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Engine Tuning
This page explains tuning principles for NA and boosted engines. This was to
answer the hundreds of question I get about general tuning that could be
answered in minutes by searching old posts on most forums.
Introduction
Turbo FIRE engines can work well and
not blow up, but you have to do things right. Since I have many turbo
conversions including the 999cc FIRE MPI, I have beaten the crap out of it every
day, have taken it to the track a bunch of times, and have gone to a road course
numerous times not to mention the dirt road racing we occasionally do. That was
all on stock internals, and it's still running strong with good compression
numbers. Many people claim that turbo conversions are unreliable but they have
no evidence of such.
I know it won't last forever, but considering the abuse that I have put it
through, I'm extremely pleased with how it's holding up. The key is that you
must take care of two things:
1) Oil. This is very important for keeping your bearings alive. It also cools
the engine and the turbo. Fortunately, it's pretty easy to take care of... Just
use good oil, check the level frequently, and install a pressure gauge (sometimes
oil pumps go bad, so you need to know before it's too late). While it is true
that you will want more resistance to heat, don't get something that's not good
for cold starting... cold starts cause a lot of engine wear because there's not
much oil where it needs to be. The sooner oil gets there, the longer your engine
will last. I use Mobil 1 10w40. It's good for cold temps, and it can tolerate
the heat too.
2) Heat. Excessive heat will cause detonation, melt pistons, warp heads, break
down oil, and so on. Your engine will generate a lot more heat than before, and
there are several things you need to do. The most important part to cool is
inside of the combustion chamber; that's where the heat is created, and that's
also where much of the damage would be done. Coolant surrounds the cylinders, so
it just carries away heat once it transfers through the cylinder wall. That's
important and all, but you must cool it down from the inside too. There are
three things that you are putting into the combustion chamber: air, fuel, and
spark. You can use all three of them to make it run cooler. Here's what you need
to do:
a) Fuel. You need to use premium gasoline only, and you need to make the engine
run a little rich too. I'm running about 12.5:1 for my air/fuel ratio. The extra
fuel will cool things down. You MUST tune your fuel management with a wideband
O2 sensor on a dyno (you need the load, especially for a turbo car). Don't just
guess, unless you like replacing engines. And this is not tuning for maximum
power; you are going for a specific A/F ratio.
It's also very important to have good reliable fuel management. Avoid FMUs and
check valves (aka Missing Link); those are extremely ghetto and are completely
against the way that electronic fuel injection is designed to work. Standalone
fuel management is the best choice, but you can still do a good job without
it...
A good fuel pump (Walbro 255 lr/hr), an AFC, and 450cc injectors (w/ resistor
box, if needed) is all that you need to tune for a good A/F ratio. It's not the
perfect solution that a standalone is, but it works really well and wont cause a
check engine light unless you go above 10 psi of boost... Hook the AFC up the
way it was meant to be (ie no TPS/MAP hack), and just lean it out by about 35%
at all RPMs, then take it to a dyno with a wideband for tuning.
What's happening is that the AFC is scaling down the MAP signal so that the ECU
will shorten the injector pulses and not see boost. The larger injectors are
providing much more fuel than stock, so those shorter pulses are all that is
needed. Basically, you are expanding the ECU's fuel map into boost and fine
tuning it.
b) Ignition system. Retard your base timing to 14 degrees or less, and use a
colder spark plug. Spark plugs do more than just cause the explosion, they also
serve as a heat sink. A colder spark plug means that it's insulator is designed
to carry more heat out of the combustion chamber.
