WoofWagon

As we are all aware, most gas these days has at least ten percent ethanol blended in.

My question is, what ignition timing changes are required for our big blocks to run properly? My manual shows 12 degrees of initial. Should timing be advanced or retarded?

ah64pilot

Woof, the only way to know what you should run is to know your engine specs. I don't remember what you've got...there are a ton of variables so knowing what you have done would help.

Unless you're running high compression (above 10.5:1) with iron heads I would tune it according to the manual if it's a mostly stock build.

WoofWagon

I'm running a mild cam with a .040 over 455 with headers, 750cfm edelbrock and a Toronado intake. CR is about 9.5:1, so I'm now thinking it isn't much of an issue. I am getting some pinging pulling hills, and put some octane boost with a fill up last night. I think the timing is set to about 10 degrees intial, but I may need to fatten up the mixture as the stock carb settings are always on the lean side.

oldcutlass

What octane level are you running? I would be running the highest available. It should not ping at that setting, so you may have some distributor issues. I have found what most people think are carb issues are actually ignition system problems.

ah64pilot

x2

WoofWagon

I'm running 92 octane and the ignition has new points, wires and plugs.

ah64pilot

That has me thinking it's an ignition problem. Are you using a vacuum advance? What cam do you have?

WoofWagon

Thanks in advance for the input. I posted the cam specs in the big block forum, but the duration is 280 intake by 290 exhaust, it's not a wild cam. I do know that the vacuum advance is working properly, my mechanic put in new components in the distributor. It only pings when the engine is warm and pulling a hill.

oldcutlass

Is your dwell at 30? What is your timing at 3000-3500 rpm with vacuum advance disconnected? What is it at the same rpm with it connected?

WoofWagon

I honestly don't know. I only notice the pinging on hills when the engine is around 190-200 degrees. I put in some NOS octane booster in the car Saturday evening and went out for a 'spirited' drive with the engine temp running aroung 180, and there was no pinging.

I should mention that this car was neglected mechanically by the previous owner who admitted that he had no mechanical skills. I'm wondering that now the timing is back where it should be and with a carb that isn't loading up like mad, it's burning off all the crap that's accumulated?

I'll have to get out my Timing light/dwell meter and have a look, but the car has plenty of power and no bog.

455man

Sometimes the vacuum advance increase the timing too much. That would get you the pinging at cruising speed on a hill. You could always set the air fuel mixture with a vacuum gauge. If you dont have to move it much it was set fine already.

cutlassefi

I'm guessing you mean at idle? Just an fyi if so that will do absolutely nothing for his problem.
If you're talking about attempting to adjust it while driving, I'd like to hear how that could be accomplished with a carbureted application.

And also for the record engine vacuum decreases with the loading (up a hill etc.) of the engine, therefore decreasing the vacuum advance amount.
His total/advance is too high and/or internal issues.

455man

Yes set the air/fuel at an idle. And I was suggesting to go ahead and check the air/fuel mixture because that seemed to be a concern for him. If it's good then that eliminates that option and he can concentrate on his timing. I agree it's probably timing.

So are you saying that vacuum goes down due to the loading alone or the increase in throttle to keep the constant speed going uphill?

oldcutlass

Vacuum is at its highest when there is minimum load on the engine at any given speed.

Adjusting the carb is not going to make his pinging go away because the a/f mixture screws only effect the cleanliness of the idle.

He has either a dwell/timing issue or a fault with the distributor operation.

cutlassefi

Dwell won't make it ping. It's timing, a lean air/fuel, and/or even a cooling/flow issue.

oldcutlass

If the timing was set with improper dwell, it will cause misfires due to the lack of, or over voltage in the the time it takes to charge and discharge the coil.

cutlassefi

But that's not pinging, that's misfiring. If anything that would probably ping less as it will have incomplete combustion and/or load the cylinder with unburned/excessive fuel.

