Mild 318 pinging

[1973dust]

Car and engine specs as follows. 1974 318 with Performer intake, 1406 carb, 204 214 278 288 .421 .444 112LS cam, factory 318 manifolds into duals. Short block and heads are 1974 stock original. Trans is a 904 with factory stall and rear has 2.76 gears. Idle timing is currently 11 initial at 750 with vacuum advance plugged. Its at 25 mechanical at 2000 rpm which is cruise rpm at 55 mph and 48 at 2000 with vacuum advance added. I know that my total max is 34 mechanical and 52 with vacuum advance added but I don't know what rpm as the tach I used to get these numbers only goes up to 2000. I also should add that I'm using ported vacuum advance.

My problem is pinging under load such as up hills when warmed up on hot days. This engine has always been prone to pinging since I have had it. Even when it was a bone stock 2 barrel with the untouched factory distributor in the 74 Valiant that it came from it would rattle if you put your foot in it.

If you took the time to read the book I wrote above, am I expecting too much to try to run this combo on 87 octane? Obviously, a 74 engine has fairly low compression, but I am running highway gears and I've had older guys tell me that the gas we use now wouldn't have been fit to kill weeds back in the day. My gut tells me that I should probably limit the max down to 28 - 30 and slow the curve as well. Basically try to pull 4 - 6 degrees out across the board while keeping the initial the same.

I'd appreciate any help and opinions you guys have even if you tell me I'm an idiot and have it all screwed up. With gas prices the way they are, I have no intentions of using even mid-grade gas so if I need to de-tune somewhat that's what I will do.

 

[TT5.9mag]

It’s likely rattling right around peak torque with a higher load. Sounds like you have the timing scienced out pretty well, but I’d recommend experimenting with slowing the curve down a few hundred rpm and delaying it a couple degrees through the middle. Keep the big timing numbers at cruise for mpg. If you have an adjustable v can, adjust it to come in a little later. Once the engine spins up a little does the pinging go away? You might also try a slightly colder thermostat, plugs, and/or a little more fuel if you can.

 

[318willrun]

unplug the vacuum advance and see if the pinging goes away.

 

[1973dust]

It’s likely rattling right around peak torque with a higher load. Sounds like you have the timing scienced out pretty well, but I’d recommend experimenting with slowing the curve down a few hundred rpm and delaying it a couple degrees through the middle. Keep the big timing numbers at cruise for mpg. If you have an adjustable v can, adjust it to come in a little later. Once the engine spins up a little does the pinging go away? You might also try a slightly colder thermostat, plugs, and/or a little more fuel if you can.

No, it will still ping even at higher revs. I don't often really put my foot in it, but when I have, I'll hear it rattle pulling 2nd gear which I know is not good for the longevity of the engine. What you recommended should help with that also.

 

[TT5.9mag]

WTH kind of tach only goes to 2000??

 

[1973dust]

unplug the vacuum advance and see if the pinging goes away.

At risk of sounding foolish, I actually thought about trying that, but if it works I wasn't exactly sure what that is telling me. Later vacuum advance or less mechanical?

 

[1973dust]

WTH kind of tach only goes to 2000??

Lol, I was wondering when someone would ask that. I was using an old Sears dwell/tach when I recorded the timing numbers last fall. I have since installed a tach in the car and I have a tune-up tach that will go to 10000. I just haven't had a chance to record the upper end of the curve yet.

 

[TT5.9mag]

If you carefully plot your timing curve vs rpm like @Mattax does in so many threads, (do a search here) you’ll be able to narrow down what it’s doing and when. That will help make informed decisions/adjustments. But you’ll need an accurate way to track engine rpm up to and above 2000.

 

[TT5.9mag]

If you unplug the vcan and the rattle goes away it means your initial and mechanical timing should be in the ballpark of acceptable and it’s the vacuum advance starting, rate, and amount that need some adjustment.

 

[1973dust]

Thanks for the responses. I will try plugging the vacuum advance and see what the results are and also plotting the entire curve. I already have from idle to 2000, every 200. I have looked at some of Mattax's charts and that's what made me think my mechanical curve might need slowed down using 87 octane and highway gears. It may be a few days before I get a chance to tinker again. I'm sure you all understand, the days of playing with the car all day Saturday have been gone for years now.

 

[RustyRatRod]

Just for kicks, get a compression tester on it and see what the cylinder pressure is.

 

[1973dust]

Just for kicks, get a compression tester on it and see what the cylinder pressure is.

That's actually something I've been wanting to do. I've always just assumed it wouldn't have much being a 74. Although I suppose it could be carboned up. I'll put that on my list of things to do.

