Midget,
For your permanent records.
5/30/2013 COLD leakdown test of 999cc BMC, post mega-dyno thrash:
Cylinder # Reading Leakage % Source
1 86/90 4.5% rings/cylinders
2 84/90 6.7% rings/cylinders
3 87/90 3.4% rings/cylinders
4 86/90 4.5% rings/cylinders
The consistency of this little engine is starting to amaze me - Why? It's making 95.2 bhp/litre with high quality parts. It should hang together if the oiling system continues to do its' job.
Valve clearance is still at spec. Now that everything is stabilized and you have enough valve spring pressure to control the "effective mass" at the rpm you are using . . . . . . . . Still think it might be too much valve spring pressure?
8/20/2013 Hot leak down test - after 10 runs at Bonneville, taken to 180 degrees this evening -
1 96/100 4%
2 94/100 6%
3 96/100 4%
4 96.5/100 3.5%
I'm thinking I should just throw the fenders back on, quit my job, and drag it back for WOS . . .
Just don't tell Kate . . . .
Midget,
It appears that there is approximately a 1% improvement in leakdown % between cold measurements & hot measurements. And although the results are OK, I wouldn't really label them as "good". I would like to see the numbers "improved" for the your next assault @ B'ville. Fact is that with numbers that low, you are giving away a bit of something you can't afford to lose.
Next engine rebuild should include, at a minimum:
1/ Diamond honing on an automatic honing machine with a deck plate torqued in place.
2/ Rings fitted at minimum end gap with a deck plate torqued in place.
Also to consider:
3/ perhaps a change in compression ring style for something that gives better "effective sealing". (This might require a piston change.)
None of this should be done helter/skelter. One of the regrets I have is the inability to get your C/Ratio up to where it needs to be, with the parts you are now using. Getting the C/R up is going to mean a piston change, at the minimum. And with the ultra high C/R's needed for BMC's to make respectable bhp, my experience is that a o-ringed block with a Coopers head gasket or a solid copper head gasket is going to be required.
The "Grenade" can be run as is, at this spec, at some other venues, probably with satisfying results. If you are gonna knock off that Abarth however, some extra Shetland ponies might come in handy, in addition to the aero & drag reduction modifications.
The Abarth is running a one off engine deck lid. Why can't you run a one off hardtop? Just curious.
How goes the desalination?

Marcello (currently re-engineering some MGB bits . . . . . . don't ask . . . . .)