Big six stats / piston & bore sizes

[Widge]

Just got thinking today, what sizes are the pistons/bores of the m30 engines 3.5 / 2.8. Long shot but could they be used with a stroker crank to make a 2.8/2.9/3.0 M20? If I'm going to the effort of building a 2.7 I quite fancy boreing it as well as stroking it, but I don't have the budget for custom pistons - so I was thinking what other pistons could be used.

Probably never work but an interesting tech discussion I think

[Jhonno]

dont necessarily have to look BM.. i know RS boys use Vauxhall 16v pistons to make a 1.9 or summat

[Davenotouring]

M30...

2.8 is 86x80

3.5 is 92x86

[Widge]

dont necessarily have to look BM.. i know RS boys use Vauxhall 16v pistons to make a 1.9 or summat

That's what I thought, but was thinking somthing with a 2 valve head like the 2.5 to match combustion chambers.

2.8 is 86x80

Sounds promising, the 2.5 is 84mm hmmmmm, I wonder what volume it would give boring the M20 out to that. Just a sec.

Oh soddit, I'll work it out later. I assume the M30 cylinder head is a similar shape to the M20?

[Karan]

i dont think the m20 is long enough to accomadate that bore size from the m30 3.5.... but u never know.... maybe ones froma 2.8/3.0/3.2/ could be used.....

Karan

[Widge]

Right assuming that the pistons would fit, which the 3.5 wouldn't (be nice if it did ) These are the volumes that would be had with an eta crank.

• M20B25 pistons 2693cc as we know
  M30B28 pisons 2823cc - not a lot bigger but a gain I guess
  M30B35 pistons 3230 cc - wouldn't that be a fun M20!

Oh well I may look in to the 2.8 pistons findout what shape they are etc.
Anyone know what the max an M20 can be bored to is??

[Widge]

.... but u never know.... maybe ones froma 2.8/3.0/3.2/ could be used.....

Karan

I'm pretty sure you're right would be a mean M20 Is the 3.0 & 3.2 an M30? what size bores are they? I am assuming pistons from a 12 valve head will be different, in which case I might as well do an M50 conversion. I'm determined to keep the M20 and go crazy with it though

[TOURINGDADDY]

This sounds like fun i might have to do this to mine to

[Simon13]

Ireland engineering i think they are called, in the usa do a 2.9 m20 conversion kit dunno anymore tho!

[320Touring]

Widge-thought it was 'bangs per buck on a budget'

sounds like a helluva idea though-hopefully it proves possible

[Karan]

yeh they do a 3.0l one aswell

i was thinking of doing this when i thought i had bore wear on my engine...

however it doesnt rev so well apparently...

although price is a bonus cos of the exchange rate!


Karan

[Widge]

Widge-thought it was 'bangs per buck on a budget'

I dunno, just got thinking whilst I was in the bath

Just an idea, getting it bored whilst it's being decked won't be that much more expensive. And M30 pistons can't exactly be that much. But then I suppose I'd run in to fuelling problems. Might just get hold of a set of 2.8 pistons and go a bit bigger than the average 2.7, it would add a bit more bhp rather than torque being bor rather than stroke.

[Jhonno]

Might just get hold of a set of 2.8 pistons and go a bit bigger than the average 2.7, it would add a bit more bhp rather than torque being bor rather than stroke.

wrong!

bhp and stoke both increase capacity, which both increase torque/bhp

bhp is the rate at which torque is produced and as such is a factor of it

[Widge]

Ywah but it's a well know fact that long stroke engines produce more torque - old humbers etc... All I was trying to say is that it would offset the fact that a standard 2.7 is a stroker.

[Jhonno]

Ywah but it's a well know fact that long stroke engines produce more torque - old humbers etc... All I was trying to say is that it would offset the fact that a standard 2.7 is a stroker.

they produce torque lower down the rev range which means the have less power as revs are a factor to work out the bhp from torque

[Karan]

it would make the engine more square..... and therefore more willing to rev.... although a well setup 2.7 will not be unwilling to rev...especially with good comp ratio, cam, breathing.....

