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Discussion Starter · #1 ·
Just got a call from the machine shop that put together my 331...

Not good. The rod bearings show signs of detonation, as do the plugs and the heads. Main bearings look good. Lifters seem good. It looks rich on the piston tops. Apparently the oil pan and intake bolts were very loose and the crank bolt was hand tight! I'm headed down there tomorrow to have a look myself and figure out what the heck happened.

Back story:

Had the shop put together a 420hp 331 with PW heads, scat crank, 10:1 pistons all stuffed into a roller 5.0L block with a decent cam, ford performance roller lifters. Had the original distributor rebuilt and recurved with a pertronix I and pertronix coil. Holley Sniper EFI. 20 degrees initial timing and 34 all in. Motor was broken in on the dyno and everything looked ok. Got it home, AFR's were set 12.8 WOT and 13.6 idle and cruise 13.8 which produced the best vacuum and smoothness. The motor was never zinged. rev limiter set at 6300rpm. I later swapped to a Torker II intake thinking the single plane might help with smoothness and the EFI. Torqued it all down with loctite and kept going.

From day one the motor had what I thought to be too much vibration. I changed pulleys around, spent piles of time chasing my tail making sure the plug wires, plugs and all things ignition were top notch.Had the flywheel and pressure plate rebalanced. I went through the whole driveline as well clearing up whatever i could. I just thought it never ran right and buzzed the driveline and car.

Before power tour the car felt down on power... it had what sounded like a miss and it had signs of detonation on the #2 plug. Changed plugs. backed the timing to 18 (car really didn't like that) and nudged the fuel curve a bit on the fatter side and headed out. Came home and was just annoyed with it. Yanked the motor out and dropped it at the machine shop. Sent the oil off for analysis and waited.

Oil analysis showed no fuel, no coolant, no carbon and no traces of iron or aluminum. The only comment back was a high molybdenum and silicone content and that it was most likely that the motor had recently been rebuilt.

Where the heck is the detonation coming from? Its not a high compression motor. Its got alum. heads and the timing was set with what it liked on the dyno and close to what others were running. The car sees a diet of 94 octane from chevron only and the AFR's are set on the rich side.

Is the stock dizzy, pertronix and pertronix coil with Taylor 8mm plug wires just not enough jam for it? What am I missing?

I know the plan now is to rebalance this thing as it's obvious it wasn't right to begin with and just keeps trying to shake itself apart...
 

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That does seem like a lot of motor for what is basically a stock ignition system. Since you already have the Holley EFI, maybe time to upgrade to Hyperspark? One thing I wish aftermarket EFI could do is add a knock sensor into the equation.
 

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Maybe the rich spray and the advanced timing spelled trouble especially when the engine got hot and once the plugs were damaged it created a domino effect, but it sounds like the bottom end wasn't screwed together well and the vibration may have spelled even more trouble.
 

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I don't know squat about those efi add ons, but 20* is way too much to my dinosaur likes...maybe that's not a problem? I have always run 10*-15*.


Hopefully you can find the problem - it gets expensive to rebuild motors every year.....
 

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Rowdy, my 331 vibrates much more than I think it should and It's been balanced 3 times. I don't know how long it will last but it goes really good to 6400 rpm so far! When she blows I'll build a dart blocked 347 using a 3.25 stroke Callies Magnum crank and rods. Ditching the commie stuff next time!

I'm using the stock 1965 C code dizzy for a C4 with a Pertronix 1 with no issues.
 
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What is your quench distance (the distance from the top of the piston to the closest part of the cylinder head where the air/fuel mixture gets "squished".

This is usually the sum of the distance from the block's deck to the face of the piston plus the head gasket compressed thickness. If the heads have an "open chamber" add the distance from the face of the head to the closest point in the chamber to your figure.

Ideal quench distance is between 0.038" - 0.043". Avoid anything over 0.060". If you need lower compression use a dished piston vs. putting a flat top down farther in the hole (de-stroked piston).

Another factor that adds to the risk of detonation is uncontrolled heat (high CHT) and one of the causes is the failure to drill steam holes to match block style with head style. The lack of a bleed for steam to escape leads to a pocket of superheated steam building up at the top of the block which means no coolant surrounding the area to remove the heat, just the metal. Other causes are ignition timing set too late, and too much exhaust valve preload.
 

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Discussion Starter · #7 ·
I've been considering the hyper spark for a while now. I watched the Hot rod magazine tests and man alive did they ever pick up power and street ability. Plus it seemed to help fuel consumption adding that extra timing in cruise..I think they said 30%! I'm trying to figure out if I can run it sans their coil and CD box to keep the period look of my engine bay..

I'll be popping in tomorrow to have a look and see what all has gone sideways and devise a plan for it's future. I'll check what the quench is. He's been building hot small block fords for decades...
 

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Rowdy, 20 initial probably runs real smooth at idle, but at WOT, that's probably too much for most 10:1 engines. Are you talking about mechanical + vacuum, or just a straight mechanical dizzy? What sort of cam are you running?
 

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Discussion Starter · #9 ·
Its 20 initial with 35 all in by 2800rpm. I backed it to 18 and 33 to try with no change, then tried 14 at idle and it was garbage.. It is an a code c4 vac advance dizzy that was rebuilt and curved by Dan.

The cam specs are 217/225 .050 .515/.538 115LS angle and I've got 1.6 roller rockers.

Combustion chamber is 60cc the intake port volume is 170cc. 2.02 Intake valves and 1.60 exhaust. I need to measure and get the quench.. I don't remember what pistons went into it.

Headed over to the shop now.
 

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Discussion Starter · #10 ·
Looks like it was drawing oil through the valley and into the intake and exhaust runners. Piston tops all carbon'd up. Bores look good, crank looks good. just a quick polish/hone and we'll be good to go. That explains the blow by though... Also going to do the balance again. See if we can eliminate this vibration or at least make it better.

Quench was .044 ! So pretty close to optimal.

Going to replace the lifters (had a noisy one) and change cams. Also going back to a dual plane. The Torker II I put on just killed low end. Port match the manifolds and do a little porting elsewhere before we get it back together.
 

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I assume your taking your flywheel and pressure plate to include in the balancing? I have not idea how the balancing works with bob weights and such but I'd give them everything that goes round and round this time!
 

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Discussion Starter · #12 ·
I assume your taking your flywheel and pressure plate to include in the balancing? I have not idea how the balancing works with bob weights and such but I'd give them everything that goes round and round this time!
The only thing he didn't get handed last time was the crank pulley.. and this time I've got a CVF serp kit and he'll have that front pulley for certain!
 

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I've been considering the hyper spark for a while now. I watched the Hot rod magazine tests and man alive did they ever pick up power and street ability. Plus it seemed to help fuel consumption adding that extra timing in cruise..I think they said 30%! I'm trying to figure out if I can run it sans their coil and CD box to keep the period look of my engine bay..

I'll be popping in tomorrow to have a look and see what all has gone sideways and devise a plan for it's future. I'll check what the quench is. He's been building hot small block fords for decades...
You do not need the box or coil. Any standard 12v coil will work. I just looked into this extensively, and then ran out of money.:frown2:
 

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Discussion Starter · #14 ·
You do not need the box or coil. Any standard 12v coil will work. I just looked into this extensively, and then ran out of money.:frown2:
Thats sort of what I had figured too after lots of browsing, but it does;t come out and say it anywhere, until you dig deep into the installation instructions for the distributor itself.
 
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