From: "apsilon" <apsilon@optusnet.com.au>
To: "LRO List" <lro@koan.team.net>
Date: Fri, 28 Mar 2003 19:49:12 +1100
Subject: [lro] Overbore 2.25?
Reply-To: lro@land-rover.team.net
>Just wondering what the consensus was in how far a petrol 2.25 could be
safely bored out? Anyone on the list increased the capacity of their 2.25?
Increase bore? Increase stroke? Both?
When I had the 2.25 engine in my 1973 SIII overhauled after it burned a
couple of valves at about 125,000 miles in the early 1980s, I had the
cylinders bored .010 or .020 oversize (I forget which we settled on, but I
think it was .010) to remove the wear "lip" that had formed at the top of
the piston stroke. The danger of not doing this is that with the tight,
overhauled head, the chances of getting blow-by were pretty good. At that
time Land Rover supplied pistons and rings in several oversize sizes for
just this purpose. I forget how far up you could go, but I believe the
choices at that time were .010, .020, .030, and .040 oversize.
The rule of thumb is that if you can catch your fingernail on the underside
of the wear lip at the upper end of the cylinder (where the upper piston
ring stops at the top of the stroke), you should have the cylinders bored
and honed and fit oversize pistons and rings.
This process is to deal with normal wear in the engine. Boring and/or
stroking the engine for additional performance is something else again, and
I don't know how far you can go withe 2.25 before you run the risk of
damage. I suspect you can't bore it out too much before you run the risk
of getting the cylinder walls too thin. I've heard you can take the stock
engine out to about .060 in relative safety, although I recall reading back
in the late 1970s that some folks in northern California took some SIII
2.25s out to .080 or thereabouts. However, I remember that the guys that
did this made cylinder sleeves which I guess helps deal with the thin wall
problem, and they had to make a bunch of other modifications, too. In the
end, I recall in the articles, they deemed the performance increase they
got wasn't worth the effort they'd gone to.
You know what they say, you can only polish a turd so much. I don't
remember all the details of what the guys in California did in the late
'70s, and I suppose there are things you can do today that hadn't been
figured out back then. But the utilitiarian, low-revving design of the
2.25 is such that I suspect the effort required to make anything resembling
a performance engine out of it will far exceed the cost and effort of
simply replacing it with a more powerful engine, because you're probably
looking at a custom crank, custom cam, reworked head, different valve train
to elminate float at higher revs, etc., etc., etc. If you're going to
throw time and money at trying to get noticeably better performance out of
the 2.25, it's probably better spent in forgetting that engine entirely and
thowing the time and money at an engine with more potential.
Land Rover stroked the 3.9 V-8 to get the more powerful 4.2 version (they
actually licensed the design for this from TVR) but it proved to be a
not-very-good idea in the Range Rover. In the lightweight TVR I guess the
4.2 was fine, but under heavy loads like pulling a trailer, the 4.2 block
can flex slightly, resulting in head gasket problems and oil leaks. It
soon became apparent that the 4.2 was a mistake in the Range Rover, and it
was replaced with the 4.0/4.6 versions, which have redesigned, stronger
blocks.
It would be interesting to know (I doubt Land Rover themselves ever did
this) just how much power can potentially be coaxed out of the 2.25 (making
whatever mods are necessary) before it self-destructs. Of course, there
are two kinds of maximum power. The absolute maximum you can get, period,
and the maximum you can get and still have a reliable engine that you can
drive on a thousand mile-plus trip and still expect it to get you home.
It's been my observation and experience over the years that the stock 2.25
does a very good job in the thousand mile-plus trip and get home okay
category. Modified 2.25s, while they can yield more power, also seem to
lose reliability in direct proportion to the degree to which they've been
modified. I'm sure there have been exceptions, but as a general rule, the
more this engine is modified, the more it seems to develop diminished
reliability. No big deal, I guess, if you ony use the vehicle for hill
climbs or weekend off-road outings. But for a daily driver, or a vehicle
you want to take on long trips, poor reliability can become a big factor.
________________________
C. Marin Faure
(original owner)
1973 Land Rover Series III-88
1991 Range Rover Vogue SE
Seattle, WA
marin.faure@boeing.com
faurecm@earthlink.net
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