Mercedes Power Unit Hardware & Software

[PlatinumZealot]

The hotter you run the CC, the more valve seat erosion happens. When the valve seat erodes the valve stem becomes taller relative to the rocker arm. Eventually the valve seat erodes to the point that the valve no longer fully closes because the clearance to the rocker arm has disappeared. When this happens the valve seat is no longer contributing towards valve cooling, leaving the valve guide to dissipate all the heat of the exhaust valve. This softens the metal of the guide increasing the bore of the guide. When the guide can no longer guide the valve properly, the valve begins to wobble and begins trashing the valve seat as well as the valve stem seals. This leads to lower compression and massive oil consumption.

That is not the problem though. Not with this efficient lean combustion! It is much much cooler and has lower rpms than before.

Mercedes issues are basically all over but it is nothing other than normal random wear and tear. Nothing critical.

[godlameroso]

You are suggesting that valve clearance is not adjustable. I find that unlikely.

The other consequence of such a high degree of seat erosion is a problematic reduction in gas flow. Again - unlikely that they have seat erosion as bad as that.

Depends how you adjust valve lash. I would think they'd have fixed rockers to save weight, why waste time with adjustable set screws that add mass to the rocker arm. You calculate the lash over the engine life based on projected valve seat erosion. Perhaps they had more seat erosion than anticipated, the answer would be to use different seat material or design more lash into the rocker arm. This would have a small almost negligible airflow penalty, while extending proper valve seat contact. If in fact such a thing is happening, it is a common fix in the road car world with engines that have set screw adjustments for valve lash. You make the valve lash one ten-thousandths of an inch looser than spec limit to buy yourself some time.

Obviously this is not an option with these engines, thus the money must be spent on ever more exotic materials for the valve seats.

Or none airflow penalty, if you mate a bigger clearance with a cam with more lift.

I rather take a hp hit(that's within margin of error on 99.9% of dynos) if it comes with improved reliability any day.(at least thats my experience) Also when the clearance moves into spec you now have a valve that opens more due to the more aggressive cam profile.

If Mercedes takes a new power unit, the whole point becomes moot until next year

[Hoffman900]

Lash it totally controlled by the camshaft lobe. Adding more lash shortens the valve timing and could move you further up the lash ramp, so the derivatives at opening / closing will be more severe.

I don't think any modern high performance engine isn't using rockers. It's way more compact and the rocker multiplication aspect. Buckets are velocity limited... want more velocity, make them bigger, but now you start making compromises in the geometry of everything else.

[godlameroso]

Lash it totally controlled by the camshaft lobe. Adding more lash shortens the valve timing and could move you further up the lash ramp, so the derivatives at opening / closing will be more severe.

I don't think any modern high performance engine isn't using rockers. It's way more compact and the rocker multiplication aspect. Buckets are velocity limited... want more velocity, make them bigger, but now you start making compromises in the geometry of everything else.

That all depends on the rocker ratio, you can have a static cam profile, and the geometry of the rocker itself will vary the force on the valve due to the lever length(ie position of the pad relative to the valve stem). Tolerances are built in not just to accommodate for material expansion, but also harmonics, so a slight amount of lash is desirable. With valve seat erosion maintaining proper lash becomes a moving target. As with all engineering that moving target falls within a tolerance range.

So all I'm saying is maybe you set your lash a smidge too loose then let it tighten up over time to extend the life just a hair, a simple quick change without having to spend mega bank.

I'm sure there are more sophisticated options, I lack both the talent and the capital to know them.

[Hoffman900]

Lash it totally controlled by the camshaft lobe. Adding more lash shortens the valve timing and could move you further up the lash ramp, so the derivatives at opening / closing will be more severe.

I don't think any modern high performance engine isn't using rockers. It's way more compact and the rocker multiplication aspect. Buckets are velocity limited... want more velocity, make them bigger, but now you start making compromises in the geometry of everything else.

That all depends on the rocker ratio, you can have a static cam profile, and the geometry of the rocker itself will vary the force on the valve due to the lever length(ie position of the pad relative to the valve stem). Tolerances are built in not just to accommodate for material expansion, but also harmonics, so a slight amount of lash is desirable. With valve seat erosion maintaining proper lash becomes a moving target. As with all engineering that moving target falls within a tolerance range.

So all I'm saying is maybe you set your lash a smidge too loose then let it tighten up over time to extend the life just a hair, a simple quick change without having to spend mega bank.

I'm sure there are more sophisticated options, I lack both the talent and the capital to know them.

Valve seat erosion and valve seat recession are two different things. Likely the coatings (they use coated valve seats) might be pitting some. It won't be enough to move the valves, but likely will effect the ability to cool the valve and some gas flow as well.

