Chamfer heads for 3.2SS?

[jpnovak]

I was wondering if the heads need a chamfer on the outer edge to go from a 95mm bore tg a 98mm bore on a 3.0 head. I thought you needed to but now I am not so sure.

I have a set of Mahle 98mm 10.2:1 pistons have a 2.5 mm flat ring around the outside edge before the dome starts. This is similar to the flat a 2.7 piston has. I think the 2.4 and 2.7 heads are exactly the same chamber and don't need that chamfer. However, the stock 95mm CIS piston I have does not have this flat. The 95mm JE's I have do not have this ring. I don't know if I need a chamfer or not.

Does the chamfer allow a shorter deck height for increase compression? Will I run into detonation problems if I don't chamfer? the heads will be twin plugged at the same time.

[shbop]

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[cnavarro]

I would say if the piston has no flat ring, that it is a must to chamfer the heads out to the bore size, to protect against detonation, like with a piston like this one:



Otherwise, if the ring is at least the same width as the corresponding non-chamfered surface surrounding the chamber, I don't think it will vastly affect the flame front or propensity for detonation. Twin plugging probably makes the difference between chamfer or not to chamfer that much less inconsequential.

Here is basically the same piston, for a bit larger bore, but same chamber size and shape, without any additional chamfering:

[jpnovak]

Charles, Thank you for the insight. Your pictures describe the parts exactly. I think we will just dress down the sharp edge at the perimeter of the head and build it up.

[JFairman]

Thats the squish band, and it increases turbulance as the intake chrge is squeezed into the center area of the combustion chamber at high revs and top dead center.

[onboost]

Nice Coatings on pistons...

Can you comment on what they are.. including the copper colored one?

Thanks,

[cnavarro]

The copper one is done by JE where the grey one is a piston coated by Calico. Almost all the pistons I am doing now have at least skirt coatings, even if the customer doesn't pay for it. I think it's worth it.