M20 Stroker FAQ for newbs such as myself?

[Tim Flat4]

I thought Subarus were confusing with the twenty variations of the EJ motor and the GC/GD/GM/G-whatever chassis codes but when I read these threads I'm totally lost. What I'm thinking of doing is buying a 325 motor for (my soon to be) 320 that I will build on the side as a project and learning aid because I've never built a motor. I've done head swaps, turbo swaps etc. but never built a motor.

I want to do as much of it myself as possible including head porting. From what I've read it's fairly easy to achieve 2.8l by just swapping different OEM pistons and a crank. What I need is clarification on what year and model vehicle these parts come from as well as any variations in the motors. Also, what kind of power comes from such a motor with a properly matched cam? What kind of compression ratios come from this type of build?

I look forward to learning more about BMWs and finally getting back in to a RWD car after owning AWD cars for the past four years. Thanks in advance to those that leave helpful information.

[e30 gangsta]

Search first of all. And about 200hp with good head work. You can use seta crank and conrods and drop seta pistons into any block. Thats where you get the 2.7 liters of displacemant and then you place the I head ontop. Thats the buget stroker. You can buy 1mm overbored pistons, and bore the block to 86 mm to get a 2.8. The way that i would do it if money was of no issue, would be to call up metric mechanic and order there 1mm overbored 10 to 1 compression pistons. If you have anymore questions pm me.

[Tim Flat4]

Seta?

Thanks for making things a bit clearer. The problem isn't the lack of information it's the abreviations and slang. I've been reading quite a bit and will continue to do so.

What is the life span of a budget stroker motor on average?

[nando]

just to clarify, 86mm is a 2mm overbore

the M20B25 has a 75mm stroke, 84mm bore, for 2494cc of displacement (2.5l). it uses 135mm rods for a rod/stroke ratio of 1.8.

the M20B27 has an 81mm stroke, 84mm bore, for 2693cc of displacement (2.7l). it uses 130mm rods for a rod/stroke ratio of 1.605.

most people who go with custom pistons go with the 85mm bore (who knows why, when 86 costs the same). using an E crank (81mm) and 135mm i rods, you get 2758cc or "2.8l" and a rod/stroke ratio of 1.667.

a step up is an 86mm bore with the 81mm crank, this results in 2823cc with the same rod ratio as the above combo. both 85mm and 86mm bores require custom pistons and cost about the same, so I don't get why everyone in the states is so hot for the 85mm overbore. my preference is the metric mechanic 86mm pistons, they have many advantages such as their skirt design, high sillicone content, and deep valve pockets to turn your engine into non-interference (no more worries about the timing belt and you can run a high-lift cam).

there are still more combos, using cranks from the E36. the M52B28 has an 84mm stroke, then there's the E36 M3 cranks (86mm & 89.6 mm afaik). all those motors use 135mm rods, and you will need a sleeve on the front of the crank for the oil seal, and possibly have the intermediate shaft machined down for crank clearance. you can use this calculator to figure out what the displacement would be with your choice of bore:

http://www.dunegoon.org/displacement.html

the budget stroker should last around 100,000 miles or so, which is probably plenty unless you put a lot of miles on your car every year. I finished my stroker in July and I only have 1700 miles on it so far!

that's all from the top of my head, hope this helps a little bit.

[e30 gangsta]

Good work nando. I'm on my sidekick so I just posted up as fast as I could.

[Tim Flat4]

Thank you Nando! If you don't mind me asking, what are the specs and parts used on your stroker? Also, what kind of engine management are you and others using?

[nando]

I went with the 81mm M20B27 crank, 135mm S50 rods, and 86mm Metric Mechanic pistons. my engine management is stock for now (just using my Bavauto chip from before), but I'm thinking of going with the SMT7 in the future.

[silverfbimmer]

About how much does this budget stroker run roughly?

[Mike325]

About how much does this budget stroker run roughly?

+1 here.

[Tim Flat4]

Also with a ballpark figure I would still like to know what kind of compression ratios are created with such a set up? Are people turbocharging their budget strokers?

[StereoInstaller1]

Seta?

in 1988, there was a " Super ETA" that ran an "i" head, but with single valve springs, an "eta" cam on a 2.7 block, using different rods and pistons.

The hot cheap setup is that bottom end with the "i" top end, 19lb injectors and the Mark D' chip. I understand it is around 180HP.

As far as longevity, I can't wee why you wouldn't get 150,000 miles with proper care and maintenance.

Tim, welcome to R3V.

In my neck of the woods, Subies are either boy-racers or lesbians.

Some boy-racer lesbians too.

Luke

[SA E30]

So many different ways to build up a stroker.

u can go with the 81mm (324td or ETA) crank
84mm M52b28 crank
86mm S50 or M54B30
89.6 S52

Pistons, u can go from 84mm up 2 86mm

I mean there r so many ways to build up a stroker.

U can have a 2.8lt from using the complete M52b28 internals Pistons, rods and crank.

Just depends in the end what u want.

I used a 84mm and 86mm S50B30Euro pistons with M20B25 rods, the pistons were cut down.

In the end I think the most important thing 2 remember when choosing ur combination is to make sure your rod ratio is within limits (between 1.6 and 1.8, with 1.6 geared more towards a performance engine... ) Also Rod angle, but if your ratio is right, then u dont need 2 worry about rod angle.

[Tim Flat4]

Luke, thanks for the laugh. I know in some areas Subarus have a lame name but just south of you (northern CA & NV) Subarus are the vehicle to have due to the weather and doubling as an auto-x machine as well.

There is some great information in here so far. Thanks to everyone that has contributed.

[Kilomph]

How does the ETA/S-ETA crank handle high rpm? I planned on building a 2.7i stroker for turbo, but have decided to stay N/A for 3-5 years, by then i'll probably just buy an MCoupe. I'm thinking about building the 2.7i with a 282/272 cam, running MSnS, and making that my DD. I'm not going to cut anything short because of cost, I want reliability. I'd probably be happy with a stock rebuild with that cam while making everything else flow well. Decisions decisions....

[e30 gangsta]

the crank handles fine for 7k Forged can handle 8k. The head is the weak point. Anything past 7k and youll start snapping rockers. If you get billet rockers forged crank pistons and rods the limit should be 8k. And thats safely.