Cam recommendations for present build

[Dpmulvan]

Looking for the best cam profile for present build.
3.0 small port heads
9:5 Je pistons
40mm carbs
Backroad driving mostly
Wondering what this M cam is all about.

[PeteKz]

I have 'em. I like 'em. They give a good combination of low RPM torque and high RPM power. I don't have a lot of experience with different cams in 911's though. I know that with my CIS 3.2LS engine, I can floor the pedal at 1300 RPM and it pulls cleanly to the top of the rev range. Now, as a matter of good mechanical practice, I don't usually floor the pedal below 2000 RPM, but it shows that the combination of M1's plus CIS is very drivable across the rev range, which is what I like for a street driven car that isn't a high-RPM track car. It also gets close to 30MPG at 70MPH cruise.

With 3.0 small port heads and 40mm carbs, I think they would work very well.

Let's wait for Ian to weigh in, because he helped William Knight develop the cam.

[Old H2S]

Hmm.. The verdict is still out with me. The M1 is very smooth at idle, so smooth it shows off the unbalanced fuel distributor, so the FD is out getting rebuilt by the pro's because when I tried to do it it still leaks just a little bit, but enough for you to smell it so that is enough to turn in to a car b que.
Hope to be back flogging the mule soon.

[shoooo32]

So smooth at idle! It's not rowdy at all. The M1 is a great bump in performance without any real downfall.

[PeteKz]

Originally Posted by Old H2S

Hmm.. The verdict is still out with me. The M1 is very smooth at idle, so smooth it shows off the unbalanced fuel distributor, so the FD is out getting rebuilt by the pro's because when I tried to do it it still leaks just a little bit, but enough for you to smell it so that is enough to turn in to a car b que.
Hope to be back flogging the mule soon.

Then you probably need the FD rebuilt. I was able to adjust my 1979 FD to get the delivery to within 2% across all 6 injectors.

[icarp]

Sorry I am sick as a dog
DP is using JE pistons, this opens up the cam choice tremendously .
For a 9:5/1 comp ratio , I think the most fun will come from a Kight Race. 45


Ill get back to you all later

Ian

[PeteKz]

Dpmulvan: Curious, why are you picking the JE pistons?

[Henry Schmidt]

Post the cam specs [lift, duration, lobe center] and I'll tell you what I think.
Just off the top, if the cam works well with a CIS injection you are probably leaving performance that the carburetor can provide.
CIS injections can't handle intake pulses so wide lobe centers are required. Carburetor don't haven that issue.
3.0, small port 9.5:1 with 40 Webers and a clean exhaust is a 230+ horse power engine. A CIS compatible cam will hamper that kind of output. Not knowing the M1 specs I can only guess it's performance. I would lean towards DC40 [mod "S"] based on previous experience.

[PeteKz]

IMO, it's not the induction choice that limits the cam choice as much as the piston clearance.

I understand the argument that CIS is intolerant of intake pulses, but I have not seen that. Granted, I don't have experience with high overlap cams and CIS, but I also know that CIS was used in racing cars in the 1970's (with some modifications), and that the same SC cams were used in the Carrera engines, which had Motronic controls and could have used different cam profiles (and I know that cam choice was heavily influenced by emissions regulations too). So I'm pretty sure the full explanation is more than "CIS doesn't work with high overlap cams."

I don't know the specs for the M1 cam. As far as I can tell those are not published anywhere because that's William Knight's "secret sauce." And yes, I know that cams have been around for over a hundred years and how they work is well understood. I'd like to know the specs too. But I do know this from setting up mine: They use all the available space between the valves and CIS-top pistons without running into valve interference. In my engine, (with no base gaskets) there is barely .050" clearance at the overlap checking point.

THat's part of why I think that the piston clearance is what limits the use of cams with more overlap in CIS-designed engines. And that's why Ian came back with his reply that if you use JE pistons (with valve cutouts), that opens up what cams can be used.

I chose to stay with CIS because my car is a street car, not a race car. I wanted the great drivability and fuel mileage that I get with my CIS and M1 setup. It has delivered that along with a significantly greater boot in the butt. I am waiting to get on a dyno to finish tuning, it, and when I do, I'll post the numbers.

