M54B30 Crankshaft

[Rallyprep_UK]

Has anybody here used the M54B30 crankshaft in an M20 ?

Will

[HairyScreech]

It has been done but I don't think anyone currently on here has one running.

IIRC its a bit tricky as like the m52b28tu crank the webs are large and require custom pistons to use.

[jmc330i]

I briefly looked into using one in my M20 until I got hold of an M52B28 crank.
From what I remember you'll need rods that are as long as possible (more than 135mm iirc, so 140mm rods) which means custom pistons. I'm sure I also read that the 12v head may be too restrictive for the cc, so its debatable if the expense is worthwhile.

[reggid]

I have an M54B30 crank which is the same as the S52B32 in the US with 89.6 mm stroke.
You can use 135 mm rods easily with custom pistons and this is what most do (M52/S52 rods etc. are popular and affordable). I use 138mm rods with smaller pin size as I got rods and pistons etc. in a package.

You wouldn’t want to use a longer rod than 138mm otherwise the piston doesn’t have enough compression height to fit ”aproper”a rings as the deck height is too short. As it is the oil ring needs a rail support as the pin cuts into the bottom ring with the 138mm rod. An oil ring rail is pretty common though.
The crank counterweights on the 89.6mm crank are actually smaller than some of the B28 cranks (especially those in the US and some of the later versions perhaps double vanos ones?) so clearance for this aspect is not a real issue as the custom pistons mean the skirt clears and clearance the block is easy if it is needed.

The clearance issues are the rod to bottom of the bore which may need a small chamfer depending on the rods profile near the shoulder area. 24V rods need a tiny chamfer only. Some of the much beefier H-beam aftermarket rods will need a bigger chamfer.

The other clearance is to the intermediate oil shaft which depends on the rod overall width at the big end but these are again certainly easily manageable.

The biggest issue with a big stroker is having a good enough cylinder head/induction and enough cam to make power past 6500rpm.

People don’t realize that a 3.1L engine won’t inherently make any more peak power than a smaller 2.8 or 2.9L build to the same level as power is governed by the cylinder head, camshaft, induction and exhaust. The bigger capacity bottom end will make more torque all else being equal which is certainly welcomed.

[Rallyprep_UK]

That is exactly the information which I was wondering about, thank you.

I have three M20 builds going on here.

M20 w/M52B28 crank + M54B30 rods + custom pistons

M20 w/M52B28 crank + M20B20 rods/M20B25 pistons

M20 w M54B30 crank + undecided rod/piston

Will

[reggid]

You pretty much need custom piston for the M54B30 crank; though some say you can machine down a set of M54 pistons but don’t know for sure.

Personally I would look to get custom pistons with OEM dish-dome shape as this will produce the best combustion with the 885 type of casting as you retain proper squish characteristics. If you want a flat top piston then get a 731 head ported with bigger valves also works as it is meant to be used with a flat top style piston.

OEM 24V 135mm rods will work fine, however Molnar make a economical set of quality aftermarket rods that have been proven in forced induction engines

[HairyScreech]

The oem rods are rather good compared to other companies, aftermarket rods are optional for sub 7.5k engines with light pistons.
Many many engines out there standard and stroked running to 7.5k with standard rods.
The rockers become suspect before the rods.

As above try to keep the chamber shape matching the pistons, it can and has been done with mix match pistons and heads but it is sub optimal and results have always been average.

Again as above the B30 engine will not really make more HP that the B28. It will however have a v8 like wall of torque.
This means the B30 lump should be faster provided you can get the torque to the road.

What are the intended applications for the 3 engines?

[reggid]

to clarify it should be noted that the 885 ports are a little large for the old b25 engine and using a dirty big crank brings it back into the sweet spot.

So the comments about displacement not mattering for hp are assuming that the bigger and smaller engine both have the right combination of parts and are well sorted, upon which the cylinder head flow/cam combination will be the governing factor for topend hp the most part.