I'll stick with my original diagnosis, sorry but I'll lay money it's not dwell. Plus he didn't say it was misfiring, only pinging when hot and climbing up hill.
And another FYI, it won't over voltage anything with incorrect dwelL. The coil will only put out what the plugs demand. If the plug gap requires 20,000v to fire but the coil is capable of 30,000v it will only use the 20,000.

MDchanic

It could be dwell, in that if the dwell changes (say, from wearing of the rubbing bock), the timing will change as well, but the actual culprit in that case will be the timing, however, the timing will "fix" itself when the dwell is readjusted.

So, the timing could be causing the problem, but only because the dwell changed.

Did that make sense?

- Eric

ah64pilot

So the moral of the story here kids is that we don't need to be rude to each other, uh hem, and we all agree that you have a TIMING issue.

cutlassefi

Correct.

Eric - when the rubbing block on the points wears down, that will retard the timing. Try it for yourself, reduce the gap/increase dwell, you'll see the timing retard. The points open later because the rubbing block is further away from the shaft.

It could also be a lean air/fuel under load. Remember E10 will run leaner than straight gas, apples to apples.
And being as how it sat, I wouldn't overlook the cooling system either.

455man

So it wont hurt to check the air fuel mixture. Also Ethanol runs a higher octane so I'd think E10 is not the problem.

I'd agree that the temp should stay closer to 180 and maybe the cooling system needs a look.

MDchanic

I know that the timing retards when the rubbing block wears, Mark, I've had it happen to me (after a cross-country drive at 05:00, in Monteray, CA).
I was just using that as a general example of dwell angle changing and affecting timing. I didn't mean to imply that it was the OP's problem. I used that because it's a common occurrence, which we'll all run into sooner or later.

The OP has a completely different question, for which I have no good answer, except "trial and error."

- Eric

oldcutlass

What I was trying to say is he could be mistaking a misfire as pinging. I agree its probably a timing issue!

cutlassefi

Uhh, you're not doing to well here. As mentioned air/fuel ratio at idle will have no bearing on his problem, none.
Ethanol by itself is higher octane, but the E10 may still be his problem. Once blended with gas, the E10 is still 87 octane, and 87 octane is 87 octane, no matter how you get there. The octane rating designates it's resistance to detonation, the higher the rating the more detonation resistance.
But ethanol burns with less heat than gasoline, about a third less, that's why you need more if it to equal the energy released by gasoline. Therefore his air/fuel under load, not at idle, may well be leaner than optimum. That will cause pinging/detonation as well.
You may want to check your info first before posting, but I hope this helps.

455man

It's 92 octane but I see what you are saying. I'd think a cooler burning fuel would have less pinging though. So are you thinking the cooler burning fuel is pulling more dense air and running it lean but I'd think the hotter engine temps would negate the denser air. This all seems pretty minimal cruising at 2500 RPMs. I couldnt see the air fuel mixture being that far off from idle to driving up a hill base on 10% ethanol.
I wouldnt assume that the stock carb settings on an aftermarket carb are set perfect. I alway check my air fuel mixture on a new carb.

oldcutlass

Your missing the point on the A/F mixture at idle vs cruise. They are 2 seperate circuits, idle is set with the mixture screws and cruise is set by the jetting.

455man

I must be missing it. With his mild build you think his jets could be too lean in that edelbrock? Do most carbs run too lean without rejetting?

cutlassefi

I give up.
Hopefully the original poster will know what we recommend he should check next.

380 Racer

92 octane?

455man

Post #6 above.

MDchanic

I just wanted to point out some details derived from the physics of gasahol, and how they might point toward an answer to Woof's original question.

I am neither a chemist nor an engineer, so my numbers here may not be perfectly accurate, but I am confident that they are at least close, and therefore illustrative.

Gasoline has a density of about 6.6 pounds per gallon, an effective energy density of about 115,000 BTU per gallon, and a viscosity of about 0.5 mPas.

