Plug gaps
 

Those of you with MSD ignitions; what plug gaps do you run? I am currently using .044 and considering opening it up a little. Anyone with experience and improved results??
I think many of the current OEM Ford specs are near .055-.060??

Rick,
I have moved the gaps around a bit on high and street stock compression ratio engines without much change. This was not done on a dyno so could not define gain or loss beyond plug readings and listening to engine. In the end I stuck with MSD recommendations figuring they did tests to prove reliability if nothing else.
On a 12.4 CR engine I did test wider gaps trying to get longest fire signal to point I expected to pick up a misfire. I could hear or feel no gain so went back to their recommendations thinking about reliability of unit at higher voltages. Nothing beyond a hunch without way to measure true results.

I am using a Mallory HyFire system, they recommened .044 gap and a non-resistor plug, went with the Champion racing plugs, MSD copper coil plug wires

I've tried .040, .045, and .050 with my MSD and Autolites with no discernable difference. I split the difference at .045.

Tim

I am running about a .038 gap on my Accel 416 and it seems to work quite well. When I run Autolite's I go to .042. Those were Georges recommendations several years ago. No misfires and seems to run pretty smooth given the way it is configured.


Clois

MSD uses a multiple or 3 to 5 fire sequence's per cylinder at RPM's below about 2500 RPM. Given the speed of or the time allowed to supply a firing pulse it becomes impossible to continue above about 2500 RPM. The electron is damn quick but 3 to 5 pulses per stroke just becomes peaks in output but is always a continuous burn pattern in each cylinder.
The time or lack of becomes mind boggling..... 2500 RPM with 8 cylinders means it fires cyl. #1 2500 times in 60 seconds or it has 0.024 parts of a second to complete that one cycle. At say 3 pulses in that 0.024's of a second becomes 0.008 seconds per pulse width for the MSD to charge the coil and then discharge the coil to saturate and do it again. Then remember the engine is a 4 stroke ...wow! 7000 RPM / 60 = 0.00857's of a second.
To really screw with your mind think about what your connecting rod is doing. It is a length of metal with about 600 grams (a piston) of weight on the end. If the stroke is say 3.480 inch's long then we start with it at top of cyl. or TDC on firing cycle.
At 7000 RPM it moves from top of the cyl. or power stroke = from TDC is pushed down to bottom of cylinder or BTDC (first 3.480 inches of travel) and then is stopped at the bottom and then pushed back up (3.480 inches more of travel) to complete the ex. cycle then stooped at top ,now on the intake cycle it is pushed from the top back to bottom (so another 3.480 inches of travel) to get to bottom again so here comes the last ( 3.480 inches of travel) to get back to the top of cylinder on the compression stroke or cycle to complete just one complete firing cycle IE.. 1 RPM x 7000. Remember this the next time you miss a shift at 7 grand. The poor piston has traveled 3.480 inches 4 times for what we call 1 RPM 3.480 x 4 = 13.920 inches in 1 second. What is the mile per hour of piston or connecting rod speed? The real trick is getting pushed at this MPH and getting pushed and stopped up and down 4 times. It does kinda stop or is called dwell. 13.920 inches in a second, times 60 seconds = 835.2 inches times 60 sec per min. times 60 min per hour or 50112 x 60 = 3006720.0 inches per hour. So 3006720.0 inches / 12 in. per foot = 250560.0 feet per hour. or 250560.0 / 5280 feet per mile is 4176 miles of total piston travel in an hour at 7 grand. But from a start to stop and again and so on to get those 4176 miles of travel!!!! Buy GOOD parts or you will get to look at them in many small pieces. did I do that math right? I think so, but took a couple phone calls in between this mess I made, And I did not do drugs in college so no excuse at all. jeff C
Forgot to do spell check so??

vettestr
And that diatribe answers Ricks question how?....'cuz it confused the heck out me since I'm not an engineer.

We were talking plug gap here%/ ie: What plug gap?


Make it easy on us simple folk here;) ....44, .45,.46,.38....What gap is good ?

Sorry for the retort but this type of thing happens way to much when the one asking the question only wants a simple answer/answers to their question.

We all are not blessed with engineering/mechanical knowledge.:(

Not meant in an offending manner but just answer the question.

Gary:
Thanks, glad you said that......Actually I was hoping to get someone to give me the molecular breakdown of the Atomic Table and the alloy analysis of the negative electrode on an Autolite #23 Extended reach plug. COME ON...........just KISS. Just wondered if anyone had any experience that was positive regarding incresed plug gaps.:rolleyes:

Rick,
Fwiw I was running a .45 gap on my plugs on my sb. Tried a smaller gap at first then up to .50. My car ran best with a .45. MSD ignition, dizzy, coil, plugwires. Mild build, mild cam.

GR,
No offense intended or taken. Without straying from the question or discussing the influences of a change follow MSD specs for your application. I think 0.044 will be very close.
I can and do ramble on at times. On post # 2 of this thread the simple answer I gave was no dramatic changes found straying from MSD stock spec. was noted. Ricks' question was answered but his desire to modify also means he is considering cause ans affect.
The name and sales point of MSD = Multiple Spark Discharge is all about the technology to deal with the issues I was rambling on about. Other brands discharge 1 time and at a much lower voltage. Some folks like to discuss or view things from another perspective. If I was boring you: my bad. I have my EE and plastic pocket protector so have to ramble once in a while, just hit fast forward. Jeff c

Thanks for your understanding;)