Answers provided by Senior Tech Editor Bob Bolles (unless otherwise noted)PCV PrimerQ I was wondering if there is any information on the use of PCV (positive crankcase ventilation) on circle track engines. I know it's been used on high-horsepower drag engines, but was wondering if anyone has used such a system. What would be the advantages to a 400hp engine? If there is no horsepower gain, would there be any other reason to use such a system?Darrel BauerDenver, CO
Q Do you think it would be worth my time to hook up a PCV valve and seal the oil breather? My reasoning for considering this is that the reciprocating/rotating parts would have less resistance in a vacuum. What thoughts do you have on this? Any potential pitfalls? What percentage of torque increase (if any) might I reasonable expect?John KingCedar Rapids, IA
A Even with the best of ring seal, some amount of combustion "residue" will escape into the crankcase area. One of the original purposes of venting oil pan pressure into the intake track (the so-called "PCV System") was to reduce exhaust emission levels (unburned hydrocarbons) in over-the-highway vehicles. PCV can also reduce fuel economy, but that's an entirely different subject.
From the perspective of a race engine, PCV-vented combustion by-products tend to dilute fresh air/fuel charges, thereby reducing combustion efficiency and power. Further, the higher the crankcase pressure, the greater the tendency for this residue to bypass ring seal and get back into the combustion space, essentially during the intake stroke when cylinder pressure is less than pan pressure.
If you're comparing the effects of pan pressure on crankshaft rotation to that of combustion residue on combustion efficiency, the latter is more critical. Instead, routing pan pressure into an exhaust header collector will reduce windage loss and tend not to reduce combustion efficiency. The amount of improvement largely depends on ring-seal effectiveness. Also, you'll find gains to be greater at lower rpm than higher, primarily because the lower engine speeds allow more time for dilution to occur. With an efficient venting system, I've seen net torque gains of 2 to 4 percent, but this varies with power level and ring seal. Oil attachment to crankshafts can by far cause more torque loss than pan pressure.
A pretty good rule of thumb you can apply to many types of engine modifications is, "What am I doing to combustion efficiency?" The venting of crankcase pressure falls into this category.Jim McFarlandAutotronicsAustin, TX
Housing CheckQ I race a Limited Late Model on a 11/44-mile, low-bank asphalt oval. The car is a Camaro front stub with fabricated frame and rollcage. I run a Ford 9-inch floater rearend with a conventional three-link rear suspension with a full-length, straight panhard bar.
During the last race of the season at my local track, I came out of Turn 4 a little high. The rear of the car came around and tagged the wall pretty good, directly on the right-rear tire. The rim was toast. I put on a good rim and measured the toe with toe plates. It is toed-out 11/48-inch. I did the same test with all my spare rims and came up with 11/48-inch toe-out every time. I went back out on the track for the next race and the car was definitely looser. Tire temperatures on the right-rear also changed. The inside now runs about 30 degrees hotter than the outside. I have done a close inspection of the housing and can't find any bends, kinks, changes in paint, etc. My wheelbase also has not changed.
What is the best way to try to straighten out the housing? I saw a guy on TV do it with a rose bud and a wet rag, but I have no idea where to start. Is my only option to purchase a new housing? Like everyone else, my racing budget is pretty non-existent.Name Withheld by RequestVia e-mail