airflowdevelop

Bret,
Did you figure blow by and overlap into your equation? Using the factor that I use (whether correct or not..just calibrated to my bench / dyno experience). a .270 flow factor motor should peak around 107.6% calculated. And if the heads are correct, should runoff to 101.5.

.310 factor seems to work out to 122.5 or close to current pro-stock technology.

Obviously...this formula can be Skewed quickly! When you start talking great sealing rings...great sealing VJ's...this is stuff that leaks < 4% static...and is tighter than Osuma's bung hole when it is running! very very few people can get motors sealed this tight. Close attention must be payed to the evac system and the ring package...Large clearances in second ring...and a very well designed top ring / placement.

Homebuilt / average raceshop guys should figure .260 on what they consider "Hi End". Also...the LSx platform can play havoc on this number...most of the heads that you will find off of the street are TOO FAST! and Lumpy...eventhough they can move the air, they can't deliver it well, or homogenously (sp?). Plus at these airspeeds, you almost need NASA technology to keep the air stuck to the port!

Dennis

airflowdevelop

Bret,
I also should say, that the figures I posted were based off of a 346" power plant...if the motor was of a different size...please disreguard. and remember..my bench is super-tight.

Dennis

airflowdevelop

Another interesting note...the only heads I have seen above 116 cfm/sq" are sb2.2's. What is even more puzzling, is a little chief going 114cfm/sq" will eat it up hp/cid. As jud was saying..you can't place everything on airflow. I have never had a set of GA's or WJ's heads on the bench before...But I can honestly guess that they are right around 115 - 116 CFM/SQ"...and make WAY more power per CID than any SB2x head around. The sb2 head is really a flowbench queen IMO, compared to the little chief and DRCE2 stuff around. Rumor has it...that somebody has a set of c5r heads that goes 116 cfm/"....Bret..any ideas on who did these? If the rumor is correct, the owner does an awful lot of work for gm's R project.

Dennis

Wnts2Go10O

iTrader: (12)

what if youu opened up the back of the port like a megaphone? or is it that by that point the air is moving so fast that it needs more to slow it down? maybe something to split the air current in 2 than slam it into eachother or would that just cause turbulence?

SStrokerAce

iTrader: (2)

Dennis,

Those are all Larry Meaux's old calcs, I've used them to be able to tell how well my motors make use of the CFM the bench says they have. Your right the rest of the system and sealing are a big part of it. .260 is right too, getting over that for most guys is not easy. Hell i'd like to see .270-.275 on a good LS race motor since those puppies are not the easiest to work with as you said.

FWIW he uses 87% or 85% of the max lift that the head sees and bases the calcs off of that flow number.

Bret

airflowdevelop

Bret,
You are right on with the 87% with a stable valvetrain.

Dennis

airflowdevelop

If it was only that easy....

Wnts2Go10O

iTrader: (12)

achams razor?... anyways, how would u go about slowing down the air current? cam profile seems the most likely course shor tof redesigning the head completely. i guess thats why the l92/ls7 heads' ports are the way they are

SStrokerAce

iTrader: (2)

As a head porter I'm guessing that it's his job to know how to slow down the fast spots in a cylinder head. Usually you add area to that part of the head or enlarge the radius of the curve.

Bret