47.5 rule for flat tappet camshafts

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47.5 rule for flat tappet camshafts

Post by HeinzE » Sat Nov 25, 2017 1:20 pm

Just came across an article in a Chevy forum that made reference to a "47.5" rule for flat tappet camshafts. Apparently this rule states that if you divide a cams duration at .050" by the pk lift and the answer is less than 47.5 then the cam is going to be too hard on the valve train and cause reliability issues. I've never heard of this rule and wonder if any of you, especially any cam designers, have heard of this and if it has any validity.
I'm not sure exactly how the 47.5 figure is derived because if you take a 250 deg cam and divide by .500" lift then the answer is 500. The only way this would seem to work is if you dropped the decimal point and set it up as 250/500, which would equal .5. So I guess the process requires ignoring the decimal in the lift figure and reading the first two numbers after the decimal in the answer as whole numbers and the third as a percentage. A bit confusing but maybe there is some value in looking at cam lobes in this way. As I said, never heard this before. What say you cam designers?

Heinz E.

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Re: 47.5 rule for flat tappet camshafts

Post by hoffman900 » Sat Nov 25, 2017 1:35 pm

This sounds silly.

There have been some great discussions on here from Mike Jones, Jon Schmidt, and the late Harold Brookshire.

On a flat tappet, velocity is constrained by the lifter diameter.

There are plenty of old, low lift / long duration cams that are killer on the valvetrain because they have terrible opening and closing ramp designs.

Another constraint that is more imposed by the system, is what kind of spring pressures can a flat tappet tolerate.

edit: NASCAR found a way around the limits of the flat tappet profile by running very large rocker ratios. As Jay points out below, they found no more power with a switch to roller camshafts, but it necessitated the use of less rocker ratio. If they weren't limited by valve springs (pneumatic 'springs',) then all bets are off.

Let me dig up some old posts...
Last edited by hoffman900 on Sat Nov 25, 2017 1:59 pm, edited 1 time in total.
-Bob

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Re: 47.5 rule for flat tappet camshafts

Post by hoffman900 » Sat Nov 25, 2017 1:56 pm

Mike Jones (Camking):
If you could make everything out of unubtainium and run 1,000# of spring pressure, that would be true, but it's not in the real world.
The acceleration limits of a roller are go beyond the most aggressive flat tappet cams.
If you tried to run the max acceleration on a flat tappet cam as high as I use on my inverse radius rollers, you'd need more spring pressure then a flat tappet cam could stand.

Here's some Max accelerations I just looked up.
Flat Tappets
Comp Cams restrictor plate cup cam: .000294"
Jones Cams restrictor plate cup cam: .000372"
My most aggressive flat tappet cam: .000422"

