RACE CAR SETUP LINK
Transmission Ratio Charts
Saginaw 3 Speed
Configuration 1st 2nd 3rd
No Lines 2.85 1.68
1 Line 2.54 1.50 1.00 -
2 Lines 3.11 1.84 1.00 -
3 Lines 3.50 1.89 1.00 -
Saginaw 4 Speed
1st 2nd 3rd 4th
No Lines 2.84 2.01 1.35 1.00
1 Line 2.54 1.80 1.44 1.00
2 Lines 3.11 2.20 1.47 1.00
3.50 2.47 1.65 1.00
2nd Design T-10 (Super)
Configuration 1st 2nd 3rd 4th
2 Lines 2.43 1.61 1.23 1.00
2.64 1.75 1.33 1.00
5 Lines 3.42 2.28 1.46 1.00
6 Lines 2.88 1.91 1.33 1.00
Muncie 4 Speed
2nd 3rd 4th
No Lines 2.56 1.91 1.48 1.00
1 Line 2.20 1.64 1.28 1.00
2 Lines 2.52 1.88 1.46 1.00
Transmission 1st 2nd 3rd
Power Glide * 1.76 1.00 -
Power Glide * * 1.82 1.00 -
2.52 1.52 1.00
TH-400 2.48 1.48 1.00
Ford C-4 & C-6 2.46 1.46 1.00
Chrysler 727 2.45 1.45 1.00
904 2.70 1.54 1.00
Cam Specs & Effects
Understanding cam specs and their affects will help you
select the best cam for your specific engine. The four important camshaft specs to understand are duration, centerline, separation
Duration refers to how long a valve is opened in relation to crankshaft rotation. This open valve
time period is expressed in degrees of crankshaft rotation. So, a cam specification of 220 degrees duration simply means the
cam holds the valve open for 22 0 degrees of crankshaft rotation.
As strange as this may sounds, more duration can be
helpful in high RPM engines but not low RPM engines. The extra degrees of open valve time in high RPM engines gives the air
flow a little more time to get into (or out of) the cylinder in spite of the pi ston's stroke. However, at lower RPMs, more
duration can cause less power because the valves will be open at the wrong time in relation to the piston's stroke up or down
in the cylinder.
The cam's centerline specification is used to tie the valve timing to the crankshaft's
rotation. This spec is expressed as the number of degrees the crankshaft must rotate from top dead center until the cam has
rotated to the peak (or centerline) of the lobe.
The centerline spec and the duration spec can be used to calculate when
the valves open and close in relation to the crankshaft's rotation. When the valves open (or close) relative to the crankshaft's
rotation is known as valve events or valve timing. Some cam manufacturers will provide valve event information and others
only p rovide duration and centerline information. If your cam manufacturer doesn't provide valve event information, a software
program such as Cam Shop <../software/cs/cs.htm> can calculate this info for you.
Understanding the effects of valve
events or valve timing is the real secret to understanding engine performance. For the engine to run at its peak performance,
the valves must open and close at the correct time in relation to the piston's position and the crankshaft's speed. For more
information on this subject see the Valve Timing & Performance <valvetiming.html> page.
refers to the spacing between the intake lobe and exhaust lobe on the cam shaft. This spacing (or separation) is expressed
in degrees on the cam, not on the crankshaft. So, a 108 lobe separation means the intake and exhaust lobes are 108 degrees
apart from each other on the cam shaft.
This spec by itself really doesn't mean anything. If you hear someone else is
using a cam with 108 separation, don't think that you should use cams that only have 108 separation!
like centerline, is another way to tie the duration to the crankshaft rotation and end up with valve events. This spec is
a little more complicated though, because it is in cam shaft degrees and the crankshaft rotates two degrees for each one degree
of cam rotation. Also, if the cam has been installed either advanced or retarded, the valve events will be different. This
is where the Cam Shop <../software/cs/cs.htm> software can make your decisions easier because the software does all
of the calculations for you and you don't have to guess at these confusing relationships.
The final cam spec
to understand is lift. While duration refers to how long the valve is opened, cam lift is used to determine how wide the valve
If the valves are not opened wide enough, they will cause a restriction for the air trying to enter or exit
the cylinder. However, opening the valve past a certain point will not increase the flow to (or from) the cylinder. A good
way to demonstrate this is with the garden hose in your back yard. When you first start to turn the water on, the flow increases
but after a turn or so, opening the valve more has no effect on how fast the water comes out of the hose.
