View Full Version : compression question
03-21-2009, 11:29 PM
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?
03-23-2009, 01:28 PM
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
03-23-2009, 08:47 PM
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
03-24-2009, 10:29 AM
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.
03-26-2009, 04:55 PM
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?
03-27-2009, 07:54 AM
My Excell program calculates 10.64 with a 68 cc chamber and 10.94 with the 65 cc chamber.
03-27-2009, 08:13 AM
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.
03-27-2009, 01:27 PM
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.
03-27-2009, 06:22 PM
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
03-27-2009, 07:20 PM
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.
04-05-2009, 03:11 PM
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?
04-05-2009, 08:24 PM
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
04-05-2009, 08:59 PM
im using .027 cometic head gaskets .008 deck height,
04-06-2009, 04:35 PM
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
04-06-2009, 04:36 PM
You need a 63cc chamber to put you at 10.99:1
04-06-2009, 04:49 PM
I stand corrected, Mr Big and I have the same exact program and his calculation is dead on. 10.64:1.
Anyway your quench is perfect at .035" so don't get any closer! The piston would be you best bet to make things right. I know money doesn't grow on trees but we just did a 455 with Edelbrock heads and they flow as good as any Stage 1 SE T/A head and the chambers are 68cc to start. I don't know what kind of power you are looking for but these heads will make over 600HP with 11:1 Compression.
04-06-2009, 05:02 PM
I don't know what kind of power you are looking for but these heads will make over 600HP with 11:1 Compression.
That's getting pretty close to the limit of Buick
(non band-aid) reliability.
Did you mention what your plans were for this unit?
Unless you install a "lumpy" cam to bleed some compression down low, you may be into race gas only territory. Something to think about.
04-06-2009, 07:38 PM
04-23-2009, 11:14 PM
is it safe to mill a steel 430 head to a 63 cc chamber?
any idea what theyd have to take off?
04-24-2009, 12:00 AM
Ken, I had mine angle milled to a 59cc chamber (Stage 1 valves, somewhat unshrouded) in the late '80's, then had another 0.010" flat cut done to clean up some damage that happened at a later time. I don't remember the exact details of the original angle cut, but it was a lot of metal off the big side of the chamber.
There's no guarantee how much can be taken off a particular set...you should rely on a shop with some BBB experience on that one, as inspection will be the first place to start.
04-26-2009, 02:52 PM
thanks for the reply,
dont have any bbb specialists here but the 2 shops im dealing with do very good work and have built hard core just about everything but especially ford and chevy,my car is a 65 gs 4 spd converted to th400 built,3500 and 4000 converters strange 430 spool and axles 12 bolt,29.5/9 slicks,8 pt roll bar,glass hood/decklid,front/rear bumpers,me in it is 3600 lbs,drag only race gas ok.
no street time
car ran 11.97 in 1998 w/425 race nailhead
since havent had success w/ 455 (job changes) and diff probs have delayed progress,last year finally made attemt at bg,had no sucess,spun a rod bearing/lost oil pressure.
currently have 3 455's almost ready to build,i dont know how this happend just keep finding deals on parts that just happen to fit my exact needs,anyway
hope to get 1 done to run a few times this year
hope for 10.40-10.6 range if i dont get it this year illl be going back to the nailheads and hope for lower 11 ets w/ my new t/t roller rockers a 505 c roller, mickey tompson stroker 4.310 bore 4.014 stroke,balanced,brc forged domed pistons w/superlight pins,bbc 6.38 h beam rods,ati balancer,total seal rings ready for assy.
im not sure but i think 470 cid 13-1 comp. may be a contender for my 455!even my very well ported 194/150 chevy valve nailheads just dont flow good enough
probably 1 second slower than 455 anyway
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