Just before the end of the year, some of our EngineLabs readers sent in technical questions for Nolan Jamora, the Director of Research and Development over at Isky Racing Cams, who offered up his expertise. After a busy holiday season, Nolan finally had a chance to sit down and get his answers together for the selected questions. Unfortunately we could not cover each of the dozens of questions submitted, so we have presented those which we thought would most benefit our wide reader base. Also, please understand that there are few images here; we thought it best to focus on the technical information at hand.
Without further ado, we present some of your submitted questions along with Nolan’s in-depth answers on camshaft design and other valvetrain-focused topics. Enjoy!
1) What dictates the lash on a solid roller camshaft? What are the advantages to a “tight roller” cam?
Rhyne Competition Engines
Nolan Jamora: Mike, the best way to gain perspective of this is to picture in your mind what I refer to as the “Curb Height to Driveway Slope Ratio.” Say you are traveling through town in your car and on your right side is an unusually high curb height (perhaps in an area where there is occasional street flooding that might otherwise build up and run over the curb). With such a relatively high curb height, (equate this to the lash) a longer, less-steep driveway slope to go from street level to the parking lot (equate this to the ramp rate) of the cam profile) was the “gentle”, constant velocity ramp technique employed almost exclusively up until the mid-late 1960s. Think of that higher ramp (curb) height as allowing for a more gentle transition between the cam’s base circle and the flank. Cams made this way like the Isky 505 Polydyne Profile Magnum (the first computer designed cam profiles in the hot-rod industry) in the early 1960s could easily allow a small-block Chevy to rev to 9000 rpm with stock valves and 325 pounds-per-inch springs. That’s 325 lb/in valve open spring force! Add one of Camfather Ed Isky’s revolutionary Ultra-Rev kits, and I can attest that the same engine valve train would rev to 10,000 rpm plus – and do so in a very dynamically stable manner! These cams all ran valve-lash numbers between .028/.030-inch hot.
Beginning in the middle to latter 60s, Accelerated Ramp Rate cam profiles (modest by comparison to current practice) like our 590 Torquemaster Flat Tappet and the 600 Magnum Special Roller (which captured more area under the valve lift curve) enabled more power (up to 35 horsepower at the time) without any torque losses (and in fact gains) in the lower- to middle-RPM ranges. However, these Accelerated Ramp lobe profiles (at double to triple the previous ramp rates (velocity) required considerably more valve closed and open spring forces, to prevent valve float/seat bounce. The story continues to the present day where it is difficult to even think of many contemporary cam-lobe profile designs as actually having opening and closing ramps because of how “accelerated” those ramps have become. In fact, it would be more appropriate on many of these designs to refer to their ramps as merely being “an extension of the flank”. That’s why you hear about the most radical of these requiring 450-500 lb-in seat and 1300-1500 lb-in valve open spring forces. You don’t get that big increase in area under the lift curve without paying a price somewhere else, typically with respect to engine maintenance and longevity.
Now that I’ve given you the background, the short answer to your question is that those tight-lash cams are perfect examples of accelerated ramps that capture more lift area, but those lower lash numbers must be maintained and matched to that lower curb height I referred to. That is unless you want to run the risk of your engine’s valve train doing the equivalent of “hopping the curb with the front wheels” of your car – and you can imagine the shock to both your car’s front-end alignment as well as to your engine’s valves as they unnecessarily return to their seats at high impact velocity! And since you don’t want to also unnecessarily risk the long-term stability and integrity of the rest of your engine’s valve train, my advice would be don’t try to run them indefinitely with conventional needle-bearing solid roller lifters. Instead run our revolutionary patented EZ-Roll needle-free rollers to avoid needle bearing overload, subsequent erosion and any risk of catastrophic failure. That’s why we invented them – to protect and to serve the long-term interests of your engine’s life. They weren’t required with the more gentle-ramp cams back in the early 60s, but today they have become universally recognized as the smart choice of most modern engine builds in both drag and endurance racing applications.
2) The way I understand it, in the past, 4/7 swap firing order cams were only available on high lift cam cores, somewhere up close to .700-inch lift or above, due to the “Rockwell” Hardness treatment of those cam cores that could not be ground lower, and there were simply no 4/7 low-rise cam cores.
Please comment if this is incorrect.
Will you ever be releasing milder, lower rise, Rockwell’d 4/7 cam cores?
