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Bullet Ride's 2.8L Stroker Project (Updated: Dyno Plot pg. 6)

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    Bullet Ride's 2.8L Stroker Project (Updated: Dyno Plot pg. 6)

    Well, I've been chipping away at this project for a couple months now but felt as though I should start a thread to document the process (even though it's been done plenty of times already) and to give/receive advice. So here it goes...

    First, the back story to the project...

    The spark to attempt this build came back in 2010 when this happened...

    In my hunt for a replacement oil pan I was able to get a whole M20B25 for $100 which is pretty much the going rate for a used oil pan.

    So after I finished replacing the oil pan on my car I was left with the rest of the motor and a big question mark about what to do with it. I definitely wasn't going to scrap it. I could have kept it for spare parts or sold the rest of the parts and actually made some profit off of my foray into oil pan smashing but where's the fun in that?

    I remembered reading about an M20 2.8L stroker that used a combination of OEM BMW parts, so I did a little bit of research and came across a few build threads (and a few more have popped up between then and now). The combination of parts required is as follows:
    - M20B25 cylinder head (885 casting), block and late model (short skirt) pistons... which I already had
    - M52B28 crankshaft
    - 130mm connecting rods from either the M20B20 or M20B27
    - crank spacer for front oil seal

    I figured it wouldn't be very hard to find the missing pieces so I stashed the motor away and kept my eye out for the missing pieces. Before Christmas that year I had picked up a 325e motor and stashed it away. Then last year I came across the crank I needed in Kentucky and had it shipped to a relative of mine who happens to live in Kentucky and who happens to come to Canada to visit us once or twice a year... you can see where I was going with that.

    Fast forward to this winter. It's my first winter in 5 years that I'm not in school, so with more free time on my hands than I'm use to I mustered up the gumption to dive into this project.

    Goals for the project:

    - budget stroker = keep cost to a minimum
    - make at least as much power as the 2.8L motor that the crank came out of (~190hp) but with my old shitty 2 valve head ;)
    - mainly learn about building a motor as this is the first time I've attempted to build a motor of any kind

    Performance parts to be added:

    - Ireland Engineering heavy duty rockers
    - Some sort of performance headers
    - Some sort of performance cam
    - Lightened flywheel
    - Crank scraper
    - adjustable cam gear
    - DIYPNP engine management
    - ITB set-up (this will be another project for after the motor is built and running)

    Before the snow hit I bought an engine stand and pulled the motor back into the garage to become a permanent resident for the winter...

    On a side note: After I had pulled the oil pan off that motor I ended up dumping it on a piece of plywood in the bush and covering it with a plastic tarp. It sat there for two years with the crank case open to the atmosphere. I was quite surprised to see when I brought it back into the garage that there was no rust on the cylinder bores at all.

    Unfortunately it didn't even cross my mind to take pictures of the motor during the initial tear down but I bagged and tagged all the bits that came off.

    Once I had the head disassembled I did an El Ghetto test to see if any of the valves were leaking...

    Only the one exhaust valve was leaking...

    However the shop that I'm taking the head to for decking said that they'll vacuum check the valve to valve seat seal of all the valves for $20. So I'm going to get them to do that.

    Initial inspection of the head showed quite the step from the exhaust port to the manifold...

    I figured this might be for anti-reversion, but I'd look into it further.
    Continuing the tear down, I ripped into the bottom end. Sometimes the timing gear can get seized on when corrosion creeps in between the gear and the crank. I got lucky and mine slid right off

    Then I got to cleaning up the head...

    Next I needed the connecting rods out of that 325e motor. When I bought it, I ended up putting it in the back of our wood shed. Not having a convenient way of getting it to the garage I decided to tackle it on one of the not so cold days...

    Roll out the red carpet...

    One of the concerns I had was whether or not the oil had been drained out of the motor. Obviously it wasn't... because that would be too easy. I wasn't about to just let the oil drain into the ground, especially when we get our water from a well on the property, so I had to figure out how to get the motor high enough to get a drain pan under it. It turned out to be a delicate process of kicking boards under each end as I lifted each side by hand...

    Gassed from muscling the motor around I contemplated... Does tearing apart an eta motor on the ground, in the back of an open woodshed, during the winter just to get a set of connecting rods make me a gear head? I meditated on the thought while the oil drained...

