M20B25 to stroker

[TomW]

Hi all,

I’m new here and I want to convert my m20b25 into a 2.8 and been looking on the wiki pages to what I need to convert it.

I’m sure this has been covered millions of times before but I really need some help as to what I need for this conversion.

So far I’ve been told that my standard 325i pistons are scrap because of some scratches down the sides of them (I don’t know how much of this is true) and need new ones. Plus the block has been checked and needs re-boring. Can anyone recommend anywhere in the UK that do custom pistons?

I’m also really struggling to source an e36 328i crankshaft, are there any other options I can use from other BMW’s?

Thanks guys

Tommy

[reggid]

http://www.iemotorsport.com/bmw/item/M2 ... stons.html

these have the correct dome profile and use the correct alloy, other customs ones probably wont so beware of genric scrap

i dont think there any 84mm stroke cranks that fit the m20 beside m52b28 crank

[flybynite]

I’m also really struggling to source an e36 328i crankshaft, are there any other options I can use from other BMW’s?

AFAIK You can use the 528 also. Not sure about the 728

[TomW]

Thanks guys

[fixedwheelnut]

Which con rods do you use with the M52 Crank and M20 pistons?

[flybynite]

Which con rods do you use with the M52 Crank and M20 pistons?

Its all in the wiki
https://www.e30zone.net/e30wiki/index.p ... ding_a_2.8

[fixedwheelnut]

Which con rods do you use with the M52 Crank and M20 pistons?

Its all in the wiki
https://www.e30zone.net/e30wiki/index.p ... ding_a_2.8

Cheers
I found that about five minutes after I posted

so it looks like 135mm are preferred over 130mm rods, which was my main query

[flybynite]

so it looks like 135mm are preferred over 130mm rods, which was my main query

Where does it say that in the wiki? 135mm rods will not work unless you get custom pistons made. Only the short 130mm rods work.

You have a choice of pistons bit it needs 130mm rods as it says in the wiki

[reggid]

OE pistons with M52B28 crank must use 130mm rods.

[fixedwheelnut]

OE pistons with M52B28 crank must use 130mm rods.

That was pretty much what I was trying to work out, many reports say it is better with 135mm rods using a thicker gasket so I was hoping someone had done it and tried it. Might have to have a play once I rip it apart. Cheers

[reggid]

OE pistons with M52B28 crank must use 130mm rods.

That was pretty much what I was trying to work out, many reports say it is better with 135mm rods using a thicker gasket so I was hoping someone had done it and tried it. Might have to have a play once I rip it apart. Cheers

the only person i know who looked at rod length was ANT, he did 2.7L using the eta rod and OE b25 pistons and 2.7L alpina pistons that use the 135 rods he said there was bugger all difference.

You wouldnt run a 5mm thick deck spacer/gasket to fit a 135 mm rod its not worth it and so many hassles. if you want to use 135 rods the most effective way is the Mahle MS pistons which are a good thing for the street. They are more expensive than other forged aftermarket pistons but they are the most ideal.

[flybynite]

You wouldnt run a 5mm thick deck spacer/gasket to fit a 135 mm rod its not worth it and so many hassles.

I completely agree, with a 135 rod it is custom pistons or nothing, but isn't it only 3mm you are going to need to lose on a standard block?

if you want to use 135 rods the most effective way is the Mahle MS pistons which are a good thing for the street. They are more expensive than other forged aftermarket pistons but they are the most ideal.

What makes the Mahle MS piston better than something like an Omega or JE?

I would be happy with a cast piston as I am not trying to get power over a nice running engine so I would be looking at a forged piston of 4032 alloy as opposed to 2618. I don't want a noisy engine on startup.

[SeanOB]

I’m also really struggling to source an e36 328i crankshaft, are there any other options I can use from other BMW’s?

I am thinking of selling my m20b28 parts that I bought to do the same to my 325i. PM if interested! I haven't listed it anywhere as yet due to the lockdown.

M52B28 crank
130mm rods
crank spacer

[reggid]

You wouldnt run a 5mm thick deck spacer/gasket to fit a 135 mm rod its not worth it and so many hassles.

I completely agree, with a 135 rod it is custom pistons or nothing, but isn't it only 3mm you are going to need to lose on a standard block?

if you want to use 135 rods the most effective way is the Mahle MS pistons which are a good thing for the street. They are more expensive than other forged aftermarket pistons but they are the most ideal.

What makes the Mahle MS piston better than something like an Omega or JE?

