how the heck is a few simple data sheets going to include the following factors
Chamber shape
Head temperature
Charge Air temperature
Manifold pressure
Fuel droplet size
Spark Plug temperature
residual unburned fuel
Port turbulence
Compression ratio
Piston dome shape (or dish)
Fuel octane
The list is longer but these are the high points....
Begs the question "do you want to pass the final exam but not do your homework"
There are no tables that are really current or describe all these factors that
all make a difference, out of which rod length has about the least to do with
anything. The whole dwell time deal is a myth for the most part do the math and
see if you really think there is as big a difference as you think there is. Rod
length is great for trying to get peak and average inlet port air speeds
somewhere within reason but not much else. Chamber shape and mixture quality has
far more to with it than a rod length change of a 1/2 inch.
getting the right timing is pretty easy to program.
1.You pick a sensible number
2. make a pull on the dyno for a given rpm.
3. Read the torque.
4. take out two degrees
5. repeat steps 2&3
6. not torque difference
if better take out 2 degrees and repeat steps 2&3
if worse add 2 degrees
repeat steps 2&3
repeat the above in 500 rpm increments till it runs the best. Takes about 3
hours
and 15 gallons of fuel..
then when you change air density or any of the other factors on the list you get
to do it all again LOL....
EGT can give you a good clue too when it is very high the timing is generally
retarded and when when very low too advanced, as long as the air fuel ration is
ok and the ignition systems parts are in good repair.
If typical timing numbers don't work then you ought to suspect the following
Bad ignition system( coil and amplifier)
poor fuel quality
poor mixture quality
incorrect valve lash
incorrect cam timing
poor rotor phasing
bad ignition pick up
fuel octane is way out of bounds for application(very common usually too high)
The real secret to tuning racing engines is there is no secret, it is all 'auto
shop 101'
Dave Dahlgren
Higginbotham Land Speed Racing wrote:
> Well, I have been waiting anxiously for the "last" bit of data to enable
> calculation of proper mixture ratios and ignition timing...but alas it has
> not shown up! Several have come close though and almost touched on the
> subject of Flame Front in the combustion cycle.
> How fast your fuel burns determines when you start the fire (ignition
> timing) to get maximum power for that fuel in that engine at that RPM (all
> relative to rod angle). Induction pressures and temperatures, fuel
> composition, engine efficiency, etc all certainly affect when you start the
> fire but the question remains......how to predetermine the correct timing
> for your engine and fuel with regard to RPM.
>
> Next will be the question of how to program that timing to vary it
> constantly over the entire RPM range based on the flame front..
>
> So, again, does anybody know what happened to the flame front data sheets
> that were published in the late 50's early 60's in a "performance"
> magazine? I though that it was Hot Rod but I guess not. Some new ones would
> work......ones that include nitrous?
>
> Skip (Still looking.......)
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