N54 head work

wheela

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John can you explain how a ported head allows you to run less octane Fuels? Not saying your wrong genuinely curious how it works
My thoughts are if the exhaust valve ports are able to flow better, then a bigger percentage of exhaust gas exits the cylinder during the exhaust stroke. Less residual exhaust gas in the cylinder = less residual heat in the cylinder = more knock resistance for the next incoming air-fuel mixture. I don't know this to a certainty, but if that's what he's seeing, this is my suspicion.

Also, if the ports flow better, you could get more air flowing through the cylinder during valve overlap for better cylinder clearance. I suspect this would also allow lower effective compression ratios to be reached at the same amount of valve overlap as a non-ported head.
 

martymil

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Compression ratio is measured when the valves are shut so a ported head will not effect it.

What it will do is allow a bigger mix to enter the combustion stroke.

No chance it will make more power with less octane and more timing unless the advertised octane of the lower octane fuel is higher then what it is which is quite possible and that's where the gains come from he is seeing.
 

wheela

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Compression ratio is measured when the valves are shut so a ported head will not effect it.

What it will do is allow a bigger mix to enter the combustion stroke.

No chance it will make more power with less octane and more timing unless the advertised octane of the lower octane fuel is higher then what it is which is quite possible and that's where the gains come from he is seeing.
The compression (static) ratio of the engine actually has nothing to do with valve position, it's just the ratio of cylinder volume at bottom dead center to cylinder volume at top dead center. This is just a geometric ratio.

However there is a thing called dynamic compression ratio, which is what the air-fuel mix actually sees during compression, and this has everything to do with valve timing and overlap, as it represents the point in the piston stroke where the mixture actually starts getting compressed vs. pushed out of a valve.

Better flow through ported valves during overlap would have the same effect as more overlap in a non-ported head. More overlap in general reduces the dynamic compression ratio of the engine for reasons mentioned above. I believe this is where the ported head is helping run worse fuel and/or more timing than a non-ported head.
 

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wheela

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Likely has more to do with the point that most folks with ported heads are not on stock cams, and allow adjusted vanos tables.
Yeah, I agree those are factors too. The ported head should have the same effect as higher lift cams, and I imagine it may also tend to increase the effect of vanos changes. Anything improving flow through the head should have a positive effect on the combustion cycle.

John, are you also running different cams or just the head porting?
 
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martymil

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The compression (static) ratio of the engine actually has nothing to do with valve position, it's just the ratio of cylinder volume at bottom dead center to cylinder volume at top dead center. This is just a geometric ratio.

However there is a thing called dynamic compression ratio, which is what the air-fuel mix actually sees during compression, and this has everything to do with valve timing and overlap, as it represents the point in the piston stroke where the mixture actually starts getting compressed vs. pushed out of a valve.

Better flow through ported valves during overlap would have the same effect as more overlap in a non-ported head. More overlap in general reduces the dynamic compression ratio of the engine for reasons mentioned above. I believe this is where the ported head is helping run worse fuel and/or more timing than a non-ported head.

Ported head has nothing to do with the combustion cycle, it only allows for more air and fuel movement.

The only way you can run more timing and shittier fuel is running lower compression or decrease the boost and up the timing resulting in the same hp output due to the higher flow of the head.

No matter what you have to sacrifice boost or compression to run shittier fuel but hp can be gained back by altering the duration and lift of cams or a ported head but at a cost of both or either already mentioned.
I generalized it, a ported head by it self will not help run shittier fuel with more timing.

Static or dynamic compression you have to sacrifice something to run shittier fuel.

Whether it be cams, tuning, boost, comp or what ever other changes have been made but a ported head by itself will have no effect.

I think he broadly over generalized his statement.
 

JohnDaviz

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John can you explain how a ported head allows you to run less octane Fuels? Not saying your wrong genuinely curious how it works

I am by far no expert. But my basic understanding is that due to the increased flow i have less EGR effect and better cylinder filling with clean air.

12psi and 95RON fuel i am at 8s 100-200kph. No world record or anything breath taking. But for 12psi only it is damn quick imho and i am very happy. But i also won´t turn boost higher than 16/18psi as i built the engine for a track tool with s55 (cs/gts) power target. As i have DCT issues i couldn´t turn the boost up yet.

Yep. The stock heads are very small, and were done that way for the performance characteristics BMW was trying to achieve moving from NA to turbo motors. For making more power, etc, not what's needed.

Absolutely. The car gains power/torque above 5k rpm significantly. 7k Rev limit actually feels to be too low now :D
 

JohnDaviz

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Yeah, I agree those are factors too. The ported head should have the same effect as higher lift cams, and I imagine it may also tend to increase the effect of vanos changes. Anything improving flow through the head should have a positive effect on the combustion cycle.

John, are you also running different cams or just the head porting?

currently i am on N53 cams but thinking about going Schrick Cams some day in the future.
 
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martymil

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Thanks for clarifying, a ported head needs cams and tuning to get the benefits as it can't to it alone.

Shit fuel you need to sacrifice something.

Back in the day when e85 wasn't available we ran less timing but more boost to make power, these days it's the other way around to reach the same goal.

With cams you can make the same power with less boost due to cam duration and vanos changes.

When running cams you will make the same power levels at the same boost because for eg

22 psi with cams is like 24 to 25 psi with stock cams.

So if running shittier fuel if you run 21 psi with stock cams it's like running 17 to 18 psi with cams and that's why he is able to do that.
 
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fmorelli

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currently i am on N53 cams but thinking about going Schrick Cams some day in the future.
John, somewhere around here there was some comparison work on the N53 head and cams, if I recall. I may have this wrong but I vaguely recall there was not much benefit to putting cams on the N53 head vs the stock cams. Maybe someone will find the thread and share. Don't take my word for it!
 

JohnDaviz

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John, somewhere around here there was some comparison work on the N53 head and cams, if I recall. I may have this wrong but I vaguely recall there was not much benefit to putting cams on the N53 head vs the stock cams. Maybe someone will find the thread and share. Don't take my word for it!

i saved a lot of information i could gather but this is the brief overview:

N54 cams are int 248°/ exh261° 9.7mm/9.7mm Lift

N53 cams probably int 255°/ exh261° 9.9mm/9.7mm Lift

On thing i hear was to use the N54 Exhaust and N53 Intake cams in combination.
Someone mentioned that the cam profile is not identical between the two and that the n54 exhaust cam would be "better" for turbo application but i don´t have details. IIRC.
 

martymil

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Then that will help with a bit of extra fill but not to the extent like schricks would.

You would have to do back to back testing to determine how much exactly like I did with schricks low lifts.

Here are my results from a few years back but we ended up making 387rwk at the end on the heart breaker dyno, big gains from just cams.