While doing some research on various Mazda engines I came across a 1.6L ZM-DE engine in a 2000 Protégé. The engine block looked remarkably close to a B6/BP so I did some disassembly to inspect. What I found is that the ZM-DE shares all the same dimensions with the B6 engine except it has an aluminum lower split-block design, and two extra oil drains on the exhaust side of the block/head assembly. Other than that the block, rotating assembly and accessories are identical.
Here are a couple photos of a B6 head gasket on a ZM-DE head.
Here are some photos of the ZM-DE cylinder head on a B6 block.
I took various measurements of the head to compare to the stock B6 head. The intake ports on the ZM-DE head measure 2.10 X 1.115 and are significantly higher from the deck surface and have a straighter shot to the valve than the B6 head. A visual comparison between the ZM-DE intake ports and the BP-4W intake ports indicates that they are almost identical (the ZM-DE is perhaps a little better due to the valve angles). The exhaust ports measure 1.7 X 1.065 and are visibly larger than the B6 ports and have a better transition at the port divider.
Here is a photo of the B6 and ZM-DE exhaust manifold gaskets (the ZM-DE is on the bottom).
The cam duration I found on the Protégé forums indicate the ZM-DE has and intake duration of 226*@.003, and I measured the lobe lift at .325” using micrometers. The exhaust duration is 233* @.003 and lobe lift is .310
• IVO = 1* BTDC
• IVC = 45* ABDC
• EVO = 52* BBDC
• EVC = 1* ATDC
The lifters are also solid not hydraulic like the B6. The lobes are also much narrower than those found on the B6/BP engines. The lobes measure .400 wide at the nose of the cam lobe and tapers to .220 at the heel of the lobe. The cam spacing is 3.75 inches, which is much narrower than the “B” series engines. In order the get the valve angles tighter and the cams closer together the cam gears are smaller.
Here is a comparison between the ZM-DE cam gear and the BP-4W.
The lower drive gear on the crank must be paired with the upper.
Here are some photos of the upper portion of the cylinder head. Here you can see how much tighter the valve angles are. Tighter valve angles result in shallower combustion chambers which are generally more knock resistant.
I have yet to cc the combustion chambers. I will post the numbers when they become available. Here are the combustion chambers.
Because the combustion chambers are shallow the pistons have a significant dish to achieve the required compression ratio.
I was originally fabricating my own 36-1 ignition trigger. This design used a wheel that brazes to the damper hub.
I then came across this while removing the lower timing belt drive gear from the ZM-DE engine.
I took and laid a 99’ crank trigger wheel I had over the top of the ZM-DE trigger wheel.
O.D. and the center bolt pattern are identical!
I had also purchased a 99’ BP-4W valve cover with the intention to cut and weld the front portion of the cover with the cam angle sensor to my original B6 valve cover. However the ZM-DE valve cover comes with a cam angle sensor built in. So that solves problem of generating a cam sync pulse for the Megasquirt.
The valve cover breathers also look to be an improvement over the B6. The baffles at first glance appear to be higher flowing and have longer passages to help separate the oil from the blowby gases.
Out of curiosity I checked to see if the original CAS would fit.
Everything bolts up and seals properly, however the one problem I found with running the stock CAS is the drive lug does not fully engage with the back of the exhaust cam. There are a couple ways to solve this problem.
1) Lathe the backside of the CAS so it sits further in the head
2) Remove the drive lug from the CAS and weld/extend the ears
3) Mill the backside of the head so the CAS sits closer to the cam
The first solution would be very simple, except if the CAS fails you would need to repair the original, or lathe the new one (kind of a pain). The second is a simple solution, however that “T” shaped drive lug is harder to get off than expected and damage could occur to the CAS. The third option is a good one, except mounting the head in mill could take some time.
The intake manifold has some nice features.
• No water circulation passages
• Long tapered ports
• VTCS (most people remove)
• Equal length runners
• Dual plenums
The most interesting feature is the dual plenums. The primary plenum is very small for throttle response. At the back of the primary plenum is a port that connects to a secondary plenum under the primary which I assume is being used as a Helmholtz resonation chamber.
My plans are to remove the primary and secondary plenums and weld a stock B6 plenum to the ZM-DE runners. This may not be the best flowing system by it would be a simple way of getting all the vacuum ports and various idle components functioning. I also live in California and would like to keep the engine modifications as discrete as possible.
The VTCS many people have stated only operates during warmup. The research I have done show that “tumble valves” increase the combustion rate and reduce the chances of detonation. Obviously these valves do not present a restriction for my power levels. If I was racing the engine I may remove them.
I am contemplating a way of using them as an IRTB system, which would provide better throttle response, and would limit the amount of exhaust gas reversion into the intake ports at lower throttle inputs (if I ever run cams with a higher valve overlap).
Here is a photo of the stock B6 intake manifold with the ZM-DE intake gasket laid over the top. The port height indicated by the gasket is misleading because the intake mounting surface of the ZM-DE is machined at an angle. However the width of the ports are a correct representation of the differences in port size.
The head bolts used by the ZM-DE are a little shorter than those found in the B6/BP engines. They also use a hex head socket. McMaster-Carr sells this same bolt (M10X1.50 X 100mm) in a 12.9 grade rated at 174,000psi, which is more than adequate.
(Do not be misled by the thread length. The threads in the ZM-DE block are the same depth.)
Because the ZM-DE shares all the same dimensions as the B6 (except the extra oil drains) the head gasket is backward compatible. The head gasket is a MLS style gasket with two layers. It is significantly thinner than the stock B6 composite gasket and I would not recommend its use on stock pistons due to the fact that they protrude .010 from the deck of the block and may contact the cylinder head if the ZM-DE head gasket is used.
If aftermarket pistons are used this headgasket should work fine and I assume would be a cost effective alternative to the Cometic head gaskets.