You should also use a smaller than normal gap to keep it from missing. The
denser air and fuel mixture will require more voltage to create a spark through,
but reducing the plug's gap will counteract that problem (at the expense of
having a smaller spark). I ran the stock gap of 1.1mm on Bosch Platinum plugs
for a while and had no noticeable problems, but I suspect that the spark was
weaker than it should have been. I'm using 0.9mm now and it feels a little
smoother, but it really wasn't bad before. However, your mileage may vary,
especially if your ignition system components are more worn than mine.
c) Air. The air coming out of the turbo will be hot, even on a cold day. This is
where a good intercooler comes in, but be aware that a front mount will block
the radiator. Fortunately, the air going into the combustion chamber will be
much cooler, so you are a little less dependant on the coolant. However, coolant
is still important, and you really don't need a huge front mount, so try not to
block the radiator too much.
d) Coolant. It takes heat away from the cylinders and head, so it's pretty
important. The upgrades are pretty simple... a more efficient radiator (ie
larger), and better coolant. Glycol (main component of anti-freeze) is good for
not freezing, but pure water is much better for cooling. It's normal to run a
50/50 mix of the two. If you don't have to worry about freezing weather, then
bias the mixture to include more water. Anti-freeze does include corrosion
inhibitors, so it is beneficial to keep some in the cooling system, even it's
always warm where you live.
Porting and Polishing
A brief background ...
Most builders use the extrude hone process where you flow a thick "sand
like" material through the head. The few heads I saw, had port surfaces almost
mirror like smooth on the intake side. Let me emphasize this I COULD NOT SEE THE
GRAIN or any defects in the port passages. That in conjunction with a flow
bench is the secret. Basically you try to eliminate any "sharp" corners in the
intake ports, and to get the ports volumetrically equivalent.
I've been told to stay away from Extrude Hone because the "ooze" that flows
through your head does not actually "know" where to go. Basically, it will
take material off where ever it hits, not necessarily where it needs to be taken
off. I read some article about it in Turbo Magazine when they did a
hand-port vs. an Extrude Hone port on a Mustang head and the hand port performed
much better then the extrude honed.
Porting for a big valve naturally aspirated head requires a different
methodology to a turbo charged one. A good source of info is one the countless
English magazines that like to give in depth articles on how to port the 4
cylinder turbo ford cosworth engine. Car and car conversions has tons of
articles on this.
Cylinder Head Porting
Cylinder head porting is a great bang for
your buck mod with substantial horsepower gains. As good as current cylinder
head design may be there is still much room for improvement since during the
production process flaws do occur. During the casting process of the cylinder
head there are always lots of lumps and bumps in the ports. Though they may seem
insignificant they are since the air is traveling at supersonic speeds they can
greatly hinder air flow. Another common flaw which occurs during the production
process are leaky valves which mean loss compression which means lost
horsepower. You can take a cylinder head off of a brand new engine lay the head
on its side and pour liquid into the ports and find that liquid will leak
through the valve seats. Typically the larger the engine displacement size the
greater the horsepower gains.
Ported Turbo
exhaust ports
This is the part that hooks up to the
exhaust manifold. The Compressor output port can be polished as well, since the
the airflow velocity will increase with less heat buildup. Some drag turbos are
ported very heavily when restricted by size in a class. Helps under high boost
pressures.
Remember that twin turbos
are forbidden by many racing classes.
Increasing RPM range
Regading building an 8500 RPM engine, the main thing is
reliability of the crankshaft, connecting rod
strength and main bearings. The newer (90+) crank
and con rods can take 8500 RPM no sweat (mine does) If you have a
999, then you are safe for 9000. The reason
"some companies sell racing crankshafts
is because the
racing engines are in the 6000- 9500 rev range
continuously. Buying a billet crank if you are not racing on a professional
level is a waste of money (IMHO)
I figure if your crankshaft breaks.. you are doing
something wrong.. or something the motor was never
intended to do..
The ability to rev high and make useful power comes strictly from the head.
You have to balance the cams to the porting strategy. Note if you are
building a race engine which tends to have a narrow power range, you
have to sacrifice low end response for high end
response. There's no free lunch!
Water
Injection
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Maximum Torque occurs at a 13.2:1 Air Fuel Ratio.
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Transitional Fueling and Maximum Boost Air Fuel Ratios are about
12.5:1.
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Water Injection is most efficient with a 50/50 water alcohol
mixture.
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Methanol, as an additive, is not a practical choice as it is
prone to pre-ignition, is not safe to handle and is not readily available.
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Denatured (ethanol) alcohol, typically 95%, is cheap and is
available in paint, hardware, and Home Depot type stores in gallon containers
for about $10.00. Isopropyl alcohol can be used but it is often 30% or more
water by content.
