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camshaft manufacturer
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Discussion Starter #1
Hello,

I'd like to share some information about our OPEL CIH competition rocker arms.
We have totally redesigned the CIH rocker arm system, with following highlights (indicated per intake / exhaust pair, in order of fitment):

- 2 threaded studs which replace the original studs
- 2 aluminum 7075-T6 rocker arms with steel pushrod insert
- 1 rocker arm shaft which is fitted on the threaded studs
- 2 custom nuts which lock down the complete system
- 2 valve adjusting screws (Mahle)
- 2 solid cam followers with dedicated coating
- 2 long pushrods (Manton)

-> the rocker arms will strictly rock, no side forces on the valve stems for aligning the rocker arm
-> the valve clearance is set by setting screws, not by a floating rocker arm shaft
-> long pushrods for reduced angular movement
-> lubrification through rocker arm shaft > rocker arm > pushrod > cam follower
-> no machining required: direct replacement of OE parts in the car by just removing the valve cover
-> currently tested to 8.500rpm
-> produced 100% in Germany

Price per pair (1 intake + 1 exhaust): €370 / $370
-> you need 4 pairs for a 4 cylinder engine
-> you need 6 pairs for a 6 cylinder engine
-> volume discounts available

We are fully aware that this is a lot of money. These parts have been designed, produced and validated in Belgium / Germany with the greatest possible care, and we have chosen to make a setup without compromises to obtain the best possible performance.
These parts are intended for competition use only and may not be street legal in your region.

You can browse our homepage "www.catcams.com" for camshafts, adjustable cam wheels and more valvetrain parts. Please feel free to share your thoughts.

Kind regards,
Ken Stessens
(product development)
 

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Super Moderator
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5,808 Posts
I am posting mainly to bring this to the attention of those members who might have missed it initially. New members' posts have to be approved by an OpelGT.com Moderator, so it sat in limbo for a few hours until I approved the thread.

From my perspective, these appear to be very well designed and manufactured. One thing I wondered about was the wear surface on the rocker to valve stem. Is there an insert of some kind? The photos don't show that detail.

For the serious performance head, what would be REALLY interesting is a roller lifter AND rocker, and a cam profile designed to take advantage of the roller lifter.

Unfortunately, I don't suspect that this solid-lifter-only and flat-tappet cam design will sell very well in the North America market. The majority of our CIH engines came equipped with hydraulic lifters (and cam ramp designs of course), and the roller rocker by itself has limited advantages.

And of course there is the price.

JM2CW
 
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camshaft manufacturer
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3 Posts
Discussion Starter #3
Hi,

thanks for the comments.

Regarding your questions and remarks:

1/ On the valve side, there is the valve adjustment screw with "elephant foot". It originates from the Porsche 911 aircooled and has 3 main advantages over the regular lash adjustment screws that just have a large radius contact:
- the small radius of the inner sphere results in a much smaller end-to-end movement on the valve tip
- the inner sphere makes a much larger contact area with the inner radius of the foot
- the flat foot makes a contact AREA with the valve (a roller makes a line contact // a radius screw makes a point contact)

This design eliminates any wear on the valve tip, and greatly reduces the side forces on the valve tip.


2/ On the pushrod side, there is a hardened steel insert so no worries for wear. The insert has a small hole to pass the oil through the hollow pushrod towards the cam follower (see image)

3/ it is possible to make a roller cam follower with a shorter pushrod. The pushrod would still have a length of about 1.5", so geometrically still very good in terms of angular movement.

4/ for any serious competition, you need to convert hydraulic cam followers to solid cam followers anyway. Hence we did not consider that option at all.

5/ a follower with a roller contact on the cam lobe has 1 big geometrical advantage: you can run cams with a big lift / short duration ratio.
On a flat tappet, the contact point between cam and follower is moving towards the edge, so the small contact diameter is a "hard limit" in the cam design. In case of a roller contact, I'd call this a "soft-limit": the bigger the lift / duration ratio will get, the bigger the "pressure angle" becomes. Long story short: the direction in which the cam is pushing on the roller is not the same as the motion of the roller. You will not get a fysical limit, but the pressure angle gets more and more critical.