I'm well aware what lash is / does. In a racing engine, you're using every available margin, whether that margin is outright performance or balancing it with the how long the engine needs to live. Harmonics matter a lot less with pneumatic "springs". Most valvetrains with rockers (pushrods included) ultimately hit a wall with what a valve spring can cope with.

The closes thing I've seen published of a more modern F1 profile is in the Honda white paper. Brian with the Cosworth would ideally more accurately measure the lift at the valve (so the derivatives don't need as much smoothing) as well as get the cam lobes measured on something like an Adcole. 1) we'll be able to see what the lash ramps look like and targets for what the derivatives look like when lash is zero 2) you can figure out rocker ratio as well

[Tommy Cookers]

well just brainstorming and iirc ....
running out of exhaust valve clearance aka lash ....
causes blow-by which slightly burns away the valve which increases blow-by which burns away more valve etc etc
ie the valve seat doesn't suffer (it's liquid-cooled) - neither does the guide
(exhaust valves lose lash temporarily from expansion and permanently from stretching with heat etc)
I have seen valve guides belling with wear (even splitting) without adverse effect on anything incl valve seating
(1960s BMW 700cc car and its source motorcycle engine - these had heavily tapered (presumably inlet) guides)
blow-by should develop if inlet valve ran out of lash but this never seems to happen
Triumph motorcycles wore on their cam base circles if under-lashed

btw the 1960ish Scarab F1 car (W196-copy desmodromics) had immutably poor power
now they say that the lash (built-in) was .012" but should have been .002" and ....
using .002" was afterwards (and too late) found to give 15% more power
(a Scarab is now successful in historics but has a 3 litre or maybe 220 Offy via Intercontinental Formula rights)

finger followers are the thing - even if called rockers
aren't they settable for lash via adjustment of the pivot-end height ?

[Hoffman900]

You usually adjust them with lash caps on the valve stem, or just nail your valve lengths… F1 has the resources to do that and you don’t have to worry about lash caps popping off.

Running tighter last and making more power just means your cam was too small for what you wanted. The target derivatives when lash is zero is what dictates the height of the lash ramp, which is a by product of the kind of expansion that happens. Some cam developers get around lift limited rules by running very minimal lash, but this also requires the engine to be at temp before firing. Some of the former Grand Am Daytona Prototype engines were this way.

[BassVirolla]

Depends how you adjust valve lash. I would think they'd have fixed rockers to save weight, why waste time with adjustable set screws that add mass to the rocker arm. You calculate the lash over the engine life based on projected valve seat erosion. Perhaps they had more seat erosion than anticipated, the answer would be to use different seat material or design more lash into the rocker arm. This would have a small almost negligible airflow penalty, while extending proper valve seat contact. If in fact such a thing is happening, it is a common fix in the road car world with engines that have set screw adjustments for valve lash. You make the valve lash one ten-thousandths of an inch looser than spec limit to buy yourself some time.

Obviously this is not an option with these engines, thus the money must be spent on ever more exotic materials for the valve seats.

Or none airflow penalty, if you mate a bigger clearance with a cam with more lift.

I rather take a hp hit(that's within margin of error on 99.9% of dynos) if it comes with improved reliability any day.(at least thats my experience) Also when the clearance moves into spec you now have a valve that opens more due to the more aggressive cam profile.

If Mercedes takes a new power unit, the whole point becomes moot until next year

Touché.

Not a good idea to have greater lift with an old engine.

But if you can intrinsecally engineer a cam lobe that wears as much as valve seat does, accounting for valve stem wear...

It sounds like too much.

[gruntguru]

You are suggesting that valve clearance is not adjustable. I find that unlikely.

The other consequence of such a high degree of seat erosion is a problematic reduction in gas flow. Again - unlikely that they have seat erosion as bad as that.

Depends how you adjust valve lash. I would think they'd have fixed rockers to save weight, why waste time with adjustable set screws that add mass to the rocker arm. You calculate the lash over the engine life based on projected valve seat erosion. Perhaps they had more seat erosion than anticipated, the answer would be to use different seat material or design more lash into the rocker arm. This would have a small almost negligible airflow penalty, while extending proper valve seat contact. If in fact such a thing is happening, it is a common fix in the road car world with engines that have set screw adjustments for valve lash. You make the valve lash one ten-thousandths of an inch looser than spec limit to buy yourself some time.

Obviously this is not an option with these engines, thus the money must be spent on ever more exotic materials for the valve seats.

Or none airflow penalty, if you mate a bigger clearance with a cam with more lift.

The airflow penalty comes from the change in seat shape, not the increased lift.

[saviour stivala]

The valve clearance is adjustable as explained on page 192. The formula one valve gear which includes valve and valve seat being part of the engine is designed to last the mandated mileage of engine life at the designated temperature the engine is designed to operate at. Because of the very high compression used which necessitates the use of as compact a combustion chamber as possible but with the need of very high valve lifts The formula one engine camshaft lobe configuration uses what is called ‘the Bezier curve (created by Pierre Bezier in 1960). Using the ‘Bezier’ cam-lobe curve, the valve is made to follow the piston at very close tolerances.

