Performance Engine Tuning 101
by Eric Perez
The Bench Tune
Starting a Difficult Engine
Road Test
Wrap Up
Those who have been following my articles will notice a
pronounced change in my tuning techniques. This doesn't mean that the previous
methods where incorrect. It just means that I've found better and easier ways to tune
the engine. This month I complete the long awaited 4th and final addition to the race
series of articles, with Performance Engine tuning techniques.
When you start tweaking an engine to deliver max power it may be a little difficult to
do it right without all the right tools. It would be hard to do open heart surgery
with a 9 inch cleaver. Well, it's not any different with R/C cars...especially Nitro R/C
cars. Most people invest alot of money in worthless aluminum junk for their cars and
always dismiss the idea that a $70-$80 infrared temp gun will help them big time. I
think it's a pity that they spend so much money on the things that make the least
amount of difference (performance wise). A well tuned sport engine will always
prevail against a badly tuned Novarossi Twin Turbo inter cooled, touched by the hand
of Ron Paris engine -This is a fact.
You don't have to have a temp gun, if you only race one of your R/C cars even a
$30-$40 temp probe is not a bad idea either.
The Bench Tune:
The Bench Tune ( A very good tool for the beginner, you should do this a couple of
times and understand what is happening before you start messing with the car and try
to tune the car while it's traveling 50 mph) Most true experts that I've seen working
with a badly tuned engine (usually owned by a friend or fellow racer) will always do
a quick bench tune before putting the car on the track. After a lap or to they do
some fine tuning on the needles and they quickly get the engine running like a champ.
The problem with doing your first "race" tune while the car is moving is that the inertia
of the vehicle coupled with an engaged clutch will keep the engine running when it
really shouldn't even be moving. This "forced" engine operation mixed with a badly
tuned carb can damage an engine very quickly. When you can do a good bench tune
you will be very close to actually making the fuel mixture changes to have the
engine run like you want it. Notice that this procedure (bench tune) requires you to
either pick the car up and do some quick revs (in the air) or have some type of stand that lets the wheels
spin freely. Quick does not mean you are going to open the
throttle and wind the engine for 5 seconds or until the connecting rod snaps in
half!!! It means you are going to pull the transmitter trigger and rev it until the engine cleans the pipe. You will know this because the engines exhaust noise changes
and the RPM's jump considerably in a very short period of time. As soon as the engine cleans the pipe get the throttle back to the neutral idle setting. Do this a couple of
times to get a feel for how the engine sounds when it's on the pipe.
Starting a difficult engine:
1. Idle speed gap on the carb barrel should be from 1-2mm. For engine starting
(altough not necessary on all engines) you can temporarily increase it with throttle
trim to help you start the engine.
If the engine will still not start, check the following.
2. Take the air filter off the engine. Sometimes the engines low speed needle is so rich
that the filter becomes saturated with fuel. This makes it hard for the engine to suck
air, thus it will never start. If the engine becomes progressively harder to turn over
as your trying to start it. Or if your seeing a lot of fuel spray coming from the carb
throat, you might just need to lean the low speed needle. You may need to remove the
glow-plug and drain the cylinder to prevent hydro-lock every couple of minutes while
your trying to start it.
3. We are dealing with starting the engine and unless you start the engine in WOT (wide
open throttle) which is not a very smart thing to do, you don't really need to worry
too much about the high speed needle when your starting an engine with a 2-needle
carb. As long as the needle is open, 2,3,4 turns open it doesn't matter when your
starting the engine. We will visit the high speed needle latter in this self help article.
4. If every thing is just not working re-set all needles to factory specs. The
low-speed needle is set with the carb fully closed. don't forget this crucial step or
you won't get the low-speed needle set right.
5. It will start, no matter what. If you have "good" non-contaminated fuel. A fully
charged glow-plug igniter and an okay glow plug the thing will start -It has too!
6. Make sure your turning the engine the right direction. R/C engines will start in
reverse, they will spit fuel and cough like a sick horse, but they usually start. Verify
that the engine is turning counter clock-wise when you look straight from the clutch
bell.
7. Continue to progressively lean out the low speed needle until the engine starts.
Depending on how long it has taken the engine to start you could have enough fuel in
the crankcase that it will stall shortly thereafter. Don't worry, re-start engine and
listen to it. Slowly accelerate the engine (car is on work bench with tires off the ground).
If the engine feels sluggish on the top end after a couple of seconds of throttle
transitions lean the high speed needle (clock-wise) a little until it cleans the pipe.
8. Let the engine idle for 5 seconds and blip the throttle if it stalls or
stumbles (lots of oil and engine sounds like it's running rich again) lean out the low
speed needle a little more (clock-wise). The engine should now be able to idle for 5-10
seconds without loading up on fuel. Continue to repeat until engine idles clean and
crisply accelerates to high speed (cleans the pipe).
9. At this point you should let the engine idle for a while and temp the glow-plug.
temps should be slightly above 200F. Set the idle speed so the car doesn't creep
forward on it's own (re-check low-speed needle test setting after doing this). Then, turn
the idle speed screw until the carb will not close beyond this idle point. Even if you
slam on the brakes. Just make sure minimum idle opening is within 1-2mm.
10. Replace the air-filter and commence road testing and final engine tuning. When
you finish tuning the engine, pinch the fuel line going to the engine while it's idling.
The engine should speed up momentarily and then die. This means that you're in the
right track. If the engine doesn't speed up, then you may need to richen the low-speed
needle a bit.
Road Test:
The final road tuning test is more for checking operating temperatures and for
adjusting shift point ect. When you need to bring temps down, first open the high
speed needle a little bit. If you still need more cooling then open the low-speed
needle a little bit. Continue this process until engine temps are close to F230-250
and your able to run back to back tanks with no signs of overheating. If you are not
getting the temps down and the performance is starting to suffer, because you are
running too rich, either get more cooling air into the engine head or change to a fuel
that has a higher oil percentage. Going to a colder engine plug is also another
possibility. Remember 15-20% nitro will run cooler than 10% nitro fuel.