[PeteKz]

IMO, it's not the induction choice that limits the cam choice as much as the piston clearance.

I understand the argument that CIS is intolerant of intake pulses, but I have not seen that. Granted, I don't have experience with high overlap cams and CIS, but I also know that CIS was used in racing cars in the 1970's (with some modifications), and that the same SC cams were used in the Carrera engines, which had Motronic controls and could have used different cam profiles (and I know that cam choice was heavily influenced by emissions regulations too). So I'm pretty sure the full explanation is more than "CIS doesn't work with high overlap cams."

I don't know the specs for the M1 cam. As far as I can tell those are not published anywhere because that's William Knight's "secret sauce." And yes, I know that cams have been around for over a hundred years and how they work is well understood. I'd like to know the specs too. But I do know this from setting up mine: They use all the available space between the valves and Carrera and CIS-top pistons without running into valve interference. In my engine, (with no base gaskets) there is barely .050" clearance at the overlap checking point.

THat's part of why I think that the piston clearance is what limits the use of cams with more overlap in CIS-designed engines. And that's why Ian came back with his reply that if you use JE pistons (with valve cutouts), that opens up what cams can be used.

But, as most of you know, valve pockets have downsides too, such as reduced combustion camber efficiency and flame travel interference. Perhaps you can better satisfy those conflicts with a very different combustion chamber shape, such as what Fred Apgar was working on before his untimely departure. I have seen better head designs in Dick Elverud's shop too. But to get there, you almost have to redesign the head with a shallower chamber and probably different valve angles, such as the last developments in Harley's big twin performance engines before they went to a 4-vavle design (that was a flat top piston with a bathtub shaped chamber). Speculations for another day...

I chose to stay with CIS because my car is a street car, not a race car. I wanted the great drivability and fuel mileage that I get with my CIS and M1 setup. It has delivered that along with a significantly greater boot in the butt. I am waiting to get on a dyno to finish tuning, it, and when I do, I'll post the numbers.

[Henry Schmidt]

Originally Posted by PeteKz

IMO, it's not the induction choice that limits the cam choice as much as the piston clearance.

I understand the argument that CIS is intolerant of intake pulses, but I have not seen that. Granted, I don't have experience with high overlap cams and CIS, but I also know that CIS was used in racing cars in the 1970's (with some modifications), and that the same SC cams were used in the Carrera engines, which had Motronic controls and could have used different cam profiles (and I know that cam choice was heavily influenced by emissions regulations too). So I'm pretty sure the full explanation is more than "CIS doesn't work with high overlap cams."

I don't know the specs for the M1 cam. As far as I can tell those are not published anywhere because that's William Knight's "secret sauce." And yes, I know that cams have been around for over a hundred years and how they work is well understood. I'd like to know the specs too. But I do know this from setting up mine: They use all the available space between the valves and Carrera and CIS-top pistons without running into valve interference. In my engine, (with no base gaskets) there is barely .050" clearance at the overlap checking point.

THat's part of why I think that the piston clearance is what limits the use of cams with more overlap in CIS-designed engines. And that's why Ian came back with his reply that if you use JE pistons (with valve cutouts), that opens up what cams can be used.

But, as most of you know, valve pockets have downsides too, such as reduced combustion camber efficiency and flame travel interference. Perhaps you can better satisfy those conflicts with a very different combustion chamber shape, such as what Fred Apgar was working on before his untimely departure. I have seen better head designs in Dick Elverud's shop too. But to get there, you almost have to redesign the head with a shallower chamber and probably different valve angles, such as the last developments in Harley's big twin performance engines before they went to a 4-vavle design (that was a flat top piston with a bathtub shaped chamber). Speculations for another day...

I chose to stay with CIS because my car is a street car, not a race car. I wanted the great drivability and fuel mileage that I get with my CIS and M1 setup. It has delivered that along with a significantly greater boot in the butt. I am waiting to get on a dyno to finish tuning, it, and when I do, I'll post the numbers.

