Biggest displacement possible without crankcase boring?

blue72s · 07:39 AM

For a 2.2/2.4 crankcase with standard 92mm spigots, what's the biggest displacement can be achieved? Can the skirts of Mahle 86.7mm p/c's (nikasil) be machined down from 94.25mm to 92mm (reducing wall thickness from 3.775mm to 2.65mm)? Is this mod acceptable or bad practice?

Secondly, the 86.7mm was designed for 70.4mm stroke giving compression ratio of 10.5 to 1, so if a 66mm crank was used what would the C/R be?

Thirdly, can 013 MFI pump be modified to exactly the same as 009?

Thanks in advance.

gestalt1 · 05-01-2011, 10:11 AM

the rough estimate for the compression drop going from 70.4 to a 66mm cranks is .5 points compression. keep in mind that mahle's published claim of compression ration is usually more than reality. 10.2:1 CR mahles are often less than 10:1 when measured. as for turning down the skirts of the cylinders - i have not heard of that being done and it is not a good idea. i think the 93mm cylinders are known to crack at the skirt because of the thin skirt. i'v read in other posts that LN nickies are stronger and can be made as large as 87.2 mm to fit 92mm spigots. i would not go above 86mm with other cylinders.

356RS · 356RS's Garage

Quote:

Originally Posted by blue72s

Thirdly, can 013 MFI pump be modified to exactly the same as 009?
Thanks in advance.

The 013 can't be tuned by adjustments to flow exactly the same as the 009. You can get it close in some areas but not all. Two totality different pumps and space cams. The 013 space cam would have to be modified in areas to duplicate the 009 flow curve. This takes a lot of time/labor.

blue72s · 05-01-2011, 07:24 PM

Quote:

Originally Posted by gestalt1

as for turning down the skirts of the cylinders - i have not heard of that being done and it is not a good idea. i think the 93mm cylinders are known to crack at the skirt because of the thin skirt.

Yes but 93mm cylinders have a wall thickness of just 2.0mm. I think the minimum recommended wall thickness is about 2.5mm (as 2.8RSR). Did 2.8RSR suffer from any cracking at the skirts?

Original 86.7mm cylinders were Birals, which is why the wall was quite thick, but the new ones now are Nikasil (no iron liner) so I don't see why the skirts can't be turned down to thinner, right?