How much can be milled off the Cylinder head?

[ethanol-smart]

Re: How much can be milled off the Cylinder head?

One thing to consider is that Turbo engines run a low compression ratio for a reason. That is that you are already cramming more air and fuel into the cylinders than you would on a normally aspirated engine. So if you increase the compression ratio you will only be able to run lower boost pressure!!
I would say do not alter the compression ratio at all. Just get it 'chipped'!
Good Luck

Ched,
The main problems with turbo engines are knocking and overheating, (internally, as well as the turbo).
This limits the maximum top pressure in the cylinder, as well as the allowed temperature of the fuel/air mixture.

Many tuners use alcohol to get another 20% of power or so, Koneigsegg for instance have a gasoline engine of about 850 hp, and a similar E85 variant of about 1100 hp...
The beauty of alcohols is that they are excellent coolers due to the large steam formation energy, and they are extremely resitant to knocking. In turbo applications people are talking about a "real" octane rate of 120 or more.
E85 have an octan number of about 106 if run in the normal aspirated test engine for octan rating.

By increasing the CR there might be less need for higher boost, but this is only sound, boosting is stressing the engine turbo and all components more, and costs efficiency.
In the end, Im confident in that I will be able to get more out from the engine after a slightly increased CR, than without.

But hey, we are making science here, so it have to tested!

By the way, there are also examples of NA engines like my AMGC36 for example.
Its a straight 6 with 3.6 cylinder volume. It gives 285 REAL hp.
Tuners have taken this engine to over 700 hp by just adding a turbo and run on ethanol...
With compression ratio of 10,5:1.

[ched999uk]

Re: How much can be milled off the Cylinder head?

Thanks very much ethanol-smart. I didn't realise E85 was alcohol/ethanol. I now understand completely why you wish to raise the compression ratio.
Have fun and let us know how you get on.

[ethanol-smart]

Re: How much can be milled off the Cylinder head? Measurements

Report from measurements of the 599 cc Smart gasoline engine.

OK, so today I put back the CH on the block without CH gasket and connected the cam chain for std timing.
Since the CH gasket is only 0.3 mm I consider it as an extra safetymargin.


I put clay on top of the cyl1 piston and turned slowly the engine a couple of revs.
It seems that I got the chain one tooth too early on the sprocket.
There are 42 teeth on the cam sprocket, so I had the cam advanced 360/42 = 8,57 cam degrees, in relation to std cam timing.


The result is that on exhaust side, I have about 5 mm clearance.
On inlet side at least 3.5 mm.
Probably there would be some 4 mm on each of them with correct timing.
I checked the lift of booth valves too, and it is over 8 mm on booth so I dont think that the hydraulic lash adjusters where empty of oil. I didnt feel any valve lash either.


How about the availble material in the CH itself then?
There seems to be about 7 mm of aluminium everywhere there is not a core foot.


My conclusion is that there is at least a possible mill off of 3 mm.
3 mm would still give about 1 mm towards both valves on std cam timing, and 4 mm of aluminium left on the gasket area, which should be enough for keeping it even.


(These modern steel CH gaskets are giving a lot of support for the CH, compared to the old paper type, so things should be kept even)


How much will the CR be increased with 3 mm mill off?
From the data I have:
Cylinder bore: 63,5mm
Stroke: 63 mm
Gives a std CR of 9,5:1


How to calculate the change of CR?
Have a look here: http://en.wikipedia.org/wiki/Compression_ratio
The equation for compression ratio is:
The ratio is calculated by the following formula:


CR= ( ((pi*b^2) /4)*s + Vc ) / Vc


, where
b = cylinder bore (diameter)
s = piston stroke length
Vc = clearance volume. It is the volume of the combustion chamber (including head gasket). This is the minimum volume of the space at the end of the compression


stroke, i.e. when the piston reaches top dead center (TDC). Because of the complex shape of this space, it is usually measured directly rather than calculated.


