Can a crank

[ed325i]

from a e36 m3 3 litre be made to fit a m20 ?

[jaistanley]

I think you stand a better chance with the american M50 based 3 litre crank. The euro 3.2 litre has larger journel bearings so I assume the 3 litre does too. I say use the american ones as these are the same dia as the M50, which in turn is same as M20.

Still dont even know if you can use that. I've heard of 2.8 M50 cranks being modified somehow and used in M20's.

Not 100% but I hope it helps...

Jai

[E30Mark]

I've heard of 2.8 M50 cranks being modified somehow and used in M20's.

That's what E30Adam is running in his i believe...

No idea about the e36 m3 crank though.

[ed325i]

It was on a american site that I read about using the e36 m3 crank, so they have diffrent m3 engines over there.

[maxfield]

Ireland engineering?

I've read this too

I think the american E36 M3 engine (S52) is based on the M50

[WillG]

yeah it is max, M50 with longer throw on crank, diego on e30tech has put one in his M20 but it required custom pistons as he couldnt find any that would work

[Ant]

Hmm, undersquare engines tend to be torquey but unwilling to rev.

Theres enough meat in the cylinders to take a sizeable bore increase, and gain the extra capacity whilst retaining the revvy nature of the original capacity.

better bore and stroke , maintain the stock ratio is the way to go, well the least compromised in any case.

Only my opinion though.

[Turbo-Brown]

Think the bore/stroke ratio only has a large bearing on the way an engine performs when you've got complete control over the design of the cylinder head.

Here's a good question for people to answer bearing the above in mind as a clue:

Why would an engine of 2 litre capacity that's oversquare (larger bore than stroke) have the ability to make more power than an engine that's of 2 litre capacity that's undersquare (longer stroke than bore)?

[jaistanley]

Because of the acceleration required to get the long stroke piston a further distance in the same time requires a lot more energy. Longer stroke engines are usually set with a lower rev limiter for this reason. The force on a piston/rod is proportional to the square of engine speed remember.

The power question you pose to do with the acceleration of gass at the start of the induction stroke and the squish area of the piston's design. A large bore, small stroke engine draws a lot of charge early in the induction stroke creating a lot of acceleration/turbulence in the cylinder from early-on, improving atomisation and reducing areas of poor combustion in the cylinder during the power stroke. A long stroke engine accelerates the gasses nearer the middle of the induction stroke. The shorter stroke engine can also have a large area of squish around the piston's perimeter which can aid the speed at which the charge burns. It means you can get the power from your charge in a shorter space of time, rev higher and get more power that way.

The long stroke engine will probably make the same power if the head design is 'mild'. Using high lift cams will favour the short stroke, using high duration cams will favour the longer stroke. The long stroke engine will burn charge for longer, usually producing more torque during the power stroke. When the area under the two graphs (rpm/torque) are the same for the two engines and the peak values are different they can still be said to have the same useable power...

Jai

[Turbo-Brown]

Valid factors Jai, but the answer's much simpler than that!

Come on peeps, you can dooo eeeet!

[jaistanley]

Because you're going to boost the nuts off it?

[Ziggy]

More room for bigger valves?!

[Turbo-Brown]

nope, not even that.

It's a good one this, it relates to the basic prerequisites of power and is something you can only really effect if you're designing our mythical engine from scratch.

[jaistanley]

Well, going back to first principles I'd say that a short stroke engine goes farther from the otto cycle than closer (the heat rejection stage being shorter) so I'm getting lost.

Jai

[Turbo-Brown]

Eeeeeeven easier that that

[Turbo-Brown]

Sorry Ziggy! Missed your post! Top of the class that man

[Ziggy]

Sorry Ziggy! Missed your post! Top of the class that man

Bah! You had me puzzling for hours!

[jaistanley]

Aaaah.. I get it.

Valve size aint everything though, gas velocity is pretty important and depending on other characteristics you may well be better off with the smaller valves..

