Our first repeat expert on Ask The Experts also happens to be the very first Expert we featured in the series. Nolan Jamora, now Chief Operations Officer of Isky Racing Cams, sat down with us to answer the questions that you, the readers, submitted when we posted our original announcement. However, there were so many good questions submitted, that we had to break this up into two parts, since letting the good questions go to waste was, frankly, not an option.
So, without further ado, we bring you the first ten questions for Nolan, and his answers.
1. What experience do you have with four-pattern camshafts? I’ve been kicking around the idea and was concerned about the amount of split to run between the inner and outer cylinders. – Rylee G.
Nolan Jamora: My first experience with this multi-profile cam approach came back in the 1980s with Dave Tabor of Comptune fame. Dave, may he rest in peace, was a good man and as honest as they come. Dave had the most extensive experience porting heads for BMC “A” type cylinder heads for Austin Healey four-cylinder Sprites and Midgets. At his request, we ground hundreds of “Scatter-Pattern” cams, as he called them, to overcome the inherent problems of a shared or common intake port for the two middle cylinders. This staggered cam duration — or “split” as you called it — was effective in minimizing the effect of one cylinder robbing from another’s induction of the fuel/air mixture.
This can also sometimes help on an SBC V8 in balancing the induction on all cylinders. They’ve done it for years on NASCAR engines, primarily before the days of EFI, in order to promote equal distribution of the fuel/air mixture. Here, with carburetion, the problem was not a “Siamese” intake port but a tendency for fuel to puddle along the floor of the intake manifold in an uneven way.
Now as to your specific question about how much of a split to run: My advice is between 4 and 6 degrees. Don’t waste your time with anything less because at that point you might as well not do it at all. Also, don’t expect a big gain, as you will find this is more of a fine-tuning adjustment.
2. I have a SBC 350 that I race in a class that requires a flat tappet camshaft. In a quest for more power, I’ve heard that it’s possible to use larger diameter AMC .904-inch lifters to take advantage of a steeper ramp angle on the camshaft for more area under the curve (more average duration). Is this possible and worth the hassle? Outside of the block machining and custom pushrods, what additional expense would this add to my camshaft selection vs. a stocking camshaft straight out of the catalog? Is my money better spent on a set of higher ratio rocker arms (1.6:1) instead? – Wyatt T.
NJ: It is certainly possible to enlarge the lifter bore diameters to .904 inch to utilize a more aggressive (higher velocity or rate-of-lift) cam profile. However caution is required on multiple fronts. To begin with, the machine shop must have the capability (tooling and experience) to do the job properly (maintain a perfectly square or 90-degree relationship between cam bore and lifter bore centerlines).
Secondly, once you go beyond the Ford .874-inch diameter lifter size, it is necessary to trim the widths of certain cam lobes to prevent adjacent lobe-to-lifter interference. This engine block and camshaft preparation will cost you many hundreds of dollars without the potential for big returns. So, as far as bang for the buck goes, my advice would be to consider our Magnum XL series of aggressive increased lift-area cam lobes as an alternative, because they are designed to run with the stock lifter bore diameter. Also, they don’t require a narrowing of certain cam lobes, which is a critical “LDF” (load distribution footprint) factor in the wear life of the cam.
Lastly, employing a higher ratio rocker arm would have a similar effect, although the amplification of valve motion is not identical. However, in combination with XL series lobe pattern choices, results have proven formidable.
3. How do you go about designing a cam for a high winding DAMB (Direct Action Mechanical Bucket) engine like a Nissan VQ35 or sportbike engine? Does the lobe look something like a mechanical flat tappet cam (softer ramps and lower spring pressures) or something else altogether? How would that lobe shape compare to something like a swinging hydraulic roller follower in a Ford Modular/Coyote/Voodoo platform? Do you think that DAMB engines will start appearing more in domestic engines in the future? – Colin H.
