Big Bore Sumping

[Will-Run]

How are these guys building these Big Bore , big power , big tq. kits, without big sumping problems?. Or are they?. One
would think these 124" , 131" etc ,etc kits, would magnify this problem greatly. How is this not so?.

[1FSTRK]

Maybe it has nothing to do with case volume or engine displacement.

[hattitude]

I have no first hand knowledge, but have read posts (from smarter men than me), discussing this issue on another forum.

They point out a couple aftermarket builders have posted the HD Stage kits for the M8 engines have terrible cylinder bore QC. They found some kits where the pistons wouldn't fit in the cylinders right out of the box...

Their suspicion is that HD's poor engine bores, lead to excessive blowby, and it is one of the issues that exacerbates the conditions that can lead to sumping. These aftermarket kits apparently have better fitting cylinder/piston combos than HD OEM or Stage kits, so much less chance of damaging the delicate balance in the M8 case that, when disturbed, can lead to sumping...

That's the Reader's Digest version. I hope I condensed those discussions correctly...