Thread: help....thoughts? SBC 400

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Sealed Power 400AP pistons would not be my choice. They are what is known as a "rebuilder" piston, because the compression height is 0.020" shorter than the blueprint compression height for stock pistons. Another reason is that they are designed for use with the short 400 rod (5.565" center to center) that I wouldn't use. The side thrust was manageable when the 400's were new and being fitted to station wagons and suburbans and such, because the driver's of those vehicles were not interested in swingin' the crank to 6000 rpm's. But higher revs used in the hot rod fraternity will need a longer rod, 5.7" or 6" to help minimize piston side-loading and scuff. I don't like having to use a spacer rail to prevent snagging the oil ring in the wrist pin bore, so I shy away from using 6" rods, preferring 5.7" rods where the oil ring does not intersect the wrist pin bore.

The 24cc dish on the 400AP piston leaves a lot to be desired also. It leaves little or no flat plateau on the piston crown to mate up with the underside of the cylinder head to facilitate squish. I also don't see myself using a cast piston at 6000 rpm's. Hypereutectics are also cast, but have an overage of silicon in the mix that makes them superior to standard cast pistons in my opinion.

You can measure the block deck height yourself if you own a 12" caliper, either a dial type or an electronic type. Even a simple vernier caliper will work if you know how to read it. Here's one on Buy It Now for 33 bucks.
12" 300mm Precision Vernier inch Metric 4 Way Caliper | eBay
Here's one with a case for 29 bucks....
Inside Outside Vernier Caliper w Case 12" | eBay
Here's a cheezy offshore dial caliper for 49 bucks.....
12" Precision Stainless Steel Black Face Dial Caliper New | eBay
My best advice is to sidetrack the electronic units. My experience is that every time I reached for my digital, the batteries were dead.

Hook one jaw onto the machined surface of the main bearing bore like shown and hook the other jaw of the caliper over the block deck where the heads bolt on. Add 1.420" to the measurement you get from the calipers. 1.420" is roughly the radius of the main bearing bore on a 400 block. So, for instance, if you read 7.605" on your calipers and add 1.420" to that, you find 9.025", the blueprint dimension for block deck height for all Gen I small block Chevies. Do this measuring on all four corners of the block to find if the block was milled catty-wampus at the factory. It's not at all unusual to find the decks machined uphill or downhill from one end to the other. Simply visualize a chip that lodges itself in the register when a new block is being loaded into the mill at the factory and you can see how easy it would be to mis-machine the block by ten to fifteen thousandths or more. (0.010" to 0.015")
http://www.jamisonequipment.com/picPage/BHM-24-1.gif

Note of caution: Look at the jaws of a caliper. The last 1/4" or so is sharpened like a knife edge. This is to allow the machinist to read the diameter of a circle or other curved part. If the jaws were thick all the way to the end of the jaw, you would get an erroneous reading because of the gap between the part being measured and the jaw of the caliper. What I'm getting at is, use only the very tips of the jaws of the caliper to measure the block deck height. Eyeball carefully to see that you have the same amount of jaw on the parts on both jaws of the caliper.

For the rest of you fellows out there who are interested in measuring the block deck height of your SBC, see page two here, where it says "Main Journals". This is the measurement less bearings, just the raw bore.....
http://www.theengineshop.com/product...f_file-124.pdf

I was busy typing and did not see your posts 5 or 6 until after I posted this.

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