[jpg69bird]

I am ready to send off my 455 for a rebuild. Originally with a 7.6 CR, I plan on swapping heads.

I have a set of 1973 #46 heads and a set of 1976 #6X-4 heads.

I've seen two different cc sizes for the #46. Wallace lists them as 96.17 cc's, Butler lists them as 89 cc's. Any idea which is correct?

Most sources show the #6X-4 as 93.74 cc's.

I would like to use the Butler 068 HR cam, but am afraid the cr might get too high for a 212 cam. Will either head work?

If not, would the Butler 224/230 HR help the issue?

Car has the original 3.23 gears and ST10 Four Speed. Using original intake and q-jet. Switching to ram air exhaust manifolds and dual exhaust with cross-over, if that matters.

[JSuchma]

Go with the 6X-4 heads and build around them. You will be glad you did!

[b-man]

Agree 6X-4.

Just a better head in every way compared to the #46.

[steve25]

A big CID over square ( long stroke ) motor like a 455 needs all the intake air flow it can get.

Here’s some info that should help you to solidify your choice of a head to use.

The first column is the stock intake flow of the 1,96” intake valve in a # 46 head and the second column is the stock intake flow of the 2.11” valve in a 6X-4 head.

.050”——40.1—-45

.100”——75.8—-77.6

.200”——-142.2—-145.2

.300”——172——-179.8

.400”——185.7—-203.2

.450”——188.2—-206.5

.500”——189.5—-208.8

.550”——190.7—-211

.600”——192—-213

Also the shape of the 6X intake port allow more of an even velocity profile in its cross sectional area and this allows for a slower nose over of peak hp.

10 minutes of grinding on the intake eye brow in the 6X chamber will help out to the tune of 6 or 8 more cfm also.

When your heads get rebuilt use new valves with undercut stems and have the shop back cut the exh valves with a 30 degree.

To take full advantage of the 6X heads and that HR cam I would run 1.65 rockers , you will then end up with .495” lift so the heads will have to be set up spring wise to deal with at least.525” lift and the intake push rod holes will needed to be checked up top for clearance due to the 1.65 rockers.

If the machine shop is doing a multi angle valve job then intakes should get no top cut, just 30 seat and a 60 bottom cut to bring the 30 degree main seat to within .010” of the OD of the 2.11” intake valve .

The stock seat OD is well less then 2.11”.

You should have no problem making a solid 390 hp out of this combo, but note that it will be crucial to get your Q-jet reworked to feed the extra 100 hp and to deal with what will be lower idle vacuum levels.

Your fuel system should be reworked also as should whatever your running for a distributor.

For safety reasons I would start off with one heat range colder spark plugs.

If your budget permits I would mill the heads .050” on the deck and .045” on the intake flange.

This will knock some 7 CCs off of your chamber volume .

[jpg69bird]

Thanks for the detailed analysis Steve25. If I bring the 6X down to 87 cc's, will detonation be a concern with either cam? Once that last head bolt is tightened down, I don't ever want to get inside the engine again.

[steve25]

What over bore are you going with .030” or .045”?

[jpg69bird]

Originally Posted by steve25

What over bore are you going with .030” or .045”?

No more than absolutely necessary, so I'd hope for a max of 0.030".

[steve25]

Without knowing more details in regards to what your doing for pistons and there valve notch volume , your deck height, and your head gasket along with if you mill the heads I can tell you this information which should help some.

With a .030” over bore if you want a 9.5 to 1 compression you need a total CC volume above the piston at TDC of 113 CCs.


If you want a 9 to 1 compression then your total CC volume needs to be 118 .

Average CC volume for a head gasket is 9.4.

Average valve notch volume for a 4 valve notch piston is 6.7 CCs.

Average deck height volume = 5 CCs.

If you want to be fully inclusive then toss in 1.5 CC for top ring land volume.