Thread:

Pertronix in non marine distributor

Originally Posted by slim pickens

My boat has a 455 olds, still running points. As far as I can tell, the distributor is a stock (car not marine) delco single point distributor. I havent run the boat this way (boat is new to me). I was considering converting to the (new) Pertronix Ignitor III, which has built in rev control and has multiple spark thru redline. Sounds like an upgrade over points anyway. Since the pertronix has no way to set off a spark in the distributor body/cap, is it still necessary for me to find a (marine) distributor body to convert over? Or will it be ok to run the automotive since the pertronix is all electronic/magnetic pickup and really cant spark?
My budget is more along the lines of pertronix conversion rather than full blown MSD setup.

You forget all the sparks that jump from the rotor to the cap comtacts 8x every revolution.

If you run a closed/covered engine, you need to run a marine one, which installs little brass flame-stop screens in the back or bottom of the distrib.
People say the cap is gasketed too, but none of mine ever were.

Also, no way in hell do you get any "multiple spark discharge all the way to redline", unless redline is somewhere in the 3,000 RPM range.

Even MSD will tell you that, above arround 3,300RPM, there is insuficient TIME, with crankshaft rotational speeds, to set off more than one spark anywhere close to TDC.
Info to such is on MSD's website,
Also, you only get Multiple Sparking from MSD if you run their Capacitor Discharge boxes (up to arround 3,300RPM), not just from the distributor (I run a Ready-2-Run dizzy, without a box, becasue I don't need/have any use for a box, but could add one if I wanted to, plug right in).


Good luck in what you decide to do, I have a budget too, often a very small one.

Originally Posted by slim pickens

Yeah I called around today and my local junkyards are all the hoity-toity "late model" type places so they scoffed at an HEI olds distributor. I will have to check ebay. Summit has them for $180 but for that money I might as well buy an MSD or mallory (electronic) marine.

I know most people run mechanical advance, but is there any use for a vacuum advance for jet boats? Is cruising at 3000 rpm "light load" enough to use a well-tuned vacuum advance in additon to mechanical? My boat is pretty heavy and deep-V hull, so I imagine the 455 will be working pretty hard just to keep it up on plane.

No, there isn't, and if you adjust the advance to best effect, you will have full advance in by 3,000 RPM.

I run a chevy, but I don't even crack open the rear 1/2 of the 4-barrel untill I'm over 4,000RPM.

Boat weight has absolutely no bearing on pump load, as the pump has absolutely no idea what it is attached to, 500 pound wafer, 2,000 pound slug, or a dock piling. Pump load and power requirement is, for all practical purposes, identical. (very small difference is created by fwd motion of the hull/intake in the water, but this is minor)

Originally Posted by konajet74

Hey Smoke, ck this out! Pertronix has one w/ multiple sparks throughout
the rpm's....
http://www.pertronix.com/prod/ig/strike/default.aspx

You should do the math on that.

I think MSD's claims were always against 20* of crankshaft rotation. That's from 10* BTDC to 10*ATDC.

Figure out how many millisecconds it takes to pass thru that 20* "zone" at 1,000 RPM, then 3,000 RPM, then 5,000RPM, and 6, or 7,000RPM.

Then figure out how many millisecconds spark duration is, PER SPARK.

I don't care what the marketing hype says.
Remember Pappa John's pizza and Pizza Hut actually going to court over whose ingredients were "freshest" in PJ's advertizing?
Marketing hype, means very little against reality.

You'll find out one spark lasts far longer than 20* of rotation at the upper RPM ranges, which makes all "later" sparks than the first, fairly pointless as they are watching the piston leave, already.
According to the link you posted, and my quick read of it, it seems to proclaim DUAL sparks (not "multiple"), a minor distinction, but, 2 vs 10 has some bearing.
Again, once one spark lasts longer than the minimum time for ignition in the cylinder, #2 is waste, as are #'s 3 thru #10.
#10 happens with the piston about 1/2 way to the bottom of the cylinder at top revs.

Originally Posted by SmokinLowriderSS

You should do the math on that.

I think MSD's claims were always against 20* of crankshaft rotation. That's from 10* BTDC to 10*ATDC.

Figure out how many millisecconds it takes to pass thru that 20* "zone" at 1,000 RPM, then 3,000 RPM, then 5,000RPM, and 6, or 7,000RPM.

Then figure out how many millisecconds spark duration is, PER SPARK.

I don't care what the marketing hype says.
Remember Pappa John's pizza and Pizza Hut actually going to court over whose ingredients were "freshest" in PJ's advertizing?
Marketing hype, means very little against reality.

You'll find out one spark lasts far longer than 20* of rotation at the upper RPM ranges, which makes all "later" sparks than the first, fairly pointless as they are watching the piston leave, already.
According to the link you posted, and my quick read of it, it seems to proclaim DUAL sparks (not "multiple"), a minor distinction, but, 2 vs 10 has some bearing.
Again, once one spark lasts longer than the minimum time for ignition in the cylinder, #2 is waste, as are #'s 3 thru #10.
#10 happens with the piston about 1/2 way to the bottom of the cylinder at top revs.

Spark duration runs about 1.5 mS (millisecconds).

1,000 RPM is 360,000 crankshaft degrees per minuite, 6,000 crankshaft degrees per seccond.
20* pass in 0.0033333 secconds, at 1,000RPM 3.3 mS.
20* pass in 0.0016666 secconds, at 2,000RPM 1.6 mS
20* pass in 0.0008333 secconds, at 4,000RPM 0.8 mS
20* pass in 0.0005550 secconds, at 6,000RPM 0.55 mS
At 4,000 RPM, a SINGLE 1.5 mS spark, burns for 40 degrees of crank rotation after it is triggered, from (for the sake of discussion), from 10* BTDC to 30* ATDC, now, somehow INSTANTLY TRIGGER (by magic) the next spark, which burns from 30# ATDC to 70* ATDC, the piston verty nearly 1/2 way down the cylinder.
puts the seccond spart at least 10 to 20 crank degrees later.

The math puts the crank spinning 60 degrees @ 6-grand, just durring the FIRST spark's life-span, then, a 20* delay, and another 60* spark life.