What did you think, they're not flowing much better than stock heads with 2.14/1.81s? The port is significantly bigger though.

TBH I've been trying to figure out why my Stealth headed engine doesn't rock like it should. I had a head off a couple of weeks ago and was tempted to bring it to my machinist to flow it. I went through them, lapped the valves (looked good), and changed the springs, but the ports and valve job are just OOTB.

Its not hard to get a set of 906s to flow what these heads are flowing. I'd think cleaning up a bowls a little, and big valves, and they'd be there. Mr Porter knows for sure how much is required to get them there.

Its certainly very possible your ported iron heads flowed better. I think 906s can safely flow around 280 and not risk cracking from being too thin. Some people get over 300 out of them.

While I have 440source heads and really like them, it still irks me that they over-inflate the flow numbers on their website.

"Intakes flow about 280-290 CFM as cast, with the potential to reach at least 330 CFM or more with porting."

While I see many people posting how "normal" home port jobs on
OE iron heads can easily flow 260-270-280+, the fact is, those
cases are few and far between. The typical big valve 906/915 type
BB head that was home ported or not done by a shop that is well versed in
preparing racing heads usually flows in the 240's, or less. It's takes
a fairly skilled person with a good understanding of those heads to
get them to flow in the 270's +.
This is one of the main reasons heads like the RPM's and Stealths
so often outperform ported OE heads without any additional work
done to them. The home ported "260+ cfm" heads aren't usually as good
as the owners think they are. Unless they have been on a flow bench,
you'd really just be guessing.

Here are some numbers from some recent heads that came through
my shop for freshening/updating. Neither of these sets of heads were
home ported, but done by a regular machine shop that wasn't necessarily
specializing in head port work. They had the usual big valve install
and some amount of associated blending along with some blending
of the pushrod pinch area.

915 head, older MP 2.14 intake valve with back cut/ new Ferrea
1.81 exhaust valve with back cut, and I freshened the valve job.

Lift------in/ex
.100----70/48
.200---145/99
.300---196/133
.400---227/161
.500---236/181
.600---234/191

906 head, SI stainless 2.14/1.81, no back cut, used valve job
(But not many miles on it) with radius as bottom angle on
both intake and exhaust.

Lift------in/ex
.100----69/48
.200---124/94
.300---180/129
.400---227/158
.500---241/178
.600---245/193

So, it's pretty easy to see how even an OOTB Stealth head
should be able to provide a nice improvement in performance
over these two sets of reworked OE heads, and these are
really fairly typical of what I see.
I will add this, for the average home porter, the 346/902/452 heads
are much easier to get to flow 250+ cfm, and are also a better bang
for your porting $$$ if you're paying to have the heads reworked.

I figured I'd throw in these numbers too....
452 heads with 2.14/1.81 valves, done by a well known mopar
volume head rebuilder, no porting, no blending. To the best
of my recollection, these are the worst flowing big valve heads
I've come across. They had a big "bowl hog" type cut done under
the valve job that really hurt the flow. IIRC, these flowed less than a
completely stock head with the OE valves and valve job.

Lift------in/ex
.100----67/52
.200---118/97
.300---169/129
.400---196/141
.500---217/145
.600---222/145

Andy, were those the 75cc "RPM" heads or the "E STREET" heads?
If they were the RPM heads, were the chambers machined or as cast?

Sorry, .575" lift roller, not the .557 i had written above.

As a point of reference, these are the intake flow numbers for a
906 "F" head dated 10 11 8. While not all F heads are great, the
best flowing untouched 906's I have tested have been F heads.
This particular head had a very well preserved OE valve job and
Is tested here with an OE valve and no back cut.

Intake test only-
Lift------In
.100----62
.200---122
.300---179
.400---214
.500---224
.600---235

On a head like this, once you start to blend the bowl and increase
the potential for more air to flow through the port, the short turn will
become a limitation and the port will go turbulent, usually between
.400-.500 lift, and the flow will drop off unless you start reshaping
It.

[quote=fast68plymouth]While I see many people posting how "normal" home port jobs on
OE iron heads can easily flow 260-270-280+, the fact is, those
cases are few and far between. The typical big valve 906/915 type
BB head that was home ported or not done by a shop that is well versed in
preparing racing heads usually flows in the 240's, or less. It's takes
a fairly skilled person with a good understanding of those heads to
get them to flow in the 270's +.
This is one of the main reasons heads like the RPM's and Stealths
so often outperform ported OE heads without any additional work
done to them. The home ported "260+ cfm" heads aren't usually as good
as the owners think they are. Unless they have been on a flow bench,
you'd really just be guessing.