CIS and EFI cams require wide lobe centers to create intake vacuum no matter what piston dome configuration. Squish chamber pistons were designed around cam configuration not the other way around. Squish chamber pistons were also deemed to be more smog efficient.
Lobe centers from 110-114 degrees are basic.
Overlap creates maximum cylinder filling and because carburetor and MFI can function with narrow lobe centers they can produce better relative power.
Early performance Porsche cams 911S, ST, 911R, 906, RSR, all ran very tight lobe centers. 96 to 102 lobe centers.
In general, low duration, low overlap is the formula for CIS and EFI.
Larger overlap and longer duration for MFI and carburetors.
Lift is how you develop RPM range and torque curves.
When talking performance, CIS tends to go lean at consistent RPM. The metering plate, controls fuel mixture base on airflow plate lift. At lower rpm the air is relatively turbulent creating more lift. As rpm stabilizes, the air across the plate goes laminar and plate settles creating lean mixture. (fuel mileage is enhanced but the lean mixture create the tendency to detonate) Hemi heads are prone to detonation so compression threatens ignition. I created a peanut head that controlled flame fronts that allow lower octane performance. Some years later, Porsche made a similar head that helped control detonation in single plug race engines as per regulations.

Supertec peanut head

962 IMSA head

[PeteKz]

Henry, nice compact "peanut" combustion chamber. Did you also use a flat top piston? That's very similar to the "bathtub" shape (with one spark plug) Harley used before moving to 4 valves. Also similar to what Dick Elverud showed me in his shop. It seems you would not need 2 spark plugs with a compact chamber like that, as the flame should travel across the small chamber quickly with just one spark plug.

That's what Porsche should have done, but the hemispherical shape was carried forward from the 1960's. Heck, even VWs had more compact chambers.

Going back to the M1, I know from looking at the fatness of the lobes that the duration is increased significantly over the stock Porsche cam and it appears they have more overlap too. It would take some measuring equipment I don't have to find the LSA. And I don't think William would be happy with me if I did that.

[Henry Schmidt]

Originally Posted by PeteKz

Henry, nice compact "peanut" combustion chamber. Did you also use a flat top piston? That's very similar to the "bathtub" shape (with one spark plug) Harley used before moving to 4 valves. Also similar to what Dick Elverud showed me in his shop. It seems you would not need 2 spark plugs with a compact chamber like that, as the flame should travel across the small chamber quickly with just one spark plug.

That's what Porsche should have done, but the hemispherical shape was carried forward from the 1960's. Heck, even VWs had more compact chambers.

Going back to the M1, I know from looking at the fatness of the lobes that the duration is increased significantly over the stock Porsche cam and it appears they have more overlap too. It would take some measuring equipment I don't have to find the LSA. And I don't think William would be happy with me if I did that.

We used a relatively flat top piston [16cc dome] to achieve just over 11:1. Twin plugging was employed because street gas was our desired fuel.
Controlling the ignition as completely as possible without engine management required delaying the ignition. Dual flame fronts burn quicker requiring less ignition advance to achieve a complete burn.



Why would the supplier of a performance part be "unhappy" if an engine builder knew the specification of a part he's installing. There are no "secrets" when it comes to building these 60 year old engines . As an engine builder, I would never use a part with a "mystery" specification.
I built a race spec 356 engine for Gary Emory [Parts Obsolete] 100 years ago and he brought me a "magic" cam from a friend to use in the engine. I can't build an engine without knowing the complete formula so I called the supplier and his response was "just use it, it works great". Non-sense. Cam specs dictate cam timing based on application, compression ratio, ignition advance curve, fuel delivery and even port size and exhaust runner length.
We just measured the cam and the "magic" wasn't anything special at all.

[Neil Harvey]

Interesting topic. I find it a little odd though.

Without some shameless self promotion here, PD probably has one of the biggest "modern new" cam design inventories. We have designs for 911 air cooled NA engines from 2.7L all the way up to 4.1L NA, including our own version of a new "964" cam. The 964 cam seems to be some cam that everyone decided was the best solution. So we redesigned it as a A symmetrical solution.

Our new designs are all A symmetrical designs, not typically sold.

