Does it really matter?

will going from 6* intial timing to 7* initial timing have any "real" effect on fuel milage or power?

I've got about 7* initial timing right now, I was running like 10* and was pinging....so I backed it off like 4* down to 6* initial. I went from 7.7MPG to 9.1MPG and the pinging stopped and the car felt much stronger.

I know I should be getting better gas milage....it just doesn't look like I have much room to move the timing up before I ping again to have a significant effect on gas milage....I think I should be able to hit 12MPG in the city....and it just doesn't seem like its going to happen....I know I can't run 10* intial because I was pinging at WOT and part throttle....someone said that you can be pinging but not even hear it. Does 1* really matter that much? Or could you be pinging at 10*, move it down to 9* and find that "sweet" spot for timing and get better gas milage and power. I mean....I would think you'd have to jump the timing at least 2* to see a real change.

I dunno....I'm still having tuning nightmares on my new 350...I regret running 10.7:1 compression....it's playing hell on my ability to time the car correctly. I'm running full manifold vacuum right now...thats seemed to make the engine alot happier then ported.

 

Like the average eye is that accurate. You could be off a degree or two if you are not at the right angle. That is why I check my timing in bright sunshine.

Assuming everything is correct and no leaks, you should be getting a hell of a lot more than that. I would set it back to 6 .

I am getting about 200 miles on a tank in the city and I do romp on it and about 300 cruising.

Who did your EPROM? You are running 93 octane gas, right? Pinging can occure before you can hear it. Only way to tell is to have a scanner hooked up to your car and see if it sees ping. If it sees ping, it will retard the timing till it doesn't see it anymore.

BTW, I am running 10.8:1 compression on my aluminum heads. You do have aluminum heads, right?

 

I'm running a carbed setup, non computer controlled.

Neg on the AL heads, everyone I talked to said I could run 10.7:1 with iron heads on the street with 93 octane....even the performance shop I go to said it would work.

 

How are you setting and checking your timing?
What do you mean by, "full manifold vacuum vs ported"??
I always move my timing 2* at a time, 2* can have a significant effect on performance and pinging..
And hopefully you're running at least 93 octane?..

 

You definitely don't want to run manifold vacuum to dist. With manifold vacum hooked you will have full vacuum advance at idle and it will drop when you hit the gas. I believe that is the opposite of what you really want to happen.

Does the distributor have mechanical advance also?

Disconnect the vacuum advance and set your initial timing to your seven degrees. Then run the engine up to about 3500 rpm while still checking the timing (with the vacuum advance still disconnected) to see what the total advance (initial plus centrifugal) is at. Make sure you rev the engine high enough so that timing mark stops advancing. Then plug in the vacuum line and recheck your total. I believe with your combo you probably don't want more than 38-40 degrees total.

You may have to mess around with the vacuum cannister and advance weights to get the curve just right.

 

I thought I heard that 10 was the limit for steel heads and with aluminum heads you can go till 11 and run safely on pump gas. If you don't have an ECM you still can hook up a stand-alone detonation sensor.

 

Well it's all up for debate, the guy who helped me build my engine has been doing it for 15+ years, and he said it was fine. The local performance shop in my area that builds race engines said I would be fine with the iron heads.

My initial is set to 7*, THEN I plug my vacuum advance into full manifold vacuum, which brings my advance up to around 15* intitial. This gives me much better idle quality. I can't run low initial timing and still use ported vacuum. I would have to set initial timing to 12*+ with ported, and I can't do that.

With 7* initial timing + 24* mechanical, that is 31* total mechanical. As you can see, if I was to run 12* intial, ported vacuum, I would ping like hell at WOT because 12+24=36, which is just to much for me. Running full manifold is for idle quality and to keep me from pinging. The only way for me to run ported vacuum would be to get custom weights and recurve both my vacuum and mechanical.

 

Still think you should buy the knock sensor module thing (aftermarket, not GM) to see if you are having detonation.

 

Sorry I re-read you initial post and see that you said it was pinging at cruising speed and WOT. You may just have to much compression for the fuel you are using. When you have full manifold vacuum to the cannister it will pull out vacuum under any kind of load, which is the opposite of what you would normally want. With it setup like that if you floor it at 3000 rpm the timing would only be like 24 degrees which is not enough. In your case that may be the easiest solution but some more checking and fine tuning might get you more power, mileage and less pinging. If everything else check OK and you are only at 31 total then the compression may be just too high.

This wont help with your pinging problem but in my opinion you need to fine tune a little bit more with your idle mixture and idle speed settings with the timing set to the lower setting. You shouldn't need fifteen degrees for the motor to idle well with your set-up. Most any engine will increase in rpm at idle if you advance the timing.

Try adjusting the idle speed and and mixture, alternating between the two until you get the highest vacuum reading combined with the lowest idle rpm.

Does your dist have adjustable vacuum advance or is it stock, you may need to add an adjustable vacuum advance cannister?

If the dist is not new are you sure that the advance weights are freed up? I've seen alot of GM dist that have crusty advance weights.

Also how hot is the engine running? Does it have and EGR valve?
How do the plugs look? Have you tried to richen up the jets because if it is running to lean at cruise and WOT that could help it ping alot easier. 31 seem to low if you are trying to make good power, and 10.7 is not really that high.

 

It would be 31* @ WOT, not 24*. Old school way was to run vacuum advance off of full engine manifold. The way most people run cars today they use ported vacuum. Which does not come in until 1300+RPM. They set initial timing to around 8* and they get no vacuum advance from the distributor at idle. Under load vacuum advance comes in. I cannot get the engine to idle well with 8* initial timing.

However, by setting my timing to 7* initial, THEN plugging my vacuum to full manifold. My advance will jump to 14*+. This gives me good idle quality. The engine will not idle well at normal initial timing. I was told by my local performance shop to run 16* intial timing to get idle quality.

If I run 7* initial with 24* mechanical I get 31* total @ WOT. If I run on ported vacuum, I have to run 14*, so 14*+24*=38* which is too much. I can't run ported vacuum unless I completely recurve my distributor. If I run 8* initial timing with ported and try to use the idle mixture and idle screw to bring the idle up it has almost no effect, it goes to the point where the throttle plates are open so much the idle slits are not feeding the engine, the primaries start to drip and feed the engine. The engine is not responsive to idle mixture adjustment, I can do a half a turn and get no change in vacuum, from what I've been told, idle screws should be very sensitive, mine are not.

Mechanically the engine is fine....it just does not want to run right. The entire ignition system/fuel delivery system is brand new. Theres just no reason my MPG should be so crappy. I should be able to get 10MPG w/o much effort at all.

 

why dont you drop in a bottle of octane booster? im sure the pining would go away at a higher degree of timing

 

And what? Keep doing it every day? I opt for solving the problem without the octane booster. That is unless the compression is too high for 93. Try a different brand of gas yet?

 

I use mobil 93 octane....only other option would be sunoco ultra 94. Just doesn't make sense, with my compression I should be able to get better gas milage....

 

You might of misunderstood my reference to 24 degrees at WOT. With the manifold vacuum running to the vacuum canister you will have full vacuum advance at 3000 rpm or any cruise rpm. Then if you floor it, your manifold vacuum will drop to almost zero, therefore letting off the vacuum advance until you let off the throttle.

 

Try going with the 94 and see what happens. It might be the gas in your area for Mobil that has something in it. Some Mobils have Ethanol in my area and some don't.