    Then I realized that time would have been better spent removing the wiring harness and coolant hoses. Back to work. Shortly after I had the head off...

    The bores in the motor are in very nice condition which brings me to the question... Does anybody want parts from this motor? With the exception of the rods the rest of the bits are there and I have no need for them any more...

    Then I rolled the motor over so I could pull the rod caps and push out the pistons and rods...

    Back in the garage: A comparison between the 135mm B25 rod and short skirt piston and the 130mm B27 rod and piston...

    325e flat top vs 325i domed piston...

    Then I checked the top deck to piston relation at TDC using the stock components for later reference...

    The lowest part of the piston (on the left side of the image) comes past the deck ~1.0mm

    Last edited by Bullet Ride; 08-28-2012, 07:01 AM.

    Then I separated the pistons from the rods. These rods definitely look beefy. It's no wonder the turbo guys have been able to push 400whp on the stock bottom ends...

    A quick tip I learned, unless you have to, never fully remove the wrist pin from the piston, only push it out enough to get the rod out. Even on these floating pin pistons it's a close enough fit that it can be difficult to get the pin back in. If it's the slightest bit crooked the pin won't go anywhere and you'll end up damaging the hole if you try to tap the pin in with a hammer. in order to get the one pin that I fully removed back in I had to stick the pin out on the snow while heating the piston in a vice with a propane plumbing torch. Then it slid in no problem.

    Then I wanted to test fit the 2.8L crank with the 130mm rods and B25 pistons. Already knowing that there was going to be an interference between the counterweight on the crank and the piston skirt.

    2.5L vs forged 2.8L crank...

    Welcome to your new home M52B28 crank and M20B27 rods. M20B25 piston meet your new roomates...

    That didn't last long, they got into a fight just before TDC...

    This is to help visualize what's going on. As you can see, the counterweights are right up in the piston skirt's business and the connecting rod ends up with a separated cap...

    There's only one counterweight that gets along and it's the last one just before the rear main seal. Nice guys finish last...

    Off to the machine shop. It was hard to tell exactly how much to take off the counterweights because it's hard to measure without modelling and knowing the offset of the firing plane from the crank axis. I've been told that taking off ~0.25" will get it to clear. However after having taken off 0.2" I wasn't convinced there would be enough clearance. So to avoid having to come back to the machine shop I took off another 0.1" and put a generous chamfer on the counterweights. One thing to note is that as you get to 0.2" of material removal you will start cutting into edge on the opposite side by the connecting rod journal. I wouldn't say it's anything to worry about though as it's not really a load bearing feature.

    Make sure to tape the journal surfaces you they don't get damaged by flying metal chips...

    Back at home, another test fit shows that everything now rotates freely, even though all the parts are still up in each others business...

    As you can see in the picture above, with the extra stroke the skirt of the piston comes out of the bottom of the bore by about 4mm (add 9mm of stroke and remove 5mm of rod length) whereas the stock piston sits flush. Obviously this isn't ideal as you are losing a bit of lateral support and with the reduced rod ratio the side load is increasing. However this occurs at the point of lowest load in the cycle so it's probably not a huge concern, and the fact that this combination has already been built and proven a number of times is proof of that.

    Looks fancy, but still needs to be balanced...

    The new piston to deck relation. The piston sits ~0.5mm lower. This means the block will have to be decked 0.5mm to regain the same squish between the piston and the head. Apparently a 0.5mm deck on the block and a skin of the head should result in a ~9.5:1 compression ratio which is nice.

    A before and after comparison to help visualize...

    Then I spent some time cleaning up the crusty block so that it can go get decked and then painted...

    I tried blasting the block at work but they didn't have the right media, it helped but it didn't do as good of a job as I hoped it would. Oh well, it's good to go now...

    And I buffed the raised bits on the valve cover for the pimp factor...

    While all of this was happening I got in on that group buy for the racing dynamics headers. I tried looking around for headers. the IE shorty headers look fancy but in reality all they do is look good, the primaries are too short to be useful. The long tube ebay headers, you can't beat the price but you will have to beat the headers to make them fit which I didn't like the idea of. So these RD headers seemed like a good option at a fair price. They should look something like this...

    With that in mind and knowing that the inner diameter of the primaries was slightly larger than the gasket diameter I didn't see a need for such a large step from the gasket to the exhaust port. I decided to 'match' the ports to the gasket (still leaving a small step).

