Well, since we are voicing opinions here, I am in the Mikuni/Weber style camp.
You're right that the airflow is the key, but the manifold and carbs for a
Mikuni/Weber set up appear far more flow efficient. No offense to the SU cars,
as SU's are excellent carburetors. However, the Mikuni/Weber set ups are far
more tunable and offer many features that an SU simply cannot.
Greg Burrows (soon with SK's)
datsunmike wrote:
> At more than $100 per HP gained it's awfully expensive.
>
> I bet getting a head properly ported and better valves (Manley) a good 3
> angle valve job and a different cam would enable a SU car to out pull a
> Solex car providing you get different needles especially for the higher RPMs
> where I think the 1600s and 2000s run outta gas. A longer duration cam would
> help that too.
>
> BTW, a 240 racer at Lime Rock for the SCCA Volvo Vintage races told me the
> Mikuni factory was destroyed by fire and the carbs are NLA.
>
> Mike
>
> ----- Original Message -----
> From: "milton3" <milton3@pobox.com>
> To: "Peter Long" <Peter.Long@ecologic.ca>; "roadster list"
> <datsun-roadsters@autox.team.net>
> Sent: Monday, August 12, 2002 6:27 PM
> Subject: Re: horsepower vs. torque
>
> > Hey Peter,
> >
> > I'm not picking on you for your comments, but voicing a different opinion
> > and explanation. There are benefits to both, and I wanna talk about where
> > the power is located. I'm going to tie it in to the SU (.5*46mm) v. Solex
> > (44mm) discussion from last week since that one didn't sit well enough to
> > digest.
> >
> > Note: I'm only voicing my own opinions and trying to help folks
> > understand the difference so they too can voice an opinion.
> >
> > On 12 Aug 2002, at 14:51, Peter Long wrote:
> >
> > > The rate of acceleration is greater. These are two extreme
> > > examples to show you that 240 hp is not equal to 240 hp.... peak
> > > horsepower ratings sell magazines, torque wins races."
> >
> > Funny thing though: The BMW Z cars only get to look at S2000 tail lights.
> > I've been on track in lapping sessions with both. The S2000s are faster
> > around Texas World Speedway's 2.8 mile road course. I've watched them
> > compete at AutoX's too, and the S2000s take the nod there too.
> >
> > Why? Because acceleration from a standstill isn't the only factor when
> > winning races. I'm going to suggest that you look at the HP v. RPM curve
> > and compare the total area under the curve - matched to the right driver
> > the car with the greater total area takes the nod if it is geared
> > perfectly for the event.
> >
> > But, the average driver (like me) needs the power (yes power, not torque)
> > at the RPM they are accelerating from. It is easier for a driver like me
> > to deal with the power at the top of the RPM range because this fits with
> > the idea of press the pedal harder to go faster - it isn't always
> > convenient or safe to shift in competition.
> >
> > Sufficient torque is required to get the car moving and accelerating, but
> > it is power that determines how fast the speed (RPM) of the engine can
> > change. So, yes, a high torque car can break the tires loose with a gas
> > pedal application, but that does not imply that it is necessarily
> > accelerating (changing velocity) quickly.
> >
> > That said, it's probably pretty clear that I like a rev happy motor in a
> > car. I take the opposite fence on a motorcycle where I go for low rev'g
> > torque monsters, but I'm no motorcycle racer either.
> >
> > So, SU v. Solex carbs on our Roadsters:
> >
> > It was argued that because the SUs are only supplying one cylinder at a
> > time, they can be compared with Solex's based on inlet diameter. This
> > suggested that the SUs 46mm were larger than the Solex's 44mm inlets.
> >
> > The problem here comes from two variables not considered. One is engine
> > RPM. At 3000 RPMs, each cylinder is firing 1500 times per minute or 25
> > times per second. That suggests a lot of direction changes for the
> > airflow in the SUs, slowing the velocity of the air flow on a cylinder by
> > cylinder basis. Then, since the SUs feed two cylinders, the air flow path
> > is not straight - further slowing the velocity of the intake air.
> >
> > So, the Solex's 44mm inlet definately flows a larger volume of air
> > allowing it to stuff a larger combustible charge in each cylinder than the
> > SU's shared 46mm inlet. And, I'm betting the intake duration on the Solex
> > Cam reflects this improved ability to charge the cylinders.
> >
> > The other difference is the shape of the intake path. The faster flow
> > through a straigt path (like the Solex) leads better high RPM performance.
> > The slower flow through a curved path (like the SUs) leads better low RPM
> > performance.
> >
> > Personally, I think my SU 2000 is a little anemic above about 4.5k. And,
> > since it is easy to tach up a car by downshifting and getting into the
> > power band when needed - I'd like to move it up into the Solex type
> > territory. So, just some ramblings. Let me know if there are holes in
> > this reasoning, 'cause the investment is significant. The returns don't
> > seem cost effective from a 15hp gain perspective - but the change in the
> > power curve justifies the expense (that is, if I ever get the $) for me.
> >
> > Top Down in Houston,
> > Milton and the BeautyQueen
> >
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>
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