>> ...from my rather limited experience and what I have learned from others,
>> manifold preheaters are not a good thing if you want to maximize power
>> output.
>
>(Boy, am I gonna get flamed... Disclaimer: I'm not a professional engine
>builder!)
>Perhaps if you want to maximize power output under a narrow band of
>ideal conditions. For daily street use, consistency is required if you
>want the tune to work all the time. And stabilizing the manifold temp
>helps obtain this.
>
>Not only do you need fuel in the engine, it needs to be completely
>atomized and mixed thoroughly with the air. On a cold manifold, the
>fuel vapor will condense on the walls. Puddles of raw gas don't make
>for smooth power :-)
Like John says, Brian, both approaches work, in different applications.
back in the mid-'70s I had some interesting first hand experience with
the heated vs. unheated intake situation. We took our original 510 ('71
4-dr) with us when I was stationed at Hickam AFB in Hawaii from early '73
to mid '75. On my way over I stopped in El Segundo (before I headed to
NorCal where I shipped the car and flew to Hickam from Travis) and bought
the suspension bits from Pete Brock.
Within a year or so I had installed Z valves, a Norris Cam, and some
other engine goodies, including a single Weber 42 DCOE (yes, a 42) on an
unheated Warneford manifold. This replaced the OEM Hitachi which actually
worked very well after being rejetted and the secondary circuit tweaked
some. Trying to get the single DCOE to work involves a whole other story,
but I finally did get it to work fairly well before we moved back to San
Antonio in mid summer. While the car had been pretty much a weekend
warrior in Hawaii, I had to start using it as a daily driver again in SA.
It worked reasonably well until around mid-October when the first cold
snap hit. It was maybe in the low 50s when I left for work but the car
started fairly easily and was okay, until after I got on the freeway and
started to get on it a little. About a half mile after I pulled onto the
freeway it started stumbling and finally died, just as if I'd killed it.
After trying to restart several times, I popped the hood to take a look.
I had left the sock type filters off (a dumb move in itself) and was
surprised to actually see (small) icicles hanging off the edges of the
airhorns. I put the OEM carb and manifold back on within a few days.
Driving that car on the street with the Weber in even moderately cold
weather was a major pain.
For the cars we're putting together now the track car may get Webers, but
I know the street car will get SUs. At some point I plan on doing back to
back dyno tests between a pair of properly set up 40 DCOEs (cold
manifold) and a pair of 38mm SUs (heated manifold). Same engine, same
day. It'll be interesting to see how they compare.
My $0.02,
Ron
Ronnie Day
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Dallas/Ft. Worth
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'71 510 2-dr (Prepared Class Autocrosser)
'73 510 2-dr (Street Toy)
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