Any last words of advice on head?

[falcon fanatic]

Allright, get yer minds out of the gutter...
Finally, after years of having this thing lying around on my bench, I'm taking my head into the machine shop for a rebuild.
This is an M casting. I've cleaned up all the bowls, ported and polished the exhaust, unshrouded the valves as necessary, and polished the chambers. I have the 1.75" and 1.5" port flow valves, the fancy valve seals, and 302 springs.
The log will be modified to direct mount my weber 38.
I will have the head milled to approximately 50cc (is this realistic???? It's 63cc now)

The bottom end is totally stock.

IS THERE ANYTHING ELSE I SHOULD KNOW OR DO???? Head is going in tomorrow, Wednesday. All advice is welcome.

 

[CZLN6]

Howdy Back:

Id suggest having the intake valves back cut too.

If this is going on an otherwise stock 200 block and you want to maintain stock compression ratio, with an aftermarket type composite head gasket then a mill cut of .050" is feaseable. It will not quite maintain a stock ratio. I Haven't run the numbers on the calculator, but my guess would be a CR of about 8.7:1

Adios, David

 

[BaldEagleMav]

Hi David and Falcon Fanatic,

David, if I understand Falcon Fanatic's post correctly, he is saying he wants to mill the head to go from 63 cc volume to 50 cc volume.

It seems you understood him to say he is going to mill 0.050" off the head.

Two different things.

A 50 cc volume is going to give a much higher compression ratio, no?

Just ensuring we're all on the same page.

Regards,

 

[falcon fanatic]

Correct BaldEagleMav. I plan to mill off around .065" to .070" That ought to get me in the 51cc to 50cc range. I'm assuming the machinist will balk at taking off so much, but people around here seem to think it's safe...

As for back cutting the valves, no need. The Port Flow valves have narrowed necks and are back cut and swirl polished. Much nicer than stock.

 

[powerband]

I had the head off a D7 250 block worked as per the Falcon Six Handbook and the machinists suggestions. He milled @ .070, carefully re-checking chamber volume for size and uniformity. The final figure was @ 48cc minimum chamber volume. I planned on a composite gasket on a 250 but the head currently is on a 170 with a steel shim gasket. This yields a CR of @ 9.2:1. The 170 with a composite gasket would have a @ 8.7:1 and the same head on the 250 would yield a CR of @ 11:1 IF a steel shim gasket could be had. With the composite the CR would still be @ 10.5:1 .

The machinist was interested in the project and I left him the Schjeldahl brothers' book with notes. He said their estimate for chamber volume vs milling was right on. I had basically every recommendation for head work done and the machinist also milled the valve spring seats and added hardened centering spring seats to match the heavier rate springs. The valve seals are a soft variation of the teflon seals machined to be captive. Suppposed to not pump oil at high RPM.

Total cost was @ $900.oo

 

[Ron R]

Cool info, Thanks Guys.

 

[Hot 6t Falcon]

A word from the other Schjeldahl brother.

You might want to goto http://falconperformance.sundog.net/compcalculator.asp and play a little.

Since you'll be using a new head gasket, put .044 for the head gasket thickness. Then change the "Combustion Chamber Volume" to 50 cc. Leaving everything else alone gives you 8.8 to one compression.

You can EASILY mill the head enough to get the compression you want.

 

[falcon fanatic]

Thanks, I actually frequently fantasize on the calculator. I was hoping to be able to get into the nines on compression, but with my stock block it just isn't possible. So, I'll go high eights, and then some day rebuild my bottom end.