Building or rebuilding a successful...
Building or rebuilding a successful engine on a budget is almost an art form. We built this 460hp engine with all-new parts (other than the block) for a shade over $4,000. Almost everything came from Jeg's or T&L.
It's the end of the season and you are done racing for the year. After contemplating yet again on how you got hooked on a sport that continually outpaces whatever budget you may have, you realize it's time to plan for next year. If things run their normal course, this will be another year where finances set a limit as to what you can do to overhaul and possibly upgrade your engine.
If this scenario fits your situation, don't be lulled into thinking you are the Lone Ranger here. Probably some 75 percent of the short track racers in the country fall into this category. When money is severely limited-as it often is with racers-knowing how best to spend it by prioritizing problems can pay dividends when you hit the track for the new season.
Let's make a start at the top of the engine long-block assembly and work our way down, looking at ways to prioritize the reconditioning and upgrade of parts.
If you have access to a mill...
If you have access to a mill or a Storm Vulcan machine, milling the intake face to accommodate double gaskets on each side is worth torque and power.
Many classes call for the use of a stock intake manifold and a two-barrel carb. With this setup, heat soaking into the intake charge is a real power killer. The first move is to make sure the heat crossover passage is blocked off. If you are not in a position to pour in molten aluminum to block off this passage, fill it with fine-sand builder's cement as this works as well, if not better. Make sure the intake gaskets have the heat crossover passage blanked off. If you have access to a mill or the like, then machine off the thickness of one compressed intake gasket per side of the intake manifold and use two intake manifold gaskets (per side) cemented together. If the rules allow, make up a lifter valley tray out of any piece of thin steel or aluminum. Attach it to the underside of the intake and fill the space between with high-temperature, attic-insulating foam. All the above should not cost much more than $20 and can net as much as 10 hp.
Assuming you have to use factory production heads, the biggest power-sapping wear factor you will have to contend with may come as a surprise-it's the valveguides. When researching my book, How to Rebuild Your Small Block Chevy, I did some dyno tests on valveguide clearances to find out how influential valve-to-guide clearance actually was.
How much guide wear is too...
How much guide wear is too much? Lift the valves to about 1/2 inch and see how much they move in the direction of the arrows. About 0.005 is just acceptable, but at 0.010 it's time to do something about it.
Based on some info I got from a friend who was a very experienced engine reconditioner, I started off with a set of stock heads and installed some K-Line bronze guide liners into the guides. These were sized on the intake to run with only a couple of tenths of stem-to-guide clearance. (A word to the wise on clearance and K-line guide liners: I would not attempt this with any other guide that I can think of. The K-line liners are made from a bronze that seems highly unlikely to seize.)
With a couple of tenths of clearance on the intake and about six-tenths on the exhaust, I dyno'd the 350ci test mule. With a good baseline established, the clearances were opened up to 0.0015 on the intake and 0.002 on the exhaust. On what was an approximately 320hp motor, the power came up about four to five numbers. The heads were then pulled and the guides resized to give about another 0.0015 inch of clearance on both intake and exhaust. The power dropped by some 4-5 hp. Next, the guides were resized to produce 0.006 clearance all around. It won't come as a surprise to most of you to realize this number is not out of the ordinary when checking what may exist with old heads. What may be surprising is that the test engine lost over 28 hp with the simulated worn guides.
It's easy to see why loose guides drop power. Because the valves are not constrained to move in a straight line, they do not seat and seal as they should. What is not so easy to appreciate is the reason that the tight-fitting guides show up worse than the ones with just a little more clearance. When cylinder heads get hot, the differential expansion between the hot exhaust side of the head and the cooler intake side causes the seat's centerline to spread slightly, but not that of the valveguides. This means the valves need a little wiggle room to seat properly, hence the best results with 0.0015 and 0.002 clearances for the intake and exhaust.