[Hoffman900]

The valve clearance is adjustable as explained on page 192. The formula one valve gear which includes valve and valve seat being part of the engine is designed to last the mandated mileage of engine life at the designated temperature the engine is designed to operate at. Because of the very high compression used which necessitates the use of as compact a combustion chamber as possible but with the need of very high valve lifts The formula one engine camshaft lobe configuration uses what is called ‘the Bezier curve (created by Pierre Bezier in 1960). Using the ‘Bezier’ cam-lobe curve, the valve is made to follow the piston at very close tolerances.

The Bezier Curve just allows the lobe designer more control when designing the lobe. Honda outlined that in this:
http://www.f1-forecast.com/pdf/F1-Files ... P2_09e.pdf
With Honda, they knew their acceleration constraint, so they were able to design to that point and have a more refined control of the lift profile. I'd be really curious to see the Jerk curve with their "new" acceleration curve, but might be as much of an issue with pneumatic valve "springs".

Old school cam lobe designers typically used polynomials. You can play with one here: http://www.mjpsoft.dk/cam_instructions.html

A lot of lobe designers use Blair's software. http://www.profblairandassociates.com/G ... esign.html
It also allows them to design the acceleration or velocity curves and calculate things backwards. Helps when you know what your constraints are. It might have have as fine resolution as the software Honda designed.

A cam designer shared one time that he thought old Cosworth cams were a radius nose and base circle connected by two flanks. He was not being complimentary.... Here is what another one said. Harold Brookshire passed some years ago, but was Comp Cam's original cam lobe designer in the 1970s before doing his own thing. At the end of his life, he was doing some consultant work for the Dodge NASCAR teams. His camshafts had a lot of wins in the US in the 1970s-1990s

Jon,

Revisit Harvey Crane's web-site. He recommends AGAINST using his "No-Pulse" ramp on the closing side, and he uses the acceleration-reversal closing ramp.
Constant-velocity opening or closing ramps are so "Old-School" that I have NEVER used them since I started designing in 1972. When Harvey saw my ramps in 1974, he asked me if I had been Cosworth's designer, as they used similarly-shaped opening and closing ramps, which involved constant-acceleration/constant-jerk curves.
My main curve, from the opening point to the closing point, was of the PolyDyne method, which I stopped using by 1977, when I discovered I could do everything I wanted with regular polynomial equations.
In the Spring of 1980, when I started UltraDyne, I 'invented' Multi-Segmented Polynomial' (MSP) equations, which I still use today, and they are what you call 'Spline-Fits', or 'Knots'.
All graphs shown by me are of MSP equations, or Spline-Fits........

[saviour stivala]

The valve clearance is adjustable as explained on page 192. The formula one valve gear which includes valve and valve seat being part of the engine is designed to last the mandated mileage of engine life at the designated temperature the engine is designed to operate at. Because of the very high compression used which necessitates the use of as compact a combustion chamber as possible but with the need of very high valve lifts The formula one engine camshaft lobe configuration uses what is called ‘the Bezier curve (created by Pierre Bezier in 1960). Using the ‘Bezier’ cam-lobe curve, the valve is made to follow the piston at very close tolerances.

The Bezier Curve just allows the lobe designer more control when designing the lobe. Honda outlined that in this:
http://www.f1-forecast.com/pdf/F1-Files ... P2_09e.pdf

Old school cam lobe designers typically used polynomials. You can play with one here: http://www.mjpsoft.dk/cam_instructions.html

A lot of lobe designers use Blair's software. http://www.profblairandassociates.com/G ... esign.html
It also allows them to design the acceleration or velocity curves and calculate things backwards. Helps when you know what your constraints are.

If you don't know what your constraints are nothing can help.

[Hoffman900]

Off topic, but here is Billy Godbold's presentation from the AETC a few years ago:
https://www.designjudges.com/articles/d ... timization

Mostly dealing with pushrod designs, but the angular velocity variation of a NHRA Pro Stock cam is fun (towards the end). At 10,000rpm (crankshaft), "the camshaft speeds up to 11,800rpm and slows down to 8200rpm, 10x, per rotation".

Note: Billy Godbold is the lobe designer for Comp Cams. He is responsible for the lobes in many a NASCAR, NHRA, IMSA, etc. winner.

Fun stuff.

[_cerber1]

It looks like MB has introduced more aggressive engine maps.

[saviour stivala]

‘’Off topic’’ Yes. Off topic if ever there was one. This as a Prostock single cam in block push-rod 8.2l 90 degree v8 valve train cannot have any relevance whatsoever to the formula one engine valve train subject. And. I am still trying to figure-out an engine running at a crankshaft speed of 10k RPM with a camshaft speed of 11800 `RPM.