I didnt measure the Vc but we can let the mathematics work for us:


For a std gasoline Smart, 599 cc we have:


9.5 = (((pi*63,5^2) /4)*63 + Vc) / Vc


it gives us:


9,5 * Vc = ((pi*63,5^2) /4)*63 + Vc


9,5 * Vc - Vc = ((pi*63,5^2 )/4)*63


8.5 Vc = ((pi*63,5^2) /4)*63


Vc = (((pi*63,5^2) /4)*63)/8.5


Vc = 23472 mm3 = 23,472 cc


If we now decrease the Vc on the bore only (like milling off 3mm the cylinderblock instead as proposed earlier), the Vc would change like this:
Vc3 = 23472 mm3 - (pi*63,5^2) /4)*3 = 13971 mm3


However, since we are milling the CH instead, we need to know how the part of Vc which are in the combustion chamber will be reduced by partly milling off 3 mm from it.
This is not totally exact, but I assume that the area that will be reduced is about 90% of the full bore, there is only a small squsih area under the ehaust valve in this combustion chamber.


A more correct Vc3 will then be:
23472 mm3 - (pi*63,5^2) /4)*3*0.9 = 14921 mm3


What will the new CR be then?:
CR= ( ((pi*b^2) /4)*s + Vc ) / Vc


CR3= ( ((pi*63,5^2) /4)*63 + 14921) / 14921 = 14.37




Milling off 2 mm would give:


Vc2 = 23472 mm3 - (pi*63,5^2) /4)*2*0,9 = 17772 mm2
CR2= (199516 + 17772) / 17772 = 12,23


2 mm off the CH makes the cam timing about 2/8 of a tooth later. (one tooth is 8 mm)
If I put the timing one tooth advanced compared to stock, the end result would be 8,57 *6/8 = 6,43 cam degrees advanced.


3 mm off the CH makes the cam timing about 3/8 of a tooth later.
If I put the timing one tooth advanced compared to stock, the end result would be 8,57 *5/8 = 5,36 cam degrees advanced.


2 mm off would give about 2 mm margin to collision between inlet valve and piston (3.5 I have measured and 0.5 is the CH gasket) if there where no delay of the cam timing, in reality more what comes from 8.57-6.43 cam degrees later timing.


3 mm off would give about 1 mm margin to collision between inlet valve and piston (3.5 I have measured and 0.5 is the CH gasket) if there where no delay of the cam timing, in reality more what comes from 8.57-5,36 cam degrees later timing.


Hmm...weakness is aproaching....
I think there might be some issues with peak pressure on the bearings or conrods, and possibly a too slow running starter when cold if I would choose such a high CR as 14.37.
Maybe should make a compromise, 2.5 mm..?
It would end with a CR2,5 somewhere in between, about 13,3


What do you all say?

[Big Performance]

Re: How much can be milled off the Cylinder head?

I would go for a 2mm cut and then try it
Easy to take another .5 or 1 mm off after that if necessary

[ethanol-smart]

Re: How much can be milled off the Cylinder head?

OK, I decided to go for 2,5 mm.
A typical swedish compromise...
Will see when my workshop is done with the head milling.
I hope now only that the camchain tensioner can take up an extra 5 mm of chainlength. Anyone knows how much is the maximum that the system can handle?
How about the starter, shall I try to fix a diesel starter, now when its easily accessed...or dont the dieselstarter fit on a gasoline engine?

Another, more remote remote question, is there always a need for replacing the exhaust manifold gasket on these engines?
Or can it be used more than one time?

[Thrumbleux]

Re: How much can be milled off the Cylinder head?

I hope now only that the camchain tensioner can take up an extra 5 mm of chainlength. Anyone knows how much is the maximum that the system can handle?

Re above. A bit of trigonometry to ascertain the extra movement the tensioner sees - then...is it possible to use appropriate thickness spacers at the tensioners mount points to bring it closer to the chain?

What I don't get is how you can go lean burn without the cat throwing a fault code. I realise EGR will achieve that, but will you go the EGR route given all the hardware required? It seems that smarts are very sensitive to Lambda readings - more so than the Mercs you have experience of?

Good call on 2.5mm skim - much more would have the bottom end protesting I think!

[ethanol-smart]

Re: How much can be milled off the Cylinder head?