Rollers
My average IR cam: .000393"
A Pro stock IR cam: .000438"
A asymmetrical IR cam: .000463"
Like Harold said, the Max velocity dwell is a must.
We started doing it a couple of years after Harold(around '83)
We called those flat tappets our E.M.V. series (Extended Maximum Velocity).
I've refined the way we do it over the years, but it's still doing the same thing.
As far as ramps go, spintron testing and my own way of thinking have moved me in a different direction them most cam designers.
The roller will show benefit on any engine where the max velocity of the flat tappet is below what the engine wants.
BTW, I don't design flat tappet cams for pushrod engines. All my F.T. designs are actually roller designs, designed for a 52"-58" radius roller follower.
Harold Brookshire (UDHarold):
The cam used in Alan Johnson's Nr 1 Qualifier at the O'Reilly Mid-South Nationals the other week had a peak acceleration rate under .000330"....
And this was on a 70mm core, .850" roller wheel diameter. This is the one that would hold 10,500 for over 90 secs, 1.090" valve lift...
And EVERY SBC flat tappet cam I design has a peak acceleration rate of .000383", and a peak velocity rate of .0070400". Under .106389" I use the same ramp on all of them, ie, the opening ramp is that high, and of course, closing ramps are different. Of course SBFs and Mopar solids have different peak velocity rates, also.
Cam design is an infinitely challenging world.
If you are looking at a roller cam and a flat tappet, and they have very similar durations at .020", .050", and .200", you are looking at either a very well designed flat tappet, or a very poorly designed roller.
Back in the early 1990s at UltraDyne, I designed a .904" Mopar/AMC flat tappet that was, and still is, 282 at .020", 255 at .050", 172 at .200", and .3879" lobe lift.
A popular roller cam from Memphis is 288 at.020", 252 at .050", 169 at .200", and .420" lobe lift.
My flat tapppet is limited to a little over .0075"/* max velocity, and all roller cams are unlimited on max velocity.
My shorter seat-timing and fatter area at .200" gives a higher port velocity through part of the lift cycle. AFAIK, these 2 cams have never been compared in the same engine, so I do not know the power difference.
However, my solid lifter has always been a strong running cam.
My current roller cam is 283 at .020, 255 at .050, 180 at .200, and .4164" lobe lift. I also have this cam with .4544" lobe lift, and with .4854" lobe lift. They are all identical from .050" lobe lift on down.
This is the nice thing about roller lifter cams----Lobe lift is rarely a problem, unless limited by the core's capability.
I even have an .842" solid lifter profile that is 288 at .020, 259 at .050, 171 at .200, and .3783" lobe lift. It stays over .017" away from the edge of an .842" tappet.
We've come a long way in the past 30 years......
During overlap, it is the AREA-UNDER-THE-CURVE(Combination of valve lift and duration, of both valves) that govern what happens. Look at this:
UD 288 Flat Tappet--288@.020, 255@.050, ,128"@TDC on 104 ICL.
UD 288 Roller--------288@.020, 255@.050, .125"@TDC on 104 ICL.
The valve lifts, .200s, etc, are different.
Peak Velocitiy, Flat Tappet---.00705"/*
Peak Velocity, Roller----------.00940"/*
Dyno test, same engine, different lifters, cams, and springs---Pro Motor Engineering. Roller made 30ftlbs more at 5200, 60 BHP more at 7200.
Both were excelllent examples of the art, and are still good today.
Remember, the engine sees the total valve lift curve as the cam, not what it is at .050". The part before TDC on the intake is seen as bad, the good stuff occurs AFTER TDC.
Two cams with the same intakes and exhausts, but different LSAs, will dyno with 2 different power curves, even when both cams are put in with the identical INT CL. The differing positions of the exhaust cam give different cylinder pressures before the intake valve opens BTDC, and this affects the reversion, and the recovery, and the intake port velocity, and the cylinder filling.
Sorry I've missed so much of this thread, and this will be a short tid-bit for thought, as I have to take my wife to work.
Flat tappets are limited by velocity.
.842"=.00705"/*
.875"=.00733"/*
.904"=.00758"/*
This keeps a small distance between the edge of the lifter and the contact patch on the lifter. The smaller the distance, the smaller the area of contact, and the much higher the spring load in lvs/sq. in---Wipeout!
Rollers are controlled by max acceleration rate and BASE CIRCLE RADIUS--bigger bearings allow higher usuable max acceleration rates before too much negative radius of curvature. If the radius of curvature is too small, the cam cannot be physically made. I used to joke about designing cams with the radius of curvature so severe that the design was a teardrop of metal suspended above the base circle---the radius of curvatures had cut through to the other side......
Now on flat tappets. A Chrysler profile must be made as a roller to run in a Chevrolet, or does it?
Around 1990 Crane had, and still does, a Chrysler-only flalt tappet cam, the F-258/3735. It was 294 at .020, 258 at .050, 166 at .200, and .3735" lobe lift.
In April 1980 I designed the .842"-tappet design, my F4(4th flat tappet designed at UltraDyne). The F4 was 292 at .020, 259 at .050, 170 at .200, and .3677" lobe lift.
In 1995 I designed the .904"-tappet design, the NF63.
The NF63 was 294 at .020, 267 at .050, 185 at .200, and .4058" lobe lift.
Neither of my 2 flat tappets got any closer than .017" to the edge of the tappet, and the F4, the 292, has gone over 100,000 miles in a number of engines.
Think on that, I'll try to answer more later this afternoon.
The way I look at it, overlap is harmful to engines, not beneficial. And I call those derivatives 'snap, crackle, and pop', although Harvey Crane coined those terms. I like them a lot better than 'quirk'!!!
This information on overlap is irregardless of type of tappet. When cam lift curves are designed, the type of lifter lies in the head of the designer, and his choice of ramps.
Hydraulic-type lifters, both flat and roller, take all the compression out of the valve train by .004" lobe lift, according to the SAE. The valve is about .001" off the seat at this lobe lift. You can only accelerate the valve so fast in that short of a lift(Think 1/8 mile vs 1/4 mile.....) and hydraulic rollers, because of manufacturing difficulties, have trouble using very high acceleration values that low. When I designed the VooDoo hydraulic rollers, I, as always, used the same ramps regardless of cam lift. I had to redesign the ramps for the higher-lift cams because the base circle got too small. The ramp that worked perfectly for .510" valve lift caused trouble with .550" valve lift---in manufacturing.
I view the intake overlap as bad, and have designed my cams accordingly for 30 years. The sooner you open the intake valve, the more reversion you expose your engine to, and the more you delay filling the cylinder. I like to delay the intake valve's opening, then open it fast, both velocity and acceleration. Flat tappets, either solid or hydraulic, are limited by a maximum velocity , roller cams are not. Hydraulic cams generally run higher acceleration rates than solids do, this has a lot to do with maximum RPM expected. Roller cams, are as always limited by max acceleration rates, although I am improving my math abilities to raise the max rates usable.
Reversion hinders intake flow. Before TDC, when the intake valve opens, the cylinder has exhaust gas in it being pushed out of the cylinder. This exhaust gas has both volume and pressure, and when the intake valve starts off the seat, this exhaust gas enters around the intake valve toblock the intake port. Later intake valve openings reduce this reversion, allow earlier intake port recovery, and allow higher intake port velocities---IE, better cylinder filling.
At least it's worked this way for me for 30 years.......
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.....
These are all tools in a cam designer's tool box.
I have been using dwell at max velocity since 1980, with 90% of the UD flat tappets being that way, and at least 50% of the hydraulics.
The UD solids and hydraulics were done on a Texas Instruments pocket calculator. All of those UD printouts were 2 sheets of notebook paper.
I have never designed a roller using dwell at max velocity---It is not needed---and I know of no designers who do.
All the VooDoo hydraulics and the new solids have dwell at max velocity.
The main questions is always: How much?
This is the only way to achieve high lobe lift with a limited-diameter flat tappet, either hydraulic or solid, and keep a reasonable nose radius.
The only other way is to use higher and higher nose accelerations to keep the max velocity on the tappet, but this requires higher and higher open load on the valve springs, and the nose radius gets smaller and smaller, and the smaller nose radius is less able to withstand the open spring pressures.
Not all flat tappets, solid or hydraulic, have dwell. In fact, looking at all cam companies, probably more do not have dwell than do have dwell. Sometimes when I do hydraulics or solids that have a decent duration and not too high of a lobe lift, I don't bother with dwell either. Some of UD's most successful hydraulics, and some damn good solids, do not have dwell. Dwell is only used when it needs to be used, as it is more difficult than designing cams without dwell.
The 'No-Pulse' ramp is best explained by Harvey Crane, as he thinks it is his baby, and he charges for it, as that is how he makes his living now.
The reversals in positive acceleration are very common, on almost all factory designs, and used by most cam designers. I use them quite commonly on closing ramps. It is just a function of the exact velocity, acceleration, and jerk values you are using, and the duration of the ramp.
The charts on Harvey's website are tremendously informative, but they do not tell you everything, and all the charts are symmetrical. You need to study the charts, and do a lot of thinking.
I hope this has been of help in answering your questions.
ook at the middle chart you posted from Harvey Crane's website, the 'No-Pulse' ramp.
There is a line in red towards the bottom of the chart. This is the Jerk curve, and careful study of it will reveal some secrets.
It is not easy to design, but it works extremely good on the opening side of cam lift curves.
The 'Acceleration-Reversal' ramp is used quite commonly on the closing side, and helps ease the lifter down on the base circle.
At UltraDyne, my 288F was master F1, done in April 1980.
The following UD designs were all done using the computer printout of the 288F opening side:
F9 276 243 .3450"
F18 280 247 .3500"
F8 284 251 .3533"
F1 288 255 .3600"
F4 292 259 .3677"
F13 300 267 .3823"
F12 308 275 .3933"

