engine application. When we talked to AEM's John Concialdi about header design, he candidly stated it is a bend, weld and test item. AEM and Concialdi tested header designs for a BMW, and they found the most horsepower with the broadest torque curve using a VERY SMALL DIAMETER PRIMARY that was miles longer than anything they thought that would work. YOU NEVER REALLY KNOW UNTIL YOU TEST IT.

Ok, from reading that HONDA builders book I've gathered so much damn good specific info that It's A MUST HAVE for all honda owners...

recommended sizes below;

1.6L = 2.25inch
1.8L-2.0L = 2.50inch
2.2L-2.4L = 2.75innch

I'll be posting the theory and physics of why soon. But the main reason is maintaining VELOCITY.

 

[jugbugz]

having a bigger diameter exhuast pipe just means increasing the volume for more potential mass flow, but that MAY only happen at the last 1000rpm depending what size your pipes are and capacity of your engine. So you will loose power if theres no velocity but gain where there is velocity.

increasing velocity creates a greater pulling effect which will benefit the intake pressure which create a more filling effect in the cylinders thus making more power in the complete system.

My view is that HONDA has already made the Best combination with every part. And if we were to change anything, it will affect all other parts. And as stated before exhuast is the most sensitive part of the engine, and once we've changed the headers or muffler or exhuast pipes, it is already affecting the flow.

I've got a diagram of the original muffler box of the OEM EK9 CTR and I tell you it's pretty restrictive comparing to a free flowing muffler. So if we were to free flow that muffler box, how much has that already affected the flow? Velocity would have definately changed for a more higher end mass flow and reduced velocity for lower end flow.

I know at this point of tuning from a stock car is just basic but in my opinion, I think it's important that we know what we are doing to our cars and for what purpose are we using it for, and that would give the owners of their car a bigger smile... I believe every ek9 here behaves very different..