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SM465 eternal rattle (spark knock) on highway

So I referenced this guide tonight (http://outintheshop.com/faq/hei.htm) and I followed the recommendation of installing the vacuum lockout in the 7th position which should block out 6-8 degrees of timing advance. I then reset the base timing to 8 degrees where it was. I also set the vacuum can 9 turns out (later turned this back to 6, only seems to effect the very initial throttle tip in). The behavior of all these changes was very interesting. Seem as though I gained some very significant midrange & top end power with LESS timing. The part throttle knock seems to be entirely vanished however now i have some new spark knock in the high rpm 3/4 to full throttle range. This doesn't make any sense to me because timing should have only been subtracted there, why did spark knock get added in? Once again, changing to the 89/110 mix tank silences everything.

I am completely on the fence about whether or not i should block more advance out, add some back in, or try changing to manifold vacuum. I know for certain i want more than 8 degrees base timing because coming on and off the throttle is not smooth without 10+ degrees advance.
 
Fortunately, or unfortunately for this thread, I got out of "mechanical" timing before I really started digging into possibilities with those components.

Theoretically, using manifold vacuum, you SHOULD be able to pull a significant amount of timing at idle with the advance canister, and drop your base timing to near nothing. With all the different weights and springs available, it's probably possible to also run the desired amount of advance on the mechanical side. I don't know if you have all the components to get there or not, and/or the inclination to test it all out, but without emissions being a consideration, lots (~20*) of idle timing is a good thing, as long as it's done with vacuum so the starter isn't fighting mechanical advance.

Strategy for controlling knock is to generally stop it before it starts, and normally that is done with timing and/or fueling changes just prior to the "place" in engine operation that it occurs. IE, if it starts knocking at 2800RPM under full throttle, you'd want more fuel and/or less timing slightly before that point. Under full throttle you really shouldn't be having fuel problems though, but that is easily corrected/tested with the Quadrajet, since you can change the secondary rods and/or hangers very easily. Richening those up would add fuel only under heavy throttle. While there are a ton of adjustments on the Q-jet, if you start messing with things like air valve spring tension you introduce other potential problems. The good thing about secondary rods/hangers is that they are easily changed back to original configuration.
 
dyeager535 said:
Theoretically, using manifold vacuum, you SHOULD be able to pull a significant amount of timing at idle with the advance canister, and drop your base timing to near nothing.
Click to expand...

That's what I was saying. Most of the decisions in the 80s were done for emissions purposes and not for making things run well. High vacuum advance at idle can fix the "tip in" bog while also being very friendly to the starter.

Still, you have to know the actual real timing (to beat a dead horse) to know where to set things.

Before messing with rods and hangers visit a shop with a dyno or borrow a sensor to see where your AFRs are. If way off, adjustment will help well beyond just eliminating pinging.
 
Definitely true. If TDC and 0* on the balancer don't line up, there is another problem, and that needs verified. Throwing a bunch of effort at this while assuming timing is correct would suck. It's probably ok, but if a problem is persistent, need to eliminate variables. The balancers will "slip" the outer ring, and wrong timing markers are also a possibility.
 
Appreciate all the information fellas, I'm gonna try and spend tomorrow and wednesday night documenting where everything is at. Condition of spark plugs, compression test, check TDC, etc. I tried seafoam yesterday it barely even smoked from it and didnt appear to affect anything. I'm definitely at the point where I want to give manifold vacuum a try just need to get all the ducks in a row first. I also have a spring kit for the distributor to recurve the mechanical advance so I might go down that road too. The instructions say to set the spring tension without vacuum advance hooked up, but if im targetting a base timing around 0 degrees without vacuum advance wont it idle/run like garbage (assuming i dont turn it back up to compensate for no vacuum advance?). Or is the idea that I am doing this just long enough to tune WOT?

I have to say while I am still rather dissatisfied with how its running the added power sure with the vacuum lockout sure makes me dislike the 305 a little less. Actually kind of surprised how much power its making now. But I don't want to leave it this way because heavy throttle knocks and its a turd anything less than 1500 rpm before the advance comes in. If the low rpm response wasn't so bad, I could probably get away with just adding some fuel at WOT to eliminate the knock.
 
ITS FIXED!!!!

I did a bunch of reading today and I was about 90% confident changing it to manifold vacuum was gonna be the magic bullet. Turned out it was. I changed it over tonight and set it to idle at 17 degrees and it runs and drives perfect. It seems to want a little more timing actually so tomorrow I might adjust the lockout and step up to a slightly looser spring to get me to full advance quicker. But I am 100% sure that it works in the current configuration. I'm so happy I finally get to enjoy this truck now and start concentrating on the little details! I'll post updates on the fine tuning yet, but i wholeheartedly appreciate the advice from everyone in this thread. If any of you are ever in the metro detroit area hit me up for a beer :thumb:
 
Last night I tried changing to the heaviest springs in the recurve kit, and it improved the performance but knocked just a bit a WOT. So now I have one stock spring and one "heavy" spring (which is lighter than the stock spring). I also changed the lockout to the 6th setting for a little more vacuum advance since which it seemed to like, and dialed the adjustable can back all the way so the advance comes in quickly. Seems to run good! Beat the snot out of it for about 20 miles last night and it seems happy. The power is still a little meh, but I guess its still a 305 afterall. :pimp:

The last thing I need to do is figure out cold starts and potentially some other PCV/emission equipment. Previously the ported vacuum was running through a vacuum switch on the thermostat. I have the manifold vacuum connected directly to the distributor right now and it bogs until it gets to temperature. Might try running that manifold vacuum through the same switched line. Also need to verify everything with the PCV/emissions can is working so im causing any long term problems there.
 