The other, bigger, cams were either 4-equation cams, or else Dwell-at Max-Velocity designs where I traded dwell for a lower nose acceleration and a more rounded nose, for higher open pressures and RPM.
My 288/296H8 hydraulic, .485"/.507" valve lift with 1.5s, was my first hydraulic with dwell at max velocity.
These were my more successful cams for all of UltraDyne's life.
Jay Wiles (Warp Speed, dyno operator at Hendricks)
Efi and roller cams have had a minimul impact on power output!
We actually lost power going to EFI, but were able to get most of it back due to the ignition system, and being able to optomize the ignition map through the whole rpm range.
Roller cams essentially do very little, as we are velocity limited by current valve spring technology already.
Mike's response to the above:
That's really not relevant to this application. NASCAR had learned to get around the max velocity limits of the flat tappet lifters, by increasing the rocker ratios(up to 2.4:1), so they could get the valve velocity the engine wanted, without over-riding the tappet diameter. The roller profiles they're running in NASCAR now, have basically the same valve lift profile as the flat tappet cams they were running.
That's not going to be the case, with conventional rocker ratios.
If you're dealing with a rocker ratio in the 1.5 to 1.7 range, if you didn't pick up 20hp going to a roller with similar duration, it would have to be one real bad cam design.
As Jay points out, you can take care of what is happening at the valve, with a flat tappet, with very large rocker ratios, since what is happening at the lobe is limited. On the rollers, they have dialed out rocker ratio in turn for 'fatter' lobes.
-Bob

