I chopped open the exhaust manifold on my Corolla to see what's inside, and how it works.


The exhaust manifold is located behind the engine:



This is where it mounts to:



It consists of piping and a collector down to the flange:



The manifold is the first part of the exhaust system:



I chopped the section near the flange. To my surprise, it is double walled:





Then I cut the section near the collector:



Its a bunch of tubing that flows into a X-shaped frame and then the collector:



Manifolds are designed to optimize airflow out of the engine. Pressure pulses are created, with a low pressure zone trailing:



The low pressure zone helps suck remaining exhaust gases out of the combustion chamber. This is called the scavenging effect:



When moving to aftermarket headers which are more freer flowing, the velocity of the pressure pulses decrease, and thus the scavenging effect:



This its important to strike a balance between the header size to ensure enough gases are sucked away, but that there isn't too much back pressure caused by restricted flow.

Enjoy

 

at the end there i thought you were going to toss the cut manifold onto the car, like your other videos *phew*! good work mr. rolla!

not sure i like the double wall as it's even smaller inside! i do see some aftermarket headers employ chambers where the exhaust gas can enter in between the pipes - doesn't seem to be the case with the toyota design.

 

Kinda funny cutting a Corolla manifold....To add the hot exhaust gases add velocity exiting the exhaust ports...... 180 degree headers on a v/8 is your best scavenging headers....Add to the fact.....Whats the flow rates of the heads? If they're under 75% then that dictate a dual pattern cam, which would dictate a 1.625'' to 1.750'' primary tubes w/ a 32-35'' primary tube lengths..... Better flowing heads such as a pr of Apache heads(385 @ .600''- 395 @ .700'' cfm) go w/ a 2.125''- 2.250'' primary diameter tubes as well as a 30''-34'' primary lengths. Great kinda write up on a Corolla manifold......Lets see a write up on a reverse flow setup ......or reverse induction set up such on a 6.7 'stroke, or on early 255'' Ford Gurney/Westlake heads.....