I think that Nolan does make valid points and descriptions.
I agree the throttle is their to impede flow BUT in such a way as to give
controlled acceleration. If you are driving at half throttle this might be
because you have reached cruising speed in top gear and this in it self is
not a reason for putting a more restrictive carb on.
To put a more restrictive carb on to impede air flow (eg fit the ZS in
preference to the HS2s) is not really making a valid point because the ZS
would not only limit rpm but power as well. For example the engine in my car
will rev to 7,500rpm whether I run a 40 DCOE with 34mm main venturi or a 45
DCOE with 40mm main venturi BUT it will take longer in any given gear to
reach 7,500rpm and will produce less power at that rpm. In fact I would have
to fit a pretty restrictive carb before it limited rpm. Another example
would be a formula 3 race car which has to have an air restrictor fitted to
the intake to limit power, rather than rpm.
Looking at one of David Vizards earlier books (the mini book) suggests that
(at least on a A series) twin HS2 are only worth a small amount of power over
over a single 1.5" Stromberg but that there is a big jump on switching to
twin HS4. I would expect though that because the single stromberg manifold
design is pretty restrictive on the 1500 compared to an A-series the twin
HS2s will represent a reasonable step up.
The thing that really interests me though is whether or not a single HS6 or
HIF6/HIF44 is superior to twin HS2 on the 1500 Midget - certainly it is on
the A-series but this is with a performance orientated manifold.
In a message dated 10/12/00 19:27:56 Pacific Standard Time, firstname.lastname@example.org
<< Nolan Penney wrote:
> Remember something though about SU's and the 1500. The SU flows quite
> freely, up to the full open throttle position. To put it losely, at half
> throttle, there isn't diddly difference between the two.
At half throttle? That's not a meaningful data point.
If you are part throttle, you aren't caring about
performance. The goal of the throttle is specifically to
impede air flow, that's what it's there for. If you
are intentionally impeding air flow by not opening
the throttle, you might as well leave the ZS on.
If you want to improve "part throttle" performance,
the easiest thing to do is just change your throttle
cam so that "pedal 50% down" is "throttle 80% open".
Car manufacturers do it all the time to make
cars seem peppier!
> So the larger HS4's
> will allow the 1500 to rev higher then the HS2's would.
That's not true really, even with the ZS you can
redline the car easily.
A more accurate but similar statement is that the
HS4s will accelerate much faster at high revs than
the HS2s or the ZS.
So, cruising along the highway at 3500rpm, put the
pedal down to pass. That's where the gains are, because
the smaller carbs are getting a little out of breath.
> Is this a good
> thing? Maybe not. After all, the 1500 is just a stroked out 1300; hence
> it self destructs more readily when over-reved.
Ok Nolan, we know you like your HS2s, but let's stop
grabbing the straws, ok. If you don't want to rev your
1500, why not put a nice ZS on there. ;>
Trevor Boicey, P. Eng.
Ottawa, Canada, email@example.com
ICQ #17432933 http://www.brit.ca/~tboicey/
"...if never to be seen again, you're in my air" - Ajax