I had a similar experience a few years ago with HS6 carbs. I could
not get any power over 6000 rpm on the track. I just could not get
them to flow enough fuel. I put air cleaners on to add some
restriction and gained 300 rpm on the straights. I did not, however,
go so far as to add the weber style spacers. Joe(B)
----- Original Message -----
From: "Greg Solow" <gregmogdoc@surfnetusa.com>
To: "Friends of Triumph" <fot@autox.team.net>
Sent: Sunday, October 12, 2003 2:38 AM
Subject: dyno test of TR-4
> We were recently doing some engine dyno testing of a 3/4 race "fast
road" TR-4
> engine destined for a Morgan. We had what I thought were some very
interesting
> results.
> The engine is an 87 mm bore Hepolite piston engine with standard
size
> valves, 10:1 CR, 280 degree seat to seat cam (similar to the
Competition Dept
> "D" cam), a "pocket ported" head with a 3 angle valve job. The
testing was
> done with both HS-6 carburetors on a long manifold (these carbs and
manifold
> were dead stock and in perfect shape with the float bowls mounted on
rubber
> using MG-B mounting insulators) and with a fully race prepared set
of H-6
> carbs on a race prepared short inlet manifold. The engine had
"Tri-Y" style
> headers and was run both with an open exhaust and with a straight
through
> English style muffler.
> The first and most important thing that we found was that the
first day of
> testing we could not get the engine to repeat power runs accurately
enough to
> learn anything at all until we modified a 45 DCOE Weber "soft mount"
and put
> it in between the HS-6 carbs and the inlet manifold to insulate the
carbs from
> engine vibration that apparently was upsetting the fuel delivery to
the
> engine. As soon as this was done, we were able to start to get some
testing
> results.
> The next surprise was when we added velocity stacks to the HS-6
carb set
> up. We tried the old aluminum parabolic stacks that I had seen on
the
> Competition Department TR-4s, and also a set of stacks that I had
made many
> years ago that look like Weber Velocity stacks. Either stacks just
killed the
> power above 5500 rpm. I mean it just took a nose dive, whereas
without any
> stacks the power would peak at about 5400 rpm and then stay almost
level until
> 6,000 rpm. Unfortunately we did not have a set of "stub stacks to
try.
> Apparently the 13.2" length of the intake and carbs is very much a
"tuned
> length, at least on a 3/4 race engine. At least that is what I
concluded. What
> a shame, because the Velocity stacks look so cool!
> We then found that with no stacks, the stock HS-6 carb setup
made a higher
> torque peak by almost 8 ft. lbs. than the race prepared H-6
setup.Above 5,000
> rpm the H-6s on the short manifold was slightly superior. The H-6
carbs did
> not need the "soft mounts" and the "weber like" velocity stacks
worked well on
> them.
> It made very little difference whether the muffler was on or
the engine
> had a straight open exhaust! But remember the muffler we were using
is a very
> free flowing unit, we have used it on engines making up to 150 hp
and this
> engine was in 120s.
> Our best runs made 123 hp with a very broad peak that gave over
120 hp
> from 5,000 to 5700 rpm and 138 ft lbs of torque with over 130 lbs.
from 3300
> to 4700 rpm and with the peak around 3900 rpm.
> All of the testing was done on 91 octane pump gas. The best
power was with
> 34-36 degrees total advance measured on the outside of the flywheel.
>
Regar
> ds,
>
> Greg Solow
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