JimV

iTrader: (1)

I'm in the process of modifing another couple of sets of cnc'd AFR heads. In my opinion the intake ports flow extremly well but the exhaust ports are in question. There have been questions about using a "cheater pipe" when flowing the exhaust ports. The 6" pipe increases airflow, scewing the numbers. This can confuse the builder for camshaft selection. I found some interesting information that I will share for those interested. Below are some numbers using my flow bench. I use a 4.6" bore plate and all numbers are at 28" of water, pretty much the industry standard. Here are the factory cnc'd exhaust ports on my Superflow 600 with and without the pipe.


Lift...........CFM without pipe.............CFM with Pipe

.200.........135.................................1 44
.300.........186.................................1 95
.400.........221.................................2 48
.500.........250.................................2 77
.600.........248.................................2 81
.700.........249.................................2 88
.800.........250.................................2 91

Pictured is the valve seat area. Notice the dark spots that didn't clean up when I used scotch brite to clean the carbon off before I flowed the port. These are ridges left by the cnc machining process. Knowing this area is extremly sensitive and knowing how much a 1.880 exhaust port should flow I wanted see what kind of improvements can be made. (I'm out of time so I will add later, it gets better)

JimV

iTrader: (1)

Sutphen

I did try different pipes. I will post tommorow.

Linster

Jim,

It looks like the seats in these heads has been sunk deep when doing the valve job. Looking at the picture, it appears the seat is about .100 wide. Normal after use with a .080 seat. The Intake looks to be sunk even more. Notice the black around the exit of the seat. The intake looks like there is a wall in the area entering the bowl. That affects a lot of flow on the .100 & .200 and maybe the .300 lift. That is the where most airflow gain is on the opening and closing of the valves. When the valve is wide open flow is usually not a big problem. I always tell the machine shop not to sink the seats, only cut enough to clean it up. If you do not tell them, it seems you end up with a seat like that. I have had to install taller seats to correct these poor valve jobs.

I am curious to see what you find. I think you can help some by cleaning the wrinkles on the exhaust port. After that try unshouding the bowl area that is black especially in the .100 to .300 lift range. The intake appears to be the beneficial from the picture.

I do not pay much attention to the .700 or .800 lift numbers, Actually I do not get my shop to flow them since the most cam lift is .632 on a hydraulic roller. If they increase, usually the lower lift numbers fall.

Keep us posted

Crazyhorse

Jim, you up for another west Michigan party? It's been a while since you and I had a soda pop so I'll give you a call to se if we can maybe meet up at Applebee's or something.

Raylar

Interesting results on your bench. We have found during the development of our new 496 heads that 1.88 exhaust valves on big blocks are a little to big and hence they tend to kill velocity at mid lift numbers especially. We use a 1.75 exhaust valve on our smaller port and get about 250 cfm at .500 without a pipe. The numbers are still climbing all the way to .700. I also noticed the numbers on your AFR heads show the exhaust flow is "hitting the wall" at about .500 ,with or without the pipe and does not increase much beyond that. Not Good! I know Tony at AFR and usually his work does better than this. I am curious if any other AFR heads exhausts flow like this. Do the heads come with a standard 12 degree backside on the valve @1/2"radius? We see a lot better results when we use a 20 degree exhaust valve with a 1/2" radius and finish the front edge of the exhaust valve with a small .0625 radius at the edge. We also use a two angle plus 10 degree radius valve seat. Try this and see if the numbers improve. I have spent so much time on our flow bench the last two years that my wife claims I am operating the dam thing in my sleep!
Great Post!
Ray @ Raylar

JimV

iTrader: (1)

After some chamber mods and bowl work to the AFR port the numbers significantly improved



Lift................CFM................CFM W/pipe

.2.................140.................149
.3.................214.................228
.4.................259.................280
.5.................276.................305
.6.................283.................323
.7.................286.................332

JimV

iTrader: (1)

For compairison Dart Iron Eagle Exhaust ports

mjb

Jim- by chance do you also have the intake #'s for the iron eagles? What size intake ports where they? Where they out of the box or worked? and last but not least...did you flow these heads or are these #'s from dart? I just bought a set and the #'s they gave me seem a little high. I am planning on flowing them but I would also like to see your #'s. THANKS

JimV

iTrader: (1)

Thanks Sutphen 30!


Here is the interesting part. The Dart port nets 138 cc's volume. The AFR is a 128 cc port.

The 6" pipe helps the AFR port more than the Dart


lift...........CFM Increase AFR................Dart

.2...............9................................ ........7
.3..............14................................ ......19
.4..............21................................ ......16
.5..............29................................ ......22
.6..............40................................ ......35
.7..............46................................ ......39

JimV

iTrader: (1)

MJB the Dart numbers are from a hand ported set of heads that were ported here. The numbers out of the box from Dart are better than the numbers on my flow bench. I can post some intake numbers from a 343cc head.