F2X First N55 Build

[wheela]

From everything I've read they are the same engine, except for............the water pumps, the N55s' is electric and the S55 is mechanical so it's bolted to the block and the N55 uses a water pipe to get the water to the block. The heads can be interchanged, but the turbocharges cannot be without an adapter. The oiling system is different but the better S55 parts fit the N55, this was OEM with the M235R . I'll be using the S55 pumps, suction pipe and oil pan on my N55. All the sensors are the same and the N55 vacuum pump will work on the S55 block as well. The N55 DME should be returned if the dual HPFP's and twin turbos from the S55 are NOT utilized. The only peeve I have with the S55 is the "upgraded" aluminum sprayed cylinders, they cannot be over-bored like the steel ones used in the n55.

I guess a watch out for swapping heads between engine types is maybe the coolant channels? I'm not sure if it's a difference in the actual head cooling channels, or just the head gasket cooling channels.

On both n55 and s55, hot coolant leaves the head on the intake side at cylinder #1. On n55, cool coolant enters the block on the exhaust side between cylinders #3 and #4 (Or 4 & 5 for n54). If you look at the gasket cooling channels for n55, you'll see that they are sized to normalize flow at each cylinder, based on where the coolant enters the block and leaves the head (longer flow path cylinders have bigger flow ports). But on s55, cool coolant enters the block on the exhaust side at cylinder #1 I believe. This provides significantly different coolant flow paths for each cylinder compared to n54/n55.

I haven't compared n55 and s55 head gaskets, but if you do compare them I'd wager that the coolant channels in the gaskets are set up differently so that flow is equalized for each cylinder based on that engine's flow dynamics inside the block/head. So probably best to use the head gasket that goes with whatever block you're using (n55 gasket for n55 block, s55 gasket for s55 block).

Mind you, this is just speculation on my part though.

 

[Dumaurier7]

Good point, I didn't think of that. I assumed they referred to different valve springs and valves to support the higher redline of the s55, but you're right the port and combustion chamber geometries could be different. I'm guessing combustion chambers are the same, since bore and stroke are the same, as is compression?

So based on this I think the Combustion Chamber Modification is a GO!

 

[Boorda]

Honestly, I would love to hear VAC's experience on the S55 head since they see them every day.

 

[Dumaurier7]

I guess a watch out for swapping heads between engine types is maybe the coolant channels? I'm not sure if it's a difference in the actual head cooling channels, or just the head gasket cooling channels.

On both n55 and s55, hot coolant leaves the head on the intake side at cylinder #1. On n55, cool coolant enters the block on the exhaust side between cylinders #3 and #4 (Or 4 & 5 for n54). If you look at the gasket cooling channels for n55, you'll see that they are sized to normalize flow at each cylinder, based on where the coolant enters the block and leaves the head (longer flow path cylinders have bigger flow ports). But on s55, cool coolant enters the block on the exhaust side at cylinder #1 I believe. This provides significantly different coolant flow paths for each cylinder compared to n54/n55.

I haven't compared n55 and s55 head gaskets, but if you do compare them I'd wager that the coolant channels in the gaskets are set up differently so that flow is equalized for each cylinder based on that engine's flow dynamics inside the block/head. So probably best to use the head gasket that goes with whatever block you're using (n55 gasket for n55 block, s55 gasket for s55 block).

Mind you, this is just speculation on my part though.

I'd say the only way to know for sure would be to get cylinder head gaskets from both and match them up.

 

[Boorda]

I have both heads and blocks, sometime in the next couple of days I'll go take some comparison pics.

 

[wheela]

I have both heads and blocks, sometime in the next couple of days I'll go take some comparison pics.

If you have both heads, try and see if you can tell if the intake and exhaust ports look any different! If s55 head really does flow better, maybe s55 head swap could be a cheap alternative to head porting.

Have you seen any actual data supporting s55 head flowing better than n55, or just peoples' anecdotal comments on forums?

 

[Boorda]

Have you seen any actual data supporting s55 head flowing better than n55, or just peoples' anecdotal comments on forums?

Great question, and honestly speaking I have not seen actual data such as head-flow analysis. Just from reading the technical doc stating the head has been modified for race applications and good 'ol butt dyno. But to be fair my butt dyno does like to exaggerate sometimes.

I think maybe I'll order some silicone and pull some port plugs off each head (intake and exhaust) to see if there is any difference in shape or volume.

 

[Boorda]

Im almost finished uploading the S55 technical documentation from BMW, once done I'll post a link to the resource.

As promised, here is the S55 Technical Training Document.

 

[CalvinNismo]

A bit late to the party, but the combustion chamber on the S55 head may well be slightly different to the N55. CP, Mahle, and other big name piston manufacturers list the same pistons for both N55 and S55 but in the S55 their pistons have a 10.2 (standard) compression ratio, but in the N55 the compression ratio is stated as 11. It could be that one person/company has tested it and they all copied each other, or it could be that there are, in fact, changes between the S55 and N55 head confirmed by several big piston manufacturers.

Head ports could therefore likely be different as a result too.

 

[wheela]

A bit late to the party, but the combustion chamber on the S55 head may well be slightly different to the N55. CP, Mahle, and other big name piston manufacturers list the same pistons for both N55 and S55 but in the S55 their pistons have a 10.2 (standard) compression ratio, but in the N55 the compression ratio is stated as 11. It could be that one person/company has tested it and they all copied each other, or it could be that there are, in fact, changes between the S55 and N55 head confirmed by several big piston manufacturers.

Head ports could therefore likely be different as a result too.

Great to know, thanks for sharing!

So both s55 and n55 start out at 10.2:1. If the same aftermarket piston still yields 10.2:1 in an s55, but 11:1 in an n55, that would mean more head volume in the n55 head vs. s55 head, right? If so, then if you swapped an s55 head onto an n55, you'd increase the compression ratio to higher than 10.2:1, and could potentially (depending on the specific differences in geometry) be placing the spark plugs closer to the pistons? Am I thinking about that correctly? Those things may or may not be a problem, but would definately be good to know about if one was swapping heads.

 

[wheela]

Great to know, thanks for sharing!

So both s55 and n55 start out at 10.2:1. If the same aftermarket piston still yields 10.2:1 in an s55, but 11:1 in an n55, that would mean more head volume in the n55 head vs. s55 head, right? If so, then if you swapped an s55 head onto an n55, you'd increase the compression ratio to higher than 10.2:1, and could potentially (depending on the specific differences in geometry) be placing the spark plugs closer to the pistons? Am I thinking about that correctly? Those things may or may not be a problem, but would definately be good to know about if one was swapping heads.

Wait, I think what I said above is backwards... It would be less headspace in the n55 vs. s55, right?