Hello Everyone,
Long-time lurker but first post.
I am rebuilding a 225 out of a 1968 Barracuda and would like to mill the head for more compression (as well as get some larger valves and smooth out the ports/bowl).

This engine was rebuilt at some point and I don't want to mill too much!

Does anyone know the factory measurements of the head, from block deck to valve cover surface?

Thanks!

Someone will chime in with the stock head thickness. But - the combustion chamber volume varies a LOT from head to head. You will be much better off CC'ing the chambers and using that information to calculate how much to mill.

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If your plans are to mill the haed for more compression anyway, then the amount (if any) that the head has been milled in the past is irrelevant because you should be CCing the head and measuring the deck height of the pictons at TDC anyway to calculate your dynamic compression ratio. Your combustion chamber volumes are what they are and you should be measuring them and doing the math anyway before you decide how much (if any) to cut off the head to raise compression.

Okay - got it.

So is this a logical order?

1) Get block back and install new pistons (will be 0.040" over)
2) Measure deck height of pistons at TDC
3) (meanwhile) Have machinist hog out and install new valves
4) Take head home, do whatever cleaning up inside the head I can, and then CC it
5) Do calculations for compression
6) Take head back to machinist for milling

Please forgive me my ignorance - I am new to the slant six and have never done much in the way of head milling!

Also - it would appear that a favorite source for oversized valves, "Engnbldr" on Ebay, has retired and is no longer providing! Would someone please recommend a good alternative source? Thanks.

Sounds like a good series of steps to me. The only oversize valves I have ever put in a slant head were Ford 300 valves. However, they require machining on the valve stem to work (shortening and new keepr grooves cut, and possibly turning the valve stem diameter smaller) and also require a .060 overbore of the cylinders to not be shrouded.

Lots of extra machine work, but the Ford 300 valves are the absolute biggest valves you can put in a slant six head.

I was thinking the 1.7" and 1.44" valves. Or something close.
Is that not going big enough? I'm not looking for maximum performance or a race car, just a little more oomph. Going to stay naturally aspirated.

Other info in case it is needed/wanted:
Electronic ignition
2 bbl carter on super six intake
Header
Factory hi stall converter
904 Torqueflite
3.23 Suregrip rear gears, SBP 14" wheels

Have not yet decided on cams and am doing (probably too much) reading.

SI Valves has stock and the oversize valves you want. They are @ $9 each

http://slantsix.org/forum/viewtopic.php ... ght=valves

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12.70 @ 104.6

My 1971 uncut head measured 3.617 from the deck surface to the machined lip where the valve cover seats. This measurement was with a 4 in. Starrett older than me.

I probably would not bother with the OS valves if all you are doing is a super six and a little more compression... if going headers, and OS valves, I'd be looking at a 4 barrel with vacuum secondaries to get the most out of your power "adders" (headers, high stall convertor, etc...)

Not quite:

Proper order once you put the engine on the stand (but is not 100% comprehensive):

1) Pull accessories and head.
2) Run piston up to TDC and check current deck height (check #1, #3 and #5 mostly for conformity)
3) clean out a couple of chambers (like 2 and 6) and check current CC
4) Calc current compression ratio and note what you will need to get to your target static compression ratio.
5) Disassemble the rest of the engine and check the crank rod and main journals to see if they are in tolerance or need a regrind (this step not necessary if you are just trading for a crank kit).

6) take to parts and block to machinist, let him know what you will need him to deck the block to get you 'close' to your SCR goal. Ask to have the block, head, and rods checked (magnaflux for cracks, rods for twist, etc...
7) Ask to have the head back after it's hot tanked and checked
8 ) Do your rough porting on the head (Reason for this is... if you slip with the die grinder they can take that back out when they mill it... if done afterward you may have issues... also if you are really going to town on the porting, and you break through the water jacket...you can get another head before all the major machining is done...)

Meanwhile machinist will bore/hone/etc your bottom end...

9) Hand back head to machinist...have him do the valve work, guides, seats, etc....
10) clean and check your parts then assemble your bottom end and check the deck height...Calc your displacement so you can dial in the CC needed at the head. degree your cam, etc...

11) Once machinist is done with the valve work, check the CC, using the formula .0066 cut=1cc and looking at your equation solve for the required CC of the head and let the machinist know how much to cut the head (note to remember to take into consideration the head gasket crush height... it's not a bad mistake on a 9:1 motor...but can be very ugly on 11:1 and above)

12) Inspect the work, pay the dude, take it home, disassemble finish the fine porting work. Clean things up.

13) check CC, check calcs and if good reassemble

Thanks! I'll order some right away.

DusterIdiot - Thank you. I can always add the 4 bbl later! Unfortunately, the engine is already disassembled and the machinist has the block, crank, and head. I can certainly get the head back and do the rough porting, before returning it for hogging. This is good stuff and a big help!

Oversize exhaust valves and hardened valve seat question!

My machinist raised concerns about hogging out for the 1.44" exhaust valves I got from SI. He was worried that if he expanded the valve seat, it wouldn't leave enough of the hardened seat to handle the heat - it might pop out or not have enough material to properly conduct heat.

On the other hand, he worried that expanding the hole enough for an oversize valve seat might nick the water jacket.

What is the answer?

Thanks!

This happens on occasion on the drool tube heads, I have not had a problem on the 1975+ heads... and I always replace the seats on those since they ran them fairly lean for smog and they usually don't look to good afte ran into the ground after 200K miles....

Mine has drool tubes!

Since you are installing stainless valves, you likely don't need hardened seats. I have a couple of heads w/o new seats and they have been fine on pump gas.

That said, I have not had trouble with heads with hardened seats installed. If he is nervous about it, maybe he has had trouble in the past and you want to steer clear of him? 1.44s are not that big and hardened seats at that size should be fine.

Lou

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