http://mototuneusa.com/think_fast_intake_porting.htm
This is the latest installment.
There are 16 all together some are kind of bike only but a lot go for all 4 stroke engines
There is one called the 8 phase engine, if you have ever made your own cam grind you will think like this.
Check out the engine break in if nothing else. I tell people the same thing he tells, but before I know it I have a mob out to get me. My Air Force Techinacal Orders tell me to do something just like this when we get a new diesel engine for a generator or when we get new gas turbine compresser.
You have to see to belive.

 

Their deling with a whole different evil when spinning 12,000+rpms. At those r's you do rely on port velocity speed to feed the cylinder and a cam degreed correctly to shut it down at the proper moment on the upstroke.

Our slower engines (5-8k rpms max based on stock or what your building) Need as much flow into the cylinder as possible. It has been proven on the 60*V6 iron heads that they suffer from major restriction due to the bends. Porting those bends to straighten airflow will help velocity.

 

on a side note, i have a Honda Hawk and hes right..... proper tapering of the intake ports works alot better then hogging them out.

 

Come on guys, he's not saying anything anyone with half a brain doesn't know already.

It's all about how to cram as much air as possible into each cylinder. As Dean stated, velocity plays a HUGE role when over 6-8k rpm. (ahem - VTEC, variable intakes, etc) The intake plays just as much a role as the head's flow, and the camshaft.

You have to look at an engine as a whole. You can have the best flowing heads in the world, but if your camshaft and intake are not MATCHED to those heads, then you will end up with a sum that is less than the parts. Understand?

 

just so you dont mis understand me, i was talking about JUST my honda hawk.



my 400SBC doesnt rev nearly that high..... lol.

 

I'm not saying this is for all engines, if you have a higher revving engine and want smooth predictable power this type of porting is for you maybe.
If you want tons of torque that will break burn your tires then hoged out porting is for you.
Read the other one too if you haven't.
I posted this link mainly so you can get to the 8 phase engine, those are the things you have to consider when you start swaping cams and when you move your power band higher in the rpm range.
Now most of us won't be useing cams that open the intake valve 15* BTDC. It will give you a better idea of what will realy hapen when you advance or retard your cam timing and why you might want to do it.
Doward is saying what I have told people of years (ricers more than any one) that you have to build an engine as a hole, and that the heads, cam, intake, (turbo if there is one) Tq. converter, rear gears all have to want to make power in the same range. They have to all work together at the same time to move the car.

 

But you still want to have your 400 matched, right? I mean, think of this -

AFR 205 heads
Victor Intake
950 Holley DP

all on a 305, with a stock stall, stock 2.73 gears, and stock bumpstick.

Gonna run like crap, right?

As for the break in - sure, that'll seat the rings real quick. And you won't get more than 60k miles out of that engine - why do you think GM and the big guys actually spin the motors to simulate the first 500 miles on them?

 

it doesnt matter what heads you put on a 305, its runs like crap anyway.