Based on inlet type.
Sounds a bit odd but the regulations l must abide by suggest the engine must use the standard inlet type from the factory. Currently l have a 16v smallport that has all of the expected modifications, properly ported head, high compression pistons etc. but it must retain a standard type inlet. l'm getting away with a modified smallport inlet at the moment and this appears to be a restriction.
I can fit a complete 20v engine complete with itb's or l can return to a bigport head and inlet.
l'm completely un-interested in what it sounds like but l am interested in any benefit of using a 20v head.
If l was going the 20v route, ideally l would use my current bottom end but l don't really know if that is viable.

bigport manifolds are quite restrictive - especially just above the bend. Even without TVIS I don't believe it flow as much as the smallport manifold. The 20V is likely got the best potential as far as capable intake flow. The Silvertop head has 36cc chamber volume same as the 16V heads, while the Blacktop has 38cc chambers - so swapping to a silvertop would affect compression the least.

I can buy a 20v silvertop head quite cheaply to try, do you know if there is any truth in coolant passages not aligning correctly with 16v engine blocks? l thought all of the later blocks were the same.

totta crolla wrote:I can buy a 20v silvertop head quite cheaply to try, do you know if there is any truth in coolant passages not aligning correctly with 16v engine blocks? l thought all of the later blocks were the same.

as far as I know the only issue with using a 20V block is one of the cast reinforcements (with /T50) will not mount to the block. As far as head alignment - I've not heard about this. What you may have heard is to use the headgasket that fits the head - so you would want a 20V head gasket

totta crolla wrote:I can buy a 20v silvertop head quite cheaply to try, do you know if there is any truth in coolant passages not aligning correctly with 16v engine blocks? l thought all of the later blocks were the same.

no truth, just use a 20v HG and you're good to go.

oldeskewltoy wrote:

totta crolla wrote: the only issue with using a 20V block is one of the cast reinforcements (with /T50) will not mount to the block.

This is correct one of the (feather braces) as Toyota calls them will not mount the T50 trans to a Sivertop block but I found I could easily modify one of the bolt holes in the brace to make it bolt to the block. I'm not convinced they are even necessary.