The main reasons why SU's were so popular with the auto manufacturers
are price and simplicity and they work well on medium output engines.
If SU's work dont mess with them. The reasons to use them in racing
are either regulations or cost. Even Jaguar used Webers (or similar carbs)
on their racing cars. The problem with SU's on street cars is they often fail
the idle speed emission test that is used in many countries in Europe. The
needles wear out quickly with todays gasoline. This require adjusting the
carbs to run rich on idle to run okay while driving without using the choke
all the time.
Given the choise of SU or Weber I would take a Weber set in the correct
size for the application every time. If I'm not restricted to carbs, I use fuel
injection instead. No carbs can match the driveability and power output
from a fuel injection system. The bad thing with fuel injection is the
amount of time it takes to properly adjust it for custom applications.
15-20 years ago Weber carbs were still prefered over Bosch L-Jetronic
with the flap door air mass meter because of better torque with Webers
for Rally car applications but with the introduction of the hot wire air
mass meter the preference changed among these engine builders.
Like you say
My 2 cents worth
Thomas
datsunmike wrote:
> Dan,
>
> Or you could get the SUs modified to flow more air as shown in the Bob Sharp
> Comp manual. I do believe Rebello offers this service. Ithink a modified SU
> will flow as much air as a street/strip engine will need and will be a lot
> cheaper too. Solexs look great but . . . most modified street cars just need
> SUs.
>
> In Grassroots they tested a Z with Webers then ripped them out and put on
> SUs and the car generally ran better w/only a slight sacrifice of top end
> power.
>
> The key to power ain't the carbs, it's in the head to let the engine breath
> better as was related to me by a well respected Cosworth/foreign race engine
> builder. Too bad he's so damn expensive though.
>
> Mike
>
> ----- Original Message -----
> From: Daniel Neuman <dneuman@stars.sfsu.edu>
> To: <datsun-roadsters@autox.team.net>
> Sent: Friday, September 22, 2000 5:02 PM
> Subject: Solex's vs. SU's ..again and again and again...
>
> > Hello All,
> > Just because we have not had a good Solex vs. SU thread for a while
> > I thought I would pose this question.
> > Okay besides the cool induction noise of the solex I see the main
> > differences between the two being..
> > Solex's are fixed choke/venturi designs with one carb per cylinder.
> > These are 'better' than SU's because at higher rpm's they don't
> > choke off the engine. No balence tubes between cylinders bad midrange and
> > off idle performance because of fixed venturi creates less than adequate
> > vacuum.
> > Su's are 'better' because they have a variable venturi which self-
> > regulates its size so you always have a good vacuum. You get lots better
> > off idle perfomance and midrange. They are 'bad' because their maximum
> > venturi size does not allow enough air/fuel mixture at higher rpm's and it
> > chokes of the engine. The balance tubes also help smooth out the intake
> > pulses and you get a smoother running engine.
> > Now heres my question:
> > Has anybody ever tried fitted bigger su's to a 2000 engine?? What
> > about fitting 4 SU's to the engine and having one carb per cylinder??
> Would
> > either of these ideas fix the high rpm flow problem?? Could you have a car
> > that had good off idle performance good midrange and good top end??
> >
> > Just Wondering.
> > Daniel 69 2000
> > SF CA
> >
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