[DeTomaso] Stack Filters& cool air

JDeRyke at aol.com JDeRyke at aol.com
Sat Jul 11 15:01:04 EDT 2009


In a message dated 7/10/09 5:33:41 PM, wdemelo at cogeco.ca writes:
snip.....
> I'll remove the quarter glass to introduce cool air. The plenum will 
> extend rearward by about 4" so it is under the decklid and I'll use foam under 
> the deck to create a seal against the plenum.
> 
You're going to lots of trouble to get a pure-racing look in a mostly 
street car, so you really need to choose between -A- the engine wears out its 
rings rapidly due to inadequate air filtration but looks 'right', or -B- the 
'look' is not what Euro race cars of the day had but you won't need to rebore 
the block and replace rings & pistons every few thousand miles or so.
I think rear quarter glass removal will do nothing except remove 6 lbs of 
weight. Airflow below 140 mph is OUTWARD thru the glass openings due to high 
velocity air from under the car coming up & out; outside air will not bend 
inward against that flow at lower speeds, even with big scoops. The only 
known ways to get cool(er) air to the carbs is to fabricate a rear-facing 
carb-box like Shelby did with the Cobras, build a roof-top air scoop, or take air 
in from far away from the carbs- near the tail lights- like Ferrari did with 
the Boxer.
Second, one of the neat things about Webers is the extremely strong 
pulsations in individual-runner intakes. I assume your 'plenum' will interconnect 
two or more intakes together but I'm unsure of what your design will be with 
this device. It may change normally fussy Weber tuning to some sort of unk 
own so you- and your dyno man- may be on your own here. 
My suggestion is to stay far away from any kind of foam near Weber carbs; 
the reverse intake pulsations carry fuel back up to the foam which soaks it 
up like a sponge. Any backfire (very easy with choke-less Webers during 
starting & warm-up) and they burst into flame. The main venturis & protruding 
aux. venturis are zinc and melt very quickly in a flame. The molten zinc then 
flows down past open valves and sets up again as a metal lump on top of one 
or more pistons. Which impact the head and crack when you hit the starter. 
Been there, done that and it ain't fun..... Incidently, ANYONE running Webers 
needs to carry at least a good 2-1/2 lb Halon fire extinguisher; better is 
an on-board fire suppression system. And a cell phone with a good tow company 
on speed-dial. Even old well-soaked paper filters can catch fire, as I 
found. This is way-too exciting in the middle of a six-lane freeway....
Your website photo showed K & N filters which work fine if you follow K&N's 
instructions religiously. For instance, use their oil on their filters at 
their suggested intervals, and do NOT use soap & water to clean them in place 
of K&N's expensive cleaner. Soapy water will swell the fibers in the 
filters, and your nice clean air filters will suddenly not pass rated amounts of 
air, losing mucho horsepower for no obvious reason. 
Welcome to the wonderful world of Weber carbs! They're great when they work 
right. Otherwise, its like being married to a beautiful woman with 
permanent PMS and a concealed-weapon permit....Good luck - J Deryke


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