On Mon, 31 Jul 1995, Roger Garnett wrote:
> Andrew Mace writes:
>
>
> > 1964 Spitfire
>
> Is this the white Spit?
Yes, one and the same!
> > Only one thing was strange: I have yet to find any evidence of the middle
> > ring! ... Does anyone have any good ideas as to
> > 2. why it would not have been used when the engine was last assembled
>
> I can think of a couple possibilities- but you won't know for sure until you
> pull all the pistons.
>
> One obvious answer would be that someone broke one of the rings, but put
> it together anyhow. Hey- it works, right?
>
> Another possibility, is a build decision. The second ring is to help hold
> compression & reduce blowby. If you carefully size the top ring so that is
> seals just right when hot, you won't need it as much. Each ring you
> install increases the friction caused by the piston movement, so leaving
> out a set of rings could reduce friction, and *possibly* gain some power,
> if not offset by compression losses. The problem here, is that gains made
> by reducing compression losses are very important to producing power.
It turned out to be the latter possibility, as all four pistons were
sans middle ring. Of course, I have no real way of knowing the gain
power v. lost compression ratio, but the three good cylinders, all @
~160 lbs. on compression test, lead me to believe it worked fairly well
up to this point. And that spans many, many years. Rik and I got the car
in 1983. It had been "abandoned" for some period of time previous to
that, and in getting this ex-GP racer ready for life as an autocross
car, we did nothing more to the engine than put new gaskets in and paint
the block! It served quite well off an on over the years.
All evidence points to the engine having been very well built, whenever
that was. Nice machine work, porting, polishing, rods look really
pretty, the teflon plugs on the ends of the wrist pins. And either
someone started with a very low mileage engine, or they bought a new
crank when building it up, as the rod bearings are still standard size
(and showing virtually NO wear). Again, as a running check just before
the teardown yielded instant 70-80 lbs. oil pressure, dropping only to 50
lb. at hot idle, I see no reason to mess at all with the bottom end,
although I will throw in new rod bearings!
> I can't beleive how many people run race engines with *NO* air filters.
> This is one area that the "vintage way" is the wrong way. The wear in the
> cylinders due to any dust sucked in very quickly results in enough power
> loss more than surpass any power gained by not sucking through an air
> filter. Not to mention what happens if you suck in something bigger, or
> get a big load of dust or sand kicked up by another car!
I agree completely, except for one factor on this particular car. As
hinted above, all the engine work was absolutely first class.
Additionally, the carburetors received some very nice "massaging" in the
form of carefully rounding out the throat on the face where the air
cleaners normally would bolt on. I say normally because, for some
reason, the front carburetor "ears" were broken off, leaving somewhat
less than a half-circle of threads for the air cleaners to bolt into.
Other than that, the carbs still are fine, tight, leak-free, etc. to
this day. I just pray that a given autocross course will not be too
dusty!
Oh, yes, the damper pistons were nicely reshaped as well. Again, I don't
know if it's all good or not, but it has worked well, albeit without the
protection of filters.
I also used to remove the filters and the large airbox where they
resided when I autocrossed my GT6+. The weight loss of that assemblage
probably "increased" power as much or more than the less restricted air
intake!
Andy Mace
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