I was saying to Chris offlist that 40s can supposedly be overbored into 44s
while getting the best of both types.
This from the excerpted from the same posting:
"How about a way to keep your bottom end and lower midrange while increasing
upper midrange to top end? There is a way - Oval Boring. The carb is bored
in an oval shape, keeping the bottom half of the carb near stock proportions
(smaller) while gaining a significant flow increase on to top end with a
larger bore. The oval bore is a better shape for a carburetor than any
other. . The actual area bored is a modified crescent shape. The bore
becomes larger gradually as the carb slide is raised. As the engine rpm pick
up so does the engines ability to handle the increased air fuel mixture.
Compare this to the straight bore carb that increases the bore diameter very
quickly.
Here is a general guideline for oval boring dimensions for Mikuni round
slide carburetors.
Standard Bore Oval Bore to 32mm 32/35.5 34mm 34/35.5 36mm 36/39.2 38mm
38/39.2 40mm 40/44 40mm 40/45.5 44mm 44/45.5 "
I have not done this, so I suppose its either hit or miss depending on the
quality of the work.
But it sounds like an interesting scenario.
I wonder if anyone has compared the performance of stock 40s vs 44s on the
track?
Anyone have an opinion on it?
-ed
----- Original Message -----
From: "Gordon Glasgow" <glasgow@serv.net>
To: <datsun-roadsters@autox.team.net>
Sent: Sunday, January 28, 2001 12:55 AM
Subject: RE: Solex carbs 44mm vs 40mm
> I think the claim that was being made a while back was that, if a 44 is
> choked down to the same size as a 40 (let's say 34, which was a pretty
> common street size), the air flow velocity through the choke will be the
> same in both carbs, but downstream of the choke it will drop quite a bit
> more in the 44 (bigger cross-section means lower velocity for a given flow
> volume). This will make the 44 more susceptible to inconsistent fuel
> mixture, etc. Basically that's true.
>
> But what is missing is that the downstream velocity is determined by the
> manifold size and the port size. If these are the same in both cases, the
> flow velocity will be the same. The only way you could get the full
benefit
> of the "lower disruption" 40mm carb would be if the manifold and ports
were
> sized to match.
>
> A 44mm bore has an area of 2.35 sq in. A 40mm bore is 1.92 sq in. Now, as
an
> exercise for the reader, go measure your manifold and ports.
>
> Gordon Glasgow
> Renton, WA
>
> -----Original Message-----
> From: owner-datsun-roadsters@autox.team.net
> [mailto:owner-datsun-roadsters@autox.team.net]On Behalf Of Chris
> Robertson
> Sent: Saturday, January 27, 2001 8:33 PM
> To: datsun-roadsters@autox.team.net
> Subject: Re: Solex carbs 44mm vs 40mm
>
>
> True, BUT...all you do is put in smaller diameter chokes. You can make
the
> 44's as small as the 40's, but you can never make the 40's as large as the
> 44's!
>
> Chris
>
>
> > > >From: "aryasura" <aryasu19@idt.net>
> > > >Reply-To: "aryasura" <aryasu19@idt.net>
> > > >To: <datsun-roadsters@autox.team.net>
> > > >Subject: Solex carbs 44mm vs 40mm
> > > >Date: Sat, 27 Jan 2001 22:06:44 -0500
> > > >
> > > >I saw this posted to the web recently.... is this guy correct in
> >preferring
> > > >the 40mm over the 44mm?
> > > >If so, how come everyone uses 44mm on our roadsters?
> > > >
> > > >"Let's say your engine makes 150 hp with either a set of 44mm carbs
or
> >40mm
> > > >carbs.
> > > >Use the 40mm; they will give you a higher air velocity through the
> >power
> > > >band.
> > > >This means better efficiency in terms of throttle response, fuel
> > > >atomization
> > > >and economy.
> > > >Horsepower is measured and determined by air flow so take all you can
> >get
> > > >as
> > > >long as you get good flow and velocity all the way through the rpm
band
> >and
> > > >your engine is equipped to handle it."
> > > >
> > > >-ed
> > >
> > > _________________________________________________________________
> > > Get your FREE download of MSN Explorer at http://explorer.msn.com
> > >
> > >
> >
>
> _________________________________________________________________
|