Subject: Re: SU book/big SU's

On Wed, 2 Nov 1994 caldwell@seas.ucla.edu wrote:

> Hey Z'ers
> 
> I have seen mention in a couple of places (inc. the Motorsport cat.,
> although they don't still have any) of a book just about Hit. SU
> carbs.  I have not been able to find this book (seems it's out of 
> print).  Does anyone have a method of getting one, or would be willing
> to photo copy one?  Also, if anyone has comments on the book or 
>  an alternative I would be interested in that too.

I have never seen this book, but if it exists I sure would like a copy 
too. There is a Haynes book on SU's which is very informative but it only 
covers British SU's, so its specifics are not applicable.


> p.s.  awhile back, I think I saw something about larger SU's (up
> to 2 inches, I think).  Is this correct?  What are you measuring to 
> get that number?  Are they just like stock, only larger?   Do they
> mount to the stock manifold?  Are there other mods that have to go with
> them?  What are the advantages/disadvantages that go with this?
> How non-smog legal is this? (CA smog laws)
> 

That measurement is the throttle bore size, in ohter words the size of 
the throttle plate. It is also the smallest ID of the main air passage 
(throat) of the carb. They are English SU's and the model # is HD8. For 
you non-British fans here's how SU identifies carbs;

H = Horizontal 
D = Diaphgram type jet 
8 = Bore size in 1/8's of an inch OVER 1" (they never made any automotive 
carbs under an inch so all sizes assume 1" and then tell you how much 
bigger than an inch they are) ie. an H4 carb is 4/8" over 1", or 1 and 
1/2 inches. 

Some later SU's did use mm sizes, such as the HIF44 which was (not 
surprisingly 44mm in diameter. Anyway, the available SU sizes and their 
aproximate metric equivalents are;

1.25" or 32mm
1.5"  or 38mm
1.75" or 44mm
2"    or 51mm

The 2" carbs will work on the same manifolds, but the manifolds need to 
be opened up. Linkage would have to be fabricated but that's no big deal.
none of this would be legal (in fact there is a federal law that says you 
may not alter any "emmisions control device" period. Anything can be 
construed as an emmisions device if altering it will change the total 
emmisions of the car, so even your tires could be called an emmisions control
device). As for performance, given improvements in the intake and exhaust 
manifolds the carbs will give you better top end, but no better 
accelleration. You could improve the accelleration by altering cam 
profile, valve size, rotational weight, etc.. The drawback to SU's 
(Hitachi or otherwise) is that they are sensitive to manifold vacum and 
so changes to cam profile can have unexpected adverse effects on idle and 
driveability.


Marc Sayer 
eye of the non-storm :-)