Hi guyz/gals.
In the process of sorting an L18 engine I've recently purchased. Was rebuilt a long, long time ago & sat in shed, under covers. The 2 builders aren't around anymore so, apart from them swapping the head for a U67 L20B head (it was to be turbocharged & came with old school turbo & exh mani) I knew nothing about it.
So, the other day I shone a light down plug holes to find it has flat tops. Pulled the U67 head off. The flat tops are numbered & have been cleaned. Light Hone marks still visible on bores. All good. I'll be installing the old L18 A87 closed chamber head onto this replacement engine & head looks to have been refurbished @ some point as valve heads are clean & all in great nic. Bit grubby looking through ports.
My Q I have is this. I know the L18 runs 8.5:1 in stock form (with open chamber) & 9:1 (with closed) The SSS engines run 9.5:1 comp so, when I read a post here on the L20B engine stating with closed chamber L18 head & flat tops it'd be 11:1 comp ratio. Uhm, how the hell is that when they are 8.5:1 in stock form, same as the L18 stocker??? Only difference with the SSS is having the flat tops & peanut head (compression-wise). So, why would the L20B with same specs be so much higher?
I do get unswept vs swept volume & the fact the 2L has a longer stroke.
What I calculated comps to be for the SSS was 9.6:1 & the L20B with flats & peanut head to be 10.2:1 & even that still baffles me...