Mini-Stock Classes - Big Power from Little Engines

The Mini-Stock divisions racing four-cylinder engines were originallydevised as a great way to allow new racers to get their feet wet. Fewercylinders (and cubic inches) meant the cars were slower, and the ruleswere designed around keeping things affordable. That's still the way itis in many Mini-Stock divisions, but others have become much morecompetitive. Today, the four-cylinder classes at many tracks feature carcounts that are the same as the V-8s, and the competition is every bitas fierce.

Because maximum displacement in many Mini-Stock classes is limited to2,500 cc or less (152.5 ci), every little bit of power you can find isvaluable. Racers and engine builders fight for fractions of a pound oftorque, so it shouldn't be surprising that in many areas the mostcompetitive Mini-Stock engines are just as advanced as their V-8cousins. Lighter rotating assemblies, featherweight flywheels,small-journal cranks and rods, highly efficient belt and pulley systems,and the list goes on.

The biggest difference between the four-cylinder engines most commonlyraced--Ford's 2.3L and Toyota's 20R and 22R engines--and the V-8s isthat these tiny powerplants feature more modern overhead cam designs.Eliminating the pushrods and the associated weight that comes with itallows more rev-happy engines, but it also brings its own set ofoddities when it comes to setting up the valvetrain. For example, if yourun solid lifters in a Ford 2.3, they don't actually move. Need anotherexample? OK, valve stem length is just as important as the camshaft lobewhen it comes to determining valve lift.

Cam Protection

But the valvetrain, which in many ways has a moreefficient and simpler design than what is found in a traditional pushrodengine, also has its weaknesses when it comes to racing. Changing thecamshaft is one of the most effective things you can do whentransforming an engine designed for over-the-road service into a pieceof racing hardware. For both the intake and exhaust, anything you can doto increase flow through the speed at which the valve opens, the lengthof time it stays open (within limits), and maximum lift should increasepower. This results in some pretty radical camshaft lobes, and when youcombine this with the increased spring pressures necessary to controlthe valves at maximum rpm, conditions start getting pretty harsh. Thiswas particularly damaging in Ford 2.3 motors. The solution was to borrowtechnology from the F1 sector and start "nitride hardening" cams. Thenitriding process uses ammonia gas and high temperatures to infuse thecam with a ferrous nitride on the surface and significantly increasesboth the hardness and lubricity (how easily the material will slideagainst another). Today, most engine builders use nitrided cams in allracing applications for the Ford motor. It's easy to recognize one ofthese cams because they will appear matte black.

Easy Rings

Racers have been competing with the same Ford 2.3 block forover 20 years. When Ford switched to fuel injection, engine builderssimply began milling out a hole in the block for the fuel pump.Thankfully, Ford has never made significant changes to the blockcasting, and the fuel-pump boss still remains.

So you imagine that there are very few big tricks left to be discoveredwhen it comes to building these little engines. Better metallurgy anddesigns are allowing manufacturers to pursue lighter parts, but thegains being made these days are in terms of fractions of a horsepower.

Race Engineering is one of the top companies supplying the four-cylinderengine builders. Its ultra-light components, such as the company'sadjustable square- and round-tooth timing pulleys and custom piston androd sets, are already well known among engine builders. But presidentBob Koch says he thinks there is more power yet in the piston rings.

Besides oval-track racing, Race Engineering is also a big supplier ofengine parts for import cars, which are usually involved in drag racing.He's looking at using the lightweight rings designed for Hondas andother Japanese manufacturers and using them in the Ford engines. Thesemetric rings, he says, are not only thinner but also have less radialdepth (the thickness from the outside edge to the inside edge of thering) and less tension against the cylinder wall when not underpressure. Under compression, the pressure in the cylinder pushes therings against the cylinder wall to provide proper sealing, but otherwisethe rings cause less drag as the piston travels up and down. The rings'lighter mass also causes less ring flutter. Flutter, Koch says, is mostprominent in heavy rings, which have a greater resistance to changes indirection. Lighter rings carry less momentum, and when the pistonchanges direction they tend to stay seated against the piston's ringland better which improves the seal.

However, smaller metric rings require pistons with ring grooves cut tomatch. They also aren't available in some of the usual diameters. Kochsays that if an engine builder plans to use some of the most aggressivemetric rings, he must make the appropriate plans before machining theengine block. While good metric rings are available in the popular0.030-inch oversize, other cylinder bores must be planned around thereadily available metric diameter sizes. Koch says Race Engineeringoffers matched ring and piston sets and can give engine builders theexact dimensions to machine the block so that everything works togethercorrectly.

The Toyotas are Coming

For years, the Fords have been the overwhelmingmajority in all levels of Mini-Stock racing, but lately the popularityof Toyotas among racers has been growing exponentially. Much of that isbecause the engines are plentiful and can be found in anything fromCelicas to pickups, and they are both simple and reliable.

When it comes to making power from Toyota's four-cylinder engines, oneof the top names in the business is definitely LC Engineering. Thecompany has specialized in Toyota racing engines for years in dragracing and off-road racing and has a long history of R&D on the littlemachines. Officials at LC Engineering say the most popular engines foroval-track racing use are the 20R and 22R cylinder heads (the blocks areinterchangeable with minor work), which are still readily availableeither in the junkyard or new. The 20R head features round intake andexhaust ports, 80cc combustion chambers, 43mm intake valves, and 35mmexhaust valves. It can be found in Toyotas built between 1975 and 1980.The 22R head was produced between 1981 and 1984. It features squareintake round exhaust ports, 82cc combustion chambers, and 44.5mm intakevalves matched with 36.5mm exhausts. Finally, the 22RE cylinder head wasproduced between 1985 and 1995. It can be identified by its squareintake ports and pear-shaped exhaust ports. They have 53cc combustionchambers and valves that are the same size as the 22R heads.

LC Engineering says that all three engine combinations are workable foroval-track racing. All three designs used the same crankshaft andconnecting rods. The deck heights on the blocks vary, and Toyota handledthis by changing the compression height on the pistons. LC Engineering'stop-end race motor is called its "Stage Five" design and can use any ofthe heads. They do have different flow characteristics, but after portwork they are all capable of flowing the same numbers. The crankjournals are ground to accept Chevy rods, which gives LC Engineering agreater variety of choices when it comes to lightweight aftermarketrods. According to LC Engineering's tech department, the biggestweakness in the Toyota engines is the timing chain, which is asingle-row chain in stock form. They recommend upgrading to a double-rowchain so that it will hold up under racing stresses--something that LCEngineering does in all of its high-output engines.