My project car is an ’85 C-4 with a Mercury Marine 523 CID Mk. V E-Z EFI’d, an Edelbrock Twisted Torker 2.0 and a ZF6, and I’m looking for the crank stability and consequent driveline smoothness. The C4 Chassis suspends the engine by only two front engine mounts through the bell housing/trans, to a rigid “C” beam, bolted on both ends from the trans tail tock, to the Dana 44 rear housing pinion input flange and consequently is very sensitive to all sources of driveline harmonics. It runs and drives fantastic with the driveline dial indicated to within .004-inch of the pilot bearing, but there’s no doubt you can feel the pulse and presence of a very large rotating mass, even though it was balanced to a couple of grams.
I have been known to cruise it for up to 12 hours for Track Days, and with a Z51-based SCCA suspension, I can tell you ANY reduction in harmonics is an asset. Am I wrong to be looking for further smoothness refinement and overall component durability with the 4/7 swap in this application?
Thanks for taking the question!
Nolan Jamora: I noticed with great interest that the focus of your question about the availability of #4 and #7 cylinder big-block Chevy cam cores was with regard to the usually ignored benefit of engine/driveline smoothness (the only really tangible benefit) as opposed to the normally promoted horsepower advantage (unfortunately little more than hype). And, you are absolutely correct to do so because that would be the primary benefit in your case (for an independent comparison of back-to-back horsepower tests with the same cam profile, changing only the firing order, I like to refer to Reher-Morrison’s famous test results which clearly demonstrate only about one half of one percent difference at and around the horsepower peak). Congratulations to you for the ability to read between the lines and disregard the fluff.
Now, regarding that real benefit of engine/driveline smoothness (the result of reduced crankshaft torsional vibration), the benefit increases with the increase in engine stroke length of higher (500 +) c.i.d. engines, because that’s where the torsional vibration really gets nasty!
We do have a good more moderate lift 4/7 swap cam core available for our .372-inch lobe lift series lobes (.632-inch valve lift at 1.7:1 rocker ratio) with a deep case hardening, for Lobe Separation Angles (LSA) of 112-114 degrees. This series of lobes is available in durations between 236 and 268 deg. @.050-inch in 4 degree increments, and there is also a 274 degree lobe.
3) Hi, I have read that if you have efficient exhaust port flow e.g. 80% + of your intake port flow, that a single pattern camshaft will perform as well or better than a dual-pattern cam?
Nolan Jamora: Hi Jim, in most cases you are absolutely correct! The Longer Exhaust Duration thing is not mandatory and often way over-done! For a full treatise of this subject, please refer to our Tech Tips 2000 article, “Longer Exhaust Duration: Is This Really Necessary?”
The primary exception seems to be in situations where a really big motor (say 500-600ci) is installed in a very light car. Here, you may want to run longer exhaust duration – but not necessarily to make more power! Actually, its just the opposite – you’d often want to kill some bottom end/mid-range torque to avoid uncontrollably “frying” the tires trying to launch the car.
4) Hi Nolan: I work with the Corvair engine a great deal and am usually disappointed especially when it comes to turbocharged cams. Because our stock engines work with a carburetor on the other side of the turbo, we have boost coming on above 3000 RPM. We have made modifications over the years including larger carburetors and now fuel injection increase the boost at lower RPM.
However, the Corvair is still stuck with relatively poor heads and ports, even when cleaned up. Most owners don’t want to go too far from stock. Because of this, we have been using all-purpose cams on our turbo engines.
Can you suggest a better alternative?
Nolan Jamora: Dear Ron, I want to emphasize that what you need is a “Reverse” Dual Pattern camshaft to reduce engine throttle lag by improving boost response. And, because of the issues and factors you have touched upon, my recommendation would be as follows;
.450-inch lift /264 degrees/214 deg. @ .050-inch INTAKE (Profile #H-520)
.435-inch lift /258 degrees/208 deg. @ .050-inch EXHAUST (Profile # H-606)
112 degree LSA and 106 degree intake centerline.
5) Please explain the effect of lobe separation on engine performance. Any rules of thumbs on deciding correct lobe separation angle? I find that narrower lobe separation angles seem to make more HP in smaller CI BBC (427-496 ci) yet for an RV style cam they are much wider.
Nolan Jamora: Bruce, closer LSA cams always make higher average horsepower because of the low end and mid-range torque gains achieved. The tighter centerlines cause the intake valve to close earlier on the compression stroke and the resulting longer effective compression stroke yields a broader effective torque range (much like advancing the cam). That’s why they’re always a good bet for lower cubic inch displacement engines where low end and mid range torque is harder to achieve. Conversely, sometimes a wider LSA cam can achieve a little more power at the top end of the curve, but the engine will seem more peaky. The best analogy would be to compare the closer LSA cam’s performance to that of a 4-stroke motorcycle, while the wider LSA cam’s performance equates more closely to that of a 2-stroke. The latter must be kept high revving to avoid falling flat (too far off the very peaky peak)!
