ok i've run into a snag in my project. im currently out at sea and im lookin forward to getting back to drop my motor in. its all ready to go all i gotta do is slap on the oilpan heads intake and acces. however the problem is i dont have enough money to buy a set of heads at all. i will eventually get a set world sr torquer heads when i get the chance. 76cc chamber with 2.02 1.60 valves but im wondering if my stock lg4 heads would work under the circumstances. the engine is a 60 over 350 and i calculated to c/r to be around 12/1. i know thats really high but would it work until i can afford the new heads?

 

It is impossible for your compression to be 12.0:1 with 76cc heads. First of all, you have to get more info about the pistons adn I assume they must be domed pistons and find out the cr for 64 cc heads and for 76 cc heads. And if compression is high anyway, why would you want sr torquer heads. I would do a little more research fist of all and find out what can be done with your stock heads to head with breathing. Don't mean to sound rude, but I would definitely do more research from the person that built the engine or the manufacture of the pistons.

 

Yeah I dont think you're compression ratio is that high, unles you put a stroked crank in it.

 

Read what he said again:

"...im wondering if my stock lg4 heads would work under the circumstances. the engine is a 60 over 350 and i calculated to c/r to be around 12/1." {emphasis added}

ksith, what pistons, deck height, and head gasket thickness (volume) did you assume?

 

12:1 is too high for pump gas and iron heads, you would need around 10:1 to run iron heads.

 

It's HARD to get to 12:1, even with the little LG4 heads. You'd need massive domed pistons to pull that one off.
Lets see the math, as five7 mentioned, we can correct you.
You can port the LG4 heads, and you'll be off to the races. They can be as good as the SR torquer's at least.
Plus you can port out the chambers to help drop your cr, if need be.

 

i didnt figure a dome or dish into the piston when i calculated the c/r. i also figured a .040 gasket thickness, and a gasket bore of 4.100. thats a set of felpro gaskets i can get from summit. i assume the builder is using a standard 4 valve relief piston no dome or dish other then what would be there like a stock piston. thanks guys for your help im trying to figure this out and 12:1 did sound high. this is the site i used numbers i plugged in are as follows http://www.torinocobra.com/Randys_tools.htm
4.060 bore, 3.48 stroke, 8 cyl, .040 gasket thickness, 4.1 gasket bore, 58 cc chamber, didnt figure in the rest cause i dont know it being out to sea in a giant ship. i'll email the guy and see if he can get me the info though

 

The only data left that you need is the piston relief volume ( or dome ) and the piston deck height. Using standard values, piston relief comes in around -5 to -12 cc and deck height at stock value is about .025" below deck.
Using a 5cc relief you'll get 10.6:1 . Using a 12 cc relief will get you 9.8:1.
Given those values it's really going to depend on the cam you choose. A short duration cam will really jack the cylinder pressure with the relatively high static compression ratio (for iron heads maybe too much) however a longer cam will need the higher static ratio to perform.
I currently run a 9.9:1 static compression ratio with a 218* @ .050" cam that's 4* advanced and Vortec heads. That's as far as I care to go. As it is I require 94 octane fuel and have to keep an eye on engine temperature. It'll ping only occasionally so it's dicey sometimes.

 

Yes they will work and no the cr will not be 12:1.

If the pistons are .045" down the bore at TDC use a 4.166"x .041" gasket
If the flat top pistons are .025" down the bore at TDC use a 4.166" x .051" "corvette gasket"

Use a high performance application spark plug like a Champion RV8C or Autolite 144.

If you were to fully home port your LG4 (#416 or #081) 58cc heads for improved airflow and fit them with new larger 1.94x 1.60" valves, and drill and pin the rocker studs, you'll find the performance very good. Rivaling and/or exceeding the airflow and power of a S/R type head at less cost.
The process of fitting larger valves in these heads (relieving the combustion chamber wall around the larger valve diameter) makes the chamber volume larger. 61-62cc finished chamber volume is typical when all done.

 

this is the cam im using CCA-K12-262-4 off summit

 

Here's the data used to calculate your static and dynamic compression ratio.
Bore. 4.060"
Gasket 4.1" x .040"
Chamber volume 58cc
Stock rod 5.7"
Deck height (assumed average stock). .025" below deck
Piston volume ( 2 valve reliefs) 5 cc
262 Comp cam adv duration 262 intake (intake closing angle 61 abdc)

Staic C.R. 10.69:1
Dynamic C.R. 8.69:1

With the short cam ( and the values supplied or assumed ) you won't be able to run that engine on anything short of racing fuel. A dynamic compression beyond 8.5:1 appears to be the realm of a racing engine and isn't suitable for the 'street'. The term street is subjective. Works for some but not for all.

 

dicey. Did he zero deck the block? If not, add another .020" onto that, since they are aftermarket pistons, and most likely have a lowered compression height. Also, a 4.100" gasket is a "305 gasket", most 350 gaskets are 4.150 or 4.166".

 

The deck height should be measured to be sure. I'm using Speed Pro H345NCP 4 relief piston to calculate deck height based on my own block which hasn't been decked. That works out .025".
The 4.100" gasket was supplied by ksith.

 

ok so if i was to open up the combustion chamber that would help things out then im guessing right? if thats the case i'll just have the guy open up my heads and install larger valves and open the c/c. might as well port and polish them too if the price is right.

 

Checked my books. Found most 350 gaskets are 4.100". Anything beyond that and you run into sealing problems with the water jacket holes adjacent to the cylinder bore. (source: Kevin McClelland @ Chevy High Performance)
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If you end up with a chamber volume of around 64 cc then you should be able to run many different combinations. There are lots of 350's with 64cc heads.

 

That's a new one on me. Any gasket set/kit i've bought came with a 4.150" or 4.166" gasket. Unless it's a gasket from a parts store, specifically meant for a 305. oh well, it's small potatoes.

 

Hey Sonix,
I dougled checked my source. Looks like aftermarket gaskets like FelPro ARE 4.166". It's factory gaskets that are 4.100". The same relationship to the water jacket applies however it does make a difference in the c.r. calculation.
I'll have to check on my own Corteco gasket (.028") and double check my own c.r.
Thanks for the heads up.

 

ah, yes! Steel shim gaskets would be 4.100", i'll buy that. But I think most of us are using composition style fel-pro type gaskets. Not many people trust the steel shims to seal well, unless block and heads are decked ultra flat.