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Re: 47.5 rule for flat tappet camshafts

Post by hoffman900 » Sat Nov 25, 2017 2:12 pm

Some more:

Harold Brookshire:
Since if there's anything I know, it's History, here goes.....
Prior to the widespread use of computers, very few mushroom cams were made. The earlier designers had enough trouble making cams follow their normal lifters, much less an extra-wide one.
By the mid-70's, NASCAR racers had learned enough to know that the Chrysler .904" tappets allowed more aggressive lift curves than the .842"-.874" tappets. NASCAR's compromise?---Let everyone use a Mushroom lifter. Chevrolet went to .960", and NASCAR settled on that, even though Chrysler had some 1.000" ones. Those were used in drag racing.
In 1978 I designed the Comp Cams' 310/318 mushroom cam, 268/276 at .050, .390"/.410" lobe lift. In 1980 Buddy Baker won the 1980 Daytona 500 with this cam, and it is still the fastest Daytona 500 ever run. NASCAR went to restrictor plates, and then to .874" max tappet diameter.
Cams with flat-bottom lifters, either hydraulic, solid, or mushroom, are design-limited by velocity. Here are the max safe velocities(more or less) for the various lifter diameters:
.842" .00705"/°
.874" .00733"/°
.904" .00759"/°
.960" .00808"/°
There ARE tricks around these numbers, but not all cam designers know them, or else how to use them right.....
Cams with rolller lifters, either hydraulic or solid rollers, are design-limited by acceleration and base circle diameter. A peak acceleration rate that may be un-makable for a .900" base circle may be usable for a 1.100" base circle.
There are obviously tricks around these limitations, also. The hard part is knowing the tricks, not the basic theory, and when and how to use the tricks....
You and I are probably calling different things 'aggressive', but basically, yes, mushroom tappet cams are more aggressive, even older ones.
The thing is, whatever you can do to a .842" tappet, you can also do to a .960", only the lifter is moving about 15% faster. That is a whole lot faster in cam design.
If you're not careful, you can move the intake valve faster than the air can follow the intake valve/piston. Then the engine is always overcammed---I have done this in NASCAR, and I have had to slow the cam down---dealing with .874" tappets!
My famous 288R roller cam would require a 1.155"(VW-size!) mushroon tappet if I cut it out as a flat tappet cam, as it is over .0094"/° at max velocity.
Flat tappets, hydraulic or solid, are limited by max cam velocity. If the velocity gets too high, the point of contact between the lifter and the cam moves to a point OFF the lifter. The edge of the lifter starts digging into the cam lobe, and it wears out in a very short time.
Each different diameter lifter has its' own limiting velocity, however, bigger lifters on a smaller-diameter lifter profile do not lift the valve any faster. They only make a larger contact point, lowering wear on that combination.
The limitiing velocities are around .007"/* for .842" lifters, about .0073"/* for .874" lifters, and over .0075"/* for .904" lifters.
Roller cams are not limited by velocity at all, but by peak acceleration rates.
If you accelerate the lifter too soon and too hard, the cam becomes hard to manufacture, and even impossible in some cases.
Flat tappets accept a higher acceleration rate than roller tappets do. Flat tappet rates run from .00035"/*2, to over .000600"/*2. Small block Chevrolet roller cams start forming inverse radii(the plural of radius) at .000350"/*2. At the same time, peak velocities run in the .009/" to .010"/* range.

