Camshaft lobe design

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kirkwoodken
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Post by kirkwoodken »

Larry Heath:
Last year, I ordered one of UDHarold's old grinds from Lunati, ground on a .900 BC. When I checked out the cam, it was 4 degrees short @.200 lift. I was disturbed by this and called Steve at Lunati. He checked a standard base circle cam in stock and said it came up to spec. Out of curiosity, I called Kirk at Bullet and asked him if grinding a cam to a smaller base circle would change the specs by 4 degrees. He said he didn't know for sure if there would be a change, but he had the same cam on the shelf in both standard and .900 BC. He called back about three days later and confirmed that there was a 4 degree difference in the two cams he had.

I sent the cam Lunati cam back for a standard base grind, and got the 4* back that was supposed to be on the cam.

What I found interesting was two different companies ground four different cams with two different masters on two different machines, were measured by two different people, and came up with the same measurements that I came up with. I think that tells a lot about the cam grinding process and the cam grinding industry's QC.

I enjoyed a no hassle process with Steve at Lunati, and got some mind soothing help from Kirk at Bullet, even though I did not buy a cam from Bullet. For future reference, I learned that going to a small base circle makes a cam smaller, and going to a larger base circle, than the original design was for, makes a cam bigger.

If you want a small base circle cam, you should talk to the cam grinder about going to the next size up cam, if that cam was designed for a larger base circle. All the pros know this. I'm an occaisonal backyard cam buyer, so it was news to me.
Last edited by kirkwoodken on Sun Jan 20, 2008 6:23 pm, edited 2 times in total.
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Post by Larry Heath »

Yes I have run afoul of this problem in the past. I like to choose lobes for myself I have in the past ended up with the opposite problem as your example. Most of the profiles I use are, I assume designed around a different, smaller, BC than that of the typical BBF billet core, the BC of the BBF Billets tend to be bigger I guess and I therefore need to select a few degrees less duration to actually get what I want when it is ground on the larger Ford billet.

I have also run into this problem a time or two when using tech support recommendations as well. I assume that the people on Democrat Road have the mindset that I am just another guy that doesn’t know and that can’t or won’t check that I got, precisely, what I asked for before sticking it in the engine. Still all in all the suff I've used from them over the years has worked as good as any.

Later Larry
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Post by SWR »

Larry Heath wrote: I assume that the people on Democrat Road have the mindset that I am just another guy that doesn’t know and that can’t or won’t check that I got, precisely, what I asked for before sticking it in the engine.
That's a problem more than one place... I have stopped believing the cam cards I get with cams,I have yet to recieve an off-the-shelf cam that's exactly what it says on the card. :roll:
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Post by SchmidtMotorWorks »

Jon,
Just looked up a lobe and in this case, over the nose the proposed tappet lift increase was .0035--" in 6° cam. Much the same for the closing 6°. To illustrate how little movement there is around lobe C/L.
The curves are laid out from the center to both sides.
Generally a narrow lobe with a fixed tdc lift will have a narrow C/L and so on. regards
I think I understand what you are saying but would like to be clear.

Are you saying that the lobe center is determined by a a target valve lift at TDC?
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Post by AROT »

Jon,
No, more or less trying to say that lobe C/L is a design point in the layout but not a critical point to the engine. There being so little movement around it. With a lower rpm application where the power curve wants to be as broad as possible, overlap will be limited. As the rpm increases the duration will also. Trying to maintain some low speed
performance will move things more toward the closing side (inlet). So it may turn out 2/3 of the duration increase moves toward the closing side
thus shifting the lobe C/L in the same direction. (mostly thinking of push rod application) regards,
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Cam Manufacture

Post by UDHarold »

