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Preventing detonation and selecting spark plugs

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AbandonedBronco
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Preventing detonation and selecting spark plugs

Post #1 by AbandonedBronco » Mon Feb 10, 2020 5:55 pm

Hi all,
I posted this over on FTE but thought I would here, as this site is a bit more performance oriented.

As the title says, I'm trying to figure out spark plugs for my engine, as well as other ideas for preventing detonation.

As some of you know, my engine got ruined. It somehow experienced detonation that hammered down all the rings, ruined the valve guides, and trashed all the bearings.

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Last month, I broke it down, disassembled it, and did another full rebuild. Fortunately, it was a lot less involved than the first go-around since it was just now a "basic rebuild". It's now bored 40 over (instead of 30) and has new pistons, rings, bearings, valve guides, etc. Had a new valve job done and had the crank polished.

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It's now back together and running.

I need to make sure detonation never occurs again.

I *think* I know what caused it, but there's no way to be sure. To better control my timing, I locked out my distributor so that I can control it with the Holley Sniper EFI unit.
However, while breaking it down, I found that the pegs that the weights ride on were about worn halfway through. I'm thinking that the weights were binding and not returning properly, which would cause advanced timing at low RPMs.
This is only speculation, but I'm really hoping that's all it is.

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So, now I'm taking extra steps to be sure detonation is a thing of the past. I have my mixture richened up a bit. Cruise is around 14.7. I'm used to leaning out a carb, and did the same initially with this build, to around 16 - 16.5 at cruise, which I thought was plenty fine. But, maybe not?
I also have a very tame timing table loaded at the moment.

After some reading and research, I have surmised that you need to run a colder plug if you increase the heat in the cylinder. That's not a lot to go on. Would that be my application? How do I figure out what I need to do?

Thanks for any ideas and insight in keeping this from happening again.
1985 Ford Bronco Eddie Bauer. 300 I6. 9.1:1 CR, roller rockers, EFI manifolds and 2.5" exhaust. DUI ignition. 3.55 final drive, 5 speed ZF5. Holley Sniper EFI w/Offenhauser C Intake. 32" BFG KO2 A/Ts.

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bubba22349
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Re: Preventing detonation and selecting spark plugs

Post #2 by bubba22349 » Mon Feb 10, 2020 7:08 pm

On a stock build I start with 1 range colder and on a mild build up with 2 ranges colder plugs and work from there. This is based on the engines use of mostly higher speed operation on the freeway / hyway etc. How much timing were you runing for base, and total timing? Good luck :thumbup: :nod:
A bad day Drag Racing is still better than a good day at work!

My Ex-Fleet of Sixes sadly these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

sdiesel
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Re: Preventing detonation and selecting spark plugs

Post #3 by sdiesel » Tue Feb 11, 2020 12:36 am

Ur pins are a VERY common problem on HEI.
And the weights will stick, even freeze in one place cause they misalign.
Ur speculation is sound. . I like the way u think, ur persistence and that's a lovely engine.
I avoid the HEI gm system but admire their engineering. I use d spark dist body with HEI MOdule.
Best of both and best to u on this
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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AbandonedBronco
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Re: Preventing detonation and selecting spark plugs

Post #4 by AbandonedBronco » Tue Feb 11, 2020 12:12 pm

bubba22349 wrote:On a stock build I start with 1 range colder and on a mild build up with 2 ranges colder plugs and work from there. This is based on the engines use of mostly higher speed operation on the freeway / hyway etc. How much timing were you runing for base, and total timing? Good luck :thumbup: :nod:


Thanks for the ideas. Yes, this isn't a dragstrip vehicle, so it sees a lot of highway and daily driving, so I would like a leaner cruise, more timing, etc. for some better gas mileage.

Since the timing is now controlled by the computer, it works just a little differently than a mechanical distributor as there's no base, mechanical, vacuum, etc. It's simply a table of RPM vs manifold pressure. But, roughly translated:

idle: 15° (would be the same as base + vacuum)
cruise: 20°
WOT: 25°

Again, I purposefully have these extremely tame until I can get things sorted out. This is to keep things safe for the moment.

sdiesel wrote:Ur pins are a VERY common problem on HEI.
And the weights will stick, even freeze in one place cause they misalign.
Ur speculation is sound. . I like the way u think, ur persistence and that's a lovely engine.
I avoid the HEI gm system but admire their engineering. I use d spark dist body with HEI MOdule.
Best of both and best to u on this


That is really good to know on the pins. I don't think the pictures illustrate how worn they really were, either. The weights moved very erratically when I tried to move them by hand, so I can't imagine how they must've moved when they were on their own while spinning.
Fortunately, this is now no longer a problem since I've removed the weights and vacuum advance and have locked it out for computer controlled timing. So, now it has many of the benefits of the HEI combined with the Holley Sniper and a Holley Coil Driver (in place of the HEI ignition module) to fire it. It's now a very nice system.

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I'm a bit gun shy with the engine as there was obviously something wrong enough to destroy it. So I definitely want to make sure I have everything accounted for to prevent it from happening again.
1985 Ford Bronco Eddie Bauer. 300 I6. 9.1:1 CR, roller rockers, EFI manifolds and 2.5" exhaust. DUI ignition. 3.55 final drive, 5 speed ZF5. Holley Sniper EFI w/Offenhauser C Intake. 32" BFG KO2 A/Ts.

sdiesel
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Location: NW Oregon,Buxton currently

Re: Preventing detonation and selecting spark plugs

Post #5 by sdiesel » Thu Feb 13, 2020 12:51 am

Any further developments? On this engine?.
I'm deeply intrigued by this, and look forward to whenu finally nail down a cause .
It's a most peculiar circumstance
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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AbandonedBronco
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Joined: Thu Feb 09, 2006 2:29 pm
Location: Boise, ID
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Re: Preventing detonation and selecting spark plugs

Post #6 by AbandonedBronco » Thu Feb 13, 2020 6:36 pm

sdiesel wrote:Any further developments? On this engine?.
I'm deeply intrigued by this, and look forward to whenu finally nail down a cause .
It's a most peculiar circumstance


I really don't think I'll ever know what happened.
And honestly, at this point, I sincerely don't want to find out, because the only way for that to happen is for it to happen again with my new engine! :rolflmao:

So, unless someone can look at the pictures and knows from experience what they're looking at, I think it'll stay speculation. I'll just keep taking it slow with the new one to be sure it's running nicely.

Any advice on how to properly do that is of course welcome. Creating a proper timing curve, spark plug temp, AFR, etc.
1985 Ford Bronco Eddie Bauer. 300 I6. 9.1:1 CR, roller rockers, EFI manifolds and 2.5" exhaust. DUI ignition. 3.55 final drive, 5 speed ZF5. Holley Sniper EFI w/Offenhauser C Intake. 32" BFG KO2 A/Ts.

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