compression question

[all455]

hello
any guess as to my compression ratio?
69 430 heads stg 1 milled.030 (valves unshrouded)
weiseco dished and notched forged 4.350
3.9 stroke .027 cometic
.008 under deck
if below 11-1 what would you sugg to get it over 11-1
are .018 steel gaskets avail. anywhere?
thx
ken

[Bigwedgie]

You quench is right on so I would not go any thinner on the head gasket. Why did you buy a dished piston? A flat top would have put you right in the ball park.

O.K. I'll tell you exactly what your compression ratio is if you can answer a couple questions for me.

1.) CC's of the head
2.) CC's of the piston

Examples - Head = 66cc's, Piston = 16cc's Final compession is 11.25 to 1

[all455]

hi thx for the reply
the weiseco box reads #91594473 14dished455buick
i have no cc kit,going from what you said piston could be 14cc and head is 65-68 cc range so im closer to 11-1 than 10-1,thats what i was hoping for.
maybe ill call weiseco and verify cc to be sure,dish is only 1/2 piston top,other half is only notched for valves
thx alot
ken

[Bigwedgie]

With a 68cc Chamber and a 14cc dish my caculator said 11.31:1. I guess that is why you bought a dish piston. Now that is for a 455 with (3.900" stroke) x (4.350" bore).

I use 10cc for the gasket and the piston in the hole .008" plus your 14cc piston. Then I add the chamber size 68cc.

If you call Weisco ask them about the total cc's of the piston if it is 14cc then the only guess is the chamber size. In the future I would cc at least on chamber just to know where you are at.

Bottom line is it sounds like your real close to your 11:1 compression ratio.

[all455]

today i called wiseco they said these and all wiseco dished 455 buick forged are 22 cc dish
as a baseline i would use 68 cc for the head
is this 11.08-1?

[MR BIG]

My Excell program calculates 10.64 with a 68 cc chamber and 10.94 with the 65 cc chamber.

[DaWildcat]

If you really want to go nuts on the calculation, we'll need:

exact chamber volume with spark plug in place
actual head gasket inside diameter
actual cylinder bore diameter
actual piston diameter above top ring
height of upper cylinder chamfer
width of upper cylinder chamfer
distance from piston crown to top ring

While many of the above items don't contribute much volume by themselves, taking all of them into consideration will give you a better understanding of what's up. Admittedly overkill for most.

Devon

[No Lift]

I'd say forget about thinner head gaskets. Right now you're at .008" deck and .027" which adds up to .035" piston to head clearance which I believe is close. You're probably pushing your luck now especially if the pistons are loose in the bore. Maybe somebody knows different.
Mill the heads if you have to. It won't cost any more than the head gaskets.

[all455]

thx for the replies
ill post my chamber cc when i get them from the machine shop next week
i hope under 68cc
since these were milled .030 1 time already from stock, could i go more?
if so, how much more?
i already know i need shorter pushrods and shave the intake as needed
ken

[DaWildcat]

Don't cut the intake manifold. If thicker aftermarket composition intake gaskets don't take care of bolt/port mismatch, have the shop take some material off the intake side of the heads.

If you mill the intake manifold to match your heads, that intake won't work on another set down the road.

Devon

[all455]

hi
still no reply as to my chamber volume,if it is 68 cc im gonna be 10.3 -1
too low for me
heads are already milled .030
how much more would i need cut off to get up close to 11-1?

[ap1672]

I don't think you can get to 11 with those pistons.
If you zero deck the block your up to 10.5 or so. (with .04 head gaskets)

A piston swap to the flat 7cc wiseco's will get your around 11.8

[all455]

im using .027 cometic head gaskets .008 deck height,
ken

[Bigwedgie]

Mr. Big and I must have the same program but he forgot the piston .008" in the hole.

I have with the piston @ 22cc and the head at 68cc CR=10.48

[Bigwedgie]

You need a 63cc chamber to put you at 10.99:1