More timing = less gas mileage?

[Darkwriter77]

I know the answer to this might seem obvious to some, but does advancing the timing negatively affect gas mileage? Or is it the fact that I run a higher octane to avoid ping with advanced timing that lowers the mileage?

In my '84, last year at this time of year, when I had it set at 10* BTDC (stock) and was running cheap (87 octane) gas in it and getting close to 26 MPG ... one of the few reasons why I've kept the crappy low-powered stock CFI setup on there. However, this year (same MTBE blend, not the ethanol crap in the winter months), I'm only getting between 23 and 24 MPG. The only thing changed in my setup is that I've increased the timing to 12* BTDC and I'm running premium (91 octane). I bumped the timing not so much for performance (because "CFI" and "performance" just don't belong in the same sentence) but just as a standard tweak I do to my 5.0's, and I was hoping that having it run better might actually improve my mileage, if anything. Same tires, same exhaust, same driving habits, pretty much the same everything as before.

FWIW, I've got fresh plugs, wires, cap/rotor, filters, and fluids in the whole thing right now, I've fixed several vacuum leaks, and changed out/cleaned the EGR valve since last year ... stuff that I would've expected to IMPROVE mileage, if anything at all. I'm honestly starting to wonder if maybe I was better off with the crappy worn-out ignition parts, old fluids, clogged-up filter, and base-level timing...

Any thoughts? Should I just roll it back to 10* and go back to cheap gas?

EDIT: Oh yeah, forgot to mention ... already pulled codes, found nothing.

 

[mustangsquared]

did you check the plug gap?? I never trust the "preset" ones.

 

[GTOreturns]

It shouldn't effect your mileage like that! If anything it will give it some added torque off the line and will make it run a little cooler.

Put the timing back to 10, and look at the results.

 

[Darkwriter77]

did you check the plug gap?? I never trust the "preset" ones.

Yep. I always check plug gap before I poke 'em in. I've worked in a few parts stores, so I know how much those things get knocked around before they're sold. I've even had a couple with the electrode mashed flat against the center post when I took 'em out of the box. Plus, they usually give them a one-gap-fits-all setting from the factory, as the common plugs for a 302 will fit more than one application. I can't recall what the number was I set 'em to, exactly, but it was whatever was listed in my Chilton manual's specs (no legible stock underhood emissions sticker to reference on my car) ... I wanna say it was close to or just under 0.045", and like 6 out of 8 of the Motorcraft plugs were at like 0.035" out of the box, so most took a bit of tweaking before I stuck 'em in there.

 

[HotFox]

My first thought is too much octane. Why did you switch from 87 to 91? Remember that higher octane is harder to light. Two degrees of timing is not any reason to jump four octane on fuel?

Scott

 

[GTOreturns]

My first thought is too much octane. Why did you switch from 87 to 91? Remember that higher octane is harder to light. Two degrees of timing is not any reason to jump four octane on fuel?

Scott

+1

 

[Darkwriter77]

Well, at least on my '89, I can't advance the timing to 12 or 14* and run anything less than '91 without getting ping, especially when the temps outside go over 100*F. If I run 89 octane in my '84 right now, I will get a little bit of pinging, but with 91, no ping.

I'll have to go back and double-check, I might have advanced it to 14* but I can't remember for sure; the '89 I know for a fact is at 12* because it's REALLY prone to ping at 14* in the summer months. (FWIW, the '89 is an AOD-to-T5 conversion car and still has the AOD computer in place. I think the timing it adds might be a bit more than on a manual computer, but I'm not sure ... but if so, that might explain why it doesn't like much added timing.) If the '84 is at 14*, I'll dial it back to 12* and run 89 octane and then see if that helps my mileage. But if it's at 12* ... I guess I'll have to just go back to 10* for a week or two to see if it helps.

EDIT: Btw, I know running higher octane fuel won't, in and of itself, add any power, and the ONLY reason I run higher octane is to avoid pinging issues. But do the higher octanes, themselves, actually tend to give poorer gas mileage because it's a slower burn?

