3.3 Stroker - Has anyone built one

[DrMcDave]

I'm going to do a stroker build on my m20 and I've been casually researching online and I noticed that there is a 3.3 kit (it's expensive) being offered. My car is really just a street car. I'm looking for drivability and while it's nice to have more hp and torque I don't need to go crazy. That being said I guess once you start to increase displacement isn't a huge cost difference to go a little larger.

I think a 2.8-3.0 would more than fit the bill but I'm just curious if anyone has any experience with a 3.3. I can't find much info online.

[It's Soda Not Pop]

3.1 is the max I believe.

[hasa]

digger is building a 3.3 stroker. He is using some special long stroke crank. You can find the thread with search.

I believe it's the torque you can gain over 2.8-3.1


edit: here is the posting:

https://www.r3vlimited.com/board/forum/general-forums/members-rides/the-project-forum/286645-m20-b3x-naturally-aspirated-stroker-build-past-present-and-future?p=7003743#post7003743

[digger]

I'm going to do a stroker build on my m20 and I've been casually researching online and I noticed that there is a 3.3 kit (it's expensive) being offered. My car is really just a street car. I'm looking for drivability and while it's nice to have more hp and torque I don't need to go crazy. That being said I guess once you start to increase displacement isn't a huge cost difference to go a little larger.

I think a 2.8-3.0 would more than fit the bill but I'm just curious if anyone has any experience with a 3.3. I can't find much info online.

I am building a 3.3L (86 bore and 93.8 stroke). Its about as big as you can practially go for stroke. TBH unless you want to spend a bunch on the head with porting and expensive valvtrain bits a 2.9L seems to be a decent middle ground thats a good alrounder. Once youre building a maximum effort engine the intake valve and port are the limiting factors to hp and you very quickly reach that on the m20 once you start throwing some more cubes at it. So the peak hp will be the same whether 2.9, 3, 3.1, 3.2 etc once you fully work the head as is an airflow limitation thing the only difference will be the rpm for peak hp lowers as cubes go up as the engine makes more torque.

Metric Mechanic at one point were doing 93mm stroke (iirc) based on s54 reground cranks for the M50/52 platform not sure if they do but this would need a bespoke crank snount setup though not difficult. There are some diesel cranks that are slighty more stroke than the s52B32/M54B30 crank but only slightly.

VAC sell a 97mm stroke for the m50/52 engines but thats going to cause a quite a few issues on the m20 block that IMO would push it over the edge of practical. I think you could fit that much stroke but not the way that crank would be configured as it would foul the intermdiate shaft so you likely need to run a smaller crank pin or relocate the intermediate shaft a bit and run dry sump.

[DrMcDave]

Sounds like more than I care to go through. I have an mcoupe and a 1m but my 325ix is what got me into cars so it holds a special nostalgic place in my heart. It's been sitting in the garage for like 10 years so I just want to get it cleaned up and add a little fun factor.

[digger]

The crank am using requires the same mods as the s52 crank but I went with custom intermediate shaft as the stock one is cast iron and wasn’t comfortable hacking it up that much.

i don’t know what stroker kit you were referring to but I suspect it would be more difficult

[DrMcDave]

I would probably just order a kit from bimmerheads. I'm not super knowledgeable when it comes to engine building. I also don't have much desire to spend the time to piece one together.


https://5150autosport.com/products/5...er-kit-bmw-m20 - this is the kit I saw when googling

[digger]

I would probably just order a kit from bimmerheads. I'm not super knowledgeable when it comes to engine building. I also don't have much desire to spend the time to piece one together.

there is a fair bit to be saved piecing stuff together e.g. For a 2.9L bottom end
Molnar rods $700,
Mahle MS 2.9 pistons $1300,
spacer sleeve, bolt and modified washer $250,
main + rod bearings $200,
Used crank m52B28 $400

you end up paying alot more for a kit

https://5150autosport.com/products/5...er-kit-bmw-m20 - this is the kit I saw when googling

yeah looks like a m50 kit but youd probably get pistons with 2 reliefs instead of 4 and unlikely to have the bits to address the issues that arise when stroking m20 past 3L

[DrMcDave]

I think a 2.9 sounds like a good option. Thanks for the feedback on pricing.

[digger]

I think a 2.9 sounds like a good option. Thanks for the feedback on pricing.

A 3L/3.1L needs same basic parts except pistons to be adjusted to suit. Also light shaving of the intermediate shaft is usually required and sometimes chamfering the bottom of bore depending on the rods used.

you can also save a bit and using OE 135mm rods from M52/S52/M54 etc but you may want to check them and they might need a refresh so there is cost in that. I wouldn’t use OE m20b25 rods

[DrMcDave]

Fortunately I don't have to be super cost conscious so new rods aren't a problem. I'm just looking for something a little quicker and more reliable.

[Archibald]

When it comes to the bearings for the stroker build, one key thing you’ll want to focus on is the quality of the main and rod bearings. Since you’re going for an increased displacement, the extra torque and stress on the engine will require high-quality bearings to ensure longevity and avoid premature wear. Brands like ACL Race Bearings and Spherical Roller Bearings are often recommended for builds like this. They offer higher performance tolerances to handle the increased loads that come with a stroker kit.

[hasa]

Anyone ever used 5150 stroker kit ? Sounds unbelievable that 97mm stroke crank turns in M20 block. Even 84mm M52B28TU creates problems.

[digger]

Anyone ever used 5150 stroker kit ? Sounds unbelievable that 97mm stroke crank turns in M20 block. Even 84mm M52B28TU creates problems.

the 5150 is pretty much just the same generic stuff they flog for m5x etc etc because the bore spacing, rod and main sizes are the same etc so that must mean it will fit right.........it wouldn't be engineered to work at all.

You could in theory fit a crank in the block if you engineered to do so but there would be a number of serious issues to resolve around the intermediate shaft clearance and piston compression height and these need to be properly though out so they don't cause a failure (over machining the intermediate shaft) or result in a solution that is so poor that it negates any benefit. Simply using the same approach as for m5x will not end up with a good solution

here is the 3.4 engine they claim capable of producing 500 naturally aspirated hp which is also nonsense, the generic claims are the same as for the m5x based stroker

https://5150autosport.com/products/bmw-m20-race-engine-build

https://5150autosport.com/products/bmw-m20-stroker-kit

[varg]

Wow those are some extraordinary claims. I'm incredulous of claims of over 200whp NA without good evidence, forget 500hp.