best muffler for my L20

[banzai510(hainz)]

http://www.cherrybomb.com/turbo-mufflers.html

 

these are cheap $$$$ and somewhat quiet

However do not how long they last .

 

I have Dynomax brand myself. This might be more quiet than my Dynomax Super Turbo. But Superturbo is a little bit higher quality.

[DatDoug]

What is the best size exhaust pipe to have for the L20 with a weber 32/36 downdraft? Can you go to big?

[Bamadawg]

Exhaust size from factory on my '82 Z22 is tiny (like 1.325")- not sure about the stock size of a L20B. You want to increase the size when you tweak around with the engine... esp adding a aftermarket header and porting/polishing your cyl head. Most people will add some type of performance cam if they rebuild their motor - increasing the duration/lift of the valve system. A bigger exhaust helps to carry away the exhaust waves faster - more efficient, just like tweaking the intake side with a better intake manifold/carb set-up.

 

Most V-8's will add a 2.5" - 4" exhaust system, according to how many horses they push through... 275-500ish HP. Of course a L20 doesn't make that much HP - so somewhere between a 1.5" - 2" exhaust should be plenty to handle <200 HP. If you go too large, and your engine isn't large enuff (efficient enuff) to fill the exhaust pipe with the right velocity of waves... then you defeat the helpfulness, like hogging out a intake manifold too much, and adding too large a carb... the engine cant keep up with the excess... you need to match your systems needs with the correct hardware.

 

Thats how I understand it... I am sure there are other opinions.

 

A guide I found online:

 

Gasoline Engines

Up to 100hp - 2" diameter

Up to 160hp - 2.5" diameter

Up to 200hp - 3" diameter

200hp + - 3.5" diameter

 

Diesel Engines

Up to 450hp - 4" diameter

Up to 550hp - 5" diameter

Above 550hp - 6" diameter

 

Some technical jargon:

There are two primary considerations involved in designing/choosing an exhaust. The first deals with the exhaust gas that travels at 200-300 feet per second. Here we are concerned with reducing the back pressure while maintaining flow velocity to get the best cylinder exhaust purging. The second is exhaust pulses or finite-amplitude pressure waves which travel the speed of sound or at about 1700 feet per second. These pulses can be tuned to create an effect known as scavenging (sucking additional exhaust out and intake charge in, with a properly timed negative pressure pulse).

 

Exhaust gas - General rule of thumb, a narrower diameter pipe will improve low rpm flow hence torque but may limit top end. A wide diameter pipe will enable top end power but have poor low end velocity (eg great for the track but lacking on the street). So choose the where you want your power band and set diameter accordingly. Increasing or decreasing pipe diameter 1/8th will move the torque peak about 500 rpm up or down. Varying the length of the pipe will fill in the power curve around the torque peak. Shorter pipes fill above and longer pipes below. A good starting point for exhaust pipe area is the circumference of the valves times the maximum lift plus about 15%. A good starting point for the length of the primaries is 28-32 inches.

 

Exhaust pulses - When a positive exhaust pulse traveling down the pipe reaches an opening or increased diameter it is reflected back as a negative pulse. This negative pulse can be timed to reach an open exhaust valve to provide scavenging. The rpm's that this occurs is at peak torque and continues in the upper portions of the bike's power range. However, there is a trade off. In the lower rpm's the valves are open longer and thus also allow a positive wave to hit. This usually occurs around 2/3's - 3/4's of the torque peak (between 4000-5000 rpm range on the Max) and is why you see a lot of dyno dips in the power band in this range. The positive wave pushes exhaust back into the cylinder and in some cases, if there is enough valve overlap it will travel up the intake track and cause triple loading of the intake charge (air is drawn through, pushed back and drawn through again.) Here is where the 4-1 versus 4-2-1 make a difference. The 4-1 will have a STRONG tuned pulse. Therefore it will have a higher top end (strong negative wave) but a bigger hole in the mid range (strong positive pulse hits while valve is open). A 4-2-1 will soften and lengthen the pulses, as the 4-2 connection provides an interference wave in addition to the primary waves. A similar effect can be done with stepped pipes. The top end effect won't be as great but it will be longer. The mid range dip will also be shallower hence, the adage that a 4-2-1 improves mid-range.

 

In a nutshell, the biggest decision for power is the diameter of the pipe and then the length. Choose these based on where you want your power band. Tuning the exhaust pulses with a 4-1 or 4-2-1 then should be done with the idea to compliment your first choice....and of course always have a high-flow muffler.

 

Nate