We discussed previously how an engine exhibiting below normal total ignition
requirements is indicative of an efficient engine. The example given
previously was that of a Racing Engine producing maximum power with 34-38
degrees of total lead or timing.
Engine builder #1. After the builder removed the heads and freshened the
block he went ahead and ported/polished the heads. In his zeal for increased
airflow utilizing a flow bench he got overzealous in porting and chamber
work. When everything was said and done the heads now flowed more than
before! Seems like now this car is going to run like a champ!!!
Engine builder #2. Decided to port/polish his heads and paid attention to
his chambers and was careful not to increase chamber volume and elected to
sacrifice flowing less and keep the chamber small! His airflow improvements
where modest compared to builder #1.
Who do you think will run better at the track???
After preliminary testing Engine #1 exhibited more horsepower and
performance all around. His total ignition lead INCREASED to now 38-40
degrees for best performance. The added airflow made this a success as it
shows at the track…
- After doing the same Engine #2 exhibited the same performance and
somewhat more responsive on all the speed ranges than #1! His powerplant did
not flow as much on the flow bench and should have been relegated to and
also ran…his total timing requirements DECREASED to now a total of 32
degrees? What happened to this ? - If you ran these two head to head, engine #2 will probably make as
much power or maybe even more than #1! Why? #1 engine’s compression was
compromised and reduced by the chamber work to get airflow! (The added
airflow could not compensate for the compression loss. The resultant
negative torque load also added to this loss.) - Second and the most telling to a very competent Racing Engine
Builder is the total ignition requirements! Engine 1 has to work against
itself (loosing power) to get around the added 8 degrees of timing (called
negative torque). Not only this is harder on the pistons, crank, and rods,
also think about the bearings’ added loading. - Engine #2. Less timing requirements exhibited a more EFFICIENT
COMBUSTION CHAMBER. This engines compression ratio was not compromised or
reduced in search of airflow. This equals to more power because of its
higher compression ratio. - If these two would road race for a distance #2 will go farther
because it is running efficiently than #1. How many races was lost when the
other guy had to pit earlier and more or just plain ran out of gas!!! Racing
Engines are not about all power but of efficiency as well… The only
exceptions are probably Top-Fuel or Funny Cars. - Drag Race? Same thing, the car exhibiting higher compression
normally leaves or launches harder! And pulling ahead of the other engines
because it is building more heat in the chamber! HIGHER COMPRESSION IS MORE
HEAT = HEAT IS POWER!
I tested this extensively to evaluate the correlation of Chamber Volume
primarily and flow second and how it affects power:
Car: Ford Mustang.
Weight: 2900 lbs
Engine: SVO Ford Race Block (Nascar)
427 cid Small Block 4.125 bore X 4.00 stroke
Comp. Ratio 15.8+
Induction modified Holley 1050/Sheetmetal Intake
Headers 2.0- 2.1/8- 2.1/4 3 step with 4.00 collector
Combustion Chamber Volume 40cc’s
Best Pass: Medium Ports 285cfm’s @ 28 inches,40cc chambers
9.38@ 148mph! Normally Aspirated.
HP/CYL. .265 x 285 x 8 = 604hp. Flywheel. Theoretical HP based on airflow
capability!
Actual HP based on E.T. MPH and Weight:
660 hp @ the wheels= 720-740 Flywheel.
This proves that with a compact 40cc chamber, this engine exhibited the
performance of an engine with airflow capability of approximately 348cfms
instead of the actual
285 cfm when i tested it on my flow bench!!!
.265 x 348 x 8 cyl= 737 hp.
63 CFM LESS AND ABOUT 120-140 MORE HORSEPOWER!
TOTAL IGNITION TIMING REQUIREMENTS = 30 BTDC!!!!
KEEP THAT CHAMBER SMALL! NO BIG DOME! AND HIGH COMPRESSION WITH A FLAT TOP.
FLAME FRONT/BURN IS EFFICIENT AND NO DOME = LIGHTER PISTON AND NO DOME TO
IMPEDE THE FLAME FRONT AND LOOSING POWER…
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