Bullet Ride's 2.8L Stroker Project
Well, I've been chipping away at this project for a couple months now but haven't really felt like putting the work into starting a thread. However a lazy Sunday afternoon is a better time than any 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 Rob (El Gato Liso) told me that I could have his old B25 motor (that he pulled to swap in his now oil pissing M50 :P) for pretty much the cost of a used oil pan at the time. He even let me borrow his engine hoist so that I could unload the motor at home; nice guy *th-up*.
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, one local example is NOTORIOUS VR who built that turbo 2.8L stroker last year). 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 (for all day 7000rpm duty)
- Some sort of performance headers
- Some sort of performance cam
- Lightened flywheel
- Crank scraper
- adjustable cam gear
- DIYPNP engine management (which in turn will give AFM delete)
- 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 Rob's old 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
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...
And that's all for now folks!
Enjoyed, subbed and looking forward to more!! :)
Looking forward to the out come. I also have a M20b27 just lying around. Maybe this will motivate me lol
Looks good! Can't wait to see it in action.
looks awesome! keep it coming!
Thanks guys. The head and the block will be going to the machine shop this week to get decked. I will also be sending the crank for balancing, which reminds me. I need to call Rene to pick up that single mass flywheel so I can lighten it...
On the exhaust side it's not so much the head port It's the exhaust header /manifold you need to worry about. Ideally it should be smooth airflow from the engine.
I left the ports on my head slightly larger(SMALLER!!! thx bullet) than the gasket. And opened the ports of the manifold slightly larger than the gasket. They never seem to fit 100% and that will ensure you don't have a ledge of material sticking out someplace. Also I wasn't too worried about disturbing the back-flow.
Looks like fun... I'd love to be playing around with a motor again. Maybe one day....
haha... yes I talked myself backwards there, what I meant was,
BIGGEST --------------- Smallest
We're not talking a wall here, more like a very small .5 - 1mm lip.
That way the flow steps out to the larger area... when/if you get back flow it will hit the lip but that's not important.
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