Below is an example of a competition profile that works on the flat tappet design:
- duration at 0.1mm: 340° (measured at 0.1mm valve lift after setting the valve clearance at 0.30mm)
- duration at 1.0mm: 280° (measured at 1.0mm valve lift after setting the valve clearance at 0.30mm)
- peak valve lift: 14.00mm (measured at the valve with ZERO valve clearance)
- TDC valve lift: 5.5mm (measured at the valve with ZERO valve clearance)
- centerline: 104°
- valve clearance: 0.30mm (hot) --- 0.20/0.25mm (cold)

The advantage of the roller cam is that you would be able to run:
- more lift with the same duration
- the same lift with a shorter duration

The question is obviously what the engine really likes. Sinces the big advantage of the new rocker arm setup is the increased stability at high rpm, you would probably run profiles with a large duration anyway. But it is correct that there will be applications where a roller design will have the advantage over the flat tappet.

A profile similar to the specs above but with 13mm valve lift, gives about 250hp at 7800rpm in a 2.5L rally engine (with throttle bodies etc etc).

Kind regards,
Ken
 

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Just Some Dude in Jersey
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14,606 Posts
Very interesting.

Norbert? Can you or any of our other trusted European friends tell us if anyone has successfully installed these?
 

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I am posting mainly to bring this to the attention of those members who might have missed it initially. New members' posts have to be approved by an OpelGT.com Moderator, so it sat in limbo for a few hours until I approved the thread.

From my perspective, these appear to be very well designed and manufactured. One thing I wondered about was the wear surface on the rocker to valve stem. Is there an insert of some kind? The photos don't show that detail.

For the serious performance head, what would be REALLY interesting is a roller lifter AND rocker, and a cam profile designed to take advantage of the roller lifter.

Unfortunately, I don't suspect that this solid-lifter-only and flat-tappet cam design will sell very well in the North America market. The majority of our CIH engines came equipped with hydraulic lifters (and cam ramp designs of course), and the roller rocker by itself has limited advantages.

And of course there is the price.

JM2CW
They look pretty good but would probably cost about $2000 CAD for a set. 370 Euro equals 548.49 Canadian Dollar , so $2500 after shipping and duties/taxes.

Keith, the adjuster screw with the swivel pad is what contacts the valve stem, the pushrod fits to the shorter side.
 

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These are gorgeous. It is really nice to see these made.

I'd love to have a set for my build but, unfortunately, they are out of my price range.
 

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Pedal Smasher
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2,159 Posts
Why did Cat Cams decide to use a pushrod design when it isn't needed and a roller rocker design would be better for competition use? The genius of the CIH is that it blended an OHV and an OHC by eliminating the need for pushrods, even though the smarter design would have just went with a OHC setup. I don't see a good reason to now add pushrods to the engine, it's just another way the valve train could fail and is likely an inferior design for this application.

I'm not sure how many customers Cat Cams is really going to have for this setup. $370 a pair would be $1,480 for a 4 cylinder CIH. It's simply too expensive and for something that doesn't really fit what a performance minded Opeler would be looking for. In the past, there have been roller rocker and roller lifter designs that have come to market. Below are images of roller rocker setups that aren't exactly on the market anymore, and there would be demand for this if another version was to be marketed again.

I've heard of Cat Cams, your competitor Piper Cams in the UK (who make what looks like a nice adjustable timing chain set) and then Isky Cams of course. I could be wrong, but I think you guys went to market with something that won't sell as well as you might have hoped.
 

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camshaft manufacturer
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Discussion Starter #10
Hi Joseph,

before moving on with the discussion, maybe we need to distinguish between:
- the roller between cam lobe and cam follower (let's say the cam roller)
- the roller between tappet and the rocker (let's say the tappet roller)
- the roller between valve and the rocker (let's say the valve roller)


I'm not convinced that the reliability of the setup with the roller between follower and rocker is more reliable then the pushrod setup.
The pushrod obviously has its flexibility drawback, but since it is so short (compared to regular V8's) this is hardly an issue.
It is much lighter as well.

The big advantage of using the setting screw instead of the valve roller is that you can set the lash with the screw, so the rocker arm is not floating anymore. It is much more stable, and given the track record of the Porsche 911 we should be safe on reliability (we use genuine Mahle screws).

