47.5 rule for flat tappet camshafts

[hoffman900]

Stan,

It was more to just get the mental gears turning.

Since he has a cam that breaks parts, he should profile that. At least then he would have an idea of what not to go over with peak acceleration numbers and minimize any jerk.

The issue might be several things with that cam however. It’s possible that you could design a more “aggressive” cam than with more area under the curve, but still have good dynamics that won’t break parts. I think both Mike and Harold have displayed their talent to do so and throw some numbers out there to at least get all of us thinking.

[Stan Weiss]

Let me add just one more thing about the intake lobe. It is a little asymmetrical. The center line got at 0.006" lifter raise (which just short of lash point) is about a degree different than at 0.250" lifter raise.

Stan

[CamKing]

Camking wrote---we have positive flow before TDC because the exiting exhaust flow causes a low pressure area below the intake valve during overlap. This siphon, suction or whatever one wishes to call it was discovered in the mid 1950's by none other than the legendary Ed Iskenderian. This was given the name 5th cycle, which was waaay before most cam companies came into existence. So for those of you folks who don't know the history ? The term 5th cycle is a lot more than a catchy name, it was a discovery !! Now you know the rest of the story Mark H.

False. Ed Winfield knew all about it. Long before Ed did. Ed just came up with a catchy name.
Try not to "Learn" your history from Isky catalogs.

[Frankshaft]

Camking wrote---we have positive flow before TDC because the exiting exhaust flow causes a low pressure area below the intake valve during overlap. This siphon, suction or whatever one wishes to call it was discovered in the mid 1950's by none other than the legendary Ed Iskenderian. This was given the name 5th cycle, which was waaay before most cam companies came into existence. So for those of you folks who don't know the history ? The term 5th cycle is a lot more than a catchy name, it was a discovery !! Now you know the rest of the story Mark H.

False. Ed Winfield knew all about it. Long before Ed did. Ed just came up with a catchy name.
Try not to "Learn" your history from Isky catalogs.

Lots of people make big claims in this industry. Just remember, a good salesman can sell ice cubes to eskimos.

[CamKing]

Camking wrote---we have positive flow before TDC because the exiting exhaust flow causes a low pressure area below the intake valve during overlap. This siphon, suction or whatever one wishes to call it was discovered in the mid 1950's by none other than the legendary Ed Iskenderian. This was given the name 5th cycle, which was waaay before most cam companies came into existence. So for those of you folks who don't know the history ? The term 5th cycle is a lot more than a catchy name, it was a discovery !! Now you know the rest of the story Mark H.

False. Ed Winfield knew all about it. Long before Ed did. Ed just came up with a catchy name.
Try not to "Learn" your history from Isky catalogs.

Lots of people make big claims in this industry. Just remember, a good salesman can sell ice cubes to eskimos.

Ed was once asked what his "5th cycle" cams provide, and he said something like "about $100k a year". He was a master salesman.

[Walter R. Malik]

When listening to ISKY talk at his seminars ...
He gives a LOT of the credit for some things he has marketed to Ed Winfield.

[HeinzE]

Bob,

Not sure if this adds anything but the intake lobe I have is .300" lift and the exhaust is .310" and are supposed to act through a 1.5 to 1 rocker. But in the Aermacchi engines, which clearly were never really intended to be "performance" engines, the lifters are in a horizontal plane on the right side of the cylinder on a center to center distance of 21mm and the pushrod cups on the rockers are on a vertical plane more or less on line with the midway point between the two lifters. Because of this the pushrods angle off toward the mid line of the lifter bore spacing and also upward to the intake rocker and downward to the exhaust rocker. This skewed pushrod ailignment certainly has to effect the transfer of the cam lobe shape to the valve motion, and is one of the main reason that anyone trying to maintain valve train stability in these engines and is still using the standard aluminum pushrods should think again, IMO. For what it's worth, the intake duration @ .050 measured at the vlave with .010" lash is 259degs. Pk lift is .435" At the exhaust valve @ .050 with .012" lash the duration is 269degs. Pk lift is .452" Maybe Stan can check this and shed some light on how the pushrod angles are affecting the transfer of the lobe profile to the valves.

