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Thread: Engine Choices
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post #12 of (permalink) Old Jul 21st, 15, 07:45 AM
Larger Dave
Senior Tech
Dave
 
Join Date: Dec 2005
Location: Tampa, Florida
Posts: 4,705
Re: Engine Choices

That is the kit I would use with a 4.00 bore 350 block. I would verify the block is a large journal two piece rear main seal block before I ordered any parts. The SBC went to the large journal in 1967 with the introduction of the 350. At the same time Chevy continued to produce the small journal 283 (307) and 327 up until 1968 when all small blocks went to the large journal and had bolt holes in the head for the use of a long water pump that wasn't introduced until 1969.

The picture for the kit shows BBC pistons, and the description states that the it can have a number of different parts in the box (two possible cranks, three possible piston tops and three vendors offering bearings and rings). I suspect that those pistons are flat tops with deep valve reliefs based upon the negative eleven dome size. This kit offers a chromemoly crank and chrome moly H-beam rods with ARP 2000 series rod bolts (ARP's BIGGEST and strongest cap screws). H-beam rods do not require as much clearancing of the block as the cap screws are recessed. You should be able to run a cam with a lift in the neighborhood of a half inch at the valves. Any higher you might have to go to a smaller base circle cam. But in either case you always measure the clearance between the rod and the cam (I use a nylon plastic tie strap of about 0.050" inch thickness to verify there is enough room as a go no go gauge).

As far as balancing at home you can buy a rod balance jig for your scale to determine weights and grind them to match the lightest weight.

http://www.summitracing.com/parts/pr...FY2RHwodGa8JVg

The crank has to be spun with bob weights. A bob weight is a steel mass bolted to the crank throw that is equal to the mass of the piston, piston pin, rings (and the oil on the rings) as well as the reciprocating mass of the rod). This is where the art of balancing enters the process. The bob weight and rod weight depends upon where you determine where the reciprocating weight begins on the rod (less than half the weight is counted and you have to choose a point based upon years of experience). The electronic balancing tool used to balance the crank can detect a difference of a tenth of a gram. But it is a judgment call to determine the actual bob weight mass.

I can accept the weight of a dime spread across the entire reciprocating mass in variance (a little over two grams) as I run four bolt blocks that have been line honed and the registers verified for a tight fit. I tell my machinist to balance to a half a gram, which informs him that I am fussy about balance. But I also know that the process will only yield a plus or minus two gram balance with the equipment that he uses. Before any one gets excited think of the variables; oil on the rod pin offset, or even over balancing an engine for higher RPM operation. Economically you just draw a line and accept that level unless you have unlimited funds that the pros do.

I also grind a knife edge on my counterweights if I buy a cheap crank which throws the weight way off from the what SCAT said it is, so It has to be rebalanced (preferably without heavy metal but that is a better choice than the flat edge of the counter weight creating excessive windage. But once again every choice you make affects something else. Reduce windage and control the oil in a wet sump pan with louvers and scrapers and you reduce the oil needed to lubricate the cam (which is splash lubricated). So I then have to spend over a grand to buy Isky Red Zone solid rollers to lubricate the cam and the tappets. Like I said how fast can you afford to go? Building a reliable high horse motor isn't cheap. Most don't even concern themselves with a the bottom end. Concentrating their entire budget on the Heads and the Cam, the two items that most profoundly effect power.

Big Dave
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