Don Terrill’s Speed-Talk

swampbuggy wrote: ↑Fri Dec 01, 2017 10:38 pm 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.

CamKing wrote: ↑Sat Dec 02, 2017 10:27 am

swampbuggy wrote: ↑Fri Dec 01, 2017 10:38 pm 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 wrote: ↑Sat Dec 02, 2017 10:29 am

CamKing wrote: ↑Sat Dec 02, 2017 10:27 am

swampbuggy wrote: ↑Fri Dec 01, 2017 10:38 pm 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.

HeinzE wrote: ↑Sat Dec 02, 2017 3:53 pm 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)

HeinzE wrote: ↑Sun Dec 03, 2017 12:37 pm 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

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.....

hoffman900 wrote: ↑Sun Dec 03, 2017 5:30 pm 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:

hoffman900 wrote: ↑Mon Dec 04, 2017 11:19 am 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).

Stan Weiss wrote: ↑Sat Dec 02, 2017 9:30 am 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