What is the CFM rating for the stock Holley carburetor, model 4150, number 3367 on my 66 327-300hp roadster? Also, what is the rated output of the coil on the same engine?
Thank you!
Thank you!
-
-
Re: Holley Carburetor
You can check the Holley web site, but I recall them being rated at 585 CFM. I have the 3810 on my 350 horse and it's also 585 cfm. -
Re: Holley Carburetor
What do you mean by "rated output" for the coil?
DukeComment
-
Re: Holley Carburetor
By rated output, I mean the amount of voltage the coil is capable of generating to the plug.Comment
-
Ignition system performance ratings
Advertised voltage ratings that the aftermarket uses to hype their coils are meaningless. Ignore them!
The basic performance specification for an ignition system is per spark ignition energy. Ever heard of that? Probably not because the aftermarket doesn't want you to know that their systems aren't much better than OEM, and some may not even be as good.
From some SAE papers I've extracted the following data. The Delco single point is rated at 41 millijoules per spark, but the versions with the 0.3 ohm resistor are probably more. The old TI is 74 millijoules and the HEI is 76.
All these are inductive systems that provide relatively long duration sparks, on the order of 1200 microseconds, which is what is needed to ignite low density, lean, or exhaust gas diluted mixtures. A steet engine operates in this mode 99.9 percent of the time - idle and part throttle. CD ignition systems have short duration sparks, on the order of 200 microseconds, which is fine for a racing engine running at WOT, but not so great for a street engine. That's why MSDs have multiple sparks. Ignition reliability at less than WOT is not reliable with a single spark CD system no matter how much energy is has, which is why OEMs don't use them. Low density, lean, and exhaust gas diluted mixtures need long duration sparks to minimize misfires.
The voltage rating you see hyped for coils is the open circuit voltage - what one might measure if there was no spark plug to complete the circuit. The typical required voltage at the plug to initiate a spark is a few thousand volts, and if your plugs require more than 10K volts to initiate a spark, there's something wrong with them. Once a spark starts, the voltage drops way down. The OEM systems provide at least 25KV open circuit voltage, which is more than adequate for reliable spark initiation. You don't need a 50,000 volt super duper whazzo blaster coil because the plugs will fire long before that voltage level is reached.
DukeComment
-
Re: Holley Carburetor
Got me curious! I went to the Holley website and found it's a 585 CFM. However, your model is shown as a 4160. The only difference between two is the 4150 has a secondary metering block, while a 4160 has a secondary metering plate.Comment
-
Re: Ignition system performance ratings
Duke I appreciate your postings on this board. You mentioned multiple spark MSD's. On a street driven Corvette rarely going to redline, would a person enhance their performance with a aftermarket system like this added to a HEI or a conventional points system?Comment
-
Re: Ignition system performance ratings
Not really. The HEI is a great system - simple, reliable, with readily available, inexpensive repair parts.
Low density, exhaust gas diluted mixtures, such as what an engine see at idle and low speed/load need a long duration spark to achieve reliable ignition and minimal misfires. That's why OEMs use inductive systems rather than CD. CD systems are good for racing engines that see mostly WOT because their rich, dense mixtures have good ignitibililty, but more voltage is required to bridge the gap. In addition to short duration sparks, CD ignitions have short rise times - the time it takes for voltage to rise to a level that will cause a spark to bridge the plug gap. During this rise time, energy can bleed away due to shunt resistance paths such as spark plug deposit build up or leaky spark plug wires. I don't have a spec for the MSD rise time, but it was 35 microseconds for the old Delco CD system from the late sixties. Inductive systems typically have a rise times of about 150 microseconds. It's interesting to note that the Delco CD system, which used the same magnetic pulse distributor as the TI was only avaialable for a few years. I think Olds offered it beginning in '67, and the last year might have been '69. I'm not sure why it was so short lived, but it could be that it was just not suitable for street engines.
The reason why MSDs have multiple sparks at low revs is to ensure that ignition occurs because of the greater tendency for a short duration sparks to not light the fire at idle and low load. The only trouble is that the second spark is retarded 10 to 20 degrees.
Overall, a good electronic inductive ignition is the way to go for a street high performance engine. The HEI is excellent as is and the single point can always be converted to a Pertronix. The single point can be made to work satisfactorily, also, by blueprinting the dist. and using the high breaker arm tension points on SHP engines. It will require more maintenance such as point adjustments, point replacement, and plug changes, but on a collector car that sees low annual mileage this is not going to be a lot of work, and one nice thing about points is that you can keep a spare set in the glove box to get you home if they fail, and they usually give you some advance warning that there's a problem. Electronic igntions rarely give you any warning. They just quit and leave you stranded
If I see one more MSD box on the cowl of a Chevelle at a car show, I'll probably puke.
DukeComment
-
Re: Ignition system performance ratings
Given the advertising behind MSD, the chances are your gonna "spew like beer" at the next car show! Most guys can't wait to get that red box on their car!
I run an HEI on my FORD vintage road race Shelby GT-350. Yes, a GM distributor in a FORD for all the reasons outlined above. The HEI I use is from Performance Distributors. It is good to 9,000 RPM's (my rev limiter is set at 7,000) and can be repaired with a trip to Autozone should it fail at the track. In 3 years of racing there has NEVER been a failure. This distributor "replaced" a MSD dual box Winston Cup setup. To many wires (bunch), red boxes (two) and coils (two). Now one red 12 volt wire and the distributor works. Much too simple!
MSD certainly has its place. On race cars MSD works well however those little "red boxes" are also the reason a lot of Vintage Road Race Cars miss their grid call when "they" puke like Duke! I'll take the reliability of an HEI over a little extra spark of a MSD since Vintage Racing pays such big bucks, $0.00 for first throught last AND you get to pay an entry fee for the priveledge.
Mike Strinich
Nashville, Tn.
#11202Comment
-
Re: Ignition system performance ratings
Very interesting!!! Being as how the second order unbalanced vertical shaking force (13G peak/233 Hz at 7000) in my Cosworth Vega beats the hell out of the HEI and it has failed three times - probably because of the 4000 miles of race track hot laps I have on the car - I carry a spare HEI and 9/16" combination wrench in the spare tire drop center, so if it every goes TU on me again I can swap it out in about one minute.
Since typical American V-8s with cruciform crankshafts don't have any unbalanced shaking forces or rocking couples below fourth order, the vibration environment is much less severe and the HEI will probably perform virtually forever.
DukeComment
Comment