Ken,
Optimal for power would probably be a quad Mikuni or Keihin set-up. (one
carb per cylinder) http://www.prirace.com.
But due to the cost ($1000.00?), gas consumption and lack of practical
knowledge on the Mikunis, you're probably better off with a Weber set-up.
(There is all kinds of documentation on Paul Tegler's web page for needle,
jet and spring suggestions and more people are current owners of Webers to
be able to aid you with experienced help.)
You'll get arguments from people, but I think anyone in the know, would say
that it's progressive; Zenith Stromberg is the low end of the performance
scale (and for most part are unadjustable no matter what the manuals say),
Skinner's Union (SU) is low tech but adjustable. Webers are your classical
racing fare (DCOE and DGV), and Mikuni's are contemporary bike carbs
modified for use on a Spitfire.
I believe I've read that that the ZS and SU's are considered a "fixed
venturi" type. Which I'm not sure what that means, but it appears to limit
the carbs in some form.
The cost is reflective of the performance as well.
A single Zenith Stromberg (150CD or ? cfm) can be had rebuilt for as low as
$100-$200.
Dual SU HS2 (1.25" or 90 cfm per carb) set-up can cost anywhere from
$150-$350.
Dual SU HS4 (1.5" or 142 cfm per carb) will cost around $200-$400.
Dual SU HS6 (1.75" or 210 cfm per carb) will cost around $300-$600.
Weber 32/36 DGV (255 cfm) will cost around $400-$500.
Weber 45 DCOE (400 cfm (32 mm choke), 420 cfm (34mm choke), 440 cfm (36 mm
choke)) I have no clue how much $$$.
These set-ups all would be rebuilt (as new) and have the intake manifold and
linkage to accelorator cable/arm.
I've read several disertations on Carb set-ups for Spits and MG's (the later
being more informative), and according to so called experts, you can have
too much CFM on a car. My ford 302 had a 4bbl (4 venturi) carb with 600 cfm.
Our stock 1493's are 91 CID and logical math would lead you to believe that
a third of the 600 cfm would be plenty. In fact atleast one paper on carb
suggestions, has said that the HIF6's (240 cfm per carb) are a waste of
money on the stock1800 cc MGB's. The only thing you're going to get out of
it would be a big headache from trying to find a needle that leans out two
240 cmf carbs enough for an 1800 cc B.
Finally, as an end note. Some carbs have clearance problems on the Spitfire
due to the side-drafts sticking out so close to the front wheel well. And so
thought has to be put into the air canister or K&N filter you're utilizing
as well.
This is an interesting white page on carbs for MGs. Though it is a different
animal, it will give you an idea of certain things to look out on certain
carb brands (SU's and Webers specifically):
http://www.mgbmga.com/tech/mgb19.htm
Terry L. Thompson
'76 Spit 1500 w/dual HIF4's from a 72 MGB
Maryland
----- Original Message -----
From: Ken C <sdspitfire@worldnet.att.net>
To: Spit Elist <spitfires@autox.team.net>
Sent: Tuesday, June 20, 2000 11:43 AM
Subject: Which carb
>
> Spitsters,
>
> Just got a larger motor for the '72 Spit, a 1500, to replace the 1300. It
> will be nice to have a little more power !! (Jeff, are you listening?).
The
> motor is out of a '79 and has a Stromberg carb.
>
> What is the optimal carb setup ? Stromberg, SU's, Weber(s), Holly 4150...
>
> It's going to be a street car, running on super high-octane (not)
California
> gas. Not sure what the compression ratio is, but, after the rebuild, it
> should be between 8.5 and 9 to 1
>
> Now, I know it won't beat Jeff's MKIII, but it would be nice not to lose
> sight of him !
>
> TIA...Ken C
>
>
|