Cylinder Heads
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From: Jxn, Ms
Cylinder Heads Which is better to have, a high intake port volume or a low intake port volume head ? What's better on power hi cc's or low cc's ? ( Given both heads have same compression [if you can do that] with the same cam ) ? Naturally asp or nitrous injected ? Which ?
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From: Jxn, Ms
And how long will the camshaft be in the 600lift range of the heads? what i mean to say is , will the cam be at 200, 300,400, or 500 all the time and then 600 for 2 sec? Or what ? If your heads flow 315@ 600 and you have a cam that goes to 595 lift, what if those same heads flowed horrible at low/mid lifts? How would your car respond powerwise if directly compared to a head that made 300@600 but killer low/mid airflow ?
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From: LaConner WA
It's not as simple as that. It's better to have a port that flows very well, but is NOT overly large. You want both hi port velocity ( small port volume ) AND hi flow #'s, and not just at peak valve lifts, but at low lifts too. This is not easy to do. You eventually reach a point where you have to go to larger port volumes to get higher flow numbers, but it's not the higher port volumes you're after, it's higher flow #'s. Large port volumes by themselves only kill low and mid range cylinder filling and therefore torque. Understand ?
If your cam does not approach the .600 lift range, the flow specs are meaningless for that lift. You can only use the flow of the head upto your cams max lift. It is good to have good low/mid lift numbers for any set of heads. Your valve is only open at max lift for an instant, it spends most of the cycle in the mid and low lift range. For a forced induction head(supercharger), a crazy huge port with huge top end flow numbers is what you want because any velocity lost due to the big port is made up for with the blower on it.
I am not completely certain, but I believe that a head that has a huge port loses part throttle driveability when compared to a similiar flowing head that has good low lift numbers.
I am not completely certain, but I believe that a head that has a huge port loses part throttle driveability when compared to a similiar flowing head that has good low lift numbers.
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Verdad Gallardo Yes, the .600 flow number on the head would be a very good indication of what you will see. The flow benches vary so much from one to the next that the .005 less lift would probably see the same flow number on the head on a different bench and different day....
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From: Jxn, Ms
Thank you guys for your intuitive insight on this matter ! Let's compare heads, if I have a set of Bill Will heads that flow 200-140, 300-200, 400- 250, 500- 260, 600- 290 ....and a set of Chill Dill heads that flow 200-150, 300-210,400-255, 500-270, 600- 300...same cc's and intake volume, and Bill's heads are $500 cheaper with a 595 lift camshaft on both heads , How much more power will I see with Chill Dill's heads ? 5 horses, 10 horses or what night and day ? What ?
~10 cfm across the entire board would be about 5-10 rwhp. This depends on cam size (duration) though....whether this power is worth $500 is dependent on what you are trying to do. If you are trying to get every last hp out of it then obviously it would be worth it. If it was me, I would get the cheaper heads and then buy a cam with 4 to 6 degrees more duration. By the time you have sold the current cam you will have come out ~$250 cheaper with this route. Like I said it depends on whether it is just a quick daily driver or a max effort motor setup.
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From: LaConner WA
This gets into personal preferance. I'd without a doubt go with the extra 5-10 hp from the better flowing heads and less cam duration so as to retain more of the low/mid throttle response and torque while still having the top end. This route you could also go with a wilder cam later and realize more power without sending the heads off for more work. Neither right nor wrong, just differant personalities that's all 
Very much agreed....I was just stating what I would do in his situation. I personally got some Patriot 59 cc heads that I am porting out, so....
Also, keep in mind a higher flowing head will support a bigger motor down the road much better, if you ever choose to go that route.
Originally Posted by Racehead
This gets into personal preferance. I'd without a doubt go with the extra 5-10 hp from the better flowing heads and less cam duration so as to retain more of the low/mid throttle response and torque while still having the top end. This route you could also go with a wilder cam later and realize more power without sending the heads off for more work. Neither right nor wrong, just differant personalities that's all