It is necessary
to understand a large amount of science to understand how the flow is related to how wide the valve is opened and how this
affects the engine's power. However, the simplest and easiest way to see how the lift affects engine power is with a software
program like Engine Shop <../software/es/eswin.htm> or Engine Analyzer <../software/ea/ea.htm>.
Copyright AutoWare 1998
Valve Timing & Performance
If racing is your thing, or you are an automotive hobbyist,
then you are most likely not afraid of swapping cams in your engine. However, the trick to making your car faster is not just
replacing the cam, but replacing it with the "right" camshaft. This is where your understanding of valve timing becomes crucial
in selecting the proper cam. To help you better understand valve timing, this page will cov er blow down overlap and the ram
On the power stroke, the combustion pushes the piston down in the cylinder. During this stroke,
it is necessary to open the exhaust valve before the piston gets to the bottom of the cylinder. This will allow the excess
pressure in the cylinder to "vent out" just before the piston reaches the bottom of the stroke. The term "Blow Down" is used
to describe this event.
Timing the exhaust valve in this manner assures no pressure is left in the cylinder to push against
the piston on the exhaust stroke. Otherwise, there could be 20 PSI (or so) pushing against the piston as it starts up the
cylinder. This would require some of your engine's power just to push the exhaust out of the cylinder!
High RPM engines
need to have the exhaust valve open sooner so the pressure has a better chance to exit the cylinder. However, at lower RPMs,
opening the exhaust valve too soon means you didn't take full advantage of the power stroke. The Engine Analyzer Pro <../software/eap/eap.htm>
software is a good program to use for experimenting with blow down because you can quickly try different valve timing and
see the cylinder pressure on your computer screen.
As the engine cycles, there is a period when both the intake
and exhaust valves are open at the same time. This valve timing is known as "overlap." Think of this as the exhaust and intake
cycles overlapping each other.
The valves are timed so the intake valve opens slightly before the piston reaches top dead
center (TDC) on the exhaust stroke. Likewise, the exhaust valve is timed to close just after the piston starts down on the
The objective of overlap is for the exhaust gas which is already running down the exhaust pipe, to create
an effect like a siphon and pull a fresh mixture into the combustion chamber. Otherwise, a small amount of burned gasses would
remain in the combustion chamber and dilute the incoming mixture on the intake stroke. This valve timing is a product of the
cam's duration and separation specs. For more information on these cam specs see the Cam Specs & Effects <camspecs.html>
The science involved with overlap is quite complex. Pressures, runner lengths, temperature, and many other aspects
influence how well the overlap effect works. The advantage to using software like Engine Analyzer Pro <../software/eap/eap.htm>is
that the software does all of the calculations for you. Simply enter a different duration and separation in the computer and
the software will show you whether or not to expect more power from your engine.
When the piston reaches
the bottom of the cylinder on the intake stroke, the intake valve doesn't immediately close at this point. The intake valve
remains open even though the piston is starting up the cylinder on the compression stroke. The expression "ram effect" is
used to describe this event.
Timing the intake valve in this manner allows an additional amount of fresh mixture to be
rammed into the cylinder. The effect is very similar to water hammer in plumbing. What happens is that during the intake stroke
the fresh mixture is running fast enough down the intake manifold and into the cylinder that it can not instantly stop when
the piston stops at the bottom of the intake stroke. Just like the water hammer effect, the incoming mixture is rammed into
the cylinder even though the piston may be starting up on the compression stroke.
High RPM engines can have the intake
valve remain open longer to take advantage of this ram effect. However, at low RPMs, the ram effect is not strong enough and
the piston will start to push the fresh mixture back out of the cylinder. Of all the different valve timing effects, this
one can have the greatest impact on your engine's performance. By advancing or retarding the cam or trying a different camshaft
in the Engine Shop <../software/es/eswin.htm> or the Engine Analyzer Pro <../software/eap/eap.htm> software, you
will know if you have the correct valve timing to take advantage of the ram effect.
Copyright AutoWare 1998