Peter, I had been thinking the same thing as you. However,
the RAW horsepower is not often an issue (but interesting).
People are often more interested in determining how much
their power has changed. For this you could use the top
gear acceleration time from 50 to 90 mph as your baseline.
Then on the same strech of highway do the same speed run
after the modifications. The ratio of the after & before power
would be approximately [old time divided by new time].
This way drag, etc are factored out since the speed range and
highway effects are the same on both sides. If you had a good
idea of the original HP, then you could determine the new HP fairly well.=
-Tony
Message text written by INTERNET:triumphs-owner@autox.team.net
>Date: Sun, 27 Dec 1998 14:00:00 -0000
From: "Peter French" <peter@pmfrench.free-online.co.uk>
Subject: My favorite LBC, Tuning & HP measurement
Hello All,
I have been lurking now for a few months with only one previous post as I=
have only had my GT6 since July. She is now bedded down for the worst of
the
British winter and I have had the chance to get to know Triumphs again
after
a gap of some 30 years. I have been meaning to contribute for a while but=
never got round to it till now, I hope I don't go on too long!
John Mac was talking about Jaguars and the Bentley Mulsanne turbo which
caught my eye as I have recently defected from Jaguars (Only on grounds o=
f
cost, they are lovely cars) and I have done a lot of work for Rolls-Royce=
on
the Bentley and other cars. They are as John describes, very comfortable,=
very large, very quick and very expensive! They are also the only modern
car
I know that you have to step UP into ! All this leads back to list matter=
s
via the fact that I am an engineer working for a subcontractor supplying
the
electronic control unit for the electrically adjustable shock absorbers o=
n
all Rolls and Bentley cars. (This sometimes involves a lot of high speed
driving on closed test tracks! but I digress) This control unit contains
accelerometers to measure car acceleration and it is possible to use the
acceleration and weight of a car to calculate the actual Horse-power. Whe=
n
the thread started about measuring HP of a car from the top speed I thoug=
ht
of using one of my control units to do this but on reflection there is a
much easier way, unfortunately involving a bit of maths. If you measure t=
he
time needed to accelerate between two speeds you can calculate the
acceleration and if you know the car weight you can work out the HP
required. You have to compensate for wind and rolling resistance but that=
can be done by measuring the time needed to decelerate between the two sa=
me
speeds on the same bit of road when in neutral. This will allow a figure
for
HP at the flywheel to be calculated. The two speeds involved must be eith=
er
side of the engine speed at which you want your HP reading. I will try to=
generate a simple formula and step by step procedure which is applicable =
to
all our cars. Any body interested please contact me or if of sufficient
interest I will post it to the list.
My car is a 1969 GT6 with about a stage three tune as defined by
Triumphtune. It was done by the PO to a very high standard but I think he=
over did it with the camshaft which is a "Sprint 83" spec. The engine is
powerful but only over 4500rpm, for a road car a milder cam would have be=
en
better. I might be able to improve things after I have done some work on
the
distributor advance curve which is not optimum. I must be careful as we a=
re
shortly going to lose our leaded fuel.
One interesting point on the car is the fact that instead of using 1.75" =
SU
HS6 carbs the PO used 1.75" SU HIF6 versions. These seem to have been
dismissed on this list as "emission" carbs with no adjustment and of no
use.
I have investigated and as far as I can see they seem to be as good if no=
t
better. They can use the standard needles available for the HS6, they hav=
e
a
concentric float bowl with a sensible fuel temperature compensation, the
overrun valve built into the throttle butterfly can be easily removed and=
soldered up, and they have a mixture adjustment by screwdriver. Finally
they
seem to be more plentiful, at least in this country, in good condition fr=
om
breakers yards.
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