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It was a common practice on four cylinder cars to modify an eight cylinder dist to fit and use every other hole to eliminate cross firing. Not much of that going on now.
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I too have done this, but on a 8800 RPM Datsun 510 with crank fired ignition. The holes were put midway between the plug towers directly in the plane that the rotor traveled in horizontally. Condensation, moisture and or humidity will cause cross firing within the cap. The holes are intended to allow the humidity to disipate from the heat of the distributor body/engine or that produced by the action of the sparks themselves.
Some of the later large diameter Ford distributor caps have an actual vent designed in the top near the center terminal, covered by a little black plastic cap that was held open by design to allow venting for the purposes described above. This may have merit in some climatic conditions but I can't say it ever benefited me, perhaps if there was more humidity. Rick |
A little more info for all of you fanatics; when you drill the 1/8th inch holes, from the bottom of the cap, just above the ridge, drill upwards-toward the center button.
This will allow you to wash the engine compartment at will. Avoiding a direct spray on the cap the water will not run uphill. Or just replace the cap once a season! DV...another 2-cent tip |
r u sure??
I am going to look at the distributor cap tomorrow and see if you guys r kidding or not...have had dist (small cap)and 6AL for going on 8 years and never had this problem. I saw this on a friends car and questioned him about it and he gave me the story about letting charged particles.ions out.....trust me there is not a more humid environment than my basement...will update tomorrow!!!
ps what happens if you are caught out in the rain....the hood scoop dumps water directly down onto your dist??????? well, I opened the cap and to my surprise...I found NOTHING..no black marks, no corrosion and no pesky charged ion particles...guess they heard I was going to open the cap and ran into the oil pan....trust me when I say that my basement is not the dryest place in the world and if something was going to happen/corrode/grow it would have down there...so I defer to the Mythbusters on this one and will NOT drill holes to let the water into my distributor!!!! (I have driven in the rain before and know how much water goes through that hood opening) Also..the dist is a Mallory Unilite..maybe they are innoculated against charged ion particles and green gunt..etc????? |
I think we are going to need a template so that we get the spacing correct! :LOL:
Rick |
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Fellow Geeks,
Some specific info about this subject can be found here: see below Open the Document, Select chapter 4, when it opens, go to page 183. It will answer your questions about distributor venting. I'm not sure how to cut info from a PDF document or I would have done it and just posted it here for you guys. Steve another try: http://www1.airweb.faa.gov/Regulator...0?OpenDocument |
I too am using an 8478. I never drilled holes in my cap. I wish I had. After 2 years and 6500 miles, my original black MSD cap was beyond fried. I had more than significant corrosion all over the cap. I took it to a parts store and the veteran behind the counter said he'd never seen a cap so bad.
Anyhow, I ordered a replacement cap, which was red, not black like the original. Of note, the red replacement cap comes with a hole in the top of the cap that allows moisture to escape. Too bad my origianl cap didn't have this. And as for humidity, I live in Houston, so I'm sure this had something to do with the corrosion. Scott, SPF#1230 / 393 |
Was the Red cap an MSD item that fit your distributor (#8478) or was it another brand. The original application for the cap used on the MSD small diameter pro billet Ford distributors was an International V8 (pretty racey ??)of all things. The aluminum terminals get eaten up pretty quickly. NAPA offered a high quality cap with brass terminals that was also black, but appeared to be made out of a better material. I am curious about the 'Red" cap with a vent. Is it a new item from MSD?
Thanks Rick |
Rick - It's a MSD red cap that fits my Pro Billet distributor (#8478). Let me go out to the garage and get you a part number.
Scott, SPF#1230 |
Rick - the MSD part number is MSD-8431. Here's a link to the Summit Racing page with a picture of the cap:
http://store.summitracing.com/defaul...&part=msd-8431 Notice the red piece of plastic on top of the cap (that says "MSD"). You do not have to use this piece. As for the original black cap, I couldn't ever find a replacement part number so I ended up with the red. Scott, SPF#1230 |
Thank you for your efforts. Nice item.
Rick |
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