Crazy flow question

[user-9274568]

I have a port that flows great up to .700 then at .800 drops 12 cfm, then at .900 goes back to the .700 number and at 1.000 keeps climbing. Any ideas what to try? Ever had this happen. I know something isn't happy, but what?

Chad

example:

.700 407
.800 395
.900 407
1.00 409

[airflowdevelop]

by chance is this a BBC?

[Darin Morgan]

I have a port that flows great up to .700 then at .800 drops 12 cfm, then at .900 goes back to the .700 number and at 1.000 keeps climbing. Any ideas what to try? Ever had this happen. I know something isn't happy, but what?

Chad

example:

.700 407
.800 395
.900 407
1.00 409

Diagnosing a port is almost impossible unless you flow it, measure it and hear it yourself but I will take a shot at it. If this is an SB2.2 head, try the left hand corner of the SSR apex and area just behind the turn. Make the corner broader than the push rod side and fill it in behind the turn a little. Your playing with .050 of material so it takes some finesse and some hand sanding but you will probably find that area to be responsive to this problem. If its not an SB2.2 what head is it?

[maxracesoftware]

its not a "crazy" flow question .

its pretty common problem,
the Short Turn Radius is too fat or wrong,
especially with a Valve BackCut angle

your Short Turn velocity FPS is also probably very high or biased in location or changing thru Lift Curve

lets say you shape the Short Turn area to barely get
stable gradually increasing Numbers,
it will look great on a FlowBench , but those Numbers will be false Flow

you have to reduce Short Turn sensitivity
so when Fuel Mixture is in the Port, it can make the turn also

if the Dry Flow Air Numbers have trouble making the Turn or barely making the Turn, what's going to happen with Mixture with more inertia

Fuel skipping over the Short Turn is going to disrupt/change the actual Dry Flow Numbers -vs- Live Engine

1/3rd to 1/2half the time the Dry Flow Numbers with a hidden Short Turn problem will not make the HP/TQ numbers it should on a Live Engine

[dbusch]

I have seen this problem on some SBF Victor heads too. On the Ford, the pushrod/curved wall is the one next to the cyl. wall, the straight wall next to the ex. port. So, which part of the short turn could be causing a flow stability problem like the other guy posted? Does this problem area need a more gradual turn vs. the other side of the short turn? Trying to understand this...

[user-9274568]

Thanks Guys.. I'm off to try it. Darin, yes it is a SB2.2. But I didn't want to tell you! It's decent, but not great. The good thing is it's a 45 degree seat. I have sunnen making me a 45-50-65-72.5 cutter. It's basically my first "try" at a SB2.2. The head is 2.180/1.580 valve, 3.50 CSA, 3.17 at choke, Average velocity is 330 in the port. The ST area average is 310. But it's 380 over the turn.

The thing sounds awesome! It's weird, it sounds really crisp at .700 then it's like it kicks into high gear at .800 and sounds really good! Make sense? Just don't flow a ton of air, yet.

What's your feeling on chamber size? currently it's 41 cc. Compression isn't a problem, 3.700 stroke.