Cruise and happily are not synonomous with 70mph in a series. If my figures
are correct, your turning 4,147rpm at 70mph. That's an rpm that will wear
out the top half of the engine quite rapidly. Because of the slop, weight,
gravity, and friction, push rod engines aren't high speed engines. Yes they
can be made to spin up in the 7,000rpm range but internal dynamics greatly
increase wear at higher rpm. If you don't mind rebuilding the engine
regularly, you are going to dump the truck on an unsuspecting soul, or you
simply don't put many highway miles on the truck, yes you can go 70mph per
hour with stock gearing. Will the engine do it happily with stock gearing,
no way!!
By the way, you can almost do it with a stock engine but it takes all the
71hp to force the rover through the wind. Wind resistance increases
exponentially. It doesn't just take a little but a lof of hp to increase
mph. An aerodynamic car may cruise at 70mph with only 40 hp or so but will
take considerably more, like double, to go 90mph. These figures are not
scientific, by the way, just to illustrate that something can be done but it
takes a lot more than just putting your foot farther in the carburetor. The
example of Timm going 90+ in his 140hp series illustrates my point. A stock
series with 71hp will go 65. It takes double that hp to go just 30mph
faster.
High speed engines can and are built. Formula 1 engines regularly run into
the high teens and street motorcycle engines are redlined in the low teens.
Apparently they will happily run near 10,000 rpm for very long periods. To
get this rpm/longevity they have super lightweight valve systems with direct
actuation of the valves by the cam. Short blocks are severely oversquare
and reciprocating masses are very light weight to reduce the effects of
accelerations and mass. They also don't produce any significant torque or
hp below the redline of a series engine. Otherwise, they are absolutely
unsuited to the type of use that a Series truck is supposed to be used for.
High center of gravity vehicles, pushrod engines, long travel suspensions,
etc. just aren't meant for high speed perambulation. Driving an SUV at high
speeds is asking for it, just ask Ford. Look at all the electrickery on a
Disco II to get decent road handling and still keep the legendary off road
capabilities of a Rover. Yes they will do very high speeds in a straight
line, but blow a tire, have to maneuver quickly, or horror of horrors in a
Series, stop quickly, and you will be facing an interesting situation, to
put it mildly. Even though our trucks equal or excede the technology of
typical English sports car of the period, they were designed to stay below
65mph and cruise well below that. If you want to do long commutes at the
speed limit on the interstate, change the gearing either by changing the
diffs, an ashcroft transfer case or an overdrive. To hold that higher speed
over a reasonable range of conditions at the lower rpm, you will probably
have to tweak the engine, by the way.
My tweaked engined 109 wants to cruise above 60mph because its got the hp to
push the brick faster. Since the gearing is stock, I resist the temptation
as faster speeds still mean higher rpm despite the fact that I still have
plenty of throttle left. If I regularly ran the truck at freeway speeds,
I'd slap an overdrive on in a second. Since I do most of my driving under
55, will live with it. For those of you in the real world, be kind to your
trucks, don't assume that just because it will do 75mph, my 109 will, that
it should be driven consistently at that speed without changing the gearing.
For those of you wanting to go 90 mph in a Series, you are stupid!!! You
are risking your lives and worst of all, endangering others. Yes you may
get away with it indefinitely but if it turns around and bites you, you
will be in a world of hurt. Hopefully, you will be the only one to suffer
when it does.
Modifications that make the truck better able to maintain a reasonable
speed, add efficiency, allow the trucks to motivate up steep grades or crawl
over bigger obstacles are all good for the marque. Using the side benefits
of those tweaks irresponsibly, has consequences that you don't want to face.
Aloha
Peter O.
>From: Ian Stuart <Ian.Stuart@ed.ac.uk>
>Reply-To: lro@works.team.net
>To: lro@Works.Team.Net
>Subject: Re: LRO: Re: Engine/Trans Swap
>Date: Mon, 11 Jun 2001 10:36:50 +0100
>
>On Monday 11 June 2001 08:03, you wrote:
> > On Sun, 10 Jun 2001, Peter Ogilvie wrote:
> > :Given the aerodynamics of a Series, I think you'd rue the day that
> > : you geared it so high (low numerically). Probably would take 400hp
> > : to push the brick at that speed. 3,000rpm @ 70mph would probably
> > : be a lot better as the
> >
> > I've riden in an 88 at that speed -- speed measured by a handheld
> > GPS, not a speedometer. It had a 2.25 in it, even. It was a rather
> > hopped up engine, sure, and there was a long, not too steep downhill
> > and probably a tailwind.
>
>I've a friend who's tweeked his 2.25:
>Oversized pistons;
>Skimmed head;
>Polished inlet & exhaust ports;
>Automotive inlet manifold;
>SU carb;
>Fewer baffles in the silencer;
>Larger bore tail pipe;
>Balanced engine.
>
>His engine picks up again at 4,000 rpm, and red-lines at about 7,000.
>The vehicle will happily cruise at 70mph on 235/85r16 tyres, with a
>standard SII gearbox & standard diffs...
>
>So, I can well believe that a vehicle, with a tweeked engine, a
>non-standard gearbox, non-standard diffs & oversized tyres could exceed
>100mph - given that they were heading downhill, so gravity was helping
>:)
>
>--
> --==**==--
>Ian Stuart - EDINA, DataLibrary, University computing services.
>---------------------------------
>A man depriving some village, somewhere, of a first-class idiot
>---------------------------------
>http://lucas.ucs.ed.ac.uk/
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