Back in the days when we used physical cam masters, the model and the master were ground for a desired base circle size. Making a cam off that master to a different base circle size, either larger or smaller, produces a different pressure angle between the roller lifter and the lobe. Notice, this measurement difference does not exist with flat tappets, only with rollers. A different pressure angle translates into a different duration at a given lift. I have never noticed a power difference when a 406-base circle cam is run in a 355, assuming the same cam grinds.
What I use now is the Landis 3L, which cuts to 7 decimal places, and so we design to 8 decimal places. Part of the cutting information is the base circle size AND the roller wheel diameter. Mathematically it cuts, with its' big cutting wheel, the exact place where that roller wheel runs on the cam. Every cam that we make is designed for the exact engine it is going in. We put no SBC cams in BBCs, etc.
Because CCC is part of an engine development company for Dodge Motorsports, we must ensure that all cams we cut out are accurate for their purposes.
Besides the LANDIS 3L, they got us an Adcole measuring machine. We measure EVERY cam that we make on the Adcole, on every lobe and journal on the cam. We keep the 360* information, and supply the customer with a printout showing the variation at .020", .050", .200", max lobe lift, and LSA, for every lobe on the cam.
We seem to be running 2/10ths degree variation of the cutting data. The cams seem to make better power and dynamic stability over the old ones from the 1980s, and I feel the accuracy is part of the reason.
Information about the jerk rates is propietary, and not for release.
Our Landis 3L has both a 450mm grinding wheel, and a 140 mm one.
All cam grinding data is stored in digital format.
I hope I can always grind on a Landis 3L, unless they make something better.
Do you guys know that I never calculate the overlap unless someone asks me what it is?

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Re: Cam Manufacture

Post by David Redszus »

We keep the 360* information, and supply the customer with a printout showing the variation at .020", .050", .200", max lobe lift, and LSA, for every lobe on the cam.
Harold
Since every cam is carefully measured as part of the quality control process, why is it so difficult to obtain accurate lift vs duration data for every point of lift from .0005" (not .020, .050 or .200"), from the cam makers? Why is it necessary for the serious engine builder to have to measure purchased cams on CMM equipment or use other computerized cam measuring devices?

I suspect the days of black magic designs and proprietory cam shape information are long gone. Everything can be accurately measured and reverse engineered, if there is a need and desire to do so. Just ask the Chinese how they do it.
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CamMeasuring

Post by UDHarold »

David,

Supplying data that close is revealing trade secrets. In the old days, rival cam companies just bought their competitor's cams, and made copies. The copies were so inaccurate, as were the originals, that it was difficult sometimes to tell it was a copy.
Sometimes manufacturers bought copies of their own cams to copy.......
If you doubt your cam supplier's ability to make an accurate cam, you should get another cam supplier.
The Adcole does a very good job of measuring cams, and there are tricks involved getting them to measure an unknown cam. They are really a quality-control instrument, comparing a cam AS MADE, against the cutting data used to make the cam.
Supplying 5760 data points(16X360=5760) at 5 or 6 decimal places for all 16 cam lobes would tend to stupify most racers. I suppose you also expect head porters to provide data on all 16 ports.
Without an accurate way of making a master, it doesn't matter much anyway.
Perhaps we should all just add another 0 to the cam price tag, if we have to supply manufacturing data with each lobe.
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Re: CamMeasuring

Post by CamKing »

UDHarold wrote: Perhaps we should all just add another 0 to the cam price tag, if we have to supply manufacturing data with each lobe.
Exactly.

I supply #'s at Seat, .050", and .200".
I can supply a lot more, but at what price?
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Post by Cammer »

A few years back when checking camshafts on an Adcole I had blueprints and full specifications on every camshaft and checked to this data. I was working in prove design engineering at the time and we were trying to sort supplier camshafts for a new engine design.

I see manufacturers like CompCams touting their Adcole machines and can only wonder what they used previously. Adcoles have been around for years, and though the machines I used were set up like a lathe, the principle is the same.

I can remember checking camshafts way back in the day on a manual checker. If memory serves me there was a handle you cranked and a very precise degree wheel with indicators on every surface. I have used checkers that drew traces on graph paper.

I will say that comparing camshafts by looking at 0.050" duration numbers and lift falls short of providing an accurate picture of camshaft performance. Spin fixture results would be an asset to engine builders. Racers need to find a good camshaft supplier and communicate openly to find the best camshaft.

