[Amc-list] Home built 'Blower AMC'

[Brien Tourville <hh7x@xxxxxxxxxxxxx>]

For Posts by 'Blown 7' > go here:

http://www.bulltear.com/forums/search.php?search_author=Blown7



This is an early statement by 'Blown 7' - on page 33 - of 34:






Posted: Tue Sep 06, 2005 10:06 pm    Post subject: 	Reply with quote 
<http://www.bulltear.com/forums/posting.php?mode=quote&p=30599>
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That is a centrifical supercharger, belt driven yes its probably the 
easiest to install and works well, agin the only plumbing you have to 
worry about is from the charger to carb. Question 2 The same applies 
whether it is a Roots, turbo or centrifical, if its for sale chances are 
its been lunched, I haven't met anyone who has removed a boost system 
because it worked too well, the thing you have to watch out for is if 
the engine had a backfire thru the charger bad things happen to the 
castings, (read junk) a engine that backfired will literally under the 
right circumstances grenade the charger, on the Roots I have I have a 
burst plate to act as a safety valve with low to moderate backfire and 
it hasn't burst yet but if it does I hope it may save the 6-71. Backfire 
results from running lean which is very easy to do with a boosted 
engine. (Thats why I went with a Fast EFI programmable system) less 
hassle and I can tweek if I want to barometric pressure and temperature. 
Q3 Carbs can be divided into two basic systems, Blow thru and Draw thru 
each has its good points. First blow thru is the easiest system to build 
but the things that need to be changed are , the float may collapse so 
it must have a solid float Second forget vacuum anything, (brakes, 
distrubutor advance, heat controls, QT valves) there ain't any. All the 
system is positive pressure (we call that on aircraft supercharged 
systems "upper deck pressure") also all the connections to ambient 
pressure must be plugged to prevent leaks even the throttle shaft 
bushings need to have air under boost by drilling a passage from the 
outside and plumbed tto the positive pressure side. Now if there is a 
return charcoal canister for fuel vapors you have install a check valve 
in the line to prevent fuel vapor under pressure from returning to the 
fuel tank and bypass the line to the aircleaner. Now you have to use a 
electric fuel pump as the pressure rise with boost will not allow a 
mechanical pump to overcome the increased need for fuel pressure and 
quanity several ways to do this a rising rate fuel pressure valve is one 
as the boost increases fuel pressure rises to meet the increased demand 
of the engine and to keep the vinton valve closed ( if the pressure 
rises too much the valve may never seat. The fuel line will need to be 
resized to allow more fuel flow, a 3/8" line ain't gonna cut it. (To cut 
to the chase my 401 ci uses roughly 800 ci of air under 10 psi boost) 
yes thats right I have a 800 ci AMC! so if BSFC is .5 lbs per hp we are 
talking some heavy fuel rates. Also conside the PCV system the system as 
OEMed will build up crankcase pressure unless you vent the breather back 
to the air cleaner. This ain't all but we'll move on to draw thru the 
carb mounts ahead of the compressor inlet so the charger draws the fuel 
thru the carb in normal atmospheric conditions all the stock pcv 
connections can be retained you'll have vacuum, but now the location of 
the carb is changed so you have to deal with modifing that, the heat 
riser will now be useless as the carb will be a disatnce away and fuel 
will not vaporize well when its cold so cold startup will be a problem, 
not to mention carb ice on a moist humid day because of the airflow thru 
the venturi now we are talking plenums to keep heated air around the 
carb. Then in some instances you'll have unequal fuel disribution unless 
a screen is installed before the intake runners. Then the carb has to be 
sized and jetted to allow for the increased fuel air mixtures ( the 
stochiometic mixture stays about the same but the Pounds per hour of 
fuel goes up, (all this is to prevent detonation the killer of 
supercharged engines nothing will grenade the engine in nanoseconds like 
a lean mixture) thats why we run long reach plugs to act as fuses, the 
tips burn off hopefully before bad things happen to the pistons and 
rods. Thats why EFI is sooooooo mucher easier to program. Q4 cam grinds 
ah thats a mysterious art often elusive yet so satisfying, BS first chat 
with Richard Iskedarian ( I have his number if you need it) the cam is 
gonna revolve around the basics that your misson profile will require, 
you can have it all but you pick your needs, first and number one you 
want a 110 degree overlap thats the biggie, any more any less messes up 
the volumetric efficency of the engine. Next lift, you don't need alot 
somewhere around .500@ .050" is fine actually I think mine is .523 (in 
most instances a stock cam grind will do fine) If you want I'll dig out 
my cam spec sheet. After a bunch of typing and maybe you reading their 
is yet a whole bunch I haven't touched on yet maybe your understanding 
now why the supercharger kit manufactors charge so much, somebody has to 
do all this engineering, design and testing to make a viable useful 
system. One of the reasons I went with a 6-71 is its actually simpler to 
design and make a pretty bulletproof system. Another was the EFI, to put 
it simply carbs suck, in more ways than one I'm tired of screwing with 
them they wear out, get dirty, difficult to adjust and tune for boost. 
Ok with my ranting out of the way what exactly were you planning to 
supercharge? maybe I can just point my thought in a specif direction. K 
have a good evening and will be standing by waiting for further 
questions. Jeff
_________________
1979 Jeep CJ-7 401 AMC, GMC 6-71 Blower 10% overdrive, Bugcatcher with 
electronic fuel injection and a little N2O for fun, all self built. 
(this supercharger stuff is easy)




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