I would be happy with a cast piston as I am not trying to get power over a nice running engine so I would be looking at a forged piston of 4032 alloy as opposed to 2618. I don't want a noisy engine on startup.

JE can do 4032 but you need someone with the OE piston dome profile if using a 885 head. By the time you spec the JE with slipper skirt and coated skirt it ends up more $$$ than the Mahle and the quality of the mahle seems a bit better. You can get a bare bones JE piston which is perfectly fine. TopEnd in the US are a dealer for JE but they always try to steer you away from 4032 but need to insist on it. they have the OE profile so no need to send a sample piston and pay for engineering to reverse engineer it. Mahle certainly aren’t the only ones but if you’re doing a street 2.8 it’s the simplest route with little chance of screw ups which seems to happen a lot with custom parts

[flybynite]

JE can do 4032 but you need someone with the OE piston dome profile if using a 885 head. By the time you spec the JE with slipper skirt and coated skirt it ends up more $$$ than the Mahle and the quality of the mahle seems a bit better. You can get a bare bones JE piston which is perfectly fine. TopEnd in the US are a dealer for JE but they always try to steer you away from 4032 but need to insist on it. they have the OE profile so no need to send a sample piston and pay for engineering to reverse engineer it. Mahle certainly aren’t the only ones but if you’re doing a street 2.8 it’s the simplest route with little chance of screw ups which seems to happen a lot with custom parts

Are you saying Mahle would already have a piston to go? My dilemma is whether to get Alpina pistons and work the head accordingly or get 885 profile pistons with the gudgeon pin moved up the required amount for 135 rods. I am contemplating a 'proper' build 2.7 because of the car's history but i don't need to re-invent the wheel doing it

[JungleGus]

I don't know much about it, but this may be the Mahle piston: https://www.iemotorsport.com/product/2- ... mahle-m20/

From my limited knowledge, it's a more road focused forged piston than the normal IE stroker kits...I think

[reggid]

JE can do 4032 but you need someone with the OE piston dome profile if using a 885 head. By the time you spec the JE with slipper skirt and coated skirt it ends up more $$$ than the Mahle and the quality of the mahle seems a bit better. You can get a bare bones JE piston which is perfectly fine. TopEnd in the US are a dealer for JE but they always try to steer you away from 4032 but need to insist on it. they have the OE profile so no need to send a sample piston and pay for engineering to reverse engineer it. Mahle certainly aren’t the only ones but if you’re doing a street 2.8 it’s the simplest route with little chance of screw ups which seems to happen a lot with custom parts

Are you saying Mahle would already have a piston to go? My dilemma is whether to get Alpina pistons and work the head accordingly or get 885 profile pistons with the gudgeon pin moved up the required amount for 135 rods. I am contemplating a 'proper' build 2.7 because of the car's history but i don't need to re-invent the wheel doing it

Ireland Engineering have an off the shelf Mahle MS piston for 2.9L. it is 85mm bore, 10:1 CR iirc for the 84 stroke M52b28 crank and 135mm rod. Been around for 4 or 5 years now.

https://www.iemotorsport.com/product/2- ... mahle-m20/

Mahle MS could do a custom version for a 2.7L with the pin moved 1.5mm further down but it would probably be more expensive as a one off and i'm not sure they'd be willing to just change the compression height on the IE pistons.

Top end would be able to do a 4032 from JE with the 885 shape piston (8.8 or 9.8 CR style) for a 2.7L which would work out at around 9.5:1 or 10.5:1 CR subject to the valve reliefs and whether you got the early or late dome and so forth

[Pucker]

Hi Im new here, I also am debating a 2.8 stoker build.. the only cranks i can find are the ones with the trigger wheels on the last counterweight.. anyway.... I just wanted to say that you can use 135mm rods, but you'd need to order a set of pistons with a 5mm higher wristpin. The highest hp N/A m20 Ive seen pushes 259rwkw, running JE 14:1 pistons, that are pretty flat topped, also running 135mm rods, and a 2.8 crank, along with 45mm triple webers, also a healthy amount of head work.
https://performanceforums.com/forums/fo ... k-goodness

[flybynite]

Well I have had a chat to a few people and things are different to when I looked at it a while ago.

Most piston manufacturers now need a run of between 20 and 200 so it rules the majority out like Omega that I have used before.