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Re: CamMeasuring

Post by David Redszus »

If you doubt your cam supplier's ability to make an accurate cam, you should get another cam supplier.
Using modern, computer controlled cam grinding equipment, I have no doubt that a competent cam supplier could supply accurate cams.

I have great doubts about almost any cam suppliers capability to supply the right cam for the application. Unless it is an engine in which he might specialize.

Years ago we built BMW engines for the Firehawk IMSA series. BMW Motorsports had Group N race camshafts available for the engine. But the rules specified that the cams must be bone stock; so how could there be a racing cam for a bone stock class?

Upon inquiry, we were told, "we send an apprentice to the warehouse to measure up every camshaft and select those that have the best tolerance stack up."

Meaning, they would measure cams to find those with minimum base circle dia and max nose height. Since the engine was a four valve, twin cam, that would mean finding 16 identical and perfect lobes in a warehouse with 50,000 camshafts. How many clever apprentices would this take, and for how long?

In actual fact, they did no such thing. They simply tightened up the mfg tolerances (which were already much tighter than most other mfgs) and ground special camshafts that optimized the lobe shapes within the allowed tolerances. The cams were legal but certainly not stock.

Since cam suppliers are not able or willing to provide complete product information then caveat emptor must apply.
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Re: CamMeasuring

Post by CamKing »

David Redszus wrote: I have great doubts about almost any cam suppliers capability to supply the right cam for the application. Unless it is an engine in which he might specialize.
I'm glad I'm not "almost any cam supplier" :lol: :lol: :lol:

If a customer called me up, and told me which cam he needed, I'd send him somewhere else.
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Caveat Emptor

Post by UDHarold »

David,

How do you buy an automobile? How big are the volumes of complete specifications? I would expect at least 50 pounds or more, if the manufacturer was willing to give you those. Do you insist on the specs for the automobile you are actually buying, or are the generic specifications acceptable?
Custom Cams currently provides selected accurate measurements of all cam lobes, inspection performed by a $300,000+ Adcole. It measures more accurately than any low-priced measurement device available. It is accepted by NASCAR engine builders, and the car manufacturers as the most accurate device available. If it says the cam is accurate, that is as good as it gets.
All mechanical cam grinders ran by a human operator are liable for human error, and that is generally the source of most errors, unless a cam grinding company has zero maintenance on its' machines.
At UltraDyne, we used 2 Bercos, 2 experienced cam grinders, and 2 different sets of cam masters, to grind 1 cam. Mistakes were still occasionly made, we just didn't ship them to the customer.
Here is an example when a company uses 1 grinder, 1 operator, and 1 set of masters.
Big Block Chevrolets, and other engines with canted valves, have at least 3 settings for the bank angles. On the BBC, all exhausts are on the same setting, but one bank's intakes are +6.25*, the other bank's intakes are -6.25*. BBCs with 110* LSA are actuallly ground with one bank with 103.75* LSA, the other bank 116.25* LSA.
Operators sometimes let their minds wander, and forget to shift to the second intake bank setting. They may grind a perfect cam, but the one bank may be on the wrong LSA, by a large amount.
If you check cylinder #1, you may find it is perfect, with all the correct specs. Cylinders 2,4,6,and 8 may be off 6.25* in LSA.
These errors are impossible with the Landis 3L, unless the operator does a lot of programming changes to it.
Again, I say trust the cam company, or use another one.

UDHarold
Last edited by UDHarold on Tue Jan 22, 2008 5:49 pm, edited 1 time in total.
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Re: Caveat Emptor

Post by David Redszus »

How do you buy an automobile?
Only after a careful reading of the factory shop manual which Mercedes is glad to sell to me.
Again, I say trust the cam company, or use another one.
And I say, in the field of racing, TRUST NOTHING. And no one. Everyone makes mistakes and no one stands behind their work. Do race parts come with warrantee cards?

Measure and verify every piece you buy and do not build yourself. And if you build it yourself, have someone else check your work.

In racing, 99.99% is not good enough.
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Post by SchmidtMotorWorks »

How do you buy an automobile?
Go to the Mercedes dealer and buy what fits the budget.
I didn't even open the hood on the last one (still haven't).
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