Wonder if the EFE valve (at the passenger exhaust manifold outlet) has some play in that cold engine performance? Does your EFE by any chance have a vacuum line to it? I can't recall ever seeing one on a truck, but apparently they exist.

Obviously it won't run awesome right away, but it doesn't seem to take much time for these engines to run decent, it's mainly just the first few seconds of starting that needs some choke IME.
 
JoeliusZ28 said:
I do have a functioning valve in the exhaust manifold, but not sure if I disconnected that when i changed the vacuum source.
Click to expand...

If it's vacuum operated, it may need vacuum to pull open. I suppose it could be run the other way (vacuum keeps it closed) but you'd have to figure out the hose spaghetti to know for sure.
 
Vacuum operated EFE valves default to "open" if they lose vacuum,by an internal spring in the diaphram..they are closed by vacuum via a thermal vacuum switch,usually in the thermostat housing,that only allows vacuum to close the valve after a cold start--then denies it after a certain temperature is reached,and the spring opens it..
 
Ok so its very possible that isn't functioning right now. I was thinking that temperature switch might also block out vacuum advance in the distributor, but maybe not?
 
JoeliusZ28 said:
Ok so its very possible that isn't functioning right now. I was thinking that temperature switch might also block out vacuum advance in the distributor, but maybe not?
Click to expand...

GM did all sorts of "crazy" stuff with the vacuum before electronics took over...spark delay, torque converter lockup delay, etc.

if the valve defaults to open without vacuum, probably no issue unless it's frozen up, but not likely if the problem goes away once the engine warms up.
 
Yeah,GM had a field day with ported vacuum switches back in the 70's and 80's ,they were used to control a lot of various things as Dyeagear noted..
My '69 GTO used a PVS to switch the vacuum advance from ported to manifold after it hit a certain temperature,supposedly it increased the idle speed a bit and the advanced timing would cool the cylinders down some...some vehicles seem rather un-affected when someone "deleted" the "emissions crap",others were very fussy and ran like crap without everything working as the factory intended...

Its easy enough to see if the EFE valve is stuck,you should be able to see it move when you hook the hose to manifold vacuum,or operate it manually by hand...its not too common to see one froze in the closed position,the older heat risers with only a spring often did though..
A vacuum gauge might help to detect one that is stuck closed too,you will notice the vacuum stays high for a longer period after a quick rev of the throttle before it drops back to normal,if there is a restriction in the exhaust--they use that method to help diagnose clogged catalitic converters,mufflers with baffles causing a blockage and crushed exhaust pipes too..
 
Well guys I've got a problem again. I had this thing absolutely dialed at one point until it randomly seemed like it wanted more timing despite the gun reading the same base timing. So i turned it up. Well this process repeated two more times and i got suspicious. Turns out the lockout cam is self adjusting itself down to the lowest setting which is something i was concerned with from the start since there wasnt any kind of set screw included. What do i do with this? Im about 5 days from making a road trip with the truck, and i dont know anyone familiar with these lockout kits :(
 
Its the crane cams setup. But I think i found a better solution. This one limits the top of the advance instead of the bottom like the one ive been using, which gives me more adjustability. Ordered one! Should be here 2 days before I take it on a 3.5 hour trip to the sand dunes!

MSD part number 84281
 
Update I got the MSD lockout in last night. I used the stock advance can this time. Seems to have done the trick once and for all. Truck is running the best it ever has and thats only guessing at the timing this time since i broke my timing gun. Problem solved just in time for the 200 mile trip to the dunes tomorrow!
 
I have set the timing "by ear" on many of my gas powered trucks and cars,often you can advance it a bit past stock settings and gain some mpg and power without inducing spark knock--timing marks may not always be accurate if the damper has slipped,or someone used the wrong tab on the timing cover,etc..

I used to advance the spark until I'd just hear a slight ping under hard acceleration in high gear,and then see if it would bind up while cranking after shutting it off and letting it sit a few minutes (heat soak)--if it did I would retard it a little until it cranked normally..

A 400 small block I had ran much stronger with the timing advanced about 4 degrees more than stock settings,but it would balk at cranking after it sat and got heat soaked..retarding it made it crank easier but then it felt lazy..
I ended up rigging a toggle switch to the coil so I could crank it with no spark and get it spinning fast,then flip the switch on and let it fire up..a trick many race cars use..
 
Yep @diesel4me I've been timing this engine "by ear" the entire time so far too, just using the timing gun to see where I'm at and to make changes in precise increments. I dont know where it is right now, but i think I have it just a couple degrees shy of knocking on the highway with the part throttle advanced kicked in. I think I *might* be able to get away with going a spring size looser on the mechanical advance to get it all in sooner for more low end torque, but I'll save that experiment for another day when I've got time and a working timing gun.
 
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