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Re: 1.5" SUs

To: "Geoff Branch" <branch@valinet.com>, <Daniel1312@aol.com>, <ridleymj@bis.on.ca>, <spridgets@Autox.Team.Net>
Subject: Re: 1.5" SUs
From: "Mike Gigante" <mikeg@vicnet.net.au>
Date: Wed, 11 Nov 1998 09:28:08 -0800
Reply-to: "Mike Gigante" <mikeg@vicnet.net.au>
Sender: owner-spridgets@Autox.Team.Net
You might like to compare jetting for Webers on the following URL

http://yallara.cs.rmit.edu.au/~mg/cars/goblins/tech/webers.htm

Mike

-----Original Message-----
From: Geoff Branch <branch@valinet.com>
To: Daniel1312@aol.com <Daniel1312@aol.com>; ridleymj@bis.on.ca
<ridleymj@bis.on.ca>; spridgets@autox.team.net <spridgets@autox.team.net>
Date: Tuesday, November 10, 1998 5:36 AM
Subject: Re: 1.5" SUs


>Were the comments re: Weber 45 DCOE for a 1500??  I'd love to hear what
>anyboy else is running in a 45 on a 1275.  I have 34 Main venturi, 35 aux
>vent., 125-F2 main jets, 50-F9 idle jets.  Any comments??  Geoff Branch
>'74 Midget
>-----Original Message-----
>From: Daniel1312@aol.com <Daniel1312@aol.com>
>To: ridleymj@bis.on.ca <ridleymj@bis.on.ca>; spridgets@autox.team.net
><spridgets@autox.team.net>
>Date: Sunday, November 08, 1998 4:50 PM
>Subject: Re: 1.5" SUs
>
>
>>Hi Martyn,
>>
>>I do not agree that twins are better than singles.  What matters is the
>amount
>>of airflow the engine receives (and requires) and with carbs the amount of
>air
>>the carb can flow be it a large single carb or two smaller carbs.
Although
>a
>>twin 1.5 SU set up will flow a total of more air, on many A Series engines
>you
>>will get a better result with a single 1.75 (or maybe a single 2.0?).  The
>>only usual advantage of a twin SU setup over a single is better fuel
>economy
>>(gas mileage).
>>
>>Also, when talking about SU carbs it is perhaps worth clarifying which SU.
>I
>>mention this because the later HIF carbs flow more air than earlier HS
>types.
>>
>>I am very acquainted with David Vizard's books, as well as Haynes SU
manual
>>and another book on SUs.  I also have a library of other tuning books.
>>Perhaps I can refer you to page 75 of the yellow edition of Vizard's A
>series
>>book where a table idicates airflow in cfm for a 1.5 SU H4 carb is 133, it
>>being a reasonable assumption that two of these carbs make 266 cfm.  The
>same
>>table  indicates a SU HIF6 carb making 240cfm - only 26 cfm less than the
>twin
>>setup and I would suggest that the small gain of the twins might well
>easily
>>be lost on the manifolds.
>>
>>For myself I haven't run SU carbs in a decade but as I said before, from
>what
>>I have heard (some comments originating very close to Mr Vizard) the
single
>SU
>>1.75 takes some beating.
>>
>>Further comment welcomed, especially when supported with dyno figures.
>>
>>Daniel 1312
>>
>>45 DCOE, 40mm main venturi (smaller sizes to prove it needed the 40mm
>>venturis) 185 main jets, 55 pumps, 65 F9 idles - and the mixture bang on,
>and
>>engine taking full throttle in 4th at 2,500rpm if not lower with a MD286
>>scatter cam (K&N air filter used to make sure small children are not
sucked
>>into the intake tracts)
>>
>


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