Just found this forum. Lookin good so far! I think a bad tank of gas has exacerbated my problem but I'm gettin' a HORRENDOUS ping. We built the engine with an HP cam and I'm just a little concerned about advancing the timing too far. Stock timing is (I believe) 10 deg btdc, I'm running 4 deg btdc but STILL get some ping under load in mid RPMs. So my question :confused: is, is there any big problem if I advance clear over into the AFTER tdc area to try and get away from the ping? Sure wish I could find my cam card :mad TIA.
Rons67 :D :D

 

Welcome aboard

We will need a bit of info.
Big Block or Small block

Is this a fresh engine?
If so, what is the compression ratio you're running?

You may be running way too lean

Take a look at the plugs if they are ash white you're too lean..

Try to richen up the charge

Ping will cause damage so we need to stop it..

Let us know some more details


Tony



[Modified by pittsaj, 10:10 AM 6/2/2002]

 

Also, do you have vacuum advance and if so is it working properly? Vacuum advance serves to RETARD the timing under low vacuum conditions such as acceleration.

 

This is a 327 .060 over, with maybe 8K miles on it. Just so I've got my terminology right, if I'm at 10 deg Btdc and then go to 4 deg Btdc I've ADVANCED the timing, right? If this is so then the vacuum advance seems to be fine (at least when I goose the accelerator with the timing light on it). Plugs, last time I checked maybe 500 miles ago, were a nice dark gray with little way of deposits on them. Oh yea, compression is probably in the 11-1 range. Waddya think?

 

If you go from 10 deg BTDC to 4, you have retarded the timing. Are you setting the initial timing with the vacuum advance disconnected and plugged? When you "goose" it, the timing ought to retard (go to a lower number) momentarily, and then increase as vacuum builds. Very difficult to see in a static condition since vacuum comes back so quickly. If you set the advance to say 4, with the advance disconnected, when you reconnect you should see maybe 16-18 total advance at idle. At road speed, you may be getting a total advance in the 50 deg range. However, when you open the throttle, the advance will drop to a max of around 36 deg. This is supposed to allow you to run more advance, but prevent detonation at heavy throttle settings. 11:1 is pretty tough on pump gas. :eek: Most folks settle for 9.5-10:1 unless they plan to run that $5/gal racing stuff. :eek: :eek:

 

Ok, so it sounds like I understand this a little backwards. Yes I DO disconnect and plug the vacuum advance can on the dist. But I "thought" that the ping being the "pre-detonation" meant the cylinder was firing too soon?

I agree that the pump gas can be a little crappy for this engine and I HAVE used 104+ with pretty good results, I'm going to get some right now. I just figured if the engine was pre-detonating due to timing then I should be trying to get it to fire later in the stroke. Bad logic???? :confused:

 

Ron, you are correct that less advance should reduce the ping. The downside to doing so is that it is likely reducing your power. If the pinging only occurs under light throttle, too much vacuum advance is a likey suspect. You might try leaving the vacuum advance disconnected to see if that helps. I normally wouldn't recommend that but it may be preferable to having to run less than optimum timing to get rid of the pinging. They also make vacuum canisters that give less advance and there are adjustable units too.

 

You are not backwards. Retarding the timing can help a pinging situation. Retarding too much can also cause overheating. Too lean a mixture can also cause pinging. The point I was making about the vacuum advance is that the advance needs to cut out and retard the timing when you accelerate. Your total timing at any RPM and manifold pressure is what's important. You need to check the whole curve and se how much total timing you have and how much vacuum advance you have. This can be done with a degree tape on the balancer or with a dial back timing light.

 

A "Degree tape". Is that probably specific to my harmonic balancer? Different diameter or circumference balancers would need a different scale, correct? I"m not familiar with a "dial back" timing light. Thanks!

 

A dial back timing light has a **** on the back of it and a scale of degrees.
I just help my mustang buddie(1967) tweak the timing on his 289 after he just trashed the smog pump stuff. I'm not use to fords ,but this car had only 1 mark on the cover and 1 on the balancer.
the book said to set it to the mark =zero degree (california car?wtf?) with a dial back we could see how many degrees the mechanical advance did. (not as much as a chevy) So we lined up the marks with the dial set to 6 ,which gave us 6deg initial. much better now. (we'll bump it more later)
A "mighty vac" hand vacumn pump can be helpful in checking out at how many inches of vacumn the vac starts to advance at. (along with a dial back lite or a degree tape)
As an example Lars recurved the distrutor on my '64 but the vac advance he supplied would not give me any advance at idle due to lac of vacumn. (I believe it needed 9 inched to start advancing) I install my original vac advance which would start next to 0 and be full avanced a 8 inches great idle but would ping lots under load because it wouldn't drop off. Final solution was digging thru my extra parts and finding one that starts at 7 inches just enough to help at idle and drop out quick enough when you throttle it
I'm running iron eagle 72 cc"fast burn" heads on it so my compression is less than yours.
rod

 

Weeeellllll today, after dumping some octane boost in mid week, I was able to get out and do some tweaking. Checked the dwell, it was at maybe 20%, so I goosed it also. Knocking is MUCH improved. Checked the timing and it's still at 4deg BTDC, right where I put it a few months ago. Still a little ping under HEAVY foot in lower RPMs, like 1700-2000, tho' I'll have to look closer next time. A friend tells me maybe try 4 degree experimental settings....so go to 8deg BTDC, then maybe 12deg and see what happens. Any down side to this? :confused:

 

So none of the "further advancements" helped seemingly at all, :crazy: . So I"m trying to go the other way from 4deg BTDC. Unfortunately my dist is hanging up right there at about 4 and I can't twist it any further. Hmmm, it's getting dark, I"m hanging it up for now. 4 is probably the place for it.

 

Dwell should be 30º. If your pinging is under heavy throttle at those rpms, you're probably getting too much centrifugal too soon. Check the springs to make sure that one isn't missing or broken. You can replace them with some stock springs or get a recurve kit that has an assortment of springs to fine tune it. I doubt that 4º initial is optimum for drivability or for max power. What is preventing the distributor from rotating beyond 4º advance? If the vacuum canister is hitting something, the distributor is either installed wrong or your ignition wires are not on the correct posts. Once you fix that problem (if that's a problem), set your timing at total instead of initial. Measure your damper's circumference, divide that figure by 10, and make a mark on the balancer that distance from the TDC mark (on the driver's side if the TDC mark is pointing up). That new mark will be at 36º BTDC. With the vacuum advance disconnected and plugged, and your timing light connected, rev the engine until the timing marks no longer move. Align the new mark with the 0 on your timing tab and you will be set at 36º total (minus vacuum advance). Note where initial is now and you can use that figure to set base timing in the future.

 

OK, I took this approach and the idle timing ends up being, sure enuf, 12deg BTDC. The circumference was 25.25" and I marked the balancer at 2.5+ inches from the TDC mark. Moved that point up to zero on the scale while revving the engine and then at idle we were back at 12 deg.

So, I guess I'll just leave it there. Still some ping under a good heavy load, but maybe that's just the gas. Low end accelerator was much better than before anyway. Springs looked fine. btw the 4deg point was as close to TDC as I could go with the distributor twist. Anything approaching a "usual number" is easy to do.

Thanks for all the help. Maybe I'll take it in sometime. It's running pretty good otherwise.

rpg