[Andy335Touring]

I think you will be lucky to get m30 pistons to work in an M20 with out a lot of machine work=$$$$$$$ !

Just drop a whole M30 in there !

But i wish you luck in your project and hope this table is of use.

[Widge]

Twas just an idle wonderance I had

[Boots_Walker]

I'm toying with the idea of building a crazy stroker too Widge - there are some vauxhall pistons with an 86mm bore that could work...

what has to happen with the head gasket to run an 86mm bore? custom?

[Widge]

Dunno hadn't even thought of that. I suppose you just have to make it a tiny bit bigger What shape are the top of the vauxhall pistons, and have you got any idea how far it is form the crown to the wrist pin?

[Boots_Walker]

Dunno hadn't even thought of that. I suppose you just have to make it a tiny bit bigger What shape are the top of the vauxhall pistons, and have you got any idea how far it is form the crown to the wrist pin?

there are a few different versions, basically flat top with small bowls - compression might not be optimal with a 325i head (maybe 9.5 at best)

pin>crown either 30.4/30.1/30.5mm (compared to 35.7 for the m20), so you could use the longer 135mm rods + eta crank (would end up a bit shorter obviously). wrist pin dia is 21mm (as opposed to 22mm for the m20)

i just downloaded an ACL pistons catalog and have been going through the measurements looking for possible compatibilities with the m20, there are several other possible options inculding some honda accord pistons that look very good but might be too low compression for an 885 head

i'm kind of aiming to use an 84 or 85.8mm crank from an m52/s5x though... if i can get hold of an 85.8mm crank there are some nissan pulsar pistons that would make a nice 3.0l...

[Boots_Walker]

hmm, just noticed those nissan pistons i mentioned are from the SR20DE - should be easy to get some cheap forgies perhaps... i'm liking this idea!

[Widge]

So how big are they? And what sort of shape?
And whats an SR20DE when it's at home?

[Karan]

So how big are they? And what sort of shape?
And whats an SR20DE when it's at home?

s14 200sx lump i think

[Boots_Walker]

the SR20DE is the non turbo version, down here we get them mainly in 2.0l pulsars

they are 86mm flat tops with a 5.85cc bowl according to my specs, pin to crown height is either 31.6mm or 32.0mm (i have 2 conflicting specs here), either way you would have to use the shorter 130mm rods and deck the block a little when using a 3.0l crank. pin dia is 22mm which is the same as the m20

did some calculations last night, i think CR was 9.6-9.8:1ish with a 325i head but i would have to double check.

[Widge]

when using a 3.0l crank.

Where are you getting one of those from?
Not sure I like the sound of the flat tops, probably have to have them machined to fit the valves which, is somthing I want to avoid.

[gorgeee]

would cossie pistons be any good

http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... eName=WDVW
i know this is only 1 but just a thought

[Boots_Walker]

when using a 3.0l crank.

Where are you getting one of those from?
Not sure I like the sound of the flat tops, probably have to have them machined to fit the valves which, is somthing I want to avoid.

well they arent a perfect flat top, they do have a bit of a bowl. valve cutouts might not even be necessary but i cant be sure from the data i have at the moment... the crank i have in mind is from the S50B30

[Widge]

Whats the throw on the s50b30 crank? It's just I have already bought my crank.

[Gunni]

Whats the throw on the s50b30 crank? It's just I have already bought my crank.

86mm stroke 85,9mm bore on the 3.0 motor

[Widge]

An do you reckon it would require any machining for it to fit the M20?

[Boots_Walker]

An do you reckon it would require any machining for it to fit the M20?

there is a little bit of machining involved, i think its just to make the crank pulley fit or something - need to find out for sure though. personally i dont like my chances of finding a crank in the first place

[Boots_Walker]

would cossie pistons be any good

http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... eName=WDVW
i know this is only 1 but just a thought

that looks like it would work with m20 - lots of pistons will physically fit then you have to worry about compression, valve clearance etc. i'm a bit turned off by the pistons with big big valve recesses to suit 4v per cyl heads, and then having to modify further for the m20. just got to decide if its worth it or not...