Update on C5AE-F "Small F" heads

[My427stang]

I promised an update on the C5AE-F medium riser heads, and it's not a sexy one

A while ago, about the time I started on the CnC CJ head project, I started on a set of C5AE-F heads and figured I'd document what we did there too.

We took the bone stock, near virgin C5AE-F "Small F" heads and flowed them with all the original Ford parts, Ford valve job, basically nothing done...that is column 1 on the attachment

Then I added 11/32 guides, 11/32 undercut stem valves, and a 5 angle intake seat, that's column 2...guess what, yup chicken butt...worse!.   Now as is, they would likely RPM better now because they are so much lighter valves, but not where we want them yet

This is not that surprising because the Small F port is really crappy, which kills the high lift flow, and we saw clear as day that the 11/32 valves desperately could use a back cut, which likely hurt flow as much as the 5 angle seat helped it, but wanted to do one-ish change at a time, but I sure didn't expect the results even if I can explain them!

Next will be to back cut the intakes, reflow, then a bowl port or maybe full port rework, we'll see, it really needs both. Not too impressed with these compared to the Big F versions (which start about 30 cfm higher). 

Always heard the Big Fs were better, I'd say it's true...we saw 335 cfm at .650 out of the last set, it'd take a lot of grinding away of the ugly to get these there

[69ramair]

Thanks for the good work on this , I wouldn’t have expected them to be quite that bad

[427mach1]

Those flow rates look to be very close to a stock CJ head....

[My427stang]

Factory untouched CJ head, same bench, same fixture.  The medium riser curve is a bit better sooner, but not much better overall. 

There is more in this head, don't get me wrong, but I was surprised how not happy it is as cast

[e philpott]

if you run a .600 or less lift cam the F head blows the CJ head away as they sit ... \Does the F head have 2.19 intake valve ?

[My427stang]

Sort of a "less fat kid" in a fat kid race, but yes, I agree, better by in average flow from .100 - .600 by 20 cfm  FWIW a Trick Flow in the same lift range averages WAY above that, but the small F's did beat an is about the same as an Edelbrock  (from other people's testing)

However, I don't do much street stuff under .600 if I can help it nowadays, and I'd like to see heads run at the 300+ cfm number without a honking volume.   The other reason I am surprised is my last set of Big Fs were ported at 335 cfm.  I don't see these ever getting there, but who knows?

As far as valve sizes, yes, 2.19/17.3 for the stock valve, 3/8 stem, for the second test, 2.19/1.75 5/16 undercut stem.

It's odd how Ford used a similar casting number for two heads that seem to be significantly different

[Barry_R]

FWIW I see the Edelbrocks in the middle 250s...but for comparison sake that is with a 2.090 valve vs the 2.190

[My427stang]

I must have fat fingered a number when I did average flow on the Edels.  Average flow on the Edel is 183 cfm up to .600, and the C5AE-F is 184...probably not a coincidence.  Corrected my post

Not sure it changes my thoughts opinion either head though

[e philpott]

What's a big F Medium riser flow factory stock ?

[blykins]

About 280.

[My427stang]

Brent is spot on, and the port looks cleaner overall on the Big F, as expected by the numbers.  The small F heads have big, jagged core lines, tight short side, and a big step in the bowl.

We'll see where we can end up, not leaning on them to try to get in the 330s, but want to see where we can end up with a little purposeful clean up.

[CaptCobrajet]

If you notice the low lift numbers on your stock vs the 11/32 aftermarket valve, you can see why Ford used that 30° seat and radius under it.  With the .500 lift they had net of lash, the average flow with cams of the day was way better.  The sharp corner short turn in the small F is why it stalled at the 246, no matter how far you opened the valve.  The 45 valve job caught up right about the place a stock cam was at full lift.  The flat machined chamber also likes the 30 seat.  If you lightly tuned up the short turn, put a 20° top cut on, sunk the seat just enough to get your 20 top about  60 wide, then knock the edge off with a 15, and go under the 30 and put a 54° about .030 wide to blend into that radius under the bottom, you could see 290 out of the small F at .500, and probably 300 at .600.  There ain't much room to work without poking through somewhere.  A little more short turn work and a little epoxy in the right way, and it will go 320 with low numbers pretty close to that Trick Flow you like so well.

The Big F head was something that was intentionally the same casting number to help class racers.  The NHRA tech people eventually figured it out, and gave the Big F a different HP factor and published runner volume.  153 cc versus 164cc if I remember right.

The street combo Medium Riser Small F was a mean street performer.  For what they were, they ran better than they should have, and hurt lots of feelings of the Chevrolet and Chrysler folks just because the "combo" was good.

The worst thing you can do to that head for street use less than .600 lift is cut that radius throat out and put a steep valve angle on it.

Take baby steps working on that short turn.  Too much and you will go back the wrong direction, and you can't get it back.........

[My427stang]

Thank you very much Blair.  All makes perfect sense to what I see here.  I appreciate it

[e philpott]

What do the High Riser's factory stock flow in comparison with these heads ?

[Joe-JDC]

All the factory iron HR heads I have flowed and there have been several over the years, only flow ~285 cfm @ .750".  Joe-JDC