David Darby wrote:
> ...[snip] ... The engine is a non-original +.030" 1600 with a mkII head.
> When the compression in No. 4 dropped to 60 psi it was past time for
> some attention. Strangely, it still performed pretty well, with just that
> slight fluttering exhaust action indicative of a burnt valve.
>
> When I pulled the head, I found part of the answer to why this engine
> performs so well. It easily outruns the MGB and is the strongest "A"
> I've driven. The pistons are of the flat-top high compression variety,
> ...[snip]...
Hmmm ... *very* interesting. Commencing with the 1622, high
compression ( HC - 8.9:1) and low compression (LC - 8.3:1) versions
were fitted. 'Flat-tops' are standard on the HC 1622. A 1588 overbored
+.032" equates to the 1622 standard bore of 3". Perhaps ... your 1588
was overbored to 3" and fitted with a set of HC 1622 pistons and rods.
> ... [snip] ... and someone has ported and polished the head extensively
> if not expensively. The combustion chambers have also been contoured
> and smoothed. Naturally, my palms began sweating as I hustled it off to
> the machine shop for magnafluxing and inspection. ... [snip] ... Now I
> have it back and am concerned that it may be excessively milled by
> the cumulative amount of machining it has had over the years. ... [snip]...
> I do not have the burette setup to accurately measure the combustion
> chambers, but I may have to devise one in order to answer my questions.
> Does anyone know the factory dimensions for head height? I am probably
> milled at least .095" (2.4mm) from stock.
The rule of thumb is that removal of .010" equates to a 1cc reduction in
the combustion chamber capacity, but the chambers have been modified
so your right ... you will have to cc the chambers to determine what ya have.
Assuming a 3" bore with 'flat-tops' ... my WAG is that 37.5cc equates to a
10:1 CR ... 35.5 is a 10.5:1 CR.
At some point the head becomes thin enough that the exhaust valve will
foul the block (thats why the 18V has the eyebrow cuts) ... so you may
want to insure that ya have the minimum lift clearance of .060".
> Is this excessive? Should I consider double-gasketing the head? Will I
> be able to burn 92 octane fuel?
Seems a bit radical ... did you have problems with pinging/detonation
prior to the valve work? If not, there are several of us that would love to
know
the size the combustion chambers. ;^)
Safety Fast! ... larry.g.unger@lmco.com
'61 MGA 1600 MkII
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