Iroc n roll

I've heard that you want to get as small an intake runners as possible, yet one that flows good. Like a 200cc intake runner will be better than one that is 220cc yet flows the same. Is this corect? On a similar note, if I was going to get good flowing heads and a huge cam, what size intake runner would be good with my below setup. Take into account that the larger intake runner head will out flow the smaller one on the intake side. How much is too much? 200cc? 220cc? 235cc?

89Raptor

If I were you I'd go with AFR 190's or Trick Flow 23 degree heads. Both should work well with your setup.

Iroc n roll

Anyone want to take a crack at the question???

jwscab

I would say that you would want the smallest cross-section, that gives you the flow required. For a given pressure drop, there will be a certain theoretical ariflow. Any obstruction, poor routing(like sharp bends, mismatches) will lower that value. Also, it is dependent on the air fuel mixture. In order to keep the fuel and air mixed, you want to maintain a smooth changing speed through the manifold. a slower speed(determined by cross section, again, theoretical stuff based on the pressure drop) will cause fuel to seperate from the air, effecting the power that is made, and there fore you get poor repsonse and low engine rpm, also, abrupt changes in cross section will affect the speed, which is why most poeple think the agressive home port matching in most cases helps, when in reality, it may actually cause more harm than good, since the change in speed causes the fuel to drop out, you get like a big 'lump' at the manfold/head interface. To add to that complexity, you ideally want the mixture to be turbulent, to help aid atomization, which will lower the flow through a tube(smooth airflow, laminar airflow, assumes no turbulence). All this stuff is what makes the power, and thats why porting is usually left to the guys that do it professionally. Unless you go ***** out with an engine(ALL the time), it's best to stay on the conservative side to aid in velocity and maintin a good mixture.

Ed Maher

What's been said is sound basic theory. It's important to rememeber that theory doesn't make power or win races. Withthe plethora of folks running every concievable combo on this site, there's plenty of real world experience to tell you what the various aftermarket heads are good for.
It's not necessarily true that you want the smallest intake runner possible. If you're trying to build a really hot street engine, there is no reason to not go ahead and run a big honkin head that makes great power.
I just don't want to you take your theory and warp it into something like, well the AFR 190s intake port is bigger than the edelbrock, so the edecrock must be a better street head Sure you could run good w/ the edelcrocks, but they don't have anything on the AFRs.

In short. Have a goal. Analyze what you need to get that goal, match parts, etc. Execute.

Vader

O.K. - I'll bite....

If you're going to emulate the LT1, then don't go halfway. The ports and runners on an LT1 (or mre specifically, LT4) are friggin' huge compared to an L98. The LT1/4 intake plenum/manifold is so "detuned" that flow velocity isn't the issue in the plenum and shortie runners - it's more about the volume, but you still have to maintain a little velocity in the ports.

These are LT1 180cc iron head runners/ports right out off the factory:



LT4 heads came out of the box with 195-200cc runners, and "Fast Burn" heads are supplied with 220cc intake runners.

Ported iron LT1 heads with 192-ish cc runners/bowls do very well for me with the LT1 intake (ported as well):



The intake should also not be ignored:

Guest

Theres more issues than flow and volume unfortunately. Theres port shape, taper, cooling, and then if you look at some heads, valve angles, seat locations, its just a mess to think about. The problem with trying to set yourself on the smallest cross-section with the highest flow is that the way heads are flow tested is not at all how they act on your engine. The flow test is basically static, while your engine is dynamic. Another problem is if the cross-section is too small or the port shape is wrong, you could hit an area in lift/RPM where the ports stall from too much airspeed and then you arent making any power at all. Higher airspeed isnt always a good thing, depends on where its at and how its traveling. Using Ed's example of Edelbrock's and AFR's, he is totally right on, the AFR's are going to blow the Edelbrock's right outa the water on a built engine. On something relatively close to stock, the AFR's would probably be a waste. You kinda have to decide where you want to go, what you want to spend, and then look at which head will suit you best.

89Raptor

High Velocity helps induce swirl and tumble, both of which help keep the fuel in suspension and results in a cleaner burn and more power. Higher velocity also means you get more air fuel mixture for a given lift and engine speed, again more power. You want a head with large ports that maintains high velocity like a small port head but still flows like a large port head. The AFR's and Trick Flows do this.

u r sofa king we tah did

there is a too big on heads. say if your running a tpi manifold, and you pick out a head that has 210cc intake runners, that motor isnt going to make more power due to bigger intake runners. the tpi wont be able to support the flow capabilities of the 215cc runner and the intake velocity will slow down. now if you had picked out say a 180cc dart iron eagle, then the flow numbers are more matched to what the tpi can flow and the intake velocity doesnt slow nearly as much, therefore creating more power with better flow. its all about mix and match parts, bigger doesnt always equal better.

89Raptor

What he said, he is correct. If you are using a stock base getting really big heads won't help, the AFR 190's, TFS 23 degree will work very well stock or aftermarket/modified, personally VORTEC!

tpi_roc

You've got so many things to consider its rediculous, just about everyone of them has been touched by previous posters. Money, Power range, Flow, Volume, "Swirl" spark plug location, valve angle, raised runners, its all part of the game.

For example there are some heads out there that flow increadibly well, Pro action for example, they do amazing things, then you look at their intake runners for SBC, as big as 230cc's, and you think "HOLLY CHIT" no wonder they flow, howevever their cross sectional area would be similar to say AFR190's but they use a raised runner design, the longer runner creates more volume from gasket to valve. A small cross sectional area (180 for example) will act as a smaller pipe, and at a given pressure (or in an engines scenereo) vacuum it will actually "PULL" in air from its own vaccum like how NASCAR uses drafting, The car in front clears the way and makes less resistance for the car behind. Same thing for port flow. However if you try to get a massive amount of air through it (Or there's a bigger car behind the one in front) then the smaller volume only creates a hinderance to flow. Now for big runners, they dont get the "pulling" effect for the air at low engine speeds, the cylinder pulses will pull in whatever they can grab, but there will be no port vollocity backing up air pressure behind the valve for the next lift cycle. However at high RPMS the engine needs that open volume to get as much air as possible in in the shortest amount of time.

Hope the physics help you make your own wise decision, but you also need to take into account spark plug location, its reported the closer to the exhaust valve the more power, it doesn't necissarly matter as to the angle, just the location. The combustion chamber brings in another area of theorys and physics, basically you want a valve location and angle that will swirl the air collumn down the side of the cylinder walls making it easier to fill in a short amount of time without causing turbulence that may back up the intake charge. Also during compression you want it to divide the charge and make the "swirls" that will cool hotspots, similar to quench.


Thats my attempt and $.02

camarochic

220cc

Iroc n roll

Thanks for the info guys. Has anyone had any experience with the Pro Lightning iron heads? I really like the looks of them.

Swapmaster

Give tpi_roc a cigar.
Could not have said it better myself.