M20 Stroker FAQ for newbs such as myself?

[moatilliatta]

that MM 3.2 is so tempting- anyone heard or driven one of those? 260hp from an NA m20 w/ no standalone and no ITB's is pretty much crazy.

just some numbers i was thinkin up

(STOCK) m20b20 with 127 hp = 63.5 hp per liter
(STOCK) m20b23 with 147 hp = 63.9 hp per liter
(STOCK) m20b25 with 167 hp = 66.8 hp per liter
(STOCK) m20b27 with 127 hp = 47.03 hp per liter
(MM) 3.2 with 260 hp = 81.25 hp per liter
(JORDOS) 2.8 with est 210hp = 75 hp per liter

anybody please add.
i'd be impressed by who has the best liter to power ratio.

when i build my moter all my research is going into the head. the m20b25 stock bottom end can make 250 hp... if you have a racing dynamics dohc head...

[winstontj]

This is wonderful!!! Glad it popped up because I did search and did not find this.

I'm a noob here so I'll bite my tounge a little and not piss anyone off but I feel compelled to comment on a few things here. I asked about strokers because I know they exist but didn't have facts like numbers, bores, cranks, etc. and this thread has everything - thanks again!

no offense but i think they know a bit more than you about M20's and how to make them reliable. You should take a look at their website

Has anyone verified those metric mechanic HP numbers on a dyno? I'm guessing they are a bit optimistic.

In response to the two above quotes I totally agree with pdx 528e;556714. IMO MM has put out some HP ratings and motors that I don't totally agree with. Maybe I should just leave it as that but take this for example. An early MM m10 stroker used m30 pistons, audi 5000 rods & an s14 crank. The rod ratio was BRUTAL to say the least - it ran and how long they lasted or what power they put out I don't know but their early stuff was somewhat less than top notch IMO. It's my understanding that their HP ratings have been way overstated as well and this is the reason why many others (like IE) don't put HP numbers on their sites because it makes their products look inferior because they are truly accurate ratings rather than inflated.

[braddammit]

Actually the higher the ratio the "better", although the differences for a street engine are almost negligible, IMO. There's a huge amount of debate about rod/stroke ratio on the intarweb, but no one seems to be able to consistently show an improvement on a dyno. 1.6:1 is perfectly acceptable.

What I remember about it from many (many) years ago is that the higher the R/S ratio the more if *shifts* the power band. The reason (as explained to me) behind it is that the higher ratios in effect slow down the piston speed around TDC reducing the airspeed requirements. Supposedly this lets the engine breath easier at a high rpm. The downside is that the reduced airspeed at lower rpms kills your output there.

I never quite understood it all but I was working for a guy who drag raced VWs and we built one with a R/S ration of about 2:1 (you can actually turn a VW crank and use Chevy rods to create a stroker). The thing rev'd incredibly and screamed at the top end but we couldn't get gearing low enough to get it off the line in any sort of decent manner.

[DrMcDave]

bmwsob on e30tech is running the 7.9:1 compression and ran an 11.xx 1/4 mile. I would just keep that compression and add some more boost. I think he made 400ish hp at the wheels.

[mops]

Hello Guys.

I want to build a stroker aswell.

but I'm building one to turbo it.

i got megasquirt to run it all.

Anyways, for turbo, i would ideally like 8.5:1 compression. my plan is to get eta bottom, and put i head (885) on top of that. that will result in 7.9:1. How much would i need to deck the block (or head) to get 8.5:1 ? maybe around 0.4, 0.5mm ? aparently seta pistons would be best for 8.7:1 comression, but there were no setas at thwew I live.... so i would have to import from US or something...

alternatively i was thinking about getting 84mm m50/52 crank, but hen i'll most likely need custom pistons to achieve required compression... too difficult... (read expensive). I'm prepared to rebuild head and bottom end, but I'm not really keen to make custom parts....

[DrMcDave]

I would have paid the 9k. I saved about 2 grand, but I had to build it myself and I doubt it will last as long or make as much power. plus they do extra things to their motors that I don't have the capacity to do, like the modified intermediate shaft and oil tube in the head. bascically all you'd have to do is drop it in, could be done in a couple days easily if you paid a shop, or a week if you DIY.

I know you were thinking turbo, but I prefer N/A motors for their throttle response and simplicity/reliability. even with the stock AFM and intake, my throttle response is excellent (miles better than when first bought the car).

i guess there are pluses to each side. i want to see what the 3.64 gearing is like, it should be in within the next 2-3 weeks. I have it all cleaned up, it just needs painted and then new seals done.

[nando]

I would have paid the 9k. I saved about 2 grand, but I had to build it myself and I doubt it will last as long or make as much power. plus they do extra things to their motors that I don't have the capacity to do, like the modified intermediate shaft and oil tube in the head. bascically all you'd have to do is drop it in, could be done in a couple days easily if you paid a shop, or a week if you DIY.

I know you were thinking turbo, but I prefer N/A motors for their throttle response and simplicity/reliability. even with the stock AFM and intake, my throttle response is excellent (miles better than when first bought the car).

[E30_pilot]

so wat do you guys think is a ideal/good budget for a 2.8 stroker?
I have about $2500.

[DrMcDave]

It's amazing what ITB's do... especially for a track car, the throttle response is incredible.

its my lifetime goal to have ITB's on my e30.

[SA E30]

It's amazing what ITB's do... especially for a track car, the throttle response is incredible.

[DrMcDave]

nando are you saying you'd pay the 9k to have it built there or you'd buy the parts and send them your head.

i was looking at the price. Its like 5500+ or - for the head and the bottom end parts for the 3.2. Obviously you have to send them your head, but you could save a considerable amount of money doing the bottom end yourself such as you did. I wonder if that 9k+ includes installation? Seeing all these NA motors come together always gets you thinking. I will be making a move in the next month or two one way or another.

also having the motor out lets me do the clutch and the axles as well as the new gearing.

i've got the money just not sure what i want to do. 260 hp would rock. Think of what ITB's and some standalone would do for that engine. 280+

[digger]

I'm guessing they are a bit optimistic.

based on what? They don't do backyard job strokers like most you'll see on the forums and they use components that compliment each other 200whp isn't that outrageous IMO.

[nando]

no dyno yet.. will do it eventually, but right now I'm just having fun driving my car. I don't want to work on it again for a very long time. ;)

Has anyone verified those metric mechanic HP numbers on a dyno? I'm guessing they are a bit optimistic.

I don't think they are that optimistic.. keep in mind their headwork and piston design is unique to their motors. they CNC the ports on their head and have done extensive flowbenching to get them to flow better than stock. also, that 260hp is probably with the 11.5:1 compression "rallye" pistons. they only quote 205hp at the crank on the 2900, that's not unreasonable at all for a 2.8l M20 - jordan had almost that much at the wheels with his 2.8, and he didn't have the benefits of the 86mm bore / high sillicone content pistons.

as far as piston speeds, they'd be no different than any of the other larger BMW motors. both the S52 and S54 use 135mm rods with that huge stroke of theirs, and they both work fine.. keep in mind the forged, lightweight components that were designed to work together for those particular motors.

I think if you want a 3.2 and you have the money, buying an MM engine outright is the way to go.

[DrMcDave]

i dunno they do seem to be very high. I nearly build a 3.2 last year but the cost kept going up and up and it eventually went out of my price range at the time. Whether they are right or not, they are very high quality engines and i'd take one over a lot of other options.

[pdx 528e]

no offense but i think they know a bit more than you about M20's and how to make them reliable. You should take a look at their website

Has anyone verified those metric mechanic HP numbers on a dyno? I'm guessing they are a bit optimistic.