Can someone explain to me why people make these beautiful swirling headers and the intake manifold (ITR/Skunk/OE) looks like a log with right-angle branches??

Isn't intake flow as/more important than exhaust??

Wouldn't a header-shaped equal-length intake manifold be like a million times better??

Am I missing something????

 

Well, its been a couple of days & nobody took this one, so I'll give you some BS...

Are you missing something?? Maybe you're missing the idea that it's not a steady flow. It pulsates.

The job of the exhaust manifold is to get the exhaust out of there. Less resistance is better. But for a certain length pipe, the pulses reflect back towards the head & kinda block the next pulse. It depends on RPM & speed of sound in the pipe. With a clever choice of length the pulse reflects in a way to help suck the next pulse out of the port.

The intake is a bit different. You want low resistance, but you also want turbulence so you get good mixing. The fuel has to evaporate, & turbulence helps this. You also want the reflecting pulses to help you out. The big chamber (log?) in the intake manifold is a plenum, & you'll notice that each runner coming off of it is the same length. Same kind of story about pulses reflecting back, but this time you want the pulses to help push the air into the ports.

If you only ever ran the engine at the same RPM, then it would be easy to solve for the length of the headers & intake runners. In real life I suppose its all tangled up in valve timing & everything else about the engine design. So its kind of a black art, & each design has pros & cons. Get it wrong, & the engine will still run, but at certain RPM points its just not as powerful as it could be.

 

Wow for BS that was very well done.

I believe Tuan has an article floating around somewhere expounding on the virtues of matching intake plenum & runner lengths to each engine. It goes into great detail about back pressure waves and the resonance they create when the intake valves open and close. It's not difficult to envision how a pressure wave would develop in the intake manifold when the intake valves close. If the wave then travels back down the length of the runners and into the plenum, a portion of that wave will be reflected back toward the intake valves. If they're now open when this pressure wave arrives then there will be more air/fuel pushed into the cylinder. At first glance it does seem that a simple efficient air passage to the intake side of the engine would be the way to go...similar to the exhaust manifold. However the intake side has far different requirements than the exhaust side.

 

Daaammmnnn, very nice JimBlake!!

 

Now I can finally say that all those years in engine-eering skool were not wasted!

 

I have to admit that for all the theory I've read on exhaust manifold design and head porting, I've hardly seen anything at all on intake manifold design.

Bump cause I want to read more about this

 

Individual
Throttle
Bodies


check that ish out. thats as crazy as it gets for intake setups.

 

Why do the new Toyota corolla's have equal length intake manifold runners?
I'm also curious to see if it helps, I think the Matrix and Celica also have the same thing but I don't work on those as much as Corollas.

 

WORD
well said

 

Don't they all have equal-length runners? Runner length is from the plenum, not from the throttle body. All port-fuel-injected cars I've known have equal length, way back to my '74 BMW, '82 Rabbit, etc... I thought it was only carburators & throttle-body injection that had to make the runners as short as they could 'cause the gasoline was already there & it would make puddles in the manifold.

The length gives a little 'boost' at a certain rpm, from the speed of sound in the runners. If your engine needs a little help at low revs, you use long runners. If you want help at high revs, you use short runners. My GS-R has both long (open all the time) and short (open at high revs) runners.

I suppose you could make a manifold with runners like trombone-slides. The ECU would tell them to move in & out. That would cost a couple thousand $$ and give you maybe 3 hp. You'd be better off spending your money on variable valve timing.

 

The man's on a roll ladies and gentlemen.