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Old 03-28-2013, 02:20 PM
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The chamber volume ain't all you have to be worried about cap'n.

Here are some quotes from shop owners.....
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"882's do have hardened seats!. That is one reason they are so crack prone. They were one of the first of the factory hardened seats and before GM induction seat hardening was perfected.

882's are the "Best" of the worst heads. They are the heavy weight casting. As noted, they are crack prone thru the center exhaust seats. They will flow fairly well if the intake side is port matched and the upper part of the exhaust port is blended. Bowl work is also needed, as is the case with most Chevy production heads.

There are actually three series of these castings. One has large clean intake runners and excellent bowl cutting from the factory and 1.94 intakes. Another has terrible intake runners, bowls. seat area. The third is a 1.72 intake, 3/8" stem exhaust valve head that was used on 2bbl. truck/pass car applications. I actually prefer these castings. As, they are seldom cracked and I have to cut them for guides and big intake valves anyway."

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"I willl argue with that one as those OLD heads were produced from 1970 to 1980 and DID NOT HAVE INDUCTION HARDEN SEATS. As most of the 624 castings that are the light weight casting which are prone to crack and have hardened seats. And over the years we have put enough seats in those 882 heads due to the unleaded fuel.

An easy way to tell if those heads have induction hardened seats is to look where the exhaust manifolds bolt on and if they have 7 bolt holes or the pad for the extra bolt hole they will have the factory harden seats which I believe came out in 83 or 85. And as far as I know there were no 882 with that bolt pattern that I have seen. HMMMMMMMMMMM"

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" I have been an automotive machinist and engine builder for the last 21 years and every 882 I've ever seen has hardened exhaust seats. GM began changing engines over to be compatible with unleaded fuel in 1974.

I have fixed more 882 heads than I care to remember. The center two exhaust seats are the most prone to cracking. Personally, I believe this is due to both center exhaust bowls being open to the exhaust crossover. This seems to put a lot more heat in the center of the head.
Also, the 882's were installed on Chevrolet engines from 1974-1980. Before that Chevrolet used the 993, 487, 336 and 997 castings used from 72 to 84 on the lower compression engines."

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OK, back to my personal observations. 882 heads are published at 76 cc's, but I have yet to see a production head that will pour right on the money on all chambers. I'd bet those heads you have are more like ~78 cc's and may vary 1-2 cc's between chambers.

Next is the piston compression height. Stock 327 pistons are 1.675" from the centerline of the wrist pin to the crown. If you're not careful when you choose pistons for a rebuild, you can end up with "rebuilder" pistons, which will be ~0.020" shorter. This puts the piston down in the bore further when the piston is at top dead center and can contribute to detonation because of a lack of tight "squish" if you're running enough static compression ratio.

The last thing I'll mention is the piston deck height. This is the dimension from the crown of the piston to the block deck where the heads bolt on. Stock production blocks were produced with a block deck height of ~9.025", so that when the stack of parts, 1.675" for the piston, 5.700" for the rod and 1.625" for the crankshaft radius were installed in the block, they totalled 9.000" in a 9.025" block. This left 0.025" piston deck height. When the motor was assembled at the factory with a shim head gasket ~0.022" thickness, the squish (piston crown to underside of cylinder head with the gasket in place) was ~0.047", which allowed the piston crown to "squish" the air/fuel mixture that was above the crown, across the chamber in a "jetting" action. This turbulent action homogenized the entire mixture, eliminating lean and rich spots in the chamber and allowing the mixture to be burned completely and smoothly for a very efficient burn. Many fellows have found that they can operate on a cheaper fuel grade without detonation when the squish is engineered properly on the build. Anyway, if the block is 9.025" and a rebuilder piston was used, then the piston deck height is ~0.045". Now, if you add a composition gasket (~0.040"), the squish is ~0.085" and is ineffective. I'm not saying your motor will detonate. At your current SCR, the motor is a long way from being detonation sensitive.

Anyway, long story short, I agree with Mr. Peabody that you are probably in the 8.0:1 to 8.5:1 range of static compression ratio. This SCR will support only a very short camshaft, usually the first one on the list of any cam grinder's catalog. Too much cam combined with a low SCR will make a very soggy motor and you'll be an unhappy camper.

Here's an example of a "rebuilder" piston. Remember I said that a stock 327 piston is 1.675" compression height? Look at the specs on this piston.....
http://www.summitracing.com/parts/sl...make/chevrolet

Here's an example of a cam that I might use in your motor....
Crane Cams part number 113971
Brute low end torque, smooth idle, daily usage, fuel economy, 1600-2200 cruise RPM, 7.75 to 8.75 compression ratio advised. (50 state legal, pre-computer, C.A.R.B. E.O. D-225-18)
Grind number H-248-2
Operating rpm's 800-4600
Duration @0.050" tappet lift 192/204, duration @advertised 248/260. Lobe separation angle 112, valve lift 0.400"/0.427".

Last edited by techinspector1; 03-28-2013 at 02:42 PM.
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