As you can see, there's good and bad with both of them.

UDHarold

BTW---In the 1960s possibly into the early 1970s, Crane Cams used to offer the same lift curve in solid and in roller form. They did not look alike at all, but like the typical solid tappet and the typical roller tappet camshafts.
They look the way they do because of how the models are made. At UltraDyne I used a 1 1/2" wide flat wheel to make solids and hydraulics, a different wheel with a .350" radius for hydraulic rollers, .375" for solid rollers.
To move this thread back towards its' subject, the truth is they can be of equal aggressiveness.
It all depends upon the cam designer.
Back in 1980, when I started UltraDyne, I designed a flat tappet 288 at .020 cam, and a roller tappet cam, also 288 at .020. they were both 255 at .050, but there it stopped. The flat tappet was 166 at .200, and .360" lobe lift. It was the most popular flat tappet cam we made.
The roller was 176 at .200, and .4176" lobe lift. It was the most popular roller cam we ever made. In the same 355 SBC at ProMotor Engineering, there was a 60 BHP and 30 ftlb of torque difference in favor of the roller.
Yet measuring Major Intensity from .020 to .050, they were both 33 degrees. I do not remember the offset on the flat tappet, but the roller was 15 on the opening side, 18 on the closing.
Currently, ALL my solid lifter designs, both VooDoo and racing, are 28.68 MI for the same .020 to .050, with 13.44 on the opening, 15.24 on the closing. My popular 31 MI designs are 14.02 on the opening, 17.29 on the closing side. My oval track/SuperStock rollers are 28.43 MI, 13.45 on the opening, 14.98 on the closing.
As you can see, both solid lifter and roller lifter designs have just 28 degrees of Major Intensity, and are of equal aggressiveness.
However, other factors come into play. The roller has a lower peak acceleration than the solid lifter, but a much higher peak velocity(.00937"/* vs .00704"/*).
We've been able to achieve 5* LESS Major Intensity in the past 29 years, and still keep the .050 durations and .050 offsets exactly the same. Both the .200 duration numbers and the lobe lifts have gotten higher.
Ain't science wonderful?????
ith a valve spring bucket 1.38" in diameter, you divide by 2(.690") and subtract your clearance from the edge(.690"-.020"=.670"), then divide by 57.3. Your answer should be .011693"/* max velocity. A higher design velocity gets closer to the edge of the spring bucket----How brave are you?
Finding out this number is most easily done using various cam analysis software, such as CamDoctor, etc. Trying to measure it with a degree wheel is nearly impossible. Most cam designers should be able to give you this number on any given design---For instance, all my current solid flat tappets for the SBC/BBC .842" diameter lifter are at .007041"/*. My old .960" diameter mushroom designs were around .00807"/*. Most of my roller designs are in the .0085"/*-.0095"/* range.
Velocity numbers are only important in flat tappet solid and hydraulic designs, acceleration numbers are important in roller designs.
The highest lobe lift I have designed a DOHC bucket follower for has been .575", and yes, it did not run off the tappet.
-Bob

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Re: 47.5 rule for flat tappet camshafts

Post by Frankshaft » Sat Nov 25, 2017 2:32 pm

who's concept is this?

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Re: 47.5 rule for flat tappet camshafts

Post by HeinzE » Sat Nov 25, 2017 2:50 pm

In the article on the Chevy forum someone attributed this formula to someone at Isky cams.

https://www.google.com/url?sa=t&rct=j&q ... 9Y-Mks1T7W

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Re: 47.5 rule for flat tappet camshafts

Post by CamKing » Sat Nov 25, 2017 3:17 pm

HeinzE wrote:
Sat Nov 25, 2017 2:50 pm
In the article on the Chevy forum someone attributed this formula to someone at Isky cams.
That makes sense.
Isky is about 50 years behind in camshaft design and development.
They are pretty good at coming up with catchy names, like "5th Cycle" :lol:
Mike Jones
Jones Cam Designs
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jonescams@bellsouth.net
http://www.jonescams.com
(704)489-2449

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Re: 47.5 rule for flat tappet camshafts

Post by peejay » Sat Nov 25, 2017 3:52 pm

That "rule" could only be applicable for a certain base circle and a certain lifter diameter.