Ethanol has a density of about 6.1 pounds per gallon, an effective energy density of about 79,000 BTU per gallon, and a viscosity of 1.1 mPas.

So, what's my point?

First, gasoline and ethanol weigh about the same (a gallon of either one is over 6 pounds), BUT a gallon or pound of each holds a significantly different amount of energy:
Ethanol has only about 75% of the energy that gasoline has, in spite of occupying the same volume and weighing the same.

Second, Ethanol is over twice as viscous as gasoline (0.5 versus 1.1 mPas). This means that less of it will pass through small spaces, such as... hmmmm... carburetor jets, in a given period of time.

So, if we figure that when we mix ethanol and gasoline, their viscosities intermix in a linear manner (which they probably don't, exactly, due to their different polarity characteristics, but they should be close to linear anyway), that means that a mixture of 90% gasoline and 10% ethanol will be 5% thicker than gasoline alone.
Since there is (as near as I can determine from the equations) a linear inverse relationship between viscosity and flow through a given smooth tube, a 5% thicker liquid will flow through a tube (ahem... carburetor jet) 5% slower.
This means that to get the same flow rate through your jets with 10% ethanol that you get with 100% gasoline, you would need to increase all of your jet areas by 5%, which pretty much means going up a number.

BUT remember, in addition to reducing the flow of fuel into your engine, ethanol also contains less energy in the first place, so in addition to getting less gas per unit of air, your engine is getting less energy from the gas that DOES get in (115,000 BTU per gallon of gasoline versus 79,000 BTU per gallon of ethanol, which is about 70%).

SO, a mix of 90% gasoline and 10% ethanol should have about 111,400 BTU per gallon, which is about 3% less than pure gasoline.
This means that the 5% less fuel that is getting into your engine has 3% less energy: you have space in the combustion chamber occupied by essentially inert matter (3%), which is essentially just taking up space. What it is also doing is reducing the ratio of fuel to air a second time (the first time was when we reduced flow through the jets by 5%), resulting in a mixture that is significantly lean (I'm not sure whether you can add up the 5 and 3 percent and get 8% or not, but it's close to that).

And what do we know happens when your mixture is too lean?
Right: Hotter combustion and increased detonation.

So, logically (for whatever logic is worth in this benighted age), if you plan to run 10% ethanol (and the only way not to do so seems to be to buy gas at the airport), you should richen up your mixture a little bit, OR retard your timing to take into account a greater likelihood of detonation in your lean mixture.

I would be interested in knowing what those of you who have experimented with this in practice (such as by measuring air / fuel ratios while driving) have to say about it.

- Eric

380 Racer

I thought you guys were talking Ethanol?

WoofWagon

MDchanic,

Thanks for corroborating what I feel might be the situation. My mechanic Ted has over 40 years of experience and is semi-retired, tuning and fixing cars part time in his home shop. I know that Ted set the timing per the factory specs outlined in the service manual that I gave him.

He did state however that carb might need some further fine tuning. I'm looking over the Edelbrock carburetor manual for the 1411 and am thinking that I should richen it one step for power and cruise and see what happens. Thankfully, it's pretty easy to change metering rods and jets on these AFB clones. I'd rather run slightly rich with this engine than running it lean with the timing reduced.

In reading through the manual, the idle timing is showing 10 degrees BTDC, I'll have another look at it with my timing light later this week. I put some octane boost in and it seems to help. When I pulled this particular hill it started to ping and I backed out of the throttle. Once the hill was passed, the pinging went away.

Thanks to all for your input, this is an issue that I feel needs to be chatted about for our cars' sake and continued enjoyment of our hobby.

455man

380 I was referring to the 10% blend.

Good post MDchanic. I didnt know ethanol had a higher viscosity. Makes sense.

380 Racer

Here in Iowa the 10% blend is 89 octane. Regular unleaded is 87 octane.