 

[Brooks James]

Do youhave oil blowby. Or leaks? Oil in the combustion chamber will cause pinging, perfect example 360 magnim. BEER barrel intake allowed oil to seep causing pinging

 

[1973dust]

Do youhave oil blowby. Or leaks? Oil in the combustion chamber will cause pinging, perfect example 360 magnim. BEER barrel intake allowed oil to seep causing pinging[/QUOTE
That's a good point. It does use a little oil although not enough that I've ever seen it smoking. The lower end and heads only have about 43000 miles on them from new in 74. Of course that could mean short trips for much of it's life. I'll have to see what the compression test tells me. The engine really runs well other than the occasional pinging but I've never thought it had the punch of 318's that I've had in the past. It may be more tired than the low mileage would indicate.

 

[1973dust]

Just noticed that I somehow messed up my last post. I added my response to Brooks James quote.

 

[Mattax]

Distributor still ahve its tag? It should match the number in the book.
If so, then you can get a ballpark whether yours is in spec and the shape of the curve above 2000 rpm.
Plot your engine mechanical advance vs. the advance max and min from the book.

The factory initial was basically TDC (at 700 rpm? ) and now its at 11* BTDC at maybe 700 rpm?
If so, then that's probably the crux of the problem.
Will it idle at 5 or 6* ? If so that may be a quick solution, or partial solution.
With less initial, then if it wants a bit more timing at idle - if the manifold vacuum at idle is reasonably stable - try using manifold vacuum source for the distributor's vacuum advance.
With the 4 bbl and the cam, probably should reshape the timing curve but those two steps may get you driving for now. Plot the timing first to make sure the assumptions here are true. Also this

If you unplug the vcan and the rattle goes away it means your initial and mechanical timing should be in the ballpark of acceptable and it’s the vacuum advance starting, rate, and amount that need some adjustment.

is a good check too.
It should not ping at part throttle with the vacuum advance disconnected.
It may ping near full throttle, and that would indicated too much timing at the rpm.




Notice the factory gave 4* leeway in the initial. This was to allow for different fuel, altitude and owner preferences. My folks had their '69 318 advanced a little and ran Premium until the gas crisis. 21 mpg on the highway. Pretty good at the time for a v-8 in a midsize car with an auto transmission and bias ply tires.

 

[Bewy]

Heat & load are the enemies of detonation. Unfortunately the 'fixes' will require some experimentation. And maybe some $$$$, depending on how far you want to go....
The 2.76 axle is going to load the engine more than 3.XX gears. Heat is the biggest factor; as you found, worse on hot days.
So get the engine running as cool as possible. A smaller w/pump pulley might help. Blocking the exh xovers in the intake should reduce heat soak in the intake manifold.
Cold air induction helps, & gives more power as a bonus.
Then it gets to ign timing. There are quite a few things to try here. You can try reducing the total amount of VA by limiting plunger movement; stronger spring in the dist centri curve mechanism; reduce initial timing 2-4* etc. Final fix might be a combination of the above.

 

[pauly]

Have you tried better gas than 87 octane? The “gas” they sell us today is pale in comparison to what we used to be able to buy.

 

[1973dust]

Distributor still ahve its tag? It should match the number in the book.
If so, then you can get a ballpark whether yours is in spec and the shape of the curve above 2000 rpm.
Plot your engine mechanical advance vs. the advance max and min from the book.
View attachment 1715927400

The factory initial was basically TDC (at 700 rpm? ) and now its at 11* BTDC at maybe 700 rpm?
If so, then that's probably the crux of the problem.
Will it idle at 5 or 6* ? If so that may be a quick solution, or partial solution.
With less initial, then if it wants a bit more timing at idle - if the manifold vacuum at idle is reasonably stable - try using manifold vacuum source for the distributor's vacuum advance.
With the 4 bbl and the cam, probably should reshape the timing curve but those two steps may get you driving for now. Plot the timing first to make sure the assumptions here are true. Also this

is a good check too.
It should not ping at part throttle with the vacuum advance disconnected.
It may ping near full throttle, and that would indicated too much timing at the rpm.




Notice the factory gave 4* leeway in the initial. This was to allow for different fuel, altitude and owner preferences. My folks had their '69 318 advanced a little and ran Premium until the gas crisis. 21 mpg on the highway. Pretty good at the time for a v-8 in a midsize car with an auto transmission and bias ply tires.

