Heads?

[Blade]

from the basic info provided the RaceRite oval would be a great choice.

Why is Oval better then Square port?

[DOTracer]

from the basic info provided the RaceRite oval would be a great choice.

Why is Oval better then Square port?

Port volume, not shape. The 270cc runner is better suited to your cubic inch and rpm range.

[supernova]

from the basic info provided the RaceRite oval would be a great choice.

Why is Oval better then Square port?

Port volume, not shape. The 270cc runner is better suited to your cubic inch and rpm range.

I would agree with that!
Don't overkill your heads on your small motor. Smaller ports with good port vilocity will be the way to go to get good power. Matching the cam to the output of the heads will help too.

[Blade]

from the basic info provided the RaceRite oval would be a great choice.

Why is Oval better then Square port?

Port volume, not shape. The 270cc runner is better suited to your cubic inch and rpm range.

It would probably be a good idea to figure out what Port Volume I have on my square port head now then. Then go from there

[Blade]

quote]

Port volume, not shape. The 270cc runner is better suited to your cubic inch and rpm range.[/quote]

I would agree with that!
Don't overkill your heads on your small motor. Smaller ports with good port vilocity will be the way to go to get good power. Matching the cam to the output of the heads will help too.[/quote]

The cam that I had was wipped. I'll figure out what size heads I have and go from there.

[Blade]

So you also wanna match the Cam to the Heads?

Also how do you find out the cc? Is there a tool to measure?

[DOTracer]

So you also wanna match the Cam to the Heads?

Also how do you find out the cc? Is there a tool to measure?

Yup, you need a plexiglass plate with a hole you put over the intake flange sealed with lithium grease. Use a buret filled with colored rubbing alcohol and read how many CC's were poured.

[Bruce69Camaro]

Actually with that size motor, which is not too far off from mine, my builder recommended using the oval port, Edelbrock alum heads with the 2.19/ 1.88 valves. I think (?) the CC was around 290/300.

Might want to think about those, but I'm no head expert, maybe someone can back me up on this?

[wikd69]

Actually with that size motor, which is not too far off from mine, my builder recommended using the oval port, Edelbrock alum heads with the 2.19/ 1.72 valves. I think (?) the CC was around 290/300.

Might want to think about those, but I'm no head expert, maybe someone can back me up on this?

And I'm certainly no expert either, but it also has to do with rpm, cam duration and linear air velocity. Please note that I speak from the perspective of big block builds, but the same rules apply across the board.

If you're moving very large volumes of air at very high rpm, the big rectangular or square port heads are a good bet. You get good air flow and good volume where you need it, at rpm.

If you're not looking at large volumes of air and/or need the air flow and velocity at lower rpms, then the oval or round port heads are a good fit. It's known that oval port heads yield better low end torque than larger rectangular port heads, and it has to do with air flow linear velocity.

It was explained to me in this manner:

You need to achieve high (read fast) air flow velocity to get the best yield from your cam lift and duration. For instance, with high compression and long duration/high overlap valve trains, tunnel rams help maintain high linear velocity in intake air flow providing the momentum needed to fill your cylinders during the entire intake cycle, even with an NA motor with intakes closing after BDC. It's the air flow velocity and moving air mass which continues to fill the cylinder even while the piston has started up on the compression stroke. If the incoming air flow does not have sufficient linear flow (mass in motion) the air stops moving and you fail to utilize the full intake valve duration. This is where having too big of intake runners hurts you. For the same volume of air, smaller intake runners move the air faster than larger intake runners, providing better inertial movement of the air volumes during the cycle. If the runners are too small, you don't get enough air. If the runners are too big, you don't get enough air. Like everything in the Goldilocks story, all the pieces have to be 'just right'.

How do you determine what's 'just right' ? Beats the hell out of me. I put Dart Pro-1 310cc heads on my little BBC 427 blower motor along with the larger 2.230 intake valves. I talked to a lot of people about heads and air flow and cfm and scavenging and back pressure and came to the conclusion that the 325cc or 345cc heads would be too large for my little 427 build. Not based on anything scientific, but based on what I saw others doing.

There's a lot more to head selection, beyond just air flow. There's the shape and CC volume of the combustion chambers to consider (open, closed, etc.) along with quench and plug angle. There is also the height and aspect of the exhaust ports along with the angles of the valves themselves.

I'm not nearly smart enough to go much beyond moving air in and out of the heads. Anything beyond that is lost on me, mostly because I run a combination street and track car and already make way more horsepower than I could ever use on the street. If I was building a pure race motor, that'd be a whole different thing (and trust me, I've considered doing just that - bu-wa-ha-ha :).

Dunno if this helps, but it's the approach I took when selecting my new heads. Not overly scientific on my part, just mostly common sense.

[Bruce69Camaro]

Damn Harry, you sound just like a professor but then again, what do you expect from a Camaro owner.....

Alot of good info from DOT Racer!

Again something to think about is the valve size. For something of that cubic inch, I would think a valve size of 2.19/ 1.88 would be more then enough. Does Brodex even offer valves that small on their big block heads? I think this is why Keith told me to look at Edelbrock heads because they do offer that size on the oval port heads I was referring too.

Correct me if I'm wrong but when it was mentioned that you want to match your cam to your heads, that refers to valve size, ports size and shape, spring pressures, CC's....correct?

[Blade]

Actually with that size motor, which is not too far off from mine, my builder recommended using the oval port, Edelbrock alum heads with the 2.19/ 1.88 valves. I think (?) the CC was around 290/300.

Might want to think about those, but I'm no head expert, maybe someone can back me up on this?

Bruce,

Thanks for the info. I need to figure out what size cc I have with the square ports.