Cam and valvetrain questions Mercedes 2.3-16

[GordonE]

Hello!
I am building me a better cylinder head to my Mercedes 2.3-16 engine. The head has quiet big valves from factory(38/33) and the ports are small and limiting the flow. In standard form this head flows 258CFM@28" in my bench or 153 converted to 10". The plan is to take up the ports, each port has separate channels that is 26mm in diameter. I am planning to take them out to 30mm.
The valves are going to be replaced, the intake valves is going to be 38.5mm and the exhaust will stay 33mm. Standard stem size is 7 and 8mm, and now they both are 7mm.

Now to the things that I am not sure of. I have bought a set of cams second hand, wich is not so easy to this rather rare engine. The seller said that they had an advertised duration of over 300 degrees. Before I bought them I convinced him to take a picture of the profiles and mesure the lift(12/11.5mm).
Looking at the picture I estimated the cams to be around 280degrees. I was almost certain that I knew wich profiles they had when I looked at Catcams homepage.
But when I got them they were engraved with a number wich I couldnt find at Catcams homesite, it turned out to be old profiles with a little agressive acceleration/ramp.
The thing that is obvious is that the differance in duration between 0.1 and 1mm lift is rather small compared to cat cams all other cams, just 24 degrees. Usally there is over 10 degrees more between this lifts. The cam specs for the Intake cam is 262(0.1,mm)/238(1mm)/12mm lift. The exhaust cam is 268/234/11.65mm.
One thing that looks a little odd is that the shape of the profile, there seems to be a pointy profile on top of the regularly looking one. The valve dosnt seem to dwell very long at 12mm.
The thing is that just a few more cams in their list comes close to thease values(Peugeot XU10J4RS 12.25mm lift), with 26 degrees differance.

Is this something I shall be worried about? Of cause the benefits is better driveability and low rpm range. The cams is used and still in newish condition. So it seems to have been working!

The thing is that I am going to use the OEM buckets wich in standard form has shim under bucket, but my new retainers dont have the support for that, so I will have to go with top hats or the valve stem directly against the bucket.
The benefits with the top hats should be that they distribute the load better to the bucket and prevents the valve stem to be hammered out.
The standard shim is the same size as the peugeot XU9 ones, wich i think is around 12mm in diameter. This way it feels better to have top hats to distribute the load better to the bucket. The area differance between 7mm and 12mm is quiet big!
The downside is of cause that the top hats can come off and that they whey more than the stem does.

What is your opinion on thease cams and setup?

I apply a diagram of the standard head flow.

Regards Gordon

[Guy Croft]

The first thing I must point out is that there is no problem with the valve size or the flow as it stands.

The valve area on 38/33mm sizes ie: valve E/I ratio = 72% which is OK (less than 70% would indicate ex valves too small and 75% + would be even better) and if the ex port flow to inlet flow ratio is same or higher the ex ports don't need any mods. Frequently I see inlets 'overported' and some engines inherently have very poor E/I ratios meaning that work done on the inlet side is completely pointless because the ex side will just not be able to cope.

My exp of Mercs is their valve and seat work and design is better than most and whilst the valve-in response on both sides perhaps can be improved on no account should you try and increase the inlet flow because on a 2.3 unit what you have already (equiv 153 at 10") is good for well over 290bhp.

You have not quoted ex bare port flow - test it and look at the std E/I ratio. The rest of the discussion will be relevant but not yet.

GC

[GordonE]

Thanks for the reply Guy.

I will try to flow the exhaust port soon to, I havnt set my bench up for reverse flow yet, though. Is it ok to suck through the exhaust port?
I am almost certain that the exhaust port flows more in relationship to the valve size than the intake.
The intake is a downdraft port with rather short shortside radius, very similar to the Cosworth YB head. The exhaust port has a much longer SSR and is rather big, wich should flow a lot.

What do you think about the valv stem to bucket issue? Would you prefere to have lash caps/top hats on the valves to even out the pressure on the bucket? I must order some lash caps if its a good idea.

What do you mean with valve-in response? The seat diameter is good around 87% of the valve diameter with three angles in standard.

Regards Gordon

[Guy Croft]

I am wasting my time advising in this case.

If you wish to cite power figures you must have the test data directly available and must show it.

Please remove the ref to 390bhp unless you can publish this.

GC

[GordonE]

Sorry with wasting your time. I removed the power figure.
There are a guy named Henrik Rosengren in Sweden that has bought many ex DTM Mercedes 190E cars who has stated this. I do not have a graph on it.

I will look in to the exhaust flow.

Thanks anyway /Gordon

Perhaps anyoue else has an opinion?

[GordonE]

Now I have tested exhaust side too. The exhaust flow is over 80% from 4mm lift and up.
I also tested the ports without valves, as I saw that you use to do that. The intake looses flow and the exhaust gains a lot.

So the exhaust flow is in harmony with the intake ports it seems?