Hey all,
I'm having a problem with the ignition in my 1971/1973 460 swapped into a 77 F-150. Duraspark 2 ignition. Vacuum advance small cap distributor upgraded to large cap with 9mm wires. Flamethrower coil. 93 octane fuel. 600cfm Holley, 74 jets. Heads freshly rebuilt, small combustion chambers. Small dish pistons. Aluminum intake.

So here's my problem, in the upper rpm ranges the engine knocks like a beast. Purrs like a kitten at low rpm driving and idle. Start to get over 2,000 rpm (I'm guessing no tach) and it start knocking and just gets much worse from there. I can't take the truck more than half throttle.
I thought it was fuel starvation and spent two days jetting and tuning with no changes. So I started messing with my timing and it started to get better. Not much but it was a change. So that lets me know it's timing, ignition, or compression.
I need help cause I'm just hurting my truck with it running this bad. I'm working on getting a 750 carb but with money tight with Christmas it's not happening. After rebuild I set timing 8*bBdc and now it's closer to 14* after playing with it. The more timing the later it would knock but would knock harder. Less timing sooner knocking but less violent.
What do you all think? Thanks for the help.

 

Are you setting timing with vac advance unhooked?

 

Yes I did the first time I timed the truck. Maybe I did something wrong.

 

What is your total mechanical advance and when is it all in? You're going to need a tach so you can tell what the curve looks like. If your springs are too light, you might be getting too much advance too early. Is your vac ported or manifold. Is the pinging under load? Why 93 octane?

 

Mechanical advance: please explain this to me. How do I check this?

Ported or manifold: once again I'm slightly lost on this too. The vacuum line for the distributor is hooked to my carburetor. Is that what you asked?

The noise be it pinging or knocking is the worst under load. It can be heard in neutral too, nowhere near as bad.

Why not 93? What should I be running? I'm pretty sure the compression is fairly high.

 

With the engine combination you described, I bet you are going to be running fairly high compression. Try throwing a bottle of octane booster into your fuel tank and see if that helps.

As suggested, you are going to have to figure out your ignition total advance and you will need a good timing light for that as well as a tachometer would be helpful. I know my low-compression, tired old 460 from a 1973 Lincoln likes a lot of timing advance.

To check mechanical advance, dis-connect the vaccum line to the distributor and use your timing light to see how far timing advances as rpm is increased.

Try the octane booster first cause if that helps, you will know the issue is high compression and the only fix for that is higher octane or maybe changing out your camshaft to bleed off some cylinder pressure.

 

Probably should figure out his compression ratio first...

 

Ok, but it would be good if you knew the actual numbers.

 

I'd rather start here, describe the "knock"?

You seem to be sure that it's detonation/spark knock but are you sure?

What does it sound like? Where is it coming from?

Does it change with load or just RPM? It sure sounds like it's RPM dependent, detonation is always load/vacuum dependent. Rod knock and piston slap are RPM dependent.

 

I'm fairly sure it's not a mechanical knock. Not the best audio if you skip to the three minute mark you can hear it and then again a minute later.

 

Hmmm. The audio on my computer is kind of crappy but it almost sounds like a piston may be hitting something when you accelerate, especially at 4:13 in the video. That or you have an extreme case of engine detonation (spark knock) caused by high compression.

How does the engine run now compared to before the tear down? Was it smoother before? How does it feel power wise? It sounds like it is running pretty rough and has a possible engine miss. Double check your firing order. I would also pull the plugs to see how they look and check the compression on each cylinder to make sure they are all even across the board.

Reduce your base timing by a few degrees (perhaps go with 8-10 degrees initial with vacuum hose disconnected at distributor) and pour a bottle of octane booster into the tank. As previously stated by someone else, it would be nice to know your actual compression ratio but in any case, if it is detonation, the octane booster will help immediately. If it is not detonation, the octane booster wont do any harm.

Based on what your engine sounds like, I would not drive it any further until you can get this issue sorted out.

 

I wish i could get to it sooner but ill be working OT until Wednsday but thursday morning ill let you all know what the booster and the timing re-checked turns out

The engine as a whole runs much better, but it did have the "knock" before the rebuild. The engine ran bad enough it was hard to get it to rev hard enough to make it act up. It would fall on its face before it would get as bad as it does now. Now that its running good and the timing isnt flying off the handle it can rev fast enough to get loud. If it makes any differance it gets worse with the more petal i give it even if the engine isnt turning that fast or running that hard. The second time at 4:13 seconds was a gear change to 3rd and a shot of wide open. It still knocked even tho it wasnt turning that hard.
When the heads were off the cylinder walls looked super clean but a little wore out. no marks, gouges, scaring that might indicate piston slap or anything of the sort.
I wish i knew more about my engine, its a 71 block with 73 heads and use to have a 70 intake, screams a peiced together engine. its factory bore but has a .02 ridge from being so old and worn out. when i checked everything last the lowest cyclinder was 1 at 145 and ever cylinder was 165-175. Cylinder 1 has blow by judging from the dirty spark plug, every plug is a very light tan from being a bit lean with the 600CFM

 

Sounds like detonation to me. Don't drive it like that or you will destroy it. It is caused by too much timing advance.
If you want to fix this yourself you need a timing light with a tachometer and read this...
FORDMUSCLE webmagazine: Timing is Everything - Distributor Curving for Maximum Power

Your 460 is not necessarily cobbled together. 1971 block casting numbers were used until 79 and the 73 casting numbered heads were used from 73 up to the 80s.

 

sounds like a rod knocking loose rod bearing to me

 

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