fuel consumption vs ignition timing

[gogger]

So after saying my 454 was only using only 5 gallons per hour I set the timing to the proper setting. Well last week while at wake the world in west virginia I noticed my fuel consumption increase dramatically. I filled up today and found I used 38 gallons in 5 hours. We were on the ohio river but I doubt the current made that much difference.

When I set the timing this spring I misread the proper setting and had it at about 15 degrees btdc. Then I advanced it even more one day when it was acting up. So most of the year it has been running set so advanced the timing mark was showing up an inch or so before the scale.

So I looked on line and found a website of auto drivers trying to get maximum mileage. Several running 454s were saying to set the timing at least 8 degrees more for better mileage.

So with it advanced the only problem I had was it seemed the starter was having a tough time getting it to turn over. But otherwise itcran great. So next time I head out I am setting it back to way advanced and see if fuel consumption drops. Any one else ever tried this?

[Wylietunes]

Is your 454 vacuum or electronic advance? What is the procedure for setting the base timing?

The reason its hard to start is because your are igniting the fuel charge way to early and the power stroke is beginning while the piston is still on the upward travel of the compression stroke. Too much base advance will hurt performance and increase consumption, and so will timing thats not advancing. Also, you need to make sure the outer ring of the balancer has not slipped on the hub. This will have the base timing off, thus the advance curve.

[Sdc77]

I will follow this thread.
I did a timing check last week on my 454. It is 6° BTDC at 750rpm. On the manual they say 5° BTDC. I read that we can go to 10° BTDC with those engines and >90 octane fuel.

On the 454 the timing is mecanicaly controlled with springs in the distributor. No vaccum or eletronic advance.

[Kma4444]

Could have a stuck mechanical advance in the distributor. Try checking the timing at idle and then revving the engine to see if the timing advances. If it does that isn't it. The other thing could be the outer ring of you balancer has slipped on the inner. The way to check it is by getting the #1 cylinder up on TDC and see if the pointer is pointing at 0 on the balancer.

If your advance isn't working it could be just stuck, you can tell this by grabbing the rotor and trying to twist it back and forth. It should not turn one way and turn against spring tension and then spring back on it's own in the other direction. If it is hard to twist, or won't twist at all, then you have found your problem. Some light oil on the mechanism should repair it if that is your problem. Just oil it and keep moving it back and forth until it is free. You could also have a broken advance spring, if this is the case, the rotor will flop back and forth or at least have a lot of play when you twist it. This can cause all of your advance to come in at idle speed. You can get replacement springs easily. They are available at any performance shop and they aren't hard to replace.

[Wylietunes]

Im with Kma, with a mechanical, or vacuum as found on some older engines, a stuck advance mechanism can lead to off idle performance issues.

[jasun]

The 454 that is in my Salt is mechanical and it was broken and not advancing or advancing way to much causing it to miss at higher RPM. I was able to turn the rotor clockwise and it would not spring back in place. (it didnt move much, but still when adjusting timing, it doesnt take much)

I put a new distributor on but my timing light got ate by the alternator.... so I set it by ear, but next time I am out, I will throw a light on it and see what it is set at.

If you are running a Mallor Distributor, if the model ends in AV the timing should be at 5 degrees BTDC and if it ends in MV the "Correct" Timing is 9 degrees.
I agree with Kevin, check and make sure it is advancing.

[Sdc77]

What means AV and MV ?

[cadunkle]

Too much advance will result in decreased performance and engine damage. Typically shattered rings and cracked ring lands on the pistons. Extensive wear on the rod bearings and to a lesser extend main bearings will follow. Material removed from the bearings and crank surfaces can find its way through the engine and cause further damage to bearing surfaces and also cam and lifters. There is also a chance of burning a hole in a piston.

Personally in my 454 Saltare I run 10* initial and somewhere just over 30* total. Fuel consumption is 6-7 GPH mostly at 22 MPH. On lighter cars with low gear ratios, higher compression and a fair amount of cam overlap I'll run up to about 16* initial. I would never run that much in a boat or a truck that hauls heavy loads as you'll invite detonation particularly when accelerating and at higher load lower RPM conditions. I'd say not more than 10* initial and not more than 36* total in at 2500-3000 RPM.

It's also worth noting that as you increase timing advance at any given RPM, assuming you are not running more timing than the heads require and fuel octane can support, you will require less fuel so can often lean out your jetting to reduce fuel consumption. Leaner mixtures detonate easier though so be careful.

It's also worth noting that more efficient head designs, such as most aftermarket aluminum heads with better chamber designs will not require as much ignition advance. This is because the chamber is more efficient and it takes less time for the flame front to reach the piston.

We vary ignition timing with RPM with a goal of ensuring the flame front reaches the top of the piston just after it reaches TDC and begins downward travel. This is to ensure maximum efficiency and power production. Sometimes the cylinder pressure created at optimal timing for power is too great for the octane fuel available and results on spontaneous ignition. The rattle or ping you hear is the result of multiple flame fronts colliding in the cylinder sending harsh shocks though the engine.

[CornRickey]

The 454 that is in my Salt is mechanical and it was broken and not advancing or advancing way to much causing it to miss at higher RPM. I was able to turn the rotor clockwise and it would not spring back in place. (it didnt move much, but still when adjusting timing, it doesnt take much)

I put a new distributor on but my timing light got ate by the alternator.... so I set it by ear, but next time I am out, I will throw a light on it and see what it is set at.

If you are running a Mallor Distributor, if the model ends in AV the timing should be at 5 degrees BTDC and if it ends in MV the "Correct" Timing is 9 degrees.
I agree with Kevin, check and make sure it is advancing.

I have two lights with both pickup leads melted from the number one header. glad to know I'm not the only one.

[jasun]

I have two lights with both pickup leads melted from the number one header. glad to know I'm not the only one.

I will get our tee shirts on order:

"I just bought a $50 piece of virtually obsolete testing equiptment (since none of my friends have one due to living in the 21st century) because I broke mine"

[jasun]

What means AV and MV ?

On the mallory distributor, the last 2 digits of the model

Mine was an "AV":
http://i919.photobucket.com/albums/ad38/jasunderland/boat%20rebuild/null_zpsd5a95c63.jpg (http://s919.photobucket.com/user/jasunderland/media/boat%20rebuild/null_zpsd5a95c63.jpg.html)