    Before and after...

    In order to do it I used a rotary tool, and my hands. I started with an HSS cutting bit to hog out most of the material. Then I smoothed it out with a grinding stone. Then I sanded it smooth using 60, 100, 150, and 200 grit paper consecutively. Will it make a difference? Without a flow bench I have no idea. However I do know that the heads Alpina use to do up for the E30 were gasket matched along with some other port modifications and they saw a 13% increase in flow. If anything, at least the ports are smoother now which is good on the exhaust side. Once I get an intake gasket set I'll gasket match the intake as well (if it needs it) but I won't polish the ports as that actually hurts the flow on the intake side.

    Then I spent a little bit of time cleaning up the valves...


      Last week I picked up the head and the block from the machine shop...

      Head decked

      Block decked 0.5mm

      Bores deglazed


        Last night I made my first attempt at lightening a flywheel

        I started by turning down the thick step around the outside

        Then I cut away some of the middle

        Finished result

        I just weighed it and it came in at 15lbs (started at 19lb). This was my first attempt at lightening a flywheel so I was conservative with how much material I removed. I definitely know where the other pounds can be removed next time around. However for now I'm happy with a 21% weight reduction.

        The flywheel and pressure plate are going to get balanced with the crank this evening.


          Knowing that I'm going to need an adjustable cam gear I started looking into it.
          The VAC ones are pretty expensive for my liking so I'm considering this one

          Since I've heard bad things about the cheap ebay gears with the tooth patterns being off causing belts not to fit and after seeing that this is pretty much all that's going on....

          ... I thought about modifying the stock gear. So I measured up the stock gear and drew this...

          Noticing that the ribs in the adjustable gears were a bit thicker, I moved the adjustment screws as far to the outside as I thought reasonable in order to have the most material surrounding the holes as possible.

          My plan is to get a 3/16" thick laser cut of the adjustment plate. Then I'll skin the ID and inner face of the gear to make sure it's square, then machine the OD of the adjustment plate to that it's a nice snug fit to the gear. Then I'll drill and tap the holes in the gear and use a dividing head to separate the gear into two pieces.


            Interesting project! good luck!


              Sweet! Hope this turns out better than mine! :p


                Originally posted by acolella76 View Post
                Sweet! Hope this turns out better than mine! :p
                One can hope. Hopefully yours gets back on the road with a vengeance!


                  Excited for more updates.


                    A couple more pics....

                    When I was in the shop yesterday I turned down the pulley adaptor from the M52 crank to make the oil spacer needed. I also squared up the inside of the cam gear for my attempt at a DIY adjustable cam gear (still needs to be deburred).


                      This is a might engine build big thumbs up dude.


                        This is awesome, i'm going to start mine here in about a month and a half. I'm going to follow your build closely. Whats your total costs so far. I have like 2500 saved up, but i planned on getting a head from Master-e, i think it's like 850, with a valve job, cam, port and polish, Hd rockers.


                          nice build thread bra cant wait to see the final product!!


                            Originally posted by JA1991 View Post
                            This is awesome, i'm going to start mine here in about a month and a half. I'm going to follow your build closely. Whats your total costs so far. I have like 2500 saved up, but i planned on getting a head from Master-e, i think it's like 850, with a valve job, cam, port and polish, Hd rockers.
                            I don't have an exact number but just to list out a few of the costs...

                            - Between the cam and the headers I've spent $1000
                            - All of the hardware and seals and other bits required to rebuild a motor is ~$1000
                            - I spent $250 on the machine work for the head and block
                            - The crank + flywheel balancing was ~$150

                            Things I still need to spend money on...
                            - new exhaust from headers back (probably ~$500)
                            - stand alone engine management (probably a DIYPNP kit... another $500)

                            I can see this project costing me around $3500. However things are cheaper in the US than Canada. Case in point is the rebuilt head you mentioned with an upgraded cam and rockers for $850. In Canada, at least the area where I live, just to get a head decked and get a valve job will cost $300-400, throw in a reground cam and HD rockers and that's $800 without including any porting, polishing, disassembly or reassembly.

                            One other thing to keep in mind is that I am doing some of the machining to keep costs down. If I had to pay someone to do the machining I'm doing it would add at least a few hundred dollars more to the grand total.


                              Which standalone are you thinking about buying?