On a dynamometer, you can analyze peak power and
torque, or you can analyze average power and torque
over a given rpm range; this competition only cares
about the "average". Many engine builders and racers
worship the false god of "peak".
When trying to increase an engines average power, a builder quickly learns that changes with carburetors, headers, and
spacers most often only teeter-totter the curve.
This alters peak but does not change average. A 408ci
engine might have a peak HP of 650 and a peak TQ of
550, but the average total for an rpm range of 2500 to
6500, might be closer to 500HP and 500TQ; these two
numbers are added together produce a score of 1,000.
1. HEADS, CAM, COMPRESSION - Cylinder heads, camshaft,
and compression, will always be the largest
determinants for the final power output of any given
engine.
More than 95% of an engine's power is derived
by the "big three"; this was true in the past, and it
will hold true in the future.
2. HEADS - Heads are everything. If you need more
power, then you need more air-fuel mixture flowing
through the system. When making a bigger explosion,
larger quantities of air and fuel must pass through
the system.
I personally feel that port volume is over-rated and flow is under-rated. Porting must be consistent and efficient, but generally speaking, more flow means more power. Here is a quote from John Kaase, the 2003 and 2004 engine master champion:
"Chris Howe, labored two days on porting and valve
seat work. We started the testing with full-size
intake ports and later shrunk them down, which made
very little difference at any rpm." - Jon Kaase
This is a good example where port volume had
negligible effects on flow and power. Kaase's heads
outflow the competition, especially at mid-lift. If
you have the skills to pull it off, one of the ways to
improve flow is to shrink the combustion chamber.
This reduces the quench distance and places more of the
chamber in the top of the piston. This makes for a
very efficient chamber and is referred to by my Phd
friends as a "Heron" chamber. This will not help peak
flow but does help mid-lift flow numbers since the
valves are un-shrouded sooner.
3. CAM - The camshaft determines the shape and size of
the horsepower and torque curves. Camshafts are chosen
to optimize horsepower and torque for a given rpm
range. Drag racing, roundy-round, and road racing, all
require power in different areas. Computer simulation
software is very good at finding a starting point for
picking the cam that will best match your specific
power needs.
* Duration
* Lobe Shape (Lifter Acceleration Rate)
* Lift
The computer is good at finding the correct duration.
Lift is often limited by rules. The lobe shape should
be as aggressive as possible, with practical engine
life in mind.
The lobe shape is probably the part of the cam design that is least understood by the public.
The faster you can open and close the valve, the more
efficient the system, and the more power you will
make. You can design a camshaft with a 280/288
duration and 106 centerline many different ways, based
on the many different lobe shapes. Use the computer,
talk to the cam reps, and do some testing.
Belt drives are worth the investment because you can
test various intake centerlines; wiggling the cam
finds power.
4. COMPRESSION - More compression makes more power,
assuming you can control detonation. Compression is
often limited by rules. In the Engine Masters,
contestants are limited by 92 octane pump gas.
The most popular compression in the winner's circle is
12.5:1. This ratio is too high for a street car, but
it has a place in race engines on the edge. Many
builders are scared of compression, it's worthwhile to
test and find the engine limits using a research mule.
5. MANIFOLD - If heads, cam, and compression are the
"big three", the intake manifold makes the "big four".
The manifold is an extension of the cylinder head.
Most of the top engine masters test and re-test to
find the manifold that best works for their mill..
I don't have statistical proof, but I believe a manifold
should flow the same or 5% better than heads at peak.
If you have heads that flow 350, I would start testing
with a manifold flowing in the 350cfm to 365cfm range.
If your manifold flows less than your heads, air flow
becomes restricted and total power will be reduced. If
your manifold flows way more than your heads, the air
gets lazy, loses some velocity, and power declines.
6. CARBURETOR - It surprised me and all the lads at
Westech Dyno, when we put an 830cfm on my engine and
did a baseline pull, then sleeved it up to 1050cfm,
made one jet change and repeated the pulls, and the
total average power was identical. Don't get too
hung-up on the carburetor.
Pay the money ($700 - $1,500) for a good race carburetor, tune it, and don't worry about it; retune it when conditions dictate.
