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[Spridgets] DCOE 40 or DCOE 45

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Subject: [Spridgets] DCOE 40 or DCOE 45
From: "Colin Dodds" <colin@spriteparts.com.au>
Date: Wed, 28 Apr 2010 06:24:02 +1000
G'day all

I thought I might join in on the discussion.

I have two books that list various makes and models of cars, and what size
DCOE carby (and internals) to use on them.  One book is by Warneford, I forget
who wrote the other and since it's 5.58am I'm not bothering to go to the
workshop to take a look.

In the Sprite/Midget section, both books list 40DCOE for standard 948cc
engine, and 45DCOE for everything else.

"Everything else" means:
mildly modified or highly modified 948cc;
standard,mildly or highly modified 1098cc;
ditto 1275cc.

Internals such as chokes, secondary venturies, jets, emulsion tubes etc are
different of course for different capacity engines with different
modifications.

Both books were written following extensive dyno-testing of the engines
concerned, with the aim of optimal performance.

Our own testing of both road and race engines confirms the results.  Each
engine is different, and we don't always use exactly what the books recommend,
but they're always close.  We usually end up with 34mm chokes on standard
1275cc road motors, 36mm if power output is 100 to 120 bhp, and 38 over 120
bhp.

A 40 DCOE simply doesn't flow enough air over 4,000 rpm to give the power that
a 1275cc engine is capable of producing.

You need to burn petrol and air to produce power.  There's a mathematical
formula that will tell you how much power you can potentially produce by
burning a certain volume of fuel and air mixed at the correct ratio.  I'm not
going to dig it up cos it's too complicated, but what it does demonstrate is
that a 40 DCOE at 5000 will not flow enough air to produce the power that the
engine is rated at.

Don't forget that 1200cc Alfa Romeo engines use two 40 DCOEs.

OK, so I know we're not all after max power, but also economy and drivability.
I couldn't agree more with Brad:
Most people do it for performance. This is where the mileage goes down.
The other factor is most people tend to drive the car harder after installing
a Weber.
Stop light racing  and curvy road racing - looking for the acceleration &
a rush.

and Weslake-Monza:
Most people simply never bother  to set up a DCOE to run properly and it gets
a reputation for being a race only  carb.

I've swapped twin SUs for a Weber on a lot of customers' cars.  Did they want
better economy than the SUs?  No, that's not what they asked for.  They wanted
better performance and less tuning hassles.  Not one has told me they're
unhappy with their decision.  Some I don't hear from at all, but most phone me
to tell me how pleased they are with the decision.

My own Sprite, when I bought it, had an HIF44 SU fitted, and I loved it.  I
don't drive the car fast, but I do a fair amount of touring in it so fuel
economy is important to me.  I could have fitted a Weber, but didn't as it
would have been counter-productive.  But if was acceleration and speed I was
after, the car would have a 45DCOE on it.

avagoodday
Colin
www.SpriteParts.com.au
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