1991Cc Alloy Block Mi

[SweetBadger 94]

I'm about to get my arse into gear and re-build my spare MI lump, I think a replacement crank will be in order as the one in it has already been reground, and hasn't had an easy life...

 

This got me thinking - if I need a new crank, why not use a 92mm diesel crank, to give increased stroke & capacity (I make it 1991cc)?

 

Issues with this that I am aware of are:

 

- Pistons will extend an additional 2mm, so you need a way of compensating for this

- Compression will increase significantly witht he increased swept volume

 

Most of what I have read recommends changing for custom shorter rods to compensate for the longer throw (expensive), but I think I might have figured a way to put an engine together using off the shelf parts as follows:

 

- Use DFW pistons - (1mm shorter than D6C ones & sit 1.4mm down the standard MI's bore @ TDC)

- Use a 1.9mm thick mls head gasket (cometic do these)

 

Using the above, the DFW pistons would protrude 0.6 mm into the head gasket space, but piston / valve clearance would still be maintained due to the significantly thicker gasket.

 

Taking chamber volume as 40cc, piston/valve cut outs @ 2cc, head gasket bore 84mm, compression works out at just over 11:1 - spot on for a mild road cam (i.e. catcams inlet only).

 

What do you reckon on the above? Should make for an engine with a better spread of power, but still rev happy with the high lift inlet cam...

 

Finally, obviously stand alone engine management would be preferred, but I wouldn't be able to budget for that, so how would standard 3-row MI management deal with the increased capacity? I know that the S16 runs well on 1.9MI management and that's 1998cc (albeit with a shorter stroke)...

[wicked 103 3 Cars]

I donno if the 92mm crank fits in a 1.9 alloy block wrt journal width etc.

 

If it fits, it will work probably, but I think you loose a bit of the revy 1.9 Mi byte, due to the long stroke and increased crank inertia.

Next to that; note that your piston speed will increase an make the liners wear out faster...

An S16 might be more reliable then.

[petert 586]

It seems like a backward step to me, although I've never tried it. Assuming it all fits together, you're building an 83 x 92mm engine, with a very short rod length. I can't recall the exact details, but there was local 6 cyl. produced here is the '70s and '80s by Ford. It was available in a 3.3L or 4.1L version. The 3.3L was great, but the 4.1L with its longer stroke and very short rods just refused to rev. It would hit the wall at approx. 4200-4300 from memory, regardless of the mods. Do the numbers and do the research before spending a heap of money on a potential disaster.

 

I done some digging. The 4.1L six was 93x99 with 149mm rod. So that's a rod ratio of just over 1.5:1. You're spec would be 83x92 with a rod length of approx. 141. So that's approx. 1.53:1. Dangerously low I think.

Edited May 10, 2011 by petert

[carbers205 1]

Yeah, if you are looking at a project like this you are better starting with an 86mm cylinder as the engine will be 'squarer' (ie 86x86)

The journal width of the 92mm crank is compatible, its the 96mm crank from the 2.2s that has wider journals.

[B1ack_Mi16 67]

Yeah, if you are looking at a project like this you are better starting with an 86mm cylinder as the engine will be 'squarer' (ie 86x86)

The journal width of the 92mm crank is compatible, its the 96mm crank from the 2.2s that has wider journals.

 

The journals of the 92mm crank is indeed wider than the 88mm crank in the Mi16.

26mm vs. 24mm.

 

However the Mi16 rods are piston located and have clearance on the crank-journal side anyway, so donæt think it will matter.

But I think I remember you'll run into some issues with the thrust bearings.

 

Also maybe rod hitting block but not too sure about that.

[welshpug 1,657]

92mm crank doesn't rotate in the alloy block, not sure which part stops it but I would imagine the rod angles to be quite severe, you would need special pistons anyway.

 

I believe the valve cutouts between d6c and dfw to be identical but a different height crown.

[welshpug 1,657]

why .7mm?

 

they are 2mm too tall to use with 92mm crank.

[petert 586]

Would you need to grind back the thrust surface width? I'm sure the later cranks are wider at that point.