Subject: Re: Triple Carbs
>>I'm sure that the 3 carb setup gives more power than the 2 carb . . .
>>a bit of Jag history.
>>. . .they went from 2 to 3 carb's in one of their
>>quests for more power from the engine. If more power could be extracted
>>from 2, I'm sure they would have found a way to do it when they were using
>>2 on the XK's.
>Then there's the other side of the coin. The Big Healey. . .
The 3000 started with a pair of 1.75" HD6s, good for 124hp. When the car
became the 3000 Mk.II, they went to a tri-carb set-up, using 1.5" HS4s.
When they went back to a two carb set-up they chose 1.75" HS6s. The 3000
Mk.III got the pair of 2" HD8s.
I find it interesting that both versions of the 3000 Mk.II put out
the same horsepower (132hp); plus or minus 2hp depending on whose numbers
you are using. The twin-carb set-up would seem to be more restrictive
regarding air flow. I know that along with carburation changes, they
changed the valve timings and the ignition timing. These changes could
have compensated for the more restrictive induction system.
As it has been said before, engines are *systems* and a change to one part
may or may not have the desired effect. All the sub-systems have to work
together.
By the by, BMC went to the tri-carb set-up for competition reasons. Rules
at the time would allow you to change carbs from the production set-up, but
you had to use the same number. BMC could get a hot set-up, with one
venturi per cylinder by using dual-throat side-draft Webers, but that
required three carbs. So, they added one more SU to the production cars.
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_____________ _____________ Robb Pryor,
\____________\_____________/____________/ Pyramid Technology,
\__________ __________/ Mountain View, CA 94039
\________ AUSTIN-HEALEY ________/ VOICE:(415) 965-7200
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