7. HEADERS - I took seven sets of headers to the dyno;
I was certain that one pair would have the magic.
* Hooker (2 sets)
* Heddman
* Mac Performance
* Basanni
* Kooks (2 sets)
Once again, me and the lads at Westech Dyno were
shocked that all of headers produced average scores
within 5 points of each other.
The headers had different peak horsepower and torque, but when you examine averages, the truth is revealed.
Most racers and engine builders want headers with
primary and collector tube size diameters that are
simply too large.
My rule of thumb is to choose a header with a primary tube size, ten percent larger than the exhaust valve. Start in this range and test.
In the 2004 engine master competition, most heads had
1.6" exhaust valves, and most competitors were running
with 1.75" headers.
One of the more interesting tests we did while
preparing at the dyno, was to run a set of 1.75"
Kook's with a 3" collector VS. a 1.75" to 1.875"
stepped Kook's with a merged collector.
The difference in scores between the two headers was 1-2 points at best; that is 2 points out of 1,000. I've never been
convinced that stepped headers or merged collectors
make more power, and this test reinforced my beliefs.
The two headers did have differing peak numbers, but
peak is the false god...average is the true strength
of the engine. Stepped headers and merged collectors
are expensive. If merged collectors work, why do they
work? It's my belief that they work by simply reducing
the size of the collector (people choose collector
diameters that are too large).
I wanted to test my size reduction theory; on the
fourth day of pulls, with a standard set of 1.75"
Hookers with a 3" collector,
I mounted a pair of 2.5" collector reducers, inside the collector pipe. These reducers cost $25. We ran the test and picked up 2-3 average points. You can spend $500 on a pair of merged collectors, or you might try testing a cheap pair of
collector reducers, fit inside your exhaust pipe. I
think you will be pleased with the results.
8. BIG BORE SMALL STOKE VS.. SMALL BORE BIG STROKE -
On paper, a big bore with a small stroke makes more
power than a small bore with a big stroke. I'm not
clear on all the reasons, but I do know that heads
flow more efficiently over a bigger bore. When you add
detonation to the story, suddenly the small bore big
stroke gains the advantage. Kaase was one of the first
to use this in competition.
"Because of the low test rpm range, I felt I needed
the longest stroke and smallest bore with which the
heads would work. With pump gas, detonation was a huge
factor in the design of the short-block and heads. A
smaller bore has less chance of detonation because it
doesn't have some far-off place for a secondary flame
front to start." - Jon Kaase
9. OIL - As much as I don't want to believe it, there
is hidden power in motor oil. When going from SAE
20w-50, to synthetic 30, and then to synthetic 20, 2-5
average points in power were found. Thin oil makes
more power than thick; synthetic oil makes more power
than regular. The gains aren't huge but they do exist
and they are clearly seen on the dyno runs.
A good oil pan allows oil to drain properly; a bad pan
can cost power at certain rpm levels. Too much oil
will effect power adversely and most people run with
too much oil. Don Terrill suggests testing an 8qt pan
with 5qts of oil and I have to agree. On the dyno, my
engine master's engine was happiest with 5.5-6qts.
"With a properly located oil pump pickup most engines
don't need more than 5qts of oil. Want to see how
critical oil level is to power? Test it: If you have
an 8qt pan, run it with both 5 and 8."...Don Terrill
Too much oil pressure reduces power. It takes more
energy to turn the reciprocating assembly as it slings
off excess amounts of oil. Too much pressure can
prematurely wear the cam and distributor gears. If you
have an engine that won't hold timing, pull the
distributor and look at the gear. If the gear is worn,
the cause may be excessive oil pressure or an
improperly clearances distributor gear and shaft. A
good rule of thumb is Terrill's 10lbs of pressure for
every 100hp.
10. TESTING - The best way to find the truth is
testing. Engines are tested on dynamometers. Book the
dyno for longer than you think; one day is barely
enough time to break-in an engine and set the carb.
Check the oil and water temperature every run and be
consistent. Make good notes for every run. Only test
one thing at a time. Use average horsepower and torque
for your running range as the yardstick to compare
changes.