NJ: Direct Overhead Cam or DAMB engines require less valvespring loading because they are normally employed with smaller diameter valves and they are inherently less complicated, lower-mass valvetrains (with no pushrod or rocker arms). They are often more costly to produce, however, so don’t look for them to replace all pushrod engines. And, as far as high performance is concerned, nothing is more “hop-up” friendly than a pushrod/rocker arm OHV design, especially in the bigger V8 powerplants.
As far as design considerations go, as with any flat-faced cam follower system, the diameter of that follower is the limiting factor in how aggressive you can be with the camshaft. The formula for minimum follower diameter for a given lobe would be 114.592 times the Maximum Velocity of the lobe (highest rate of lift-per-degree of the design). For example, a lobe that lifts at the peak rate of .010 inch of lift per camshaft degree of rotation would require a minimum follower cam-face of 1.146 inches, plus the normal allowance of margin at the edge for a corner break. So figure in this case about 1.200 inches in diameter.
Lastly, you cannot compare lobe shapes of different follower types, so it’s best not to get too concerned with their appearances. Roller follower cams, whether conventional or swinging arm type, are always going to appear more radical than any flat faced follower cam design ever would. Their contour is what their follower type demands for a particular valve motion.
4. When considering the design of the valvetrain, what are the concerns when increasing rocker ratio? Given that an increase in rocker ratio would reflect an increase in spring pressure to the lifters to prevent float, what does increasing the rocker ratio do to cam dynamics as reflected at the valve? – Jerry A.
NJ: Rocker arm ratio increases do of course affect valve dynamics. However, unless you are radically “amplifying” the ratio (for example going from 1.5 to 1.7 or 1.8:1, there is usually no concern about the existing valve spring’s capability to maintain dynamic control. So on a small-block Chevy, if you limit the increase to 1.6 or 1.65:1 at best, there is usually no cause for concern.
5. Can you explain the relationship between cam lift and duration? What effect does increasing lift have on the performance characteristics as opposed to increasing duration? — Lynn J.
NJ: The simplest way for me to describe the effects of increasing lift vs. duration would be as follows: Increasing duration will make more power the higher you go up in the RPM band. However, it has a “rob Peter to pay Paul” effect on bottom-end and mid-range torque.
Why? Simply put, longer valve timing events tend to bleed compression (later intake closing point) and negatively influence torque in those areas. Adding lift alone however, eliminates this negative influence in the lower and middle ranges and results in as good or better power all the way up. Of course, it also limits your gains in the upper-RPM ranges as well, because nothing allows an engine to take a “deeper breath” like adding duration.
6. I’d like to know more about doing a 4/7 swap and the real benefits of doing this. This would be for a small-block Chrysler race engine. – Steve B.
NJ: Some years ago, Reher-Morrison published their famous test results for 4/7 firing order swap vs. standard engine firing orders on a big-block Chevy V8. It was the only honest assessment that I have ever encountered and it showed clearly that the horsepower gains under controlled test conditions were less than one-percent with the 4/7 swap.
However, [horsepower gains] are not the whole story. There are definite benefits of engine/driveline smoothness (the result of reduced crankshaft torsional vibration) and the benefit increases with the increase in stroke length. Higher cubic-inch displacement engines (over 500 inches) can really benefit from this firing order change, because that’s where the torsional vibration really gets nasty.
My advice to my SBC V8 customers has always been as follows regarding making this change: 327 cubic inches and under: forget it. 350 cubic inches: neutral. 383 cubic inches: now you can start to benefit with the 3.75 stroke. Over 400 cubic inches and its even longer stroke: a definite YES! Your small-block Chrysler should be considered accordingly.
7. What is the significance of lobe separation on cam performance between street, race, and forced-induction cam profiles? – Jeff T.
NJ: Closer Lobe Centers (LC) – A.K.A. tighter Lobe Separation Angles (LSA), for the younger generation – 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 longer effective compression stroke yields a broader effective torque range (much like advancing the cam).