Regarding the cam roller, it is correct that you can use a higher lift / duration ratio with the cam roller setup. But that is only an issue when you need that much valve lift on a short duration. The benefit of the flat tappet is that you don't need a system to keep the roller aligned in the tappet bore. Again much lighter and more reliable because fewer parts involved.


So my questions in return are:
- do you have pictures with existing solutions in the CIH engine with roller followers to keep the roller aligned?
- do you have an example of a roller profile which you would like to run, so I can check if it can be achieved using a flat tappet?
- what are your thoughts for a setup with a roller on the cam + pushrod to the rocker + setting screw on the valve?


thanks for your insight,
Ken
 

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Pedal Smasher
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2,159 Posts
Hi Joseph,
I'm not convinced that the reliability of the setup with the roller between follower and rocker is more reliable then the pushrod setup.
The pushrod obviously has its flexibility drawback, but since it is so short (compared to regular V8's) this is hardly an issue.
It is much lighter as well.
Reliability in this case would likely require specifying RPM limits that have been tested over prolonged periods of time, including cycling for fatigue. I wouldn't expect anyone outside of an OE to do that though, so at least for this it's debatable. A pushrod has one major drawback compared to a roller at the rocker however, friction. Most engine wear happens when the engine is cold, which means there won't be proper oil pressure to lubricate what is essentially a ball joint. A roller will likely have less wear on the part as it is dispersed more, until a significant flat spot develops.

The big advantage of using the setting screw instead of the valve roller is that you can set the lash with the screw, so the rocker arm is not floating anymore. It is much more stable, and given the track record of the Porsche 911 we should be safe on reliability (we use genuine Mahle screws).
A lash cap is very consistent. Sure it will take longer to dial in the correct lash, but this also removes the issue of having the rockers floating. If you use a hydraulic lifter, lash becomes a moot point but like anything in life, there are shortcomings to a hydraulic setup.

Regarding the cam roller, it is correct that you can use a higher lift / duration ratio with the cam roller setup. But that is only an issue when you need that much valve lift on a short duration. The benefit of the flat tappet is that you don't need a system to keep the roller aligned in the tappet bore. Again much lighter and more reliable because fewer parts involved.
You also can use more aggressive cam profiles, generally speaking, with a roller cam than a flat tappet cam. Any design choice comes with pros and cons, flat tappet does have some strengths as you pointed out. Namely weight.

So my questions in return are:
- do you have pictures with existing solutions in the CIH engine with roller followers to keep the roller aligned?
I don't know of anyone to have done this, not that it couldn't be done. I can see the traditional method of linking the intake and exhaust lifters for a cylinder as possibly working for the CIH. Another method would be to eliminate the issue by having a ball bearing instead of a roller to follow the cam. I can't say for sure if it would be better than just connecting the lifters with a link, which is how American V8 pushrods handle the issue. The below thread is not in fact a ball bearing lifter, but it gives you the idea. Without figuring out an effective design using this idea, no one could say for certain that it isn't a good design to pursue. You would have to be lying to say it doesn't intrigue you.

? Ball Bearing Lifter ?


- do you have an example of a roller profile which you would like to run, so I can check if it can be achieved using a flat tappet?
I do not, at least not the profile. The person to ask that question would be RallyBob. The cam I would likely want to use is an Isky OR-77.

- what are your thoughts for a setup with a roller on the cam + pushrod to the rocker + setting screw on the valve?

thanks for your insight,
Ken
I'm certainly not an expert on valve train, especially around some of the fantastic brains on this forum but for me, I'd want a roller on the valve at least. An elephant foot is a weak link compared to a roller, you will have an increase in friction even if the rocker isn't moving side to side. I've seen the results of testing done for a Ford 427 SOHC (the super expensive legendary Cammer), that had two different configurations done. The first was a roller at the cam and an adjustable elephant foot at the valve, for the rocker. Under heavy use / harsh conditions, the friction between the elephant foot and the valve stem started to burn the oil that was present between the two, this was around 8,500 RPM. End result, burned valve stems. The second setup was a double roller, issue never happened. It's unrealistic to expect the elephant foot to stay exactly in the same spot with absolutely zero twisting, rotating or otherwise change in placement, movement. The results of that test, pretty much turned me off to ever using them on any engine. I do have a background in engineering, I can analyze the situation enough to know that I won't spend a bunch of money on a product I see as being flawed for at the bare minimum, having an elephant foot design. I can understand the trade offs of using the pushrod design, it allows you to run a lighter valve train and the weight of your valve train can be critical to prolonging valve surge and valve float. I'll go with peace of mind, and stick to a roller at the valve.

