hp confusion-cylinder heads
10-25-2002 | 08:07 PM
#1
Thread Starter
Registered
Joined: May 2002
Posts: 1,580
Likes: 0
From: istanbul
hp confusion-cylinder heads
we all know that horsepower is directly related to airflow (cfm).I dont understand something why dont we just put a 400+cylinder head and receive more hp. why use dart 310's or 330's
isnt bigger better when it comes to heads?!?
why?
I know some heads suggest hi-comp(why?) like bb2xtra brodix;but they also work perfect with lower comps?
do you know any www related about heads?why?/what? stuff
or any thread ?
I have to learn more....
isnt bigger better when it comes to heads?!?
why?
I know some heads suggest hi-comp(why?) like bb2xtra brodix;but they also work perfect with lower comps?
do you know any www related about heads?why?/what? stuff
or any thread ?
I have to learn more....
10-25-2002 | 10:43 PM
#2
Registered
Joined: Feb 2002
Posts: 763
Likes: 0
From: Honeoye, NY
10-26-2002 | 07:15 AM
#3
Registered
Joined: Feb 2002
Posts: 1,099
Likes: 0
From: KY
Tim;
Everything has to work as a package. heads, cam, intake, headers, etc. The biggeset reason boaters don't put hogged out big chiefs, etc on are because these heads are designed to flow at big rpm's (like 9,000) with a very long duration high lift camshafts. Many of these motors simply will not idle below 2,000 rpm due to essentially no vacuum signal. Put a set of 400-500 cfm heads on a boat motor and "only" turn it 6500 a smaller head (like the 345 or 360) will make MORE power. In over simplified terms the head is working where its most efficient for the motor. Think of air "velocity", not just flow, in the runners. Sure the 500cfm head will flow more in absolute terms, but if you never get the motor close to where those heads begin to shine (high rpm) where the velocity will pick up enough to take advantage of the higher flow potential, you're giving up a lot of power. A properly dialed in head and camshaft combination can actually create a slight "supercharging" effect in a NA motor.
Hope this helps.
Everything has to work as a package. heads, cam, intake, headers, etc. The biggeset reason boaters don't put hogged out big chiefs, etc on are because these heads are designed to flow at big rpm's (like 9,000) with a very long duration high lift camshafts. Many of these motors simply will not idle below 2,000 rpm due to essentially no vacuum signal. Put a set of 400-500 cfm heads on a boat motor and "only" turn it 6500 a smaller head (like the 345 or 360) will make MORE power. In over simplified terms the head is working where its most efficient for the motor. Think of air "velocity", not just flow, in the runners. Sure the 500cfm head will flow more in absolute terms, but if you never get the motor close to where those heads begin to shine (high rpm) where the velocity will pick up enough to take advantage of the higher flow potential, you're giving up a lot of power. A properly dialed in head and camshaft combination can actually create a slight "supercharging" effect in a NA motor.
Hope this helps.
Last edited by jdnca1; 10-26-2002 at 07:18 AM.
10-28-2002 | 07:37 AM
#4
Guest
Posts: n/a
To be real basic here a port needs to flow X amount air for any given application and at X velosity. This will pack a cylinder almost like having boost. Now a bigger port might flow the same amount of air but the air speed would be down and would be unable to really pack the cylinders like the above combo. Smaller ports would starve the engine for air at a lower RPM and in some cases actually flow so fast that fuel drops out of suspension and puddles in the runners in a wet manifold. Also I have found desk top dynos dont address air flow issue well and have been off 15 to 20 percent on power perdiction because they dont take into acount air velosity/flow coeficenty.