Karl(HeinzE)

[twl]

Bob,

Not sure if this adds anything but the intake lobe I have is .300" lift and the exhaust is .310" and are supposed to act through a 1.5 to 1 rocker. But in the Aermacchi engines, which clearly were never really intended to be "performance" engines, the lifters are in a horizontal plane on the right side of the cylinder on a center to center distance of 21mm and the pushrod cups on the rockers are on a vertical plane more or less on line with the midway point between the two lifters. Because of this the pushrods angle off toward the mid line of the lifter bore spacing and also upward to the intake rocker and downward to the exhaust rocker. This skewed pushrod ailignment certainly has to effect the transfer of the cam lobe shape to the valve motion, and is one of the main reason that anyone trying to maintain valve train stability in these engines and is still using the standard aluminum pushrods should think again, IMO. For what it's worth, the intake duration @ .050 measured at the vlave with .010" lash is 259degs. Pk lift is .435" At the exhaust valve @ .050 with .012" lash the duration is 269degs. Pk lift is .452" Maybe Stan can check this and shed some light on how the pushrod angles are affecting the transfer of the lobe profile to the valves.

Karl(HeinzE)

If I am understanding the description correctly, the pushrods are angled to some degree. Any angle offset will cause some reduction of lift over the entire lift curve, calculated by using simple triangular geometry.

I have faced something like that in a cylinder head I designed., and it resulted in a 20% lift reduction due to the angle. So, I just compensated with more rocker ratio. I am certain that my example is more extreme, but the triangular relationship concept is illustrated.

[HeinzE]

twl,

Beautiful job! Did you post some photos and info on this some time back, while it was still being developed? What engine is this for? Any dyno test of old vs new? Yes, the pushrod angle situation is definitely obvious in your picture. In my engine it is not nearly as extreme.

Karl

[twl]

twl,

Beautiful job! Did you post some photos and info on this some time back, while it was still being developed? What engine is this for? Any dyno test of old vs new? Yes, the pushrod angle situation is definitely obvious in your picture. In my engine it is not nearly as extreme.

Karl

Thank you, Karl.

It is for a Royal Enfield Continental GT 535cc(32.1 cubic inch) aircooled single motorcycle. In stock form, it makes .84 hp per cubic inch at 4700 rpm, and .93 ft-bs torque per cubic inch at 4200 rpm.

Yes, I posted some pics a while ago. Since then, we have 2 dyno tests from different customers, one in the US and one in Sweden. They both tested within a half-hp of each other, at 1.34 hp per cubic inch peaking at 6000 rpm, and 1.14 ft-lbs per cubic inch peaking at 4700 rpm.
These are street applications with hydraulic lifters, requiring easy maintenance, good reliability, and longevity.

The primary goals were changing the valve angles from 26.5° to 20°, along with a raised port, better chamber design, and high ratio roller rockers (1.8:1).

It makes more power and tq everywhere in the rpm range, runs cooler, gets better mpg, revs higher, and is more reliable.

[hoffman900]

Tom,

I didn't know you were working on a billet head, looks great! Did HS do the rockers for this head too?

Karl,

Here are some Harold quotes:

Everyone is correct. Because of pushrod angularity, the valve only gets the Cosine of the lobe lift, which is varying as the lobe turns, but should always be above .975, or thereabouts....... Only OHC engines with direct-acting cam lobes deliver true lobe lift.
Pushrod deflection is also into play, and everyone should use the stiffest pushrod they can. On the cam side of the rocker arm, stiffest is most important. On the valve side of the rocker arm, lightest pays off a lot. This is why we have the return of the BeeHive spring---It lightens the valve side of the equation, a lot.
Angularity is a fact of life in engines, and the higher the lobe lift, the more angularity. Remember, the valve movement in the 75* ATDC is really more important than a few more thousands of valve lift. The conditions for good intake port flow are set up in those first 75*, not around max valve lift.

The higher the lobe lift, the larger variation in cosine, therefore net valve lift. Also offset pushrod seats/rocker arms, etc, alter the cosine angle, normally figured as a angle off of vertical. Now it is a compound angle.
Take care of what you can; Make the pushrod very stiff and rigid to accurately transmit the lift curve from the cam lobe to the rocker. Quite often the variation is about within the range of valve lash changes, and no one complains about those. As Harvey Crane says, "WEW!!"---What Ever Works!! If you are supposed to have an .810" valve lift, and instead you have .800", or .795", it is OK.
The actual rocker ratio, the base circle diameter, and the spring loads, as well as the pushrod stiffness, are the culprits in lost valve lift. Going from a stock SBC core size to a 60mm, with everything else the same, makes the cam over 140% stiffer. Just changing the base circle size 10% makes the core 21% stiffer. These little facts are one of the main reasons for core diameter growth.....

