#437 Carby / supercharger

[dzorde at erggroup.com]

I've seen the crushed floats as well, although they were the plastic variety,
this one is brass so I think it should be OK.  According to all calculations
there should be around 16-18psi boost (if the s/c can sustain it).  I was
thinking of a 3 port regulator but don't know if they come in anything as low as
6-8psi for a carby.  Actually talked to a guy last night who told me that there
is a mechanical pump available, that drives of the crank belt so that pressure
increases as revs increases.

I will be efi'ing the car if the set-up works.  At the moment I don't know if
it'll work and so I don't want to spend money and time trying to get an efi
system going until I have proven that the engine will last and it can generate
enough power to make the car competitive.

I still haven't quite comprehended the carby thing yet, but pressurising the
whole setup does seem to work till boost exceed fuel pressure at which stage it
obviously runs out of fuel.  As for a tbi unit, I'm sure I could make a system
of a small Jap car work.

Thanks for the effort up to this stage.

Dan  dzorde at erggroup.com

<Date: Wed, 28 Jul 1999 06:45:42 -0400
<from: "Charles  Brooks" <cbrooks1 at mail.tqci.net>
<Subject: Re: DIY_EFI Digest V4 #436
<
<Hi Dan, I'm nearly certain that the Float will have to be replaced or modified
so id doesn't crush <under boost. I'm slowly putting parts together for a twin
turbocharged small block Chevy (And I'm <selling a complete single turbo system
for a SBC to finance the TT project, if anyones interested <contact me off list)
and one gentleman I ran into showed me a float from a 2bbl Holley that was on
his <Turbo Ford 2.3, the float looked like someone had stuck a straw in it and
sucked REALLY hard :)
<
<You do have to reference the regulator off of boost however, if you run more
boost than the pump itself <can handle...  The home grown turbo projects I've
seen have been on V8's and used a mechanical pump <that was modified to accept a
manifold pressure reference. The Holley Mech. pumps are easily <disassembled for
the mods. I'm not sure if you could use a high pressure EFI pump with a low
pressure <regulator or not. If you do, make sure the regulator is a 3 port (Or
more) design that has a bypass for <fuel to return to the tank. That way the
fuel flow will cool the EFI pump, if you use a "Deadhead" <regulator with no
bypass the pump will probably overheat and be damaged.
<
<I'll take a look at some of my parts books and see if I can find a regulator
that looks like it'll <work. How much boost are you thinking of running?
<
<Charles Brooks
<
<------------------------------
<Date: Wed, 28 Jul 1999 11:44:33 -0700
<From: "Buchholz, Steven" <Steven.Buchholz at kla-tencor.com>
<Subject: RE: Some efi: carby/super charger setup
<
<... by no means would I consider myself to be an expert on carburetted
<systems ... but there is one issue that seems quite apparent to me.  The
<float bowl of the carb is running in atmospheric pressure, so as you
<increase carb inlet pressure above atmospheric it sure seems to me that
<you're going to start pushing fuel (& even air) back into the bowl.  I don't
<know how you're going to be able to work around this pretty fundamental
<issue.  The carb is trying to meter fuel using Bernoulli's principle, so
<pressurizing the bowl would probably cause other problems.
<
<I wouldn't worry about the float collapsing under pressure, but it might
<tend to sink a bit lower in the fuel when the bowl is pressurized.  You
<would also need to have a fuel pump that was capable of overcoming the
<pressure in the bowl as well ...
<
<The simplest solution I can come up with would be to replace the carb with
<some sort of TBI unit ... but I don't have any suggestions as to the best
<source of such a system for a blown Fiat ...
<
<I know Smokey Yunick had a system where he put a turbocharger in front of a
<carb way back in the early 70s.  He may have had a specially made carb
<though ... I know he had some funny name for it ... what was it ...
<"homogenizer" ????  You may want to check back through Popular Mechanics ...