PRO SYSTEMS
6674 Grand Haven Rd.
Spring Lake, MI 49456
Sales/Tech (727)490-5717
Fax
(727)490-3305
email: info@pro-system.com
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UNDER THE SCOOP Myth Busting Fuel Delivery
Attached are some more responses from e
mails that cover the bulk of the questions we receive. I hope these help
and feel free to Email or call if you have any further questions.
Q: You built me
a trick pair of 4150 Holleys for my nostalgia super stocker last year.
Towards the end of the season the engine was hard to start and it seemed like
the floats were too high but after checking them out they were fine. I
guess this is too open ended of a question to troubleshoot over email but I
wanted to use you as a resource. I started to look into the fuel pressure
and regulator for answers. Some times the fuel pressure does change from
too low to too high (every two races). I am using a BG400 pump and a
Holley 4-port regulator. Should you have a return line out of the
regulator back to the gas tank? Should I swap out pumps or regulators?
A: The carburetors are probably fine. Your point of focus should
obviously be the varying fuel pressure. This will
cause the complaint. Inspect your fuel pump, pump relay, or regulator for
proper operation. ROCK SOLID fuel pressure is vital. A bypass system will
give you less pressure drop under a load, but a dead head system can still be
consistent. Although it never hurts to add a restricted return bleed line on a
dead head system.
Most times its a low side regulator issue. But varying high side pressure or
even a bad relay
will often cause inconsistent fuel pressures (oftentimes paired relay systems
will act up if one regulator cuts in and out) . In a return system be sure
the return line is larger than the forward feed line. Be sure the bypass
line goes back to the top of the cell opposite the inlet side and low fuel
levels
in your cell are a bad thing.
Q: If aerosol
or tube type boosters are so good, why aren't they used in NHRA Pro Stock.
A: You answered your own question. Against my judgement we were
hired to experiment with them in NHRA Pro Stock. I told the customer what
we would run into and to be ready as here's what to expect and I was correct.
With permission I am free to release these findings as this information is now
well known in the affected community. Here is a summary of our testing
results: During dry testing the resistance ratios looked similar to current
designs and acceptable to test with, however in a wet/live environment at low
air speeds and during shift recovery fuel atomization was poor as fuel would
just drip off the tube. The air would then striate and detonation was a
big problem (under statement). With good nozzle air velocity the tube does
a good job atomizing (it wasn't amazing...but it worked so let's test it).
We found on the track when your rpms are low like during launch or shift
recovery, the tube delivered fuel is thick and raw and just rolls off the end
like a low flowing garden hose. During launch and shift recovery the
engine displayed air to fuel ratios numbers from the 02's like the car was very
lean, but the fuel turbine numbers and shear numbers were showing that the
consumed quantities were dead on. That information confirms the poor
atomization, distribution, misfire and detonation suspicions I had concerning
the concept. The tube only atomizes toward the inboard side of its body so
the far side air is clean. During low air velocity the fuel would enter
the runner as a long thin waterfall and tended not to mix for the duration.
If a particular cylinder had a pulse issue it may steal a section of that clean
air and would ALWAYS be lean no matter what you jet that cylinder. As that
cylinder would steal the air from that particular section of the intake that was
clean.
The tube concept would work fine on a single carb on alky with a lot of air
speed and a fuel that requires very little atomization no matter the air
velocity.
But honestly if it was a great idea and head and shoulders above all others..
we'd all be using it. It was just one of the many gimmicks that was
thought to
have some merit but in our testing... did not.
The advantage that a booster has over the tube (face it, the aerosol name is a
marketing tool) is that it develops an ever expanding fuel cone
that impacts more and more air as it travels down the venturi. This not
only increases adiabatic expansion but ensures more even cylinder to cylinder air to fuel
ratios. Also modern booster technology offers
on average better low speed signal which offers the ability to install a larger
carburetor which reduces air friction. This increases cylinder fill and
horsepower.
Q: I bought a dominator from
you a few years back. Can you explain why its important to calibrate a
carburetor for a specific application. I would like
to be able to more clearly explain the specific modifications and benefits to my
friends.
A: Like port sizes in a cylinder head, metering port sizes are just as
critical to have the proper velocity for shift recovery and the proper emulsion
package for
a smooth fuel curve. If for example the carburetor is calibrated for a
horsepower level that is 75-100 hp or more below what you are using it on.
The emulsion package will max out early and the carb will go rich up high or
worse yet, if its a high emulsion package (which offers better power) it'll go
lean up high. That's typically why high emulsion packages are not offered
on "out of the box" designs.
Factory designs are not calibrated or tweaked after assembly to fill the voids
in the fuel curve from the emulsion package. Since all ports don't offer
equal
flow at all flow rates, the emulsions are tweaked to fill the gaps and improve
the fuel curve in those ranges. You may for example be lean 2-3 main jets
from 5500 rpm to 5800 rpm and then too rich between 6400 and 6800 rpm. So
you see why its critical not only to performance, but predictable consistency to
have a unit flowed and the fuel ports sized for its
intended fuel and air flow range.
Thanks for reading.
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