SBC identification

[ocezam]

The SBC in in my '32 has engine ID code 3970010 on the left rear of the block. Apparently this ID's it as a 350ci. The suffix code on the right front of the block is "TDS". According to two internet sources this ID's it as from a 1980 3/4 ton pick up, 170hp manual trans.

I'd like to put a set of aluminum heads on it. Without tearing it apart first, can anyone tell me what the chamber volume may be on the stock heads, and/or wether the piston tops might be flat or dished?

Thanks

[ocezam]

I'm getting conflicting data on the head casting numbers, they are 14014416. According to this source Chevy cylinder head Identification - Small block casting numbers, the chambers are 64cc. Several others are saying 64cc.

Anyone shed any light on this?

If the chambers are indeed 58cc, that really makes my head choices minimal.

[robot]

TDS suffix is a 1980 like you said but it is a 1/2 ton 2 wd with a manual tranny, 170horse LS9 RPO with a 4bbl carb and federal emissions.

[techinspector1]

Pop a valve cover off one of the heads and read the casting number. Then scroll down on this page to "SBC Heads" and find your casting number and description. Being a low hp motor, I would expect the chambers to be 76cc's (Probably 333882 casting number).
Chevy Small Block V8 Casting Numbers - Mortec

Your motor came from the factory with steel shim head gaskets(about 0.020" thick), which work great with iron heads. Aluminum heads don't like steel shim gaskets because they move around a lot more than iron heads and could crack due to the incompatibility with the iron block. Composition gaskets (about 0.040" thick) pose a problem though, with the squish/quench clearance on a stock block.
Here's the problem: When your motor was produced at the factory, the piston deck height (distance from the block deck to the crown of the piston, with the piston at top dead center) was about 0.025". In other words, the block deck height (distance from the centerline of the main bearing bore to the flat surface of the block where the heads bolt on) was blueprint dimension 9.025" The stack of parts used in the motor (crank radius of 1.740", rod length of 5.700" and piston compression height of 1.560" added up to 9.000", so that the piston was down in the bore 0.025. Using a steel shim gasket of 0.020" thickness, added to the piston compression height of 0.025", meant that the piston missed hitting the bottom of the head during operation by 0.045". That dimension is called squish/quench.

Now, you are planning to use aluminum heads, which will not tolerate a steel shim gasket (they move around a lot more than iron heads and are likely to crack if held too rigidly), so you have to use a composition gasket of 0.039" to 0.041" thickness (Airflow Research recommends a Fel-Pro 1003 at 0.041" thickness) and that puts the squish/quench at 0.066", which is too wide to generate a good squish, making the motor more detonation-prone on pump gas. The tighter the squish, the less chance the motor has of detonating and the more horsepower the motor makes. Us hot rodders aim for 0.035" to 0.045" squish.

The whole reason I'm telling you this is that you will have to take a cut on the block decks and shorten the block deck height in order to run the thicker gasket and still have a good squish figure. If you cut the block to zero deck (the piston crown is flat with the block decks with the piston at top dead center), then using a 0.041" gasket will produce a 0.041" squish and you'll be golden. Of course, cutting the decks means a complete teardown, so you may just as well plan for a 0.030" overbore and fresh pistons that will work well with your new heads.

I would shoot for an intake runner volume of 180-185cc's if purchasing heads for a 350. Smaller than that and you may as well keep the iron heads. Larger than that and the motor will be a pooch on the bottom end, where you do most of your driving.

If you want to learn how to do this swap properly, get back to me when you have a head off and I'll explain how to determine the volume in the piston crown so that you can purchase heads with the proper combustion chamber volume to make the proper static compression ratio for the fuel and cam you plan to use.

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[techinspector1]

I'm getting conflicting data on the head casting numbers, they are 14014416. According to this source Chevy cylinder head Identification - Small block casting numbers, the chambers are 64cc. Several others are saying 64cc.
Anyone shed any light on this?
If the chambers are indeed 58cc, that really makes my head choices minimal.

At 170 hp, I'd bet a nickel the heads are 76cc's stock. If your motor has 14014416 heads on it, then someone in the past has bolted 305 heads onto your 350 to raise the static compression ratio.

Don't worry too much about static compression ratio. Going from 8.0:1 to 9.0:1 gains 4% power. Going from 9.0:1 to 10.0:1 gains another 4% power, and so on. Headers and cam will return way more power than worrying about static compression ratio. But you must know what the static compression ratio is exactly, because you have to match the cam timing to the SCR to have a runner.

Here is some information about matching a camshaft to the static compression ratio of a motor.....
http://www.crankshaftcoalition.com/w..._compatibility

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[ocezam]

If your motor has 14014416 heads on it, then someone in the past has bolted 305 heads onto your 350 to raise the static compression ratio.

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Yeah, that's the conclusion I'm coming to also. It's hard to believe the motor has high compression. Sounds stock. Drives stock.

If I were to put 64cc heads on it. It would lower the current compression which doesn't seem high to me. I was looking forward to bolting on some aftermarket heads but I see no point in it now. It seems like this would lower the compression enough to cancel out the benefits of a performance head.

Suggestions?



....

[techinspector1]

Any aftermarket aluminum head will flow circles around those 305 heads and make more hp, regardless of static compression ratio. It's all about filling the cylinder to make a bigger bang.

If this is a budget deal, then I would opt for some L31 heads, small flat tappet hydraulic cam, using ZDDP in the oil and a good set of 1 5/8" headers. Then, as budget permits, a high-rise, dual-plane intake such as the Edelbrock 7101 or Weiand 8150 and a 750 vacuum secondaries carb.
Here's the scoop on the Vortec heads. They are thin wall castings and tend to crack when coolant temps get too high, so if you go shopping for them, make sure you include magnafluxing in the deal with the seller before you take ownership of them. Then use a cam like the circle track guys use, Isky makes a ton of the 0.420" lift rule cams. Retainer to guide clearance limits lift with the stock arrangement, unless you want to spend the dough to completely re-engineer them and if you're going to spend that much money, you might just as well buy aluminum to begin with, so stay at 0.420"-0.430", use the stock guided rocker arms and stock springs, bolt 'em on with steel shim gaskets and you'll be fine.
http://www.crankshaftcoalition.com/w...ips_and_tricks
http://www.crankshaftcoalition.com/w..._cylinder_head

Depending on the piston crown configuration, you should be somewhere around 8.5:1 to 9.0:1, so a cam something like the Crane 10003 or Isky equivalent should do the trick.
The stock L31 350 had, I believe, 9.4:1 SCR with flat-top pistons. If your pistons are flat-tops, then use a little more cam, like a Crane 10004 or equivalent. The retainers should clear the guides with a 0.440" valve lift cam, but you will want to check clearance to make sure. If there is less than 0.050" clearance at full lift, take the retainers to a machine shop and have 0.050" "surface ground" off the bottoms of them.
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