Pistons for m20 Stroker

[apostate]

Relax everyone. Life is shorter than we expect. :D

https://www.youtube.com/watch?v=B9DqykUsqRY

Whatever you chose, your choice is wrong. The only cure is to look into your kid's eyes. There is a whole universe there. And it is larger and vaster than all the pistons in the world.

Cheers.

[digger]

Everything is a compromise, you just need to choose the best compromise for what you want

[apostate]

Thank you for the insight, digger.
I'll stop reading anything else but your posts only. :up:

[bmwmaster81]

I have ordered the Mahle Motorsport pistons because I think the whole concept is better than the alternatives.

But what Im asking me now is wheather its possible to build an 3l with this piston and I think I have found a good way.


The pistons are made to work with 84mm stroke and 135mm Rods and get about 2860ccm.
My idea is to take 133mm Rods, there are available normaly to lower compression for turbo builds and not very expensive.

I would combine them with 89.6mm crank. This crank pushes the piston (5.6mm/2) 2.8mm further out of the block. The rods are 2mm shorter. So I would end up 0.8mm higher than with the old setup. Maybe I could get another 0.4 by reducing the squish to 0.8mm and by using the thicker head gasket another 0.3mm. The last modification would be to skim the chamber and it schould fit with a very tight squish.
The CR would be at about 11:1 to 11.2:1 but with an perfect tight squish and a bigger cam of about 290° is should work perfect.:devil:

Result would be an 3051ccm high comp Stroker and my rhd ITB it schould run awesome:devil:

What do you guys think?

If it gets to tight i could also use thicker MLS gasket;D

[apostate]

For a 290* cam and European high octane fuel you might want to go to 11.5-12:1 CR.
Just use the Cometic gasket to get the CR there and solve the 0.8 mm. issue.

[zaq123]

don't forget about down movement: crank - 2.8mm further down; rods-2mm further down = 4.8 mm at the piston skirt will be further down for the setup. Plus the angle of short rods/larger crank combo: rods might hit the block mid-stroke. Just a thought...

I have ordered the Mahle Motorsport pistons because I think the whole concept is better than the alternatives.

But what Im asking me now is wheather its possible to build an 3l with this piston and I think I have found a good way.


The pistons are made to work with 84mm stroke and 135mm Rods and get about 2860ccm.
My idea is to take 133mm Rods, there are available normaly to lower compression for turbo builds and not very expensive.

I would combine them with 89.6mm crank. This crank pushes the piston (5.6mm/2) 2.8mm further out of the block. The rods are 2mm shorter. So I would end up 0.8mm higher than with the old setup. Maybe I could get another 0.4 by reducing the squish to 0.8mm and by using the thicker head gasket another 0.3mm. The last modification would be to skim the chamber and it schould fit with a very tight squish.
The CR would be at about 11:1 to 11.2:1 but with an perfect tight squish and a bigger cam of about 290° is should work perfect.:devil:

Result would be an 3051ccm high comp Stroker and my rhd ITB it schould run awesome:devil:

What do you guys think?

If it gets to tight i could also use thicker MLS gasket;D

[ForcedFirebird]

If the head is near full height, you may get away with the 2mm conventional gasket with that combination.

don't forget about down movement: crank - 2.8mm further down; rods-2mm further down = 4.8 mm at the piston skirt will be further down for the setup. Plus the angle of short rods/larger crank combo: rods might hit the block mid-stroke. Just a thought...

It's common to use 130mm rods and 84mm crank, don't think there would be any more clearance issues with the OP's idea.

[zaq123]

It's common to use 130mm rods and 84mm crank, don't think there would be any more clearance issues with the OP's idea.

130mm/84mm will be further from the cylinder wall edge than 133/89.6mm. Just picture the crank/rod at 90' angle. One can always grind for some more clearance but 4.8mm of piston skirt down the cylinder could interfere with that idea as well.

[apostate]

...

[apostate]

...

[zaq123]

Actually not.
133/89.6 will be 0.2 mm higher in the cylinder than 130/84 at BDC.

We are not talkimg about height. His crank will move rod futher left/right at 90' crank than 84km crank. This wi'll move rod closer to the bottom edge of the cylinder where the interference usually occurs

Sent from my VS985 4G using Tapatalk

[apostate]

...

[digger]

Depending on rod should be able to clear bottom of cylinder especially with overbore , at worst slight chamfer required

The 89.6 crank has smaller counterweights radius by about 2mm so it depends how close the piston Is to the smaller crank and how much margin designed in , my gut tells me the piston and piston Pin boss will just clear crank Don't have envelope or pen to do a 2min calculation . If not can be fixed anyway.

With all these potential stuffing around it's a wonder you don't just get custom set to of Pistons to suit

[2mAn]

so I just found out who bought the 85mm Mahle pistons I was trying to buy :hitler:

[bmwmaster81]

I think there should be enough clearance to the clyinder walls. I had aleready a lot of combos in the m20 block and most of them with oem pistons and rods. They are much beafier and you get interference probs much earlier.

The Bore is little bigger, the rods are smaller on the relevant edge and the piston skirts are much shorter to leave room to the counterweights.

The crank, rods and pistons will be fully ballanced so if there is a problem i can let the shop knife edge the counterweights to get clearance.

@digger
i don't get custom pistons because i think the MS pistons are an good allround package.
I also would be happy to combine them with the 84mm crank, so if the 3051ccm plan doesn't work I will build the 2860ccm engine.

I have both cranks here, so when I get the pistons i will put them with the 84mm crank in the block (which has to be bored first) and see the tolerances especially sqish and true CR. If there is enough room, I will order the 133mm rods.
Have already a good ported head with race seats and rhd ITBs, and also going standalone. The Target would be about 240 bhp I think.

With the 11 to 11.5 cr im not sure if the engine will be knock limited already?
Also I don't want to throw a to big cam in it because its for street use.