Hi,
I need your help.
I need to rebuild my truck 350 engine and I need a game of pistons and rings in or on 30.
1.- I have the stock iron heads but I don´t know if are 72cc or 76 cc ?
I want to have a 9.5 of compression ratio or near with cheap game of pistons to daily use.
2.- What pistons and head gasket are for me ?

Thanks and regards

 

Eduardo, I see by your post that you're down in Mexico, land of my ancestors... Unfortunately, the quality of gas down there is variable, to an extent that a 9.5 CR with iron heads may be pushing it farther than the engine is willing to tolerate. Be that as it may here goes... Getting the squish clearance (head to piston clearance) down to around .040" becomes very important. Unfortunately, Chevy did you no favors by leaving the pistons .025" down in the bore at TDC to start with. Short of decking the block, or offset grinding the crank to 3.50", using steel shim head gaskets is your only cheap way to approach this. Last I checked Chevy has three gaskets .016, .018, .022 all of these have a compressed height .003" inch thicker, (yes - thicker) than their metal size guage. None of these will get you down to .040" but the thinest is the closest. Problem with steel shim gaskets is they demand very smooth very flat surfaces on the block and head.

From then, on acheiving your goal will depend on the heads chosen and the combustion chamber size. Keep the pistons flat, or a very short dome, since domes can hurt more than help. Using a 350 bored .030 over, flat top pistons with -7cc's valve relief, .016" gasket and .025" deck height and 72cc's chamber yields 9.21:1, a small dome +5cc's with 76cc chambers is 9.30:1, using a small dome with 72cc chmbers bumps it to 9.70:1.

Check out the Popular Hot Rodding website. They ran a series on getting the most out of 87 octane gas. Remember - running less spark lead may hurt fuel economy, but could very well save your pistons from melting. Good Luck!

 

Norm:

Thanks for your answer, is very useful.
I have some questions:

1.- How I can know if my heads are 72 or 76cc.
2.- I can´t find the article that you told me (hotrodding site ).
Can you please send me the url ?
3.- In my country don´t exist more the leaded fuel, only unleaded.

Let me know
Thanks and Regards

 

Eduardo, My interest has always run to the performance side, so I'm no expert on the range of head castings and their identification. There is also variation in chamber size in all the Chevy heads so short of measuring there's no way to determine chamber size accurately. You can identify the different castings on early production iron heads in a number of ways, but dissimilar heads have only slightly different casting markings and since I don't have any pictures your best bet is to look at some of the books that are available on the subject.

In general, you'll see the difference in the position of the spark plug in the chamber, the spark plug is further from the valves in the "open" chamber style heads which can run as high as 78cc and the plug hole is at the very edge of the chamber. In the "closed" chamber heads, which run as low as 68cc, the spark plug hole is much closer to the valves and away from the chamber's edge.

Sorry about the article mixup I made a mistake. The articles are in Chevy Hi Performance (www.chevyhiperformance.com). Select the "Top 40 Stories in the last 5 Years", then Engines. The three articles, are the Agent 87 series near the bottom of the list.

There are more "consumer advocates" in the US than Mexico and there are plenty of product liability lawyers itching to prosecute cases, so the oil companies and their distributors and the state air pollution borads are very rigorous about enforcing fuel standards. In Mexico, things are more lax and the oil companies can be less careful when blending fuel, this leads to a larger variation in octane rating for the same fuel in different places at different times.

The use of unleaded fuel required hardened valve seats. If your truck was made to use unleaded then it has hardened seats. If not make sure that who ever does your heads installs hardened seats.

 

Thanks for your answer

Can I identifie the heads by #in the head ?
I have 3 engines to choose, then I want to know if all my heads have the same cc.

Another theme, why the iron heads can handle the same cr as the aluminium heads ?
Regards