You can download a 2D CAD program for free. I use DrafSight, which is essentially AutoCad 2D pre 2008. When you have your cam and valvetrain profiled, you can easily work your way through the motion of the valvetrain, check contact points, P-V clearance, etc.

Like this:

[twl]

Tom,

I didn't know you were working on a billet head, looks great! Did HS do the rockers for this head too?

Karl,

Here are some Harold quotes:

Everyone is correct. Because of pushrod angularity, the valve only gets the Cosine of the lobe lift, which is varying as the lobe turns, but should always be above .975, or thereabouts....... Only OHC engines with direct-acting cam lobes deliver true lobe lift.
Pushrod deflection is also into play, and everyone should use the stiffest pushrod they can. On the cam side of the rocker arm, stiffest is most important. On the valve side of the rocker arm, lightest pays off a lot. This is why we have the return of the BeeHive spring---It lightens the valve side of the equation, a lot.
Angularity is a fact of life in engines, and the higher the lobe lift, the more angularity. Remember, the valve movement in the 75* ATDC is really more important than a few more thousands of valve lift. The conditions for good intake port flow are set up in those first 75*, not around max valve lift.

The higher the lobe lift, the larger variation in cosine, therefore net valve lift. Also offset pushrod seats/rocker arms, etc, alter the cosine angle, normally figured as a angle off of vertical. Now it is a compound angle.
Take care of what you can; Make the pushrod very stiff and rigid to accurately transmit the lift curve from the cam lobe to the rocker. Quite often the variation is about within the range of valve lash changes, and no one complains about those. As Harvey Crane says, "WEW!!"---What Ever Works!! If you are supposed to have an .810" valve lift, and instead you have .800", or .795", it is OK.
The actual rocker ratio, the base circle diameter, and the spring loads, as well as the pushrod stiffness, are the culprits in lost valve lift. Going from a stock SBC core size to a 60mm, with everything else the same, makes the cam over 140% stiffer. Just changing the base circle size 10% makes the core 21% stiffer. These little facts are one of the main reasons for core diameter growth.....

You can download a 2D CAD program for free. I use DrafSight, which is essentially AutoCad 2D pre 2008. When you have your cam and valvetrain profiled, you can easily work your way through the motion of the valvetrain, check contact points, P-V clearance, etc.

Like this:

Hi Bob,
Yes, been at it for a couple years now. It's for the late model Royal Enfield singles. It drops on with minimum difficulty for the user, and bolts up with all the existing inlet/exhaust/ancillaries.
The rockers on these are from T&D.
The 1.8" valve intake flows 215cfm@.500" lift.

Here's a few more pics.
Chamber


34mm intake port


34.9mm exhaust port

[hoffman900]

Looks great, Tom! Would love to see a 10/10ths build with that head.

They look like TD rockers, that's why I asked. They look like a OTS item too from some other application, I would have to imagine that was part of the plan (saving $$ and time).

[twl]

Looks great, Tom! Would love to see a 10/10ths build with that head.

They look like TD rockers, that's why I asked. They look like a OTS item too from some other application, I would have to imagine that was part of the plan (saving $$ and time).

Thanks Bob!

I have hopes of finding a customer who would like to do a shorter stroke (78mm) and larger bore(90mm) along with a 40mm throttle body on a steeper angle inlet runner. 8500 rpm. The 20° valve angle is just crying out for higher port angle, but I had to make it connect with the side-draft 34mm OEM inlet tract system for keeping the price down for street users.

It has a small chamber, so 10.5:1 compression ratio comes with the stock dished piston. A flat top could go over 11:1. Keeps piston mass low, and nice open flame travel. The street version now runs 10.5:1 without knock. Cold cranking compression tests of 190 psi, no problems.

[Momus]

Let me add just one more thing about the intake lobe. It is a little asymmetrical. The center line got at 0.006" lifter raise (which just short of lash point) is about a degree different than at 0.250" lifter raise.

Stan