Notice Brian said twin SUs vs a single Weber. With split webers
you'll make more power again.
The reason is almost certainly due to the shape of Weber manifolds
The distance b/n the inlet ports on the A series head is greater
than the distance between the throats of the weber. This puts a
slightly outward bias on the airflow and results in the center cylinders
running a little leaner than the outer two cylinders.
Using highly modified SUs or a pair of webers (each using only one
throat), you can get "straight" airflow into the inlet chambers. This
even mixture can produce an extra 1 or 2 HP in a top race motor.
Let me make the point this is one of the least effective HP/$ things
you can do. Don't even think about it unless you already have more
than 130HP.
Mike
-----Original Message-----
From: Randell Jesup <Randell.Jesup@scala.com>
To: spridgets@autox.team.net <spridgets@autox.team.net>
Date: Wednesday, February 04, 1998 7:48 AM
Subject: Re: Weber Help / SUs
>Brian Evans <brian@uunet.ca> writes:
>>>Webers don't drift out of tune, are less prone to leaking
>>>and produce more HP and they sound a whole lot better :-)
>>
>>most serious engine guys can get more power out of a race engine with SU's
>>than a single weber. Comptune is an example. But it takes a long time, a
>>dyno, several thousands of dollars, and a skilled magician. A webers big
>>advantage is that you can tune it easily to suit a modified engine, and
it's
>>better than a stock SU.
>
> Huh? Sounds pretty backwards to me. From everything I've heard,
>Weber's are a bitch to set up right, but make a bit more HP on highly
>modified engines. From my experience, SU's are far easier to set up,
>though getting the last few percent out of them takes some work, but
>they're more tractable than webers, doubly so if the setup isn't perfect.
>Getting the needles exactly right requires dyno time and swapping or
>careful filing (followed by selecting a needle that matches the filed
>one(s)), compared to Weber swapping of chokes, jets, etc, etc and dyno
>time.
>
> I had a friend (Dr. Bobwrench) who took a set of HS2's (originally
>from a 1275) I'd tuned on a modified 948 Mk II Sprite. He put them on his
>racing GT6 and much to his surprise (and mine) they worked well with no
>adjustments. He probably was losing a few percent due to non-optimal
>needles (and they're a bit small for 1 liter of engine apiece), but they
>worked well enough to do a driving school with. They didn't even need
>resynchronization apparently.
>
> IMHO.
>--
>Randell Jesup, Scala US R&D, Ex-Commodore-Amiga Engineer class of '94
>Randell.Jesup@scala.com
>#include <std/disclaimer>
>Exon food: <offensive words no longer censored - thank you ACLU, EFF, etc>
>
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