And whatever I went with, the price would have to be realistic for the application. $1,480 for the rockers and lifters in an Opel GT, holy crap. I might as well try to design them myself and have them made State-side at that point or just stay stock.

I do appreciate the open dialog with you Ken, and I will be the first to admit that I am not always correct and there are smarter people on this forum than me.
 

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So my questions in return are:
- do you have pictures with existing solutions in the CIH engine with roller followers to keep the roller aligned?
Ken
I don't know of anyone to have done this, not that it couldn't be done.
Here are a couple of pics of a roller cam/roller rocker setup. RallyBob can give more details on this. FWIW, he was the one who came up with the roller rocker design.
 

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While I like the overall design of the CatCams rockers, I would have done a couple things different. More than one way to skin a cat.

The shaft mounting is good but maybe better if all 8 rockers shared a common shaft. This would act as a stud girdle and greatly improve valvetrain stability while fitting inside the factory valve cover. The shaft mounting then dictates a different method of adjusting valve lash from OE. In the stock rocker there is a sliding ball at the lifter end anyways, so I would have put the lash adjustment there. This would have less sliding movement than the valve end, therefore less friction. Instead of a pushrod and custom tappet, a lash cap on top of the OE tappet would provide a surface for the adjuster to ride against. Both solid and hydraulic tappets could then be used. A roller can then be used on the valve tip to reduce friction further.

As for roller cams, that is a whole other league. Billet cams and roller lifters get expensive.

My 2 cents.
 

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Certified Opelholic
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I would love to see a 250HP CIH motor in the US

Cat Cams is 8500 RPM the Max RPM for those roller rockers?
 

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Opel 4 life
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78 Posts
how will you change the oil trapped in the solid cam followers?
Ive think it will get hot and worn faster if its trapped in a small cup with a pushrod inside...

Normaly a pushrod like this transport oil to its top, or is there a oil channel moving oil from the rocker arms to the pushrod? This would fiks the trapped oil problems also.
 

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how will you change the oil trapped in the solid cam followers?
Ive think it will get hot and worn faster if its trapped in a small cup with a pushrod inside...

Normaly a pushrod like this transport oil to its top, or is there a oil channel moving oil from the rocker arms to the pushrod? This would fiks the trapped oil problems also.
I had thought of that as well, but figured they probably have a drain hole near the bottom so excess oil can drain. I don't know how fast the oil would drain vs the fill rate, or maybe the rapid motion of the lifter would prevent the oil from accumulating in the first place. But yes the hollow lifter would not be an advantage if it fills with oil.
 

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While I like the overall design of the CatCams rockers, I would have done a couple things different. More than one way to skin a cat.

The shaft mounting is good but maybe better if all 8 rockers shared a common shaft. This would act as a stud girdle and greatly improve valvetrain stability while fitting inside the factory valve cover. The shaft mounting then dictates a different method of adjusting valve lash from OE. In the stock rocker there is a sliding ball at the lifter end anyways, so I would have put the lash adjustment there. This would have less sliding movement than the valve end, therefore less friction. Instead of a pushrod and custom tappet, a lash cap on top of the OE tappet would provide a surface for the adjuster to ride against. Both solid and hydraulic tappets could then be used. A roller can then be used on the valve tip to reduce friction further.

As for roller cams, that is a whole other league. Billet cams and roller lifters get expensive.

My 2 cents.
Does anyone have a source for the Lash Caps that enter into all these discussions? Largest ones I've found are for .375" valve tips while the protrusion of the lifter is .507" in diameter.
 

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Does anyone have a source for the Lash Caps that enter into all these discussions? Largest ones I've found are for .375" valve tips while the protrusion of the lifter is .507" in diameter.
They were custom made.
 
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