Yes, that is the tag that is on the distributor. I know that I already limited the total mechanical by welding and re-machining
the slots in the advance plate and I know that I got rid of the heavy with long loop spring. I think I replaced it with a 2nd factory light spring which may have been a bad idea. Am I correct that distributor degrees on the chart have to be doubled to get degrees read at the balancer? If so I am confused as I am getting 25* at the balancer at 2000 rpm which with 11* initial would only be 14* from the distributor advance which is half of what the specs say. Or I'm wrong about doubling and it
is right where it should be. I have had the initial backed off to 6-8* and it did seem to eliminate most pinging but it seems to handle the in gear drop better with more initial. I'm at a steady 19" at idle in park and a steady 15" at idle in gear at the 11* setting. I'll try driving it without the vacuum advance connected and, if that eliminates the pinging as it should,
I'll try backing the initial off and connecting to manifold vacuum and see where I'm at. If that works, maybe I can avoid having to mess with the advance slots again.

 

[toolmanmike]

Yes, that is the tag that is on the distributor. I know that I already limited the total mechanical by welding and re-machining
the slots in the advance plate and I know that I got rid of the heavy with long loop spring. I think I replaced it with a 2nd factory light spring which may have been a bad idea. Am I correct that distributor degrees on the chart have to be doubled to get degrees read at the balancer? If so I am confused as I am getting 25* at the balancer at 2000 rpm which with 11* initial would only be 14* from the distributor advance which is half of what the specs say. Or I'm wrong about doubling and it
is right where it should be. I have had the initial backed off to 6-8* and it did seem to eliminate most pinging but it seems to handle the in gear drop better with more initial. I'm at a steady 19" at idle in park and a steady 15" at idle in gear at the 11* setting. I'll try driving it without the vacuum advance connected and, if that eliminates the pinging as it should,
I'll try backing the initial off and connecting to manifold vacuum and see where I'm at. If that works, maybe I can avoid having to mess with the advance slots again.

Sounds like the similar thing I did with mine and similar results. I just disconnected the vacuum advance and it works good without it.

 

[1973dust]

Have you tried better gas than 87 octane? The “gas” they sell us today is pale in comparison to what we used to be able to buy.

Yes, I have ran 89 and possibly 91 in the past as a trial. It did seem to help which is why I think I've just got it set up a little too aggressive for 87, especially if I run into the occasional tank of "bad gas". Especially at the gas prices now, I'll do what I have to to run on 87 as I'm not looking for every last hp. I use my car more as a nice day daily driver than a "hot rod" which is probably good since it really isn't much of a hot rod. Probably should have just left the factory cam alone the way I normally drive it.

 

[1973dust]

Sounds like the similar thing I did with mine and similar results. I just disconnected the vacuum advance and it works good without it.

So you don't run vacuum advance at all? I've always been told that no vacuum advance will kill your mileage but I've never tried it myself. Of course, I know not everyone is concerned about fuel mileage when it's just their "toy" car. I didn't worry much about it when gas was in the 2's.

 

[RustyRatRod]

So you don't run vacuum advance at all? I've always been told that no vacuum advance will kill your mileage but I've never tried it myself. Of course, I know not everyone is concerned about fuel mileage when it's just their "toy" car. I didn't worry much about it when gas was in the 2's.

It puts a dent in mileage for sure. They all react a little different though. Some are affected more than others.

 

[toolmanmike]

So you don't run vacuum advance at all? I've always been told that no vacuum advance will kill your mileage but I've never tried it myself. Of course, I know not everyone is concerned about fuel mileage when it's just their "toy" car. I didn't worry much about it when gas was in the 2's.

No vacuum advance at all. I get almost 20 on the highway if I drive it nice.

 

[Mattax]

Yes, that is the tag that is on the distributor.

Great!

I know that I already limited the total mechanical by welding and re-machining
the slots in the advance plate and I know that I got rid of the heavy with long loop spring. I think I replaced it with a 2nd factory light spring which may have been a bad idea.

Well so you've learned the same way I learned. Not so great. The heavy spring was the critical one to keep. A long looped spring with even higher spring rate would be a better match for the 4 bbl and cam. We can plot that out next post.

Am I correct that distributor degrees on the chart have to be doubled to get degrees read at the balancer?

Yes. Also the RPM is doubled as the cam and distibutor run at half the crank rpm.

I have had the initial backed off to 6-8* and it did seem to eliminate most pinging but it seems to handle the in gear drop better with more initial. I'm at a steady 19" at idle in park and a steady 15" at idle in gear at the 11* setting. I'll try driving it without the vacuum advance connected and, if that eliminates the pinging as it should,

That's a strong vacuum for idle and a hot cam. Thats a good thing even though the drop is more than I'd like to see. What rpm in P and D?

I'll try backing the initial off and connecting to manifold vacuum and see where I'm at. If that works, maybe I can avoid having to mess with the advance slots again.

Well we can plot out where its at (the advance) and see if it makes sense. 15" in D can add anywhere from 19 to 25 degrees at idle. That's way more than needed - it may work but wont be the most effecient in terms of power and economy.