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Water Injection allows ignition timing to be more aggressive or
closer to stock. In other words boost does not automatically mean retard your
timing.
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Excessive amounts of ignition retard will cause a loss of power
and overheating.
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Water to Fuel ratios should be based on weight and not volume.
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Water weighs 8.33 lb per gallon.
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Alcohol weighs 6.63 lb per gallon.
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Air weighs .080645 lb per cubic foot. It takes about 150 cubic
feet of air per 100 horsepower. It takes about 12 lb of air per 100 horsepower.
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Water or Water / Alcohol to Fuel Ratios are between 12.5% to
25%. This means Air to Fluid Ratios are between 11.1:1 and 10.0:1 with water
injection.
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Maximum water delivery should be in higher load low to mid rpm
ranges tapering somewhat at peak rpms where load is less.
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Atomization of the water mixture is directly related to it
effectiveness. Finer droplets cool the inlet charge better and with less mass
they navigate the inlet plenum easier for more equal water distribution.
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Don’t flow water through an intercooler.
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Atomized water, just like fuel , does not like to make turns
thus making accurate distribution something to think about. This is why port
fuel injection is the norm. Water is a fluid just like your fuel. Multiple
nozzles, equally spaced in the plenum, although it complicates things, is a
superior design.
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The introduction of water will allow higher boost pressures to
be run without detonation. Higher pressures will increase torque. It’s always
about torque.
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Racing high octane gasoline should be used for all forms of
competition and for higher than normal boost levels. Water injection as well as
charge cooling should be used with racing gas. 91/92 Octane pump gas simply will
not cut it.
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Fuel Injectors operate in the 1 Millisecond range and are not
capable of long term usage for H20 as they will corrode or rust shut in a very
short period of time. Unless a solenoid can open as fast as a fuel injector it
should not be used to "pulse" water injection events.
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Varying voltage to water injection pumps or using similar
schemes is a recipe for disaster. You have to eliminate the variables, not
increase them.
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Fuel Injection pumps cannot be used for water injection. Water
is conductive. Gasoline is not. Water will corrode an efi pump shut in a very
short period of time.
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Water injection has a cooling effect on the engine head, valves,
and cylinder. Exhaust temperatures (EGT) are largely unaffected at recommended
water / fuel ratios.
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The cooling of potential hot spots in the combustion chamber
defeats pre-ignition, the most destructive form of uncontrolled or unplanned
combustion.
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Higher static compression ratios will require a higher
percentage of water or water / alcohol.
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No, water does not burn. We are not combusting the hydrogen in
the H2O.
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At around 13.2:1 or fuel air ratios of .75, EGT’s will peak.
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Ferrari suspended water in their fuel during their 1980’s
Formula1 period. We don’t recommend that you try this...although Acetone will
mix with water.
Fuel Consumption
High fuel economy claims are often subject to ridicule and
accusations of miscalculation, deceit, or violation of basic laws of physics.
Low mileage lamentations are often accompanied by accusations of fraudulent
misrepresentation by the manufacturer and questions regarding possible defective
or misadjusted components.
Different mileage calculations are used in other locations and may not convert
to equivalent numbers. In North America, mileage is often specified as miles per
gallon. The UK may also refer to miles per gallon. Be aware that the quantity of
fuel contained in a "gallon" depends on the type of gallon, US or Imperial. The
more common consumption rate used elsewhere in the world is liters per 100
kilometers. When comparing expenses remember that "dollar" is the name of
currency in Australia, Canada, New Zealand, and the USA. The exchange rate
fluctuates between these currencies. The conversion of one measurement to
another gives additional opportunity for errors. When comparing someone else's
set of figures to yours bear in mind that their driving style, wheel alignment,
weight, acceleration techniques, braking habits, climate, preferred cabin
temperature, tire pressure, etc., etc., are different than yours. These are some
of the reasons for the disclaimer "your mileage may vary".
Most performance improvements will not
significantly alter the original mileage, it will never increase it because that
would mean the AFR would need to be greater then 14.7 which is a big no for
modified vehicles.
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