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Re: 47.5 rule for flat tappet camshafts

Post by HeinzE » Sun Nov 26, 2017 10:52 am

Peejay,

That was one of my first thoughts also. I ran several cams in a motorcycle engine that easily passed this "test" that were absolute parts destroyers.
We broke intake valves almost every race until I finally had an experienced cam designer draw up a set of lobes specifically for this engine.
As all the posts above show, there is a LOT more to cam lobes than a simplistic relationship between just duration and lift.

HeinzE

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Re: 47.5 rule for flat tappet camshafts

Post by hoffman900 » Sun Nov 26, 2017 11:56 am

HeinzE wrote:
Sun Nov 26, 2017 10:52 am
Peejay,

That was one of my first thoughts also. I ran several cams in a motorcycle engine that easily passed this "test" that were absolute parts destroyers.
We broke intake valves almost every race until I finally had an experienced cam designer draw up a set of lobes specifically for this engine.
As all the posts above show, there is a LOT more to cam lobes than a simplistic relationship between just duration and lift.

HeinzE
Heinz, what kind of bikes are you working on?
-Bob

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Re: 47.5 rule for flat tappet camshafts

Post by HeinzE » Tue Nov 28, 2017 12:00 pm

hoffman900,

The engines I am working with at present are Aermacchi (The old Harley-Davidson Sprint) 350cc singles and are the long stroke version with a 75mm bore and 80mm stroke. These are flat tappet and pushrod and in stock form have about as bad a set of ports as is possible to create- exceeded only by the early Ducati singles and Bevel Twins. In working with these I quickly realized the factory cams were terrible, some having as much as 298degs of intake duration at @.040". I hit a real barrier with the stock cams so I turned to a local cam company for some that fit a profile more like what I thought might work a bit better. All in all I tried 6 different grinds. Most made a bit more power than the best factory cam...which turned out to be the Aermacchi N6 grind, but not like I'd hoped and the engines never accelerated the way I thought they should and broke valves almost every race. All of these cams would easily pass the 47.5 rule. Finally, by way of an old friend with a bit of history in NASCAR, I was put in contact with a cam designer in North Carolina who took an interest in my project and agreed to draw up a set of lobes for me specifically for my engine. This turned out to be without question the best money I ever spent on the engines. With a little tuning and a few exhaust pipe experiments the engines picked up over 16% more power, had a wider power band with more torque, and best of all in the 6 years of using this grind neither engine has had a single valve train issue. I configured these engines to pk at 4,000fpm piston speed, which could very easily be pushed up to 4,400 or more, but these are classic racers and parts are fairly rare with most major components custom made for or by me, and I don't relish the idea of complete (read - expensive) rebuilds every season. No one pays us to go racing and we try to keep this whole thing in some kind of perspective (although my wife would surely tell a very different story). Currently the two engines I have are within .2hp of one another and put out between 39.2 hp and 39.9 hp SAE at the rear wheel depending on the exhaust we use. Peak power is just shy of 7,800 with pk torque comming at about 5,500.

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Re: 47.5 rule for flat tappet camshafts

Post by hoffman900 » Tue Nov 28, 2017 6:04 pm

Heinz,

Very cool.

This is something I've noticed with vintage platforms - both cars and bikes. A lot of development was done decades ago. It worked then, but as you have found, it's a long way off from today. A lot of the older platforms are subject to the using period racing pieces and / or lots of pseudo science. Seeing how bad things were stock, it allows anyone to make some kind of gains and look like a hero.

That sounds like a project Dyno Cams would take on, they also have been know to grind some NASCAR lobes for some of the teams.

You'll likely enjoy this thread. It spurned out of a user building a homemade Spintron and testing different period camshafts. Not surprisingly, the older designs were pretty hard on the valvetrain for what they offered in terms of duration and lift. Another user worked with Jim Dour (Megacycle) and updated one with smoother lash ramps and gained a bit more lift as well.

