tomcat

Just read the article in Hot Rod. Air Flow Research has finally decided to sell aluminum heads for big block chevs. The flow numbers on their 315 cc CNC'd head are great. Try 375 and 302 CFM in/ex @0.600" and 28 "H2O, with 80% in/ex @ 0.400".

These flow numbers were provided by Westech Performance, who have flowed a bunch of heads for Chevy Hi Performance magazine. Since all the heads were flowed on the same bench by the same operator they are good for making comparisons in dyno programs, without being thrown by enthusiastic ratings from the manufacturers. I am assuming that the AFR numbers can be compared to the other heads they have tested.

Just for comparison I put the AFR heads on the Desktop Dyno engine simulation for my 502s, which currently have unported GM aluminum oval port heads (290 cc)and a mild hydraulic roller good for 500 HP. Changing nothing but the heads adds about 125 HP. The extra HP doesn't show until after 4500 RPM and peaks at 6000 RPM.

Putting these heads on my boat engines would increase top speed as shown on the attached graph. Since the increased power is delivered at higher RPM, no prop change is necessary. The amazing mid lift flow numbers on these heads should make them a good choice on boats where cam choice has to remain conservative.

H2Xmark

sounds like good news, glad to see air flow research. get on the stick

formula31

Some little voice in the back of my head says your not gonna get 125 hp from just changing heads. At least not from that pair. Id like to see real dyno numbers back that up and Id buy a set.

KAAMA

iTrader: (1)

I just had my heads fully ported and they make lots of TQ & HP and they carry the engine well....and because my heads flow so well I think it has made the cams too BIG now. The exhausts ports with the headers are pulling the air/fuel mixture charge and over scavenging it out the exhaust unburned which is a waste. I think I'm going to send the cams back to have them reground by having the duration reduced and lobe seps spread out from 112* to 114*...this will reduce the overlap of the cam by slowing down the exhaust side a little and make the engine more efficient burning. That's my aim anyway....

tomcat

Kaama - In the article they mention that AFR ships the smaller cc heads with nailhead exhaust valves to actually reduce flow and maintain a better in/ex ratio. On the larger or CNC'd heads they come with a tulip exhaust valve. The better flowing tulip valve is an option if you are supercharging and need more than the usual in/ex ratio.

formula31 - the reason for the big jump is all my other components are already sized for 600+ HP, the heads are the bottleneck. Porting my oval port heads is also worth HP, but they would never match the AFR numbers.

Adding 125 HP (25%) is definitely feasible. There's lots of guys on this board making that kind of power on normally aspirated 502-509 engines, but usually with lots of money invested in porting. These heads come CNC ported, and deliver this flow out of the box.

A quick way to compare different heads is the flow at 0.400" lift since the valve spends more time near mid lift than peak lift. My heads flow 233 CFM @ 0.400". The AFR heads flow 315 CFM @ 0.400". That's 35% more air.

KAAMA

iTrader: (1)

Tom,

At .400" lift JimV got the intake on my Dart 310cc Pro-1's heads flowing at 295cfm @28" water

My exhaust at .400" is 206cfm @28" water

My overall intake/exhaust percentage of flow is 75.8% @28" water

tomcat

Those seem like excellent numbers too. In the article they say that you can buy the heads as cast 305 cc for about $2000.00. It's the CNC work that takes that same casting to 315 cc at a cost of about $3000.00. How does the extra $1000.00 compare to the cost of porting? Seems like good value, especially since every port should be identical.

JimV

iTrader: (1)

I talked to AFR about their heads. Apperently the use a tube on the exhaust ports when they flow them. This adds up to 6% to the final numbers. This is nothing new, we used cheater pipes years ago on the fords. The only benifet is customer satisfaction when they see the airflow numbers with the pipe compaired to the competitons advertised numbers without it.

Im not flaming AFR but there is only so much air that will flow around a valve. All the head manufactures have great products however, airflow is limited by the valve angle, port height, overall port volume. Also there is a left and right port on the BB chevy. The right port flows as much as 5% more than the left because of design.

I would be suprised to see a 20hp difference between say a Dart and the AFR. my .02

I would never intentionally hurt a port to try to fix a problem.

tomcat

JimV - Good point about the exhaust tube. The flow data on the chevy hi performance website gives numbers with and without the tube. The difference between 295 and 315 could also be explained by different bench/operator. Both these heads will outdo my GM heads with their smaller ports and exhaust at stock location.

What do you think could be done with my GM/Edelbrock square-oval heads and Edelbrock Victor Jr. intakes? I have 800 CFM 9022 carbs and the cams are 224/234 @ .050", 115 lobe separation, .558/.576" lift with 1.8 roller rockers, Gil exhaust dry to transom.

JimV

iTrader: (1)

Tomcat,

Im sure the airflow numbers can be duplicated with that cam/ valve lift depending on the valve size. If you have a 2.250 intake It should flow high 380s @ .700 lift, more with the 2.300. Your combination should make more torque than hp......perfect for a boat.