So what!!!

Every time we sell a cam we don't worry about who may copy it. That is something we cannot control. Any engine shop that is worth its salt will have some equipment to measure the cam lobes. We use the Audie system for checking and when we get the cams cut, to ensure the lobes are cut to the design.

Something that makes this a lot easier now, to copy any of our cam designs requires 4 masters to be made, 2 per lobe. Or, a cam company that uses CNC grinders but not many do. Typically we have seen cams with extremely poor copies, what we call "cut and paste" copies.

For every design we can create multiple iterations by moving the LSA around. But the lobe design never changes.

So, go ahead and measure that cam. Measure any one of ours. If you want to go into the cam business knock your lights out. I know how much we have invested. Too much is placed on some "special" sauce. An engine is the sum of all of its parts.

[Henry Schmidt]

Hi Neal
I'm not sure I understand your symmetric vs asymmetric lobe comment.
Isn't it true that in order to get a symmetric valve lift curve you have to use an asymmetric cam lobe?
Are you saying that a symmetric valve lift is not beneficial?
Are you advocating magic ramp speed?

[Neil Harvey]

On all of our testing the A symetrical designs have outperformed the older designs by a long way.

We have ported and ported and ported heads and there is only so much you can do. So, managing the air you can get through the ports. opening and closing the valves at different speeds does help.

We are still testing some newer designs as opening and closing speeds are another way of changing the cam characteristics.

In simple terms, the larger the port volumes the faster we need to open the valve. Pretty simple. Now add in different valve sizes and back angles and you get a whole new direction to go in.

These old engine still have life in them. For years and still today, the old stuff is still sold as new.

There is new technology that can be applied to these old engines.

[Henry Schmidt]

Originally Posted by Neil Harvey

On all of our testing the A symetrical designs have outperformed the older designs by a long way.

We have ported and ported and ported heads and there is only so much you can do. So, managing the air you can get through the ports. opening and closing the valves at different speeds does help.

We are still testing some newer designs as opening and closing speeds are another way of changing the cam characteristics.

In simple terms, the larger the port volumes the faster we need to open the valve. Pretty simple. Now add in different valve sizes and back angles and you get a whole new direction to go in.

These old engine still have life in them. For years and still today, the old stuff is still sold as new.

There is new technology that can be applied to these old engines.

Why do you believe that equal intake and exhaust ramp speeds [symmetric lobes] outperform quicker intake vs exhaust speeds.
Port size and valve sizes are variables that offer changes in performance but there is very little "new" magic to be learned in those equations.

[Neil Harvey]

Maybe you misread my post. I'll give you the benefit here.

Don't ever fall for, there is nothing new to learn. I learn new stuff everyday. I look back into my history and say to myself, if only I knew then what I now know.

When people tell me there is nothing new to learn, that tells me they have a lot to learn.

[PeteKz]

Henry, thanks for posting that graph of power vs. spark timing. I'm not sure I understand it, as I'm looking for some RPM reference relative to spark advance. Could you explain it a little please? Thanks in advance (pun intended).

[Henry Schmidt]

Originally Posted by Neil Harvey

Maybe you misread my post. I'll give you the benefit here.

Don't ever fall for, there is nothing new to learn. I learn new stuff everyday. I look back into my history and say to myself, if only I knew then what I now know.

When people tell me there is nothing new to learn, that tells me they have a lot to learn.

I never said, "nothing new to learn here" what I said was there are no secrets. The fact that it's new to you does not mean others haven't already explored your "new" information. Generally "new" ideas are a question of cost vs benefit analysis.
For example, 4 valve head conversion would absolutely benefit the air cooled 911 [and people have tried it] but the cost to implement this innovation is prohibitive.

You said you make all your cam lobe symmetrical.
My question was "Why do you believe that equal intake and exhaust ramp speeds [symmetric lobes] outperform quicker intake vs exhaust speeds."

The question was goofy because I used the wrong language. It should have said "Do you believe that equal opening and closing ramp speeds [symmetric lobes] outperform differing opening vs closing speeds." Do you believe that a symmetrical valve lift curve is unimportant?