Tuning exhaust performance is very complex.
The cam profile, especially overlap and cam timing, can affect exhaust systems. I imagine most of us that have modified our engines with larger valves, porting and polishing, cam, header, and larger exhaust pipe, free flow mufflers, don’t really understand what changes have occurred to flow and volumetric efficiency, and what affects those changes make in the ultimate desire for increase power.
Are the headers we buy equal length?
usually very close, within an inch.
What lengths are best for a 22R and 22RE?
30 to 34 inch headers seem to work best for me
Why does a tri-Y design scavenge better?
because when #1 is about to suck fuel and air in #3 is still expelling so when #3 exhaust closes it finishes the syphoning effect through that #1 a split second sucking more air in.
Does it scavenge better at WOT or partial throttle?
about half throttle to wot if you have an efficient intake.
I believe exhaust tuning has been historically trial and error.
Downey offroad and LCE did extensive research in the 80's on desert trucks and ToySport in the Celica's. they all worked tirelessly to give Toyota owners a great product.
Is the testing done at WOT or a range of RPMs?
varies depending on what application
There are physical “things” going on that may not be easily measured or even calculated. Can you measure swirl on a flow bench? Can you measure the pulses at each tube and at the collector? Can you measure the sonic wave caused by exhaust pulses? Can you measure the mass flow at WOT (wide open throttle)?
yes to all
What affect does increased compression cause?
it gives you more power but if you go too high you will have to use premium or even race fuel
How about the number of angles and cut degrees on the exhaust valve?
I have done 5 angle grinds but a good smooth 3 angle grind is all you need.
How about the AF mixture – wave velocity changes depending upon a lean or rich mixture.
its very important. if your af mix is too lean your engine runs hotter and can do bad things, too rich and its going to smoke and foul plugs and just run like crap not to mention getting very bad fuel mileage.
The size of the exhaust tuning from the collector back can be critical to maintaining the performance gained by the header and the cam. Is the tubing mandrel or crimp bent? Does a 2.0” diameter flow better than a 2.5”?
whatever size your collector is is the size of tube you need to run all the way back.
Lots to think about and more that I will most likely never completely understand.
Gnarls.
