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Stroker 305 Engine Build Questions & Much More - What's Your Problem?

Valve Relief
Ronald Cooper, via I acquired an '86 5.0 small-block Ford with the intent of building a low-buck track car. Upon teardown, I discovered flat-top pistons without valve reliefs and heads with a bad combustion chamber. I was told by my head shop that the valves are sunk in the chambers to provide adequate piston-to-valve clearance. I planned to use the flat tops in a nonroller block with a set of 54cc, fully ported 289 heads. My cam has the required duration and only 0.448-inch lift. The factory roller cam specs out at 0.444-inch lift. Is there enough valve-to-piston clearance with older Windsor-style heads without notching the pistons?

Jeff Smith: There is much more going on here than just comparing valve lifts. If I'm reading your question correctly, what you're really asking is whether you can just bolt together the engine and not check valve-to-piston (V/P) clearance. The short answer is if you're a gambler, sure-why not? But the better question is if you are going to the expense of bolting together this engine with a different set of heads and a new cam, why wouldn't you spend the extra half hour it would take to measure valve-to-piston clearance. The process is really simple-all you need is a little bit of modeling clay and some patience. Before we run through the procedure, let's also touch on all the different variables that can affect V/P clearance.

Clearly, valve lift is the most important change in this situation, and since it's a fairly simple concept, we don't need to spend much time with that. Changing rocker ratio will also increase valve lift, so you need to account for the rocker ratio as well. The idea that sinking valves help V/P clearance is true in theory, but that's not a good reason to do this, since it kills flow-so we'll just ignore that one. The valves on your early heads are still in the same position in relationship to the piston as the later model heads, so little has changed there. Did you increase valve diameter? Larger valves are often culprits. Another point worth mentioning is piston deck height-or how far the pistons are below the deck surface of the block. If the engine has been decked, this will reduce the V/P clearance. Head gaskets are another point worth discussing. A thick head gasket will increase V/P clearance while a thin gasket will reduce it. And, of course, you have the valve pockets in the pistons.

Another important item is cam phasing. This is why it's important to degree the cam when it's installed so you know where the intake centerline is, for example, in relationship to the pistons. Advancing the camshaft opens the intake valve sooner and closes it sooner, so this move generally decreases intake V/P clearance and increases the room for the exhaust valve. Conversely, retarding the cam usually decreases V/P clearance for the exhaust valve and increases it for the intake. The best procedure is to degree the cam so you know it's installed properly and then check the V/P clearance.

The easiest way to check V/P clearance is to lightly oil the valves and lay down some modeler's clay in the piston valve reliefs. Then install the head gasket you will be using and cinch down the head. If the engine is using hydraulic tappets, use a solid lifter, since hydraulic lifters tend to bleed down and produce a false reading. Set the lifters with zero clearance on the rockers and slowly turn the engine over about four complete revolutions. Then remove the head and carefully cut the clay in half. The section width of the clay will indicate the total V/P clearance. If the clay is squished completely out-or worse, the engine doesn't turn over-then, as they say, your problem is obvious.

LS Oiling
Randy Yauck, Flin Flon, Manitoba, Canada: Is there a way to modify an LS engine to priority oiling like the GM cast-iron LSX and the aftermarket blocks? Can piston oil squirters be added also? A friend gave me a 4.8 out of a wrecked pickup. I will pull it out soon. If it needs work, I'll stroke it with a 5.3 crank.

Jeff Smith: There might be a way to modify the block, but why would you want to? Unless you plan to spin your LS-series engine into the stratosphere, there's really no reason for this modification. If you look at the following illustration of the stock LS oiling circuit, once it travels up the pickup and through the crank-mounted gerotor oil pump, the oil travels down a large oil gallery on the driver side of the block all the way to the rear of the engine to the oil filter. After the filter, it runs uphill to the main oil gallery located in the center of the engine. This gallery feeds the crankshaft mains and rods as well as the lifters. From the lifters, the oil runs through the pushrods, up to the rocker arms, and to the valve-springs before returning to the oil pan via drain-back areas at the front and rear of the block intended to avoid the crank as much as possible. To get the skinny on these engines from a guy who has built dozens of them, we talked to Kurt Urban of Kurt Urban Performance in Commerce, Michigan. He says the biggest issue with lubrication for these LS engines is that high rpm can suck the pan dry, especially if you are using a stock, 4-quart oil pan. Many engines have a tendency to pump large a volume of oil up into the valve covers. Limiting oil drain-back prevents the oil from quickly returning to the oil pan. A quick fix that Kurt says might work is pushrods with smaller 0.035-inch feed holes that act as restrictors to keep more oil in the pan. This was a trick GM used in some spec-series racing when lubrication modifications and restrictors were not allowed. Of course, the best solution would be an aftermarket pan with more capacity and a deeper sump, assuming you have the ground clearance. Another good idea would be to retain the factory windage tray that Kurt says works very well.

As far as oil squirters are concerned, Katech sells a piston squirter that requires block modifications, but these are only for Gen IV engines. A very low-cost alternative would be to have the stock rods milled with a small V-slot cut in the upper portion of the big end of the rod on the side of the rod shared on the same journal. This slot will be aimed directly at the bottom of the piston that could shoot oil from the rod directly into the bottom of the piston. According to Tom Lieb at Scat, this is a common trick for Honda engines that he's been doing for years.

In terms of bolting the 5.3 crank (3.62 inches) in place of the shorter 4.8L's 3.26 arm, that's an easy way to bump up the displacement on the little iron motor. Why not go a little further and find a rotating assembly for a 5.7L LS1? This assumes that the 4.8 block can handle a bore increase from 3.780 to 3.898, which is 0.108 inch. As long as the thrust surface of the cylinder wall has about 0.200 to 0.240 inch of wall thickness, you're good. Then you'd have a 5.7L engine that looks to the rest of the world like a 4.8. You supply the misinformation about its displacement, and we'll back you up-how's that?

More Info
Kurt Urban Performance
Commerce, MI; 248/345-8169;

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