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re:[T3] Cam sizes..


Jerrold wrote:

  About camshafts in general, whats 
the point of having a bigger one?  what effect does it have? would it just 
open and close the valves faster?  more?  i dont understand how having a 
larger cam effects performance.  

The cam can be your friend or your enemy. The BIG cam that 
people place on their cars are  usually made for high speeds,
highway and above. These same people also put the biggest 
carbs on these engines, sometimes too big for the engine size 
and what you get a a very rough engine, that idles badly but
at high speeds is a road warrior as well as a gas guzzler.
reguardless what size an engine is , the big cam will always 
make the engine run rough at idle and the bigger the worst
it runs at higher speeds. 

This is because the cam breaths more air at a longer time 
thus the term longer duration . With these, you will use more gas .
Suction from the piston will be longer and vacume will start 
high and then taper off causing inefficient vacume turbulance to the 
carburator (the larger the carb, worse the effect at low speeds).
These high duration are for much higher air flow with accompanying
larger volume of air , this is during high rpm engine speeds. 
This coupled with the correct carburator will
give you a good launch with a manual transmission that have those
3 puck clutches with those monster pull pressure plate (this can 
wear thrust bearing areas more than standard in your engine).
I have just described how dragsters do it. I do not think people 
launch like this at every light or stop sign. So it is best to 
get a moderate performace cam for good every day driving, your 
idle will shake a little but it will be acceptable. You will have a little
more 
umph !!! at freeway speeds than normal.  Higher lift usually accompanies 
these, I usually see more lift together with more duration. 
A lesser lasting drive train will be enjoyed if your ont the monster 
side of lift. Also mufflers and  pipes are needed for 
airflow (zzzooooommm!!!!).

Our stock engines have a balance of both lift and duration for 
the best all around driving.

Dune buggies, small cc engines and busses usually go with the 
the cam that is shorter duration than normal , this is to make the 
vacume stronger and even . The stronger vacume signal through 
a properly matched carb for the engine, the more control you get
in fuel metering thus the more rock solid your idle and low end
power . Your top speed with this limited air would be around 75
on most cars but you will feel the greater power at take off 
towing, hills (especially felt at low speeds), your engine will be
somewhat baja 1000 torquey . They call these torquey cams.
The best gas mileage longer lasting engine come from these cams.

Adding lift to these short duration enhances the torque to 
a certain extent. The short duration controls the vacum
suction to a time when suction is at it's greatest and not lost yet as in 
long duration. The high lift makes more air come in at this short duration
and just a little but almost neglegeable vacum is lost (unless you have
monster lift, your valve train will not last any how). The more 
air that comes in at the piston gives you better initial cooling
and guess what? A little more useable compression. Best not
to go high on the lift . These cams are usually known as tow truck
cams on the detroit moster world.

I will give you extreme examples of people going too far on 
'performance tricks:

At work big guy drove a toyota land cruiser with a chevy V8 on a daily basis
and decided to put all of the goodies on it, big giant  cam dual 4 throat
carbs
zoom gears on the final ratio. Well this guy never to this vehicle to work
because it turned off at every stop sign and had horribly weak slow speed
power,
it could not go up hills at 30 mph , it would cut out, it could no longer
tow his small boat. This is a speed demon once it goes beyond 55
but the zoom gears limit it to 70.

My brother's VW Baja Bug has a torquey cam, jumbo tires and seem to go
strait 
up cliffs. Burns rubber in the dirt and pavement.

When I bought (used) dodge truck had the weakest cam for it , jumbo lift and

duration , this truck really sucked gasoline and it just sucked , it did not
have
 the power to move itself on the stop signs with its auto tranny. I decided
to get 
one of those tow truck cams for 8 liter engine, wow gigantic difference. I
could tow
the world now, it even spinned tires on the pavement with 5000 pounds
in the bed . Top speed was limited to 80 by the rear gear ratio. I was able
to
slow the idle to less than 300 rpm with no engine shakes, it wouldn't turn
off
in gear. I broke the crank on this one on a torturous high speed offroad tow

incident that lated 5 hours. Will fix it later.

Be moderate with your cams and you will be happy unless you really
know what you are doing with the bigger ones. Bigger ones require more
knowlege and experience to get it working well.


I hope this helps .

LEON MARTINEZ

1969 SQUAREBACK EFI/AUTO
SAN DIEGO AND TIJUANA 


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