Re above. A bit of trigonometry to ascertain the extra movement the tensioner sees - then...is it possible to use appropriate thickness spacers at the tensioners mount points to bring it closer to the chain?

What I don't get is how you can go lean burn without the cat throwing a fault code. I realise EGR will achieve that, but will you go the EGR route given all the hardware required? It seems that smarts are very sensitive to Lambda readings - more so than the Mercs you have experience of?

Good call on 2.5mm skim - much more would have the bottom end protesting I think!

Hmm, how I can reach the tensioners mount point with out taking off the chain cover?
Or you mean the point on the tensioner chain guide where the hydraulic tensioner presses on it? The tensioner might be easy to add some extra material on in some way I think.
I hope its not needed. Will it be any issues with the chain coming too near some other part if tensed like this?
I guess I have to use my ears carefully the first miles on the road...

About the leanburn, to do this, I have to fit a piggyback system capable to send a fake lambda signal to the Smart ECU, in order to put the engine in limphome. I will probably not go the EGR-rout since the inletmanifold is from plastic.
Then I can choose to use a broadband lambda or only take off some ms from the map of injected fuel.

Yes, lets hope for a good recieval of the higher CR from the bottom end..:-)

[Thrumbleux]

Re: How much can be milled off the Cylinder head?

You will probably make sense of the tensioner by observing where it is with the chain completely slack, then seeing how far it has to be moved to accomodate the chain (at its new 'effective length'). Only if it was moving a very small amount would it be a concern. It must be capable of compensating for chain wear anyway - half of its purpose!

Lean burn provisions make sense. Not sure a Lambda reading is enough to cause 'limpmode', but pretty sure it illuminates the 'engine' light on the dash. Not such a problem I suppose.

[madDan]

Re: How much can be milled off the Cylinder head?

Erm instead of faffing about with milling the head and the associated timing chain modifications/adjustments why not manufacture new pistons to accomodate the compressionratio you require?

[tolsen]

Re: How much can be milled off the Cylinder head?

Erm instead of faffing about with milling the head and the associated timing chain modifications/adjustments why not manufacture new pistons to accomodate the compressionratio you require?

Easier said than done but perhaps you can elaborate a bit more and tell us how to make new pistons.

[ethanol-smart]

Re: How much can be milled off the Cylinder head?

Erm instead of faffing about with milling the head and the associated timing chain modifications/adjustments why not manufacture new pistons to accomodate the compressionratio you require?

Erm..yes in the case of that:
1. I was anyway bringing out the pistons and dismounted the complete engine
2. I wanted anyway to replace them
3. I knew that I wanted reinforced pistons
4. Somebody have flat pistons (without bowl) in stock, with fitting con rods..
5. I didnt need to mill the CH anyway due to warpage
6. I was made of money...

[madDan]

Re: How much can be milled off the Cylinder head?

hehe

ISBN 0 970 220 340

Who said it was cheap or simple?

[ethanol-smart]

Re: How much can be milled off the Cylinder head?

hehe

ISBN 0 970 220 340

Who said it was cheap or simple?

OK, it should be simple in this case to improve the engine design of the pistons.
Measure up the original pistons and make a drawing.
Simply take away the bowl in the piston and get a stronger and less expanding piston.
Reduce the material under the bowl to maintain the same thickness as with the bowl.
Possibly make the ring gap less, since the heating of the piston will be less with less surface exposed to the combustion, and even less due to the colder burning ethanol.
In the same time, the risk of sticking rings in the grooves are probably reduced significatly due to lower temperatures in the region of the piston rings.
Possibly increase the piston diameter some hundreds of a mm of the same reasons.

Yes, swithcing to a clean burning, anti-knocking and excellent cooling fuel, really will make the life of my Smart pistons a lot easier.
What a pity that Mercedes engineers didnt have the opportunity to optimize their engine to anything better than gasoline!

[Big Performance]

Re: How much can be milled off the Cylinder head?

Why not buy diesel smart pistons and modify them?

[ethanol-smart]

Re: How much can be milled off the Cylinder head?

Why not buy diesel smart pistons and modify them?

Hmm, are they flat?
Bore is the same?