That’s why they are usually a good bet for lower-displacement engines where low-end and mid-range torque is harder to achieve. Conversely, sometimes a wider LC cam can achieve a little more power at the top end of the curve, but the engine will seem “peakier”. 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”).
Larger C.I.D. engines nearer 500 inches and above can widen the centerlines out to keep the lighter-weight cars “hooked-up” without the dramatic drop off in torque or to gain piston-to-valve clearance with really huge camshafts. Similarly, forced induction engine cams are not as sensitive to torque losses with the wider LSA’s.
8. Why is the lobe of the cam symmetrical (i.e. opening and closing ramp identical)? Are there possible improvements by going to an asymmetrical cam lobe? What would the drawbacks be? – Graham B.
NJ: Most cams are not perfectly symmetrical. Even when it is not reflected at first glance of the cam’s specification sheet, there are often subtle differences in the cam’s closing ramps in order to more gently seat the valve. Some cam grinders have exaggerated these subtle differences in order to draw attention to their wares (a la P.T. Barnum). In fact, in my opinion the hype that is generated by some over this issue often borders on “Fake News.”
To specifically address your question, an exaggerated asymmetrical cam’s major drawback would likely be a significant loss of lower and mid-range torque. You would have to consider this likelihood and weigh it against the hypothetical gains on the very top end. From experience, I can tell you that the result is usually not a good trade-off.
9. When designing a cam, what are you looking at when you choose the lobe center, and the open and closing points for both the intake and exhaust lobes? – Micke S.
NJ: When designing a cam at Isky, the lobe centerlines and events (valve opening and closing points) are generated from other fundamental engine data. Most notable of these are bore and stroke, compression ratio, and cylinder head port flow capability. In other words, the rest of the induction system tells us how to design and subsequently recommend a camshaft for our customers. Centerlines and events are therefore not predetermined but derived from the cumulative effect of these important engine co-factors.
10. All the sales talk about the durability of bushed lifters seems to be around high valvespring pressures and drag racing. My question is, are there any limitations or concerns in using a bushed lifter with, say, a turbo cam (250-260 degrees duration with .540-.600 inch of lift) and spring rates in the order of 450-600 lbs for road racing engines spinning to 7,500 rpm? – Marvyn T.
NJ: Over a decade ago, when we developed the EZ-Roll needle-free bushing roller lifters, the overarching motivation was indeed to prevent catastrophic engine failure caused by the severely over-loaded needle roller bearings. Their patented Vortex-Wave oil delivery methodology and proprietary Epsilon ZX, ZMAX and the new EZ-Helix materials have always worked “in concert” to deliver consistent, reliable performance — something which had previously eluded racers for as long as radical cams, higher rocker ratios and their required heavier valvespring loads have been in vogue.
As such, it is sometimes assumed that utilizing a needle-free bushing style roller lifter in the more moderately loaded engine applications might not be advisable. I can’t speak for other manufactures who came out much later with their own style lifter, but let me reassure you that when it comes to the EZ-Roll lifters offered by Isky, nothing could be further from the truth.
To be certain, your results will be different than the all-out racing engines employing them. However, you will be pleasantly surprised to find out that means the lifters will last even longer – much longer – in your less severely loaded application. And EZ-Roll lifters are the only oil-restrictor-friendly needle-free rollers on the market. That should tell you something about their capabilities under adverse conditions.
Our EZ-Roll lifters are available for hydraulic roller street applications and are called the EZ Hydro. They take up to 200 pounds of seat pressure and 550 pounds open pressures, and 7,800 rpm. Our EZ Roll Solid Rollers come in several different versions including our new EZ-Helix that can take up to 1,400 pounds open pressure in very high boost applications where they can run with setups way past 50-60 psi with no RPM limits. The bushings have been shown to last 3-4 times longer than a needle roller in every application.