Jai

[e21Jason]

HI

The crank nose is differnent to the m20 damper does not bolt one, and the conrod bearing is larger, when fitted the bolts on the end of the conrond catch the clyinder wall, with a bit of machining I think you could relive the block and and clear the bolts.

The US guys us the us spec crank which is mased on an m5* engine, but the 330 crank is th one used in the us 3.1 litre kits

Jason

[ed325i]

diego on e30tech has put one in his M20 but it required custom pistons as he couldnt find any that would work

- US E36 M3 crank i.e. s52b32 crank (89.6mm stroke).
- 11:1 86mm Wiseco Forged Alusil Pistons from Metric Mechanic.
- 138mm forged rods from Metric Mechanic.

[jaistanley]

How much does that little lot cost? Sounds like V nice kit but the expense may justify an M50/52 swap.. I know some poeple want to keep the M20 so it's worth it but it's worth consideration. People like Ste and Ian are making the M50 swap V easy to do with info and group-buys.

Jai

[Ant]

Top Marks to Ziggy

Bigger bore = bigger valves, and/or less shrouding effect from the cylinder walls.

Dont like stroler engines myself, part of the "fun" is having a large capacity engine that revs like a maniac, not the case once you go undersquare again I fear.

[reggid]

Top Marks to Ziggy

Bigger bore = bigger valves, and/or less shrouding effect from the cylinder walls.

Dont like stroler engines myself, part of the "fun" is having a large capacity engine that revs like a maniac, not the case once you go undersquare again I fear.

its pointless to rev the shit out of m20 unless your engine is similar in spec to player6's car which is one of the rare ones that makes peak power close to 7k rpm. Given that, i say make the most out of it and stroke it to the max becasue thats the best way to get power out of the m20.

Another question Turbo Brown along the lines of your first one is who can say why big stroke engines theoretically do not rev as well?

[Turbo-Brown]

I'd say that any theoretical disliking for revs would come down to greater acceleration in the piston/rod assemblies based on the following:

Due to the longer throw of the crank, the peak piston/rod speed (obviously the movement of the rod is a funny one) for a given crank speed will be higher than a shorter throw crank. Given that the piston etc. must reciprocate with the same frequency for a given crank speed, the acceleration and therefore force required to accelerate the pistons must also increase.

This doesn't have anything really to do with the bore of the engine other than that a larger bore would probably require more piston and thus more mass and therefore greater force to accelerate it.

[reggid]

if you remove 1.7 kg (25%) from the 6.9kg m20b25 reciprocating mass coupled with longer rods (as diego did) this will offset the extra acceleration generated and should easily be able reach the same revs as a m20b25. Just look at the bottom end of the s50b30 and s50b32 revs fairly well. The added stroke may affect reliability though depending on the setup.

i am still a bit confused on how it affects its ability to rev except perhaps on smoothness becasue of added lateral loading which can be perceived as rev ability. I think revability is how fast it sings to the redline a properly stroked m20 will rev much faster than a m20b25.

[jaistanley]

The rev characteristics are also affected by the breathing of the engine. Stroked engines have higher velocity pistons at the mid point of their stroke compared to large bore engines and so the gass passing into the cylinder has greater pumping losses. (energy expended is proportional to the square of the velocity of gas I think).

The con-rod 2nd order (side to side) accelerations are lower with longer con rods which depends on block length as much as stroke; but this is mre of an NVH problem than a strength one. The forces are due to the increased velocity of the piston as it has to go farther in the same time period, as you said.

The japanese build many 2 litre engines with a 'suare' bore/stroke and all of these engines I have driven have felt 'just right'. Also: I once built a longer stroke (ABF) 2.0 16v engine for my golf to replace the 8000rpm 1.8 it had previously had (which got sick of 8000rpm and span a shell). Though the engine was just as happy to rev (light and responsive) I found I never really took it above 6500. This is because we all instinctively drive to the torque characteristics of the engine we are using.. The 2 litre had a lower torque peak so I would sub-conciously shift at lower RPM. The car was still faster and it wasn't till someone mentioned I was driving more sedately that I noticed I was doing it (sedate???, yea right).