Here are some numbers from some recent heads that came through
my shop for freshening/updating. Neither of these sets of heads were
home ported, but done by a regular machine shop that wasn't necessarily
specializing in head port work. They had the usual big valve install
and some amount of associated blending along with some blending
of the pushrod pinch area.

Very true. The areas of the 906 casting that need work to get the CFM in the 260 + range are kinda hard to get to. Then when you start getting real good number you cut through the short side. The numbers you are posting reflect the numbers that I get on my bench. So far the best 906 that I have tested was 300 CFM. The short side was flat as a board. No idea how they got that lucky.

So how does that guy from out west get 340+ cfm out of 906's?

A few years ago there was a magazine article where someone was
offering CNC ported 906 heads. I believe it was Muscle Motors.
As I recall they were reported to flow something 312cfm on the intake
side. I've had a set of those in the shop, just as delivered from MM
with 11/32" stem valves, 2.19 intake and 1.81 exhaust.

Lift------in/ex
.100----68/61
.200---145/109
.300---241/145
.400---256/171
.500---284/191
.600---290/204
.700---288/204
.800---290/205

On my bench, while not 312cfm, that's still a very good 906 head,
and as big as they looked, it was only like 217cc's as I recall.

I have an old article that explains that some of the well known Mopar ported head that you see for sale are advertised with flow numbers at 32 - 34. Not the 28 that most people are used to. I have had some on the bench and they flow around 275 280 at 28. Crank it up to 32 and they flow around 320.

Wonder how long it takes those 300 cfm 906 heads to crack and hydraulic cylinders?

Back to some Stealth numbers...
I had a set of Stealths come through the shop that had a season
of drag racing use on them. I re-cut the seats, back cut the valves,
and blended the exhaust bowls. On the intake side I opened the
pushrod pinch to 1.125", blended the bowl and also opened up
the bowl area in the roof adjacent to the guide boss, as well as
removing most of the guide boss itself.

Lift-----in/ex
.100---70/56
.200---143/112
.300---205/145
.400---249/170
.500---279/188
.600---286/201
.700---289/210

The straight wall in the intake ports on these heads are fairly
"lumpy". I think if you started out with the level of work the same
as the test above, then straightened out the lumps on the straight
wall, and took a little off the other three walls, and then smoothed
everything up, you'd end up with a port that flowed somewhere
around 295-300 cfm.

Fast68, you are the Man! Thanks for injecting some reality.

R.

Can't argue with real world numbers, very insightful!

Very happy flow bench. Ron

dwayne it is good to see you posting again, i had stock stealth's and changed to some of porters indy -1's that were heavily reworked. i couldent be happier with the results, the stealths went on the wifes challenger and when money allows i will send them to porter as well.

Wow, I've been missing out on all the fun..........

2" tube on the exhaust.......28"..........

Lift.............Stock 906..........906 Ported

.100................66/54................89/60
.200.............131/103............161/129
.300.............189/145............212/185
.400.............222/168............257/216
.500.............234/176............297/234
.600.............237/183............331/253
.700......................................347/264

These 906 heads were on our 500" engine when Comp Cams forgot to turn the water on to the engine. It got so hot that the paint was burning off the cylinder heads and all the exhaust valves seized to and pulled the bronze guides out of the heads. The valves were then pounded out of the guides, the guides knurled on the outside and pounded back into the heads, reamed and the valves stuffed back in. With 15 bent valves and 11-56% leakdown it then made 730 HP on 93 octane pump gas. Oh yeah, the heads never cracked and still don't leak water.

Lift......Best OOTB Stealth ever tested.......Fully ported

.100...............73...........................73
.200..............151..........................152
.300..............214..........................218
.400..............245..........................267
.500..............262..........................308
.600..............276..........................337
.700..............281..........................346

With the 2" pipe the Stealth exhaust ports will approach 300 cfm when ported.

Jim L - Are you still using a SF-110 (like myself) and having to throw big correction factors into the results (again, like myself), or have you upgraded flow benches since the last time I asked about your equipment?

When I see BIG starting numbers like this it raises LOTS of questions about flow bench calibrations.

.100...............73...........................73
.200..............151..........................152
.300..............214..........................218
.400..............245..........................267
.500..............262..........................308
.600..............276..........................337
.700..............281..........................346


I have had a lot of Stealth heads on my bench and when I test I test EVERY port on every head. The most I have ever seen was 267cfm. Start with high numbers end with high numbers and those in the know, know better.