Myth 6:Limited lift cams with higher than normal lifter acceleration rates make more power but don't last long.
Response: This is right only if you don't know the fix.
Having built a few limited-lift motors that made race-winning power (and needed to be dyno mules) has meant finding a fix for potential rapid cam lobe wear on cam profiles where rapid lifter acceleration has been pushed to the limit. Traditionally, such cams can have a short life. If the break-in procedure did not quite make the grade, a lobe (or lobes) might not even make it through the first race. About eight years ago, I found the closest thing yet toward eliminating this problem. This fix comes in a bottle labeled "Oil Extreme." Not only does it cut the likelihood of a cam failure by about 75 percent (at my best guess), but also, in 99 percent of cases, it shows a power increase amounting to about 5 hp, on average. This stuff is not available in stores because most of it is used by big corporations, naval applications, and other military operations. To get it, and it's cheap enough, you have to go directly to the manufacturer-Jet Set Life Technologies in Grand Terrace, California.
Myth 7:Those restricted classes that call for hydraulic flat-tappet cams and a minimum idle vacuum need much shorter intake and exhaust duration.
Response: No vacuum is lost faster by the exhaust part of the overlap period, so shortening this will pull the vacuum up.
Most of the vacuum at idle is lost due to the intrusion of the exhaust part of the overlap into the intake part. If the exhaust part of the overlap is cut by 10 degrees, the increase in idle vacuum is much greater than if the same had been done to the intake. If a hydraulic cam and idle vacuum rule exists for your class, try using a soft (faster leakdown) lifter on the exhaust. Don't overdo things here, as some very fast lifters never recover anything near their full duration and power may be lost. The best plan is to use as tight a lifter as you can find (or a near-bottomed-out one) with a relatively soft lifter from Crane or Comp. To make sure that the exhaust lifters regain as much duration as possible, use some Oil Extreme in the oil.
Myth 8:A big intake port tends to compensate in a valve-lift-rule engine.
Response: Absolutely not.
It is so common, especially with small-block motors, to quote the flow of heads at 0.700 (700 thousandths) that if a head fails to look strong there, it is assumed to be less than satisfactory. Having good flow at such a lift value is totally academic if the class rules call for a maximum valve lift of say 0.500 (500 thousandths). In fact, if a head goes on flowing really well, about 0.050 (50 thousandths) above the required valve lift, the port volume above this to support such flow could be hurting power, not enhancing it. Why? Because such flow characteristics are indicative of a port too big for the job. Anytime the port is too big, velocity is cut and the ramming momentum that is responsible for much of the volumetric efficiency numbers over 100 is reduced. Worse yet, it's a square law. Cut the velocity by 10 percent and the ramming pressure will drop just over 20 percent.
Shown here are all the main aspects of a camshaft. The most important factors to get right are the overlap and the LCA. The overlap has to be correct in terms of area so degrees and rate of opening dictate how optimal it may be.
1. Intake lobe lift
2. Intake opening flank
3. Intake duration
4. Exhaust lift
5. Exhaust opening flank
6. Exhaust duration
7. Lobe centerline angle (LCA)
8. Cam advance and retard
Myth 9:There isn't much to be gained from hollow stem steel valves.
Response: Think again!
This is short and sweet. Our tests, which involved spinning Ferrea hollow versus solid stem valves, have shown this: In the range between 7,000 and 8,000 rpm, the lighter, hollow stem valves not only dynamically behave better on the way up, but also deliver (depending on the spring) between 200 to 400 more rpm before loss of control sets in.
Ever wonder what the difference is between valve toss and valve float? These Spintron screens provide the answer. Shown on the left screen, as indicated by the yellow arrow, is the valve being tossed (lofted or floating) due to component separation somewhere in the valvetrain. This usually occurs at the pushrod, but it could be at the lifter or the rocker. This valve toss can actually enhance power, and it is a characteristic sought after for an all-out pushrod valvetrain. Shown on the right screen, indicated by the red arrow, is the effect of valve bounce. This is where the valve's closing velocity with the seat is too high and the valve simply bounces back off the seat. When this happens by more than a few thousandths of an inch, power starts to drop off rapidly.
Myth 10:Solids always make a better curve and more power than hydraulics.
Response: Always is an overstatement.
It is easier to make horsepower from a solid because it has less lifter related issues. That stated, a well spec'd hydraulic can actually beat a solid with the same off-the-seat duration, but it takes the right profiles and lots of dyno time to sort out the right lifter characteristics and lubes. Lastly, aeration of the oil can be an issue, so a good, functional pan becomes a must.
Myth 11:Changing pushrods isn't worth a darn.
Response: Time spent testing valvetrain combinations will reveal the contrary.
There is far more to pushrod science than even many experienced and successful engine builders might imagine. Not only must a pushrod be stiff and have as high a natural lateral resonant frequency as possible, but it also must have an ability to damp out spurious vibrations developed within the valvetrain system. Stock pushrods tend to be made of materials that are better at damping than they are at avoiding flex and lateral resonance at higher rpm.
Going from a factory pushrod to a high-tech (and that term is not an overstatement) pushrod from Crane, Comp, or the like, might net you anywhere between 0 and 15 hp, depending on the dynamic characteristics of the cam and other valvetrain components. In all our tests (over a dozen to date), a good aftermarket pushrod has never lost power. Incremental gains are the norm, but gains of 9 and 15 hp were realized on two occasions.
Myth 12:A tighter intake lash gives more duration and therefore more top-end power.
Response: Not usually.
Intake valves in general like to be opened and closed rapidly, especially when they are in the vicinity of the valve seat in the head. Using the opening ramp of the cam as a means of extending duration is not a good move because the acceleration on this part of the cam's profile is slow. It amounts more to creating a temporary valve leak than a performance enhancement. Lash figures on the loose side almost always deliver better results, but don't go too loose. Doing so will upset the dynamics, and potential gains will be offset by reduced valve control and increased seat bounce at the point of closure.