RV cams often have a little wider LSA simply because idle quality and vacuum are at a premium, so keeping the overlap factor down takes precedence. Any concerns about low-end torque loss can be addressed by merely advancing the camshaft.
6) Context of the question:
Road racing in SCCA small bore (Super Turing Light or STL).
Motor is a 4 valve DOHC 1.6 liters
Compression ratio is 11:1 (limited by the rules)
Build for up to 8,000 RPM (stock redline is 7,200)
Rule are fairly open on cams, max lift of .425 inch, no limitations on duration
Now the question:
How does rod ratio (rod length/stroke) affect cam selection and timing? I’m running aftermarket rods that are longer, thus increasing my rod ratio and dwell time at TDC.
Thanks in advance for your time!
Nolan Jamora: Charles, I will refer you to our Tech Tips 2000 article, “Rod lengths/Ratios: Much Ado About Almost Nothing.” Take the time to read the article and study the piston position to crank angle chart comparisons carefully, and it will become readily apparent to you just how hyped-up this subject has become. My advice to you is the same as to all others regarding this matter. Only professional engine builders who have exhausted all other means should ever be concerned about rod length/stroke ratios, and even they need to be aware that the big gains they have been led to believe they are chasing will end up more like a fine-tuning adjustment at best.
7) I drag race using small block fords with the better flowing Yates style SC1 heads used for high rpm racing with tunnel ram and dual quads. I use a 5 speed manual box. That means low first gear and rear gear.
When ordering a cam I am always provided a cam with 2 to 4 degrees advance over the intake centerline. I typically retard the cam but I don’t grasp the reason why the advance is a constant given in the making of the cam?
Nolan Jamora: John, when our founder, Ed Iskenderian began making cams in his garage after WWII, the Flathead Fords ruled the world of hot-rodding. They were gear driven cam to crankshaft and as such, the cam timing more or less stayed put over the life of the engine build. Not so when the OHV V8s took over in the 50s, because they virtually without exception incorporated a timing chain and sprockets. The “Camfather” (alive and well to this day at age 96) remembers when he fielded the first complaints about retarded cam timing. Customers who had degreed their cam subsequent to initial assembly and run-in found 1-2 degrees of camshaft retardation due to timing chain stretch. The phrase one customer used, “Hey Ed, you ground my cam retarded,” really got his attention.
It was at this point that Mr. Isky realized that grinding the cams to install at the perfect “straight-up” position (zero advance or retard) as he had with the flatheads, wasn’t going to cut it any more. He immediately invoked our internal default “3 degree advance rule” where, unless otherwise specified by the customer, we would intentionally grind 1.5 degrees of camshaft advance (3 crankshaft degrees) into every cam to offset the consequences of timing chain stretch. Eventually, most other cam companies adopted a similar position.
Now if you are running a gear-drive system, then aside from a slight amount of wear to the gear teeth, the cam timing will remain a constant. However, with the propensity of so many to over-cam the engine (still the biggest mistake people make to this day), a little cam advance is usually beneficial. Furthermore, it’s an established fact that in the vast majority of cases, most engines respond favorably to a cam that’s slightly advanced. Even belt drives (a good compromise between the timing chain and a gear drive) while incorporating the benefit of torsional vibration dampening like a chain, and the more precise valve timing of a gear drive, experience some deflection under load causing a slight retardation of the cam. This dynamic deflection under load occurs even before there is any permanent evidence of such belt stretch via a visual inspection.
Hopefully this background information helps you to understand the “why” of default camshaft advance and remember: If you would like the cam’s position ground a certain way at Isky, then by all means simply ask for it and we’ll be happy to accommodate you!
8) I am considering using a bushed lifter for my next motor, but I am concerned that the roller will slide across the cam rather than roll. Given the small contact area of the roller with the cam, and the close tolerance of the pin to the roller, the oil shear and friction between the roller and pin will have a greater force than the friction between the roller and cam, thus causing the roller to slide rather than roll. I admit I haven’t taken the time to do the math myself to calculate the forces involved, taking into account the different radii. What analysis has been done, and what is the risk of sliding the roller, especially when running heavier oils when cold?
