BMW M44 Head to Mazda BP Block

Something I (Braulio) have been working on the past few months, initially in some secrecy but eventually debuting the initial design concept to Instagram. The bastard child between BMW and Mazda - a BMW M44 head fitted to a Mazda BP 1.8L block.

An odd but almost fitting pairing, the quantities of coincidental dimensions that just happen to work are something to be marveled at. I’ve personally always been one that enjoys a challenge and this setup has really pushed me in way that normal building hasn’t done before. This isn’t just a simple tolerance check and reinstallation but instead a full engineering exercise.

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A common issue with the B series family’s cylinder heads is flow, mainly in the smaller displacement heads like the B6, but even the BP has plenty left to be desired even after porting. Flow in the M42 and M44 from BMW, is something that realm of the M family doesn’t seem to struggle with. These heads were the foundation for their S42 engine that powered their E36 German Super Tourenwagen Cup car after all.

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Let’s look at the basics to begin:

The Mazda BP and M44 both share a 91mm bore spacing along with an oil feed port to the head in the same location between cylinder 2 and 3. In addition, all bolt holes to clamp down the M44 head are in identical locations to the BP block, so no machining work is needed to correct any mounting or feeding of the head.

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Now for some basic technical info:

The Mazda BP cylinder head (in our case we’ll look at the best case with a BP4W head) is an all aluminum DOHC with a shim over bucket design and a 1:1 rocker ratio as it’s direct to bucket meaning any lift greater than the base circle of the camshaft becomes identical lift the valve will see.

The BMW M44 is also an aluminum DOHC but features rockers in lieu of a direct design such as shim over bucket. However, these rockers aren’t your traditional type of rocker either. In standard form, these rockers create a rocker ratio of 1:1 as the rockers here aren’t used to influence the cam lift versus valve lift ratio but instead are hydraulically actuated lever arms to keep the valve clearance in check. The equivalent in Mazda terms here would be the hydraulic lifters used in the B6 and BP05, not some like rockers used in old V8s or K series.

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Now one may ask, why an M44?

In addition to the more upright valve angle and shallower dome,  the upright valves have less potential to contact each other in shallower valve angles when seeing high lift and oversized diameters. Also, flow characteristics that may be beneficial to higher RPM applications may be present even in our near stock street version. BMW did rev out a modified version of this engine north of 10,000RPM after all.

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This setup does not come without its fair share of challenges. 

 First and foremost, the largest and most involved of the challenges. The M44 is a timing chain engine which features a wet chain area while a BP is a timing belt with a dry belt area. This means we not only need to convert from chain to belt, but also seal off the front of the head to prevent oil flow into the belt area. At bare minimum, this will require modifying the cams to accept seals, creating a sealing plate to isolate oil to the valvetrain, as well as designing a custom valve cover.

Due to this sealing plate, we run into our second major design concern, which is ensuring proper function and regulation of the cooling system within the head. Since the factory thermostat assembly will more than likely have to be modified or removed entirely, this then facilitated a need for either a new housing to be designed or an in-line thermostat, with the later being a more cost effective option. There are potentially other alternatives such as reducing the OEM Mazda water pump pulley at the expense of higher pump rotation speeds due to a smaller pulley size, but all options will be considered and then exercised accordingly.

In addition, there are other nuanced updates that will need implementation such as adapting OEM cam gears from Mazda onto the M44 cams. This will occur at the same time as the plate design as some dimensional relationships will be dependent of each other but the gears themselvez should have no issue aligning to the factory Mazda crank pulley gear.

 

 

 

from minor bits like blocking off a select few ports in the head to major ones like ensuring oil stays within the head and sealing the timing area as the M44 is a timing chain engine and therefore had oil spillover passages into the timing chain area.

This project will not be finished quickly and will not be cheap, but I think it’ll yield some interesting results regardless of the outcome!

 

M44/BP - The first of the challenges.
I had a bit of free time over this holiday weekend, so I set aside some time to really start diving into some of the obvious initial issues that would come to fruition when assembling the M44/BP.

 

M44/BP - A step further with R&D.

(Photo 1&2) Some may have seen me pick this up recently, but I secured a complete and functioning M44 in order to be able to reference dimensions and answer any kind of spacial qualms I may have while observing the setup in a OEM state (and not in 1000 pieces).

(Photo 3&4) In addition to the complete engine, @hidemefromtheweather was kind enough to provide an M44 valve cover for me to use on the two R&D M44 heads. The biggest challenge of this head swap will be what’s seen in photo 3, which will be isolating the valvetrain from the timing belt area illustrated via the green dotted line. This will require substantial R&D and design revisions as I figure out means of region sealing to keep oil isolated to the valvetrain, integrating a cam seal, and designing a new cam cap to both hold the cam as well as create the aforementioned seals. Due to the location of the oil cap and having to create the isolation areas, I may even require a complete one-off valve cover. One step at a time though, but just happy to have this all festering in my mind as I work through the various other projects here at @burst_craft

The timing belt - I had a suspicion I would run in to fitment issues and of course the thermostat / inlet housing proved exactly that. The fourth photo shows this very obvious contact. Luckily the two threaded holes nearest the intersection point are for the OEM BMW timing cover which we won’t be using, so they’ll be shaved to add additional clearance.

Coolant inlet/outlet housing - besides the aforementioned issue, the M44 head receives some cooling via a port right at the front underside of this housing which is usually fed directly from a paired housing in the M44 block. This port can be seen in the third photo where the red tool is present. The BP obviously doesn’t have anything like this to adapt, so this will more than likely be plugged unless it is critical to coolant flow. It is not the sole flow source in that area thankfully as the component that bolts to this housing also has a large house that attaches to this point as well from the front.

Water pump pulley - a minor concern compared to the prior, some test fitting with more components in place will determine if the water pump pulley or thermostat housing that bolts to the inlet/outlet casting may need to be modified to allow for clearance.

Of course this doesn’t even begin to tackle the cam gears and stopping oil flow from the head into the timing valley, so that will be discussed in a future post as I’m still implementing some design concepts to see what may work.

Stay tuned for more updates!