TeriAnn Wakeman writes:
So how's the TR3 coming? On the road yet?
>>We are trying to plan a complete engine rebuild and would like more thoughts
>>on Webers v. S-U's.
>First let me say I have DCOEs on my TR3
>
>I did it not because I wanted more power. I did it because I thought DCOEs
>were the ulimate cute accessory on an engine and I just really wanted to
>have an engine with DCOEs. Power curves doesn't matter as long as the car
>preforms acceptably. The DCOE mystic and looks is everything. They look
>exotic sitting between a finned polished aluminum valve cover and chromed
>four tube header.
>
>With my real reason confessed...
>I understand that SUs are more flexable, providing better low end power and
>better economy. The Webbers har harder to jet correctly throughout the
>curve.
>
>If I were more rational, I would have SUs on my TR3 But the DCOEs just
>have too much chrisma
Just about right. DCOE's will give _slightly_ better top-end power
and will have slightly better response due to having direct accelerator
pumps - but only if set up _exactly_ correctly. If not set up just right,
they'll flat-spot, etc.
SU's are far more forgiving in setup. Absolute maximum power and
response still requires careful needle selection, but it's still generally
easier, and it's much easier to get a reasonable (though not perfect) setup.
Dr. Bobwrench too a pair of HS2 SU's I'd set up on a 948cc sprite
(though with a modified head and headers, and the SU's were from a 1098cc
or 1275cc sprite) and dropped them on his GT6 racecar. Not only did it
run, apparently my synchronization was still spot-on, and the car ran
well on the track. Now, HS2's are on the small side for a GT6 engine
(2 liter), and of course the needles weren't optimized, but it worked pretty
well from his account.
I've been reading Vizard's "How to modify the A-series engine"
recently, and he's done extensive comparisons. The SU will produce slightly
more torque/HP in the mid-RPM range than the Weber. The Weber will produce
a bit more top-end power than the SU. Neither difference is substantial
(a HP or two).
A much cheaper/easier way to get more airflow would be to bolt on
larger SU's; but even then that won't help unless you're drawing more air
than the existing ones can easily handle, and larger SU's will reduce low-
end performance slightly (slower charge velocity). There are some things
you can do to improve the flow characteristics of an SU (rounding a few sharp
edges, etc). Vizard's book is de rigeour for anyone playing with A-series
engines, and much of what he discusses applies to other engines as well.
He also punctures many myths and mistaken common-sense tuning assumptions
people have, backed up by extensive testing.
Tom Gentry writes:
>Subject: Re: Copper/Steel/Aluminum Lines
>
><soapbox mode = on>
>Copper and aluminum are more flexible (under pressure) and weaker than
>steel. This could lead to "squishy" feel, more pedal pressure required or
>sudden, total failure. Your life (and maybe mine) depend on these lines
>withstanding a lot of pressure, and a lot of pressure on-off cycles. USE
>STEEL!!!
><soapbox mode = off>
First, most "copper" lines aren't soft pure copper. They're copper-
nickel alloys, which are harder (and I think work-harden less) than pure
copper. Some of them are multi-metal sandwiches, with steel covered with
non-rusting metals inside and out.
Second, you're over-exaggerating the softness. Rubber brake hoses
will balloon a little, especially if old or damaged, but even they don't do
so much. Copper brake lines will not balloon noticably unless there's
pressure beyond their failure point - and if they balloon they wouldn't
shrink back, so it would be obvious. A soft pedal is not going to be because
of copper brake lines.
Third, these have been used quite a bit in england (and elsewhere),
and are designed for this use.
Fourth, how well do you think the average rusty steel brake line
holds pressure after a few years compared to a copper-alloy line? I've
have steel brake lines fail on me multiple times on old british cars, always
due to rust.
--
Randell Jesup, Scala US R&D, Ex-Commodore-Amiga Engineer class of '94
Randell.Jesup@scala.com
'66 Midget, '70 TR6, '85 CRX, '85 XR4Ti
Exon food: <offensive words no longer censored - thank you ACLU, EFF, etc>
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