Nolan Jamora: As the inventors of the patented EZ-Roll Lifter (nearly 200,000 lifters rolling worldwide), we believe we are qualified to address this business of lifter slippage. Firstly, let’s call this notion about bushing roller lifters sliding across a cam lobe what it really is: Anti-Bushing Roller Lifter propaganda that was originally concocted by competitors who were against the concept of a plane bearing and fully locked-in to their positions of “needles only”. Motivated by the successful implementation of our patented design, however, these same entities have now changed their positions a full 180 degrees and risked infringement by offering bushing rollers of their own making. Yet, the propaganda they have left behind in their wake has managed to remain on life support, embraced by fellow needle-bearing-only diehards. Let me reassure you that this slippage argument does not stand up to the scrutiny of any real world/normal circumstance analysis. So think of it as a sort-of-manufactured crisis, what our own government sometimes resorts to in order to get what they want – and apply the old Roman adage “cui bono” coined by Cicero (who benefits?).
However, there are two Unfortunate/Irrational circumstances and one Critical Mistake of Choice that actually could lead to such a result. For the record, no matter how far out there in la-la-land the following two “Irrationals” may be individually, it usually takes incorporating both of the following (A and B) in combination to lead to its unfortunate occurrence. Both involve the relentless pursuit of friction reduction taken to an extreme:
A). Zero or Near-Zero-weight oils: We have observed people going off the deep end with this for years. Yes, you can eventually increase friction between the roller wheel and the camshaft lobe by running these risky oils, and a case could be made for this if you are also reducing valve spring loading to a bare minimum in a quest for temporary horsepower gains. However, one need only recall what happened in NASCAR racing some years ago when this practice was rampant. So-called “Qualifying” engines employed this technique and yes, lap times were slightly improved to gain starting position. The rest of the story is somewhat unpleasant, however. A qualifying engine run even a lap or two more began to deteriorate rapidly and in short order would self-destruct. So, long-term the pendulum swings to promoting friction (as the oils break down and the engine deteriorates) and that spells trouble everywhere in the engine.
If you apply this scenario to a bushing roller lifter wheel, what you find is an initial reduction of friction (which actually would encourage roller wheel slippage), followed soon thereafter by an increase in friction at the cam lobe to roller interface, leading to increased wear of the wheel and cam lobe. There is, simply stated, no sane advantage in either the long- or short-term by employing this technique.
B). Insufficient valve spring loading: By reducing valve spring seat and open forces you could theoretically reduce the possibility of roller wheel slippage (especially if you are also employing those risky zero-weight oils) but, would you really want to do this? The reason you would be employing a bushing roller lifter in the first place is because of extreme loading in the valve train department. Well, if you were going to back down on that radical cam profile and/or engine RPM which necessitated the heavier spring loads in the first place, that would make sense. Take that to an extreme and you could even go back to needle bearings if you wanted to. You see where I’m going with this. One factor is co-dependent on another, so if you’re willing to change the entire concept of the build, well okay then. But, is this actually realistic in most cases? No, probably not, because I’m afraid the horse has long since left the barn when it comes to matters such as these.
And finally, on to the “Critical Mistake of Choice”.
C). Employing imitation roller bushing lifter products:
It never ceases to amaze me how racers will take chances and play Russian roulette with their engine toward the end of a build. Often, this is because in contemplating how much money was spent collectively on the block, crankshaft, cylinder heads etc., they feel an obligation to be frugal and skimp on the valve train. I’ve seen it over the years on valve springs and titanium retainers (causing dropped valves and engine failures) and employing an imitation bushing roller lifter unfortunately can be just as devastating. The best advice you can receive to avoid any unnecessary problems would be to seek out the primary authority and harness their expertise.
The products you want to avoid are easily discerned by the messages attached to their usage. Warning phrases like “oil restrictors are a no-no”, or “not for use with oil restrictors” (code speak for “we buy off-the-shelf, higher friction material prone to seize the axle if you dare restrict oil flow to the lifters”) are a red flag. When challenged about this, their makers will tell you that any oil restriction will cause “unavoidable seizure” and subsequent roller wheel skidding against the cam lobe.
Is a bushing lifter better? Can it last as long as a needle? Can it survive the harshest enjoinments? As we like to say to the proof is in the pudding. After 10 years on the market its more than proven that they are the better option. Just this last year John Ens and Dave Schroeder’s, massive, nitrous-huffing, 872ci big-block 1966 Corvette, won the 2017 Drag Week overall and Unlimited class with our EZ-Roll Bushing Lifters. They drove over 1,000 miles during the week and ran an average quarter-mile ET of 6.87 at 207 mph! I think that speaks for itself.
We here at EngineLabs wish to thank Nolan for his efforts to answer each of these questions thoughtfully and completely, and hope each of you are able to glean some information from his responses.
Thanks for following along; we have another one of these sessions scheduled to hit shortly with David Fussner of JE Pistons, and more to follow in the future with other experts. Stay tuned to the site for more!