Spintron thread:
https://www.accessnorton.com/NortonComm ... ron.18787/

Updated cam:
https://www.accessnorton.com/NortonComm ... mps.23682/

Additionally, with the help of Jon Schmidt, PCNSD, and a few others, I'm working on mapping out the valvetrain for the SR/TT500. Jon has measured up the valvetrain and created it in CAD, the Johnson camshaft roller rockers, and is working on the stock style radius pad lifters. I've had the Johnson cam profiled, and have a borrowed stock cam and an older Megacycle grind to profile. What drove me to this was 1) for 1D simulation work (and the need for accurate camshaft data), and 2) the suspicion that the camshaft profiles could be more aggressive for the valvetrain or were copied from other applications and may not be ideal - leading themselves to some odd dynamics.

Here is how the Johnson J2 (.75" dia. roller follower) plays out.

Intake Lobe:
Duration @ .020: 301*
Duration @ .050: 268*
Duration @ .200: 184*
Lift: 0.419"
Peak Open Acc. 0.000331
Peak Nose Acc. -0.000258
Peak Close Acc. 0.000264
Peak Velocity 0.008525"/*


Exhaust Lobe:
Duration @ .020: 294*
Duration @ .050: 261*
Duration @ .200: 175*
Lift: 0.397"
Peak Open Acc. 0.000249
Peak Nose Acc. -0.000249
Peak Close Acc. 0.000316
Peak Velocity 0.007832"/*


Here is what it is when translated through the rocker:

Intake Valve:
Duration @ .020: 303*
Duration @ .050: 275*
Duration @ .200: 203*
Lift: 0.524"
Peak Open Acc. 0.000333
Peak Nose Acc. -0.000309
Peak Close Acc. 0.000415
Peak Velocity 0.010222"/*


Exhaust Valve:
Duration @ .020: 296*
Duration @ .050: 267*
Duration @ .200: 194*
Lift: 0.494"
Peak Open Acc. 0.000371
Peak Nose Acc. -0.000305
Peak Close Acc. 0.000326
Peak Velocity 0.01021"/*

I'm looking forward to seeing how this cam compares to others.
-Bob

pdq67
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Re: 47.5 rule for flat tappet camshafts

Post by pdq67 » Tue Nov 28, 2017 6:16 pm

Boy, I miss UDHarold!

pdq67

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Re: 47.5 rule for flat tappet camshafts

Post by hoffman900 » Tue Nov 28, 2017 7:19 pm

pdq67 wrote:
Tue Nov 28, 2017 6:16 pm
Boy, I miss UDHarold!

pdq67
No doubt. I know other cam designers can write posts like his, but I also know they're trying to make a living. Harold by the time he was posting here was semi-retired and was pretty candid. I'm glad he shared what he did. I really wish he posted more of the math behind his designs before he passed. Paraphrasing Mike Jones, "he was more a mathmatician than cam designer".

While before my time, it's pretty cool to know how accessible he was considering he designed the camshaft (among other winning designs) in Buddy Baker's car here, and as you watch Buddy's car open up car lengths on the field, read Harold's design philosophies: https://www.youtube.com/watch?v=HVgW39STUFg&t=3380s
-Bob

Walter R. Malik
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Re: 47.5 rule for flat tappet camshafts

Post by Walter R. Malik » Wed Nov 29, 2017 10:14 am

hoffman900 wrote:
Tue Nov 28, 2017 7:19 pm
pdq67 wrote:
Tue Nov 28, 2017 6:16 pm
Boy, I miss UDHarold!

pdq67
No doubt. I know other cam designers can write posts like his, but I also know they're trying to make a living. Harold by the time he was posting here was semi-retired and was pretty candid. I'm glad he shared what he did. I really wish he posted more of the math behind his designs before he passed. Paraphrasing Mike Jones, "he was more a mathmatician than cam designer".

While before my time, it's pretty cool to know how accessible he was considering he designed the camshaft (among other winning designs) in Buddy Baker's car here, and as you watch Buddy's car open up car lengths on the field, read Harold's design philosophies: https://www.youtube.com/watch?v=HVgW39STUFg&t=3380s
I remember Harold and Don Teweles collaborating in the 70's at General Kinetics Cams on quite a few really good flat tappet cam profiles ... regular and mushroom. Some great running OHC profiles for slider followers, too.
http://www.rmcompetition.com
Specialty engine building at its finest.

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