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  #16 (permalink)  
Old 03-07-2014, 11:11 AM
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lets just say i cant return this what would i have to do to make it work? i know by milling i can get some compression but i didnt want to come in to trouble with pvc my 049 measured 119 ccs u guys let me know what other type of info you need and let yall know h118 .040 piston they look like flat tops with small dish in center with valve relifes

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Old 03-07-2014, 11:21 AM
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whats your budget?

if you have one, go with aftermarket heads. keep the same cam. figure up about what size chamber youll need to hit about 10.5:1 (if you go w aluminum heads)

skip white sells aluminum bbc heads at 895 assembled, but they are 118cc chambers.

im not as familiar with bbc as sbc, may have to change the pistons to get the compression where you want it.
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Old 03-07-2014, 11:23 AM
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Quote:
Originally Posted by techinspector1 View Post
The difference in head gasket thicknesses and the volumes they represent will not have enough range to make much of a difference. Head gaskets are for sealing the cylinder head to the cylinder block, not for adjusting the static compression ratio. You do that with piston crown configuration, piston deck height and chamber volume.
For over 50 years Ive been using different head gaskets and shims to change compression from track to track and when I was on pit crews it was done all the time going from 8.5 with a thick gasket (depending on its thickness) to 8.75 and maybe 9 isn't that hard!
4cc raises the compression almost .4:1". (Thats point 4 to 1 !) .004" is equal to 1cc difference in chamber volume!

Gasket thickness changes the deck clearance so to speak to the top of the gasket and is figured into the equation for compression so is piston expansion and blow by and cam timeing!!!!!

Jester

Last edited by painted jester; 03-07-2014 at 11:29 AM.
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Old 03-07-2014, 11:24 AM
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also, you may be able to source a set of used 396 bbc heads and use them to up your compression.

ill let jester or tech who probably a lot of hands on experience with these builds guide you down that path.
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Old 03-07-2014, 11:30 AM
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Quote:
Originally Posted by ss454lemy View Post
lets just say i cant return this what would i have to do to make it work? i know by milling i can get some compression but i didnt want to come in to trouble with pvc my 049 measured 119 ccs u guys let me know what other type of info you need and let yall know h118 .040 piston they look like flat tops with small dish in center with valve relifes
H118-040 pistons are domed, not dished. If you have dished pistons, they are not H118-040 pistons. Let's go back to zero and start over please.
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Old 03-07-2014, 11:51 AM
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H118-040 pistons are domed, not dished. If you have dished pistons, they are not H118-040 pistons. Let's go back to zero and start over please.
h518cp .040 sorry
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Old 03-07-2014, 11:58 AM
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h518cp .040 sorry
Get a monitor to change your mistake!! people don't read whole threads and may miss this correction!! and post wrong recommendations!

Jester
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Old 03-07-2014, 01:59 PM
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h518cp .040 sorry
With H518CP-040 pistons and 119cc chambers bolted to a 454, the static compression ratio is 7.52:1.
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Old 03-07-2014, 02:15 PM
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Quote:
Originally Posted by techinspector1 View Post
With H518CP-040 pistons and 119cc chambers bolted to a 454, the static compression ratio is 7.52:1.

ouchhhhhhhhh

cheapest bet at this point may be to order some dome pistons and keep the heads and cam you already have. is the engine out of the truck?
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Old 03-07-2014, 02:27 PM
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Quote:
Originally Posted by painted jester View Post
Get a monitor to change your mistake!! people don't read whole threads and may miss this correction!! and post wrong recommendations!

Jester
how do i do this???

Quote:
Originally Posted by techinspector1 View Post
With H518CP-040 pistons and 119cc chambers bolted to a 454, the static compression ratio is 7.52:1.


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Originally Posted by clwhoops44 View Post
ouchhhhhhhhh

cheapest bet at this point may be to order some dome pistons and keep the heads and cam you already have. is the engine out of the truck?
motor is in the truck i was just planning a heads and a cam till i get the blower but i see these big blocks are more complicated then i thought !!! my budget is already running out i was planning on doing this under 1000 bucks im already 850 in it and now im in trouble cuz what i have ordered is wrong....
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Old 03-07-2014, 02:40 PM
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youre in a tough spot.

you have four options

1. change the pistons

2. change the heads

3. change the cam

4. borrow 4 grand and do the blower upgrade now

none of your options are cheap, but the way it sits, the local ricers will turn donuts around you.
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Old 03-07-2014, 02:41 PM
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there the piston... some one mentioned a turbo right???? this i already have left over from an old build!
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  #28 (permalink)  
Old 03-07-2014, 03:31 PM
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Itís important to make a distinction between static compression ratio ( which I think is useless) and dynamic compression ratio. The static compression is what you measure on an engine stand, Itís a very simple mathematical equation between the volume above the piston at the bottom and top of its travel that builders use for their blue print. But real world Dynamic compression is whats important but much more difficult to measure because it depends on how efficiently the cylinders are filled when the engine is running. Factors such as camshaft timing (specifically the intake valve closing point) and the tuning of the induction system, forged or cast piston expansion rates and piston to cylinder clearance, ring gaps and efficiency, intake design(ram effect) , header scavanging Etc Etc!!! All have a major impact on dynamic compression!!

Dynamic compression ratio is what really counts in a racing engine or 1 built for perfomancebecause it determines the actual cylinder pressure. Think of two engines that are identical except for their camshafts. The engine with the shorter camshaft duration will typically have higher dynamic compression at low rpm because the intake valve closes earlier on the compression stroke. The engine with the longer duration camshaft will have less dynamic compression because its intake valve closes later after the piston has traveled farther up the cylinder. On the other hand, if the long-duration cam does a better job of filling the cylinder at high rpm than the short-duration cam, more air and fuel will be trapped in the cylinder and the resulting dynamic compression ratio much higher! And the changes go on when installing different intakes, headers and on and on!!

There's a little schooling for ya LOL! I hate hearing about STATIC compression LOL its a great tool for getting parts together and planing a build but worthless when all contributing factors are figured in when the complete engine is together and running at operating temperatures! That's not an opinion that's physics!!!

Now you have the OP thinking he needs to scrap his build and start over LOL!

Jester
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  #29 (permalink)  
Old 03-07-2014, 03:49 PM
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Good luck if you use a flat tappet cam.
Make a wise choice about the future of the engine before buying the wrong parts now
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Old 03-10-2014, 06:39 AM
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hey guys im going to try and change that cam what will u guys recommend i get nx268h??? smaller version of what i got in the first place or the nx274h?.. thanks for the help so far !! greatly appreciate it...
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