Might get roasted for this question, but i have searched around a little but am finding the answers unclear. What causes the car to idle in this fashion

 

Different porting


The traditional brap brap brap often is associated with a bridge port on the intake ports

 

Porting, ignition and timing. Mostly porting but wasted spark ignition has its own extra sounds and advanced timing can make the idle lope as well.

 

the sound is from too much exhaust gas in the intake stroke. ported engines have a lot of overlap, time when the intake and exhaust are both open, so they tend to do it more than anything else. Mazda calls this "internal EGR"

if you listen really closely, the chamber will fire, and then misfire 3 times as it takes that long to get the exhaust gasses out. the other fun thing is that when the chamber does fire, VE is way higher, because the content of "internal EGR" is way lower, and well it'll blow stuff around the shop

 

What would be the benefits of modding your engine to sound like this?

I see there are different methods of porting the engine? What the difference between all of them?

Are there also cons to getting this done as well?

does it matter if it’s 12a or 13b?

 

Porting is to help the engine to breathe deeper,with the right addition of fuel/ignition=more power.
The sound is the result. Not being modified to get the sound.There are different types of porting that can be done depending on what the engine builder is trying to accomplish.
Majority of bridgeported engines are hard to live with on the street. Unhappy with low rpm operation,no fuel economy,all about making power. Any rotary engine can be ported.

In the piston engine world,a V8 with a radical camshaft with a lot of overlap makes a pukuta-pukuta-pukuta sound at idle and lo rpm operation as the valves are held open longer to let engine pull in more air to breathe better in the camshafts designed power band and the correct amount of fuel/ignition= big power gains.

All engines are air pumps,more air moved thru,more hp/tq...

 

Double post

 

First I've heard of someone calling it a wub wub sound. Usually it's a brap brap sound we are discussing. Either way, you guys were spot on in your response.

 

more power! when you add bigger ports, they become open at the same time, and idle suffers. same thing as a cam in a piston engine

basically if we start with the stock port, we can make it bigger (streetport), until the corner seal falls in, so we cut a second port and leave a bridge for corner seal to ride on, bridge-port. to go bigger than that, we fill the stock port and add a port on the periphery of the housing, Peripheral port, its basically the most ideal size/shape for a port (no bends), and it flows a lot more

yes, in any engine there is a trade-off. the stock engine is setup to idle smoothly, pass an emissions test, and be quiet. the race cars needed power, and reliability, but they didn't care if it idled, or passed an emissions test.

no not really, same things apply