I think <61.18 MPH at a piston speed of 2500><This is the piston speed
generally agreed on as
the point above which excessive wear occurs> bears out the statement that you
are on the edge at 60 MPH cruise speed.
In fact, the 2500 fpm limit can be extended with chromed bores and Teflon
coated pistons, and modern lubricants, along with proper balancing.
The XPAG engine really did not have as its design parameters max rpm
continuously. Or, so as to not overstate, not even close to it. Having said
that, I think we can all agree that these are robust long stroke engines.
In closing, I suspect that your TBO extension is more likely due to improved
lubrication with modern oils.
Monstra mihi pecuniam!
Ray
----- Original Message -----
From: Dave & Liz DuBois
To: Ray
Cc: Mike Duvall ; mg-t@autox.team.net
Sent: Thursday, September 11, 2003 3:47 PM
Subject: Re: T cruising speed
Ray,
While it is correct that piston speed in FPM determines wear in the
engines, the Blower's manual quotes 61.18 MPH at a piston speed of 2500
FPM (this can all be calculated out, but it is much easier to depend on
Mr. Blower) for the TD. This is the piston speed generally agreed on as
the point above which excessive wear occurs. 61.18 MPH is equal to an
engine speed of 4240 RPM with a 5.125 rear axle ratio and the correct
sized tires of the day on it. For the TF with a 4.875 rear axle ratio
and the correct tires, the figures are 64.3 MPH at the same engine
speed. The engine speed that I am running at, while not quite giving me
60 MPH is almost right on the level for 2500 FPM of piston speed. The
last time I had to overhaul my engine, I had put close to 70,000 miles
on it, which I wouldn't consider excessive wear for an engine that was
originally recommended for overhaul at 50,000 miles. I am quite sure
that the MG factory did not put out vehicles with engines in them that
would be destroyed by running them at speeds where the maximum HP was
being developed (5200 RPM for the TD and 5500 RPM for the TF). While I
would not run my TD up in that range nowadays (Primarily due to the
expense of overhauling the engine), I do not submit to the attitude that
"these engines cannot withstand speeds in the range of 4000 RPM". I
still maintain that the cars can withstand the high RPM levels far
better than the nerves of the drivers of today. We here in America,
particularly, have spent too many years in cars with big, slow revving,
totally inefficient V8s to be comfortable with the higher revving small
engines of European cars (or Japanese cars for that matter).
Cheers,
Dave
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