I wanted a Mahle piston and if I was doing a 2.8 I would use the one IE have had them make no question. Dealing with Mahle MS is like pulling teeth. It is like they have never heard of an M20 and want the piston designed from scratch. I just can't be bothered. That is Mahle MS USA, Mahle MS Europe won't even respond (and that is to guys in the business)

JE on the other hand have just about every permutation you could want. Places like Vac and Topend have them selectable on their web site all the way from low comp blower pistons to 14:1. For a 2.7 their pistons maintain a proper 885 squish band up to 10.2:1. They are an absolute pleasure to deal with, they even suggested using 4032 for a road car.

They are more expensive than other forged aftermarket pistons but they are the most ideal.

Still curious as to what (in practice) makes the Mahle MS piston better. They claim to use a better low-expansion alloy than 4032 but is there anything else? I wanted a Mahle piston for no other reason than I have one as a paperweight on my desk and they made the Alpina piston that I would use if it did not cost £3K per set

[steve_k]

Well I have had a chat to a few people and things are different to when I looked at it a while ago.

Most piston manufacturers now need a run of between 20 and 200 so it rules the majority out like Omega that I have used before.

I wanted a Mahle piston and if I was doing a 2.8 I would use the one IE have had them make no question. Dealing with Mahle MS is like pulling teeth. It is like they have never heard of an M20 and want the piston designed from scratch. I just can't be bothered. That is Mahle MS USA, Mahle MS Europe won't even respond (and that is to guys in the business)

JE on the other hand have just about every permutation you could want. Places like Vac and Topend have them selectable on their web site all the way from low comp blower pistons to 14:1. For a 2.7 their pistons maintain a proper 885 squish band up to 10.2:1. They are an absolute pleasure to deal with, they even suggested using 4032 for a road car.

They are more expensive than other forged aftermarket pistons but they are the most ideal.

Still curious as to what (in practice) makes the Mahle MS piston better. They claim to use a better low-expansion alloy than 4032 but is there anything else? I wanted a Mahle piston for no other reason than I have one as a paperweight on my desk and they made the Alpina piston that I would use if it did not cost £3K per set

i know what you mean about JE, my 2.7 has a set of there high comp (10.1 IIRC) custom made one's for use with the 135mm rod in it, & as far as i remember they are made from 4032 as well, though i did buy them 2nd hand off a friend who was going to build a 2.7 but never got round to it (& he was asking a very good price ).

but as i say they where a custom made set & i have to say when i took the head off to refresh it they looked just as they did when i first installed them, happy to say the least.

[reggid]

Well I have had a chat to a few people and things are different to when I looked at it a while ago.

Most piston manufacturers now need a run of between 20 and 200 so it rules the majority out like Omega that I have used before.

I wanted a Mahle piston and if I was doing a 2.8 I would use the one IE have had them make no question. Dealing with Mahle MS is like pulling teeth. It is like they have never heard of an M20 and want the piston designed from scratch. I just can't be bothered. That is Mahle MS USA, Mahle MS Europe won't even respond (and that is to guys in the business)

JE on the other hand have just about every permutation you could want. Places like Vac and Topend have them selectable on their web site all the way from low comp blower pistons to 14:1. For a 2.7 their pistons maintain a proper 885 squish band up to 10.2:1. They are an absolute pleasure to deal with, they even suggested using 4032 for a road car.

They are more expensive than other forged aftermarket pistons but they are the most ideal.

Still curious as to what (in practice) makes the Mahle MS piston better. They claim to use a better low-expansion alloy than 4032 but is there anything else? I wanted a Mahle piston for no other reason than I have one as a paperweight on my desk and they made the Alpina piston that I would use if it did not cost £3K per set

If you want a 2.7 piston for an 885 then go with TopEnd (steve) be very prescriptive with the alloy and the exact dome shape. Note that when you define the dome shape e.g. 9.8:1 style OE you basically define the CR. What CR are you after? do not go total gapless rings (total seal conventional/non gapless rings are probably worth it), don’t get any coatings it’s not required for a 2.7 and adds unnecessary cost, the same the full skirt style pistons is fine don’t need the slipper style it adds cost.

Do not use VAC under any circumstances you won’t end up with what is ideal

The Mahle seems to have slightly better machining and finish and you cant get a bare bones one, the other differences you can spec with JE as well e.g. slipper skirts, ultra-lightweight machining, skirt coating, anti-gall coating for wrist pins, accumulator grooves, etc. and the JE end up costing more. For a 2.7L street engine a barebones piston is the best BFYB it’s not an extreme engine with long stroke or lots of rpm etc. etc.

[flybynite]

If you want a 2.7 piston for an 885 then go with TopEnd (steve) .

It is Steve Nelson I have been talking to. Very good, knows his stuff, no BS and has an answer to my questions that make sense to me.

be very prescriptive with the alloy and the exact dome shape Note that when you define the dome shape e.g. 9.8:1 style OE you basically define the CR. What CR are you after?

The Alpina cast Mahle slug got 10.2:1 on an all-but standard 885 head with larger valves. Steve said they go as far as 10.2 with a full squish, perfect for the 885 head. Seems Alpina came to the same conclusion. Not re-inventing the wheel here so that is what I would go for. He suggested 4032 so should have no problem there.

do not go total gapless rings (total seal conventional/non gapless rings are probably worth it), don’t get any coatings it’s not required for a 2.7 and adds unnecessary cost, the same the full skirt style pistons is fine don’t need the slipper style it adds cost.

Bare 10.2 piston with 4032 as the only option was the conclusion I came to. I specifically don't want a slipper skirt and most other stuff is irrelevant for a street-driven N/A car.

Do not use VAC under any circumstances you won’t end up with what is ideal

Whilst I haven't dealt with them as such, it was JE USA that put me their way. Their piston is selected with simple menus, if you know what you want it is hard to see how they could get it wrong. Didn't try them for advice though

Particularly unsatisfying dealing with Ireland Engineering, one word replies and nothing helpful.

The Mahle seems to have slightly better machining and finish and you cant get a bare bones one, the other differences you can spec with JE as well e.g. slipper skirts, ultra-lightweight machining, skirt coating, anti-gall coating for wrist pins, accumulator grooves, etc. and the JE end up costing more.

I'm only trying to replicate a cast slug so a bare bones 4032 forged piston should do that with no issues

For a 2.7L street engine a barebones piston is the best BFYB it’s not an extreme engine with long stroke or lots of rpm etc. etc.

exactly Thanks for the input here, been very helpful as ever!

[reggid]

The Alpina cast Mahle slug got 10.2:1 on an all-but standard 885 head with larger valves. Steve said they go as far as 10.2 with a full squish, perfect for the 885 head. Seems Alpina came to the same conclusion.

its more that when you take a given dome then you are defining the CR inherently so there is a limit to the CR. I'm guessing you'll be getting the 9.7:1 OE squish design which works out about half a point higher when you increase the stroke for a 2.7L.
i.e. a 2.5L will be lower CR with that same exact dome. More CR offers fairly small gains for a much smaller tuning window anyway so its not a silver bullet.

With VAC you wouldn't get the OE design dome even thought you would get the CR you want. which means the shape would be wrong for the combustion characteristics.

for those not following what the OE piston its the 8.8:1, 9.4:1 and 9.7:1 b25 piston which has a angled squish band around the circumference which causes high mixture motion as the mixture is squeezed between two close fitting surfaces (head and piston) and an offset dish. the centre of the dish is moved towards the exhaust valve to improve vaporisation and ensure the sprak plug electrode is closer to the centre of the volume to improve the combustion.

https://www.e30zone.net/e30wiki/index.php/M20

Top End make a replica set of OE pistons for a racing series here. they took an OE cast pistons and replicated the geometry except it was forged rather than cast. they did this with the 8.8 and 9.7 pistons styles

[flybynite]

which works out about half a point higher when you increase the stroke for a 2.7L. i.e. a 2.5L will be lower CR with that same exact dome.

Yes I realised the CR varied with swept volume but I had not appreciated the amount or made the connection. The squish pistons they make are the 3 different original BMW dome designs adjusted to the 2.7. Exactly what I am looking for.

Gives me a bit of confidence about how it will run, like I say, not trying to reinvent the wheel.

I am just waiting to hear if they think there will be adequate clearance with that piston and a Schrick 284/272

[reggid]

which works out about half a point higher when you increase the stroke for a 2.7L. i.e. a 2.5L will be lower CR with that same exact dome.

Yes I realised the CR varied with swept volume but I had not appreciated the amount or made the connection. The squish pistons they make are the 3 different original BMW dome designs adjusted to the 2.7. Exactly what I am looking for.

Gives me a bit of confidence about how it will run, like I say, not trying to reinvent the wheel.

I am just waiting to hear if they think there will be adequate clearance with that piston and a Schrick 284/272

The only thing they do is move the pin position up to suit the stroke and change the bore if you request it. You can get them to make reliefs a bit deeper. I’d get them to make them suit a Schlick 288 as a bit of additional margin

[Lemon98]

I’m also really struggling to source an e36 328i crankshaft, are there any other options I can use from other BMW’s?

Tommy

Some is selling an M52B28 crank on here!!!!

viewtopic.php?f=6&t=280232