 

[ID89GT]

Also higher octane has more additives so less burning material.. Idk how to explain that, just what my teacher said

 

[pudman]

Yep. I always check plug gap before I poke 'em in. I've worked in a few parts stores, so I know how much those things get knocked around before they're sold. I've even had a couple with the electrode mashed flat against the center post when I took 'em out of the box. Plus, they usually give them a one-gap-fits-all setting from the factory, as the common plugs for a 302 will fit more than one application. I can't recall what the number was I set 'em to, exactly, but it was whatever was listed in my Chilton manual's specs (no legible stock underhood emissions sticker to reference on my car) ... I wanna say it was close to or just under 0.045", and like 6 out of 8 of the Motorcraft plugs were at like 0.035" out of the box, so most took a bit of tweaking before I stuck 'em in there.

plugs for a 5.0 should be set at .052-.055

 

[mustangsquared]

pudman...you sure about those numbers... I swear I have been gapping mine for 10 years to .45 ...maybe thats why I have a surge I cant get rid of!!

 

[Foxfan88]

Once your find the MBT timing that works for your car, that should produce the best MPG possible.

Once you get that peak pressure point just a few degrees after TDC, having in the right spot with the most leverage on the crank will produce the best torque for the given fuel input. over advancing it will definatly hurt mileage, as too much timing means the pistons is having to push its way against potentially higher pressures if the spark is earlier.

Having a more effcient combustion chamber should also help milage, the more effcient and faster you can make the fuel mix burn, the less total timing you can run to make the same peak torque which further reduces the pumping losses as the pistons approaches TDC.

 

[millhouse]

Well, at least on my '89, I can't advance the timing to 12 or 14* and run anything less than '91 without getting ping, especially when the temps outside go over 100*F. If I run 89 octane in my '84 right now, I will get a little bit of pinging, but with 91, no ping.

I'll have to go back and double-check, I might have advanced it to 14* but I can't remember for sure; the '89 I know for a fact is at 12* because it's REALLY prone to ping at 14* in the summer months. (FWIW, the '89 is an AOD-to-T5 conversion car and still has the AOD computer in place. I think the timing it adds might be a bit more than on a manual computer, but I'm not sure ... but if so, that might explain why it doesn't like much added timing.) If the '84 is at 14*, I'll dial it back to 12* and run 89 octane and then see if that helps my mileage. But if it's at 12* ... I guess I'll have to just go back to 10* for a week or two to see if it helps.

EDIT: Btw, I know running higher octane fuel won't, in and of itself, add any power, and the ONLY reason I run higher octane is to avoid pinging issues. But do the higher octanes, themselves, actually tend to give poorer gas mileage because it's a slower burn?

Run some seafoam through your brake booster check valve. It sounds like you have some mad carbon buildup leading to hotspots in the CC and higher CR's. Throwing octane at it may help with pinging issues...but those issues exist for a reason.

 

[mustangsquared]

Run some seafoam through your brake booster check valve. It sounds like you have some mad carbon buildup leading to hotspots in the CC and higher CR's. Throwing octane at it may help with pinging issues...but those issues exist for a reason.

Hey, you just want to see his exhaust pour white smoke for 20 minmutes!!!

All joking aside, the sea foam does work at cleaning the cylinders.

Now to add to the mix. I was told to run higher octange as well when I bumped up to 14* because it burned more slowly allowing the piston to get closer to the top before full burn.

 

[millhouse]

Hey, you just want to see his exhaust pour white smoke for 20 minmutes!!!

All joking aside, the sea foam does work at cleaning the cylinders.

Now to add to the mix. I was told to run higher octange as well when I bumped up to 14* because it burned more slowly allowing the piston to get closer to the top before full burn.

Seriously....people will damn near call the fire department!

 

[Darkwriter77]

plugs for a 5.0 should be set at .052-.055

Again, I can't recall exactly what the number was, but I gapped the plugs to spec, whatever it was - 0.045" just stuck out in my mind for some reason, but I don't remember if that was it or not.

*pulls out Chilton manual again*

Okay, so it was 0.050". My memory is poo.

Once your find the MBT timing that works for your car, that should produce the best MPG possible.

Once you get that peak pressure point just a few degrees after TDC, having in the right spot with the most leverage on the crank will produce the best torque for the given fuel input. over advancing it will definatly hurt mileage, as too much timing means the pistons is having to push its way against potentially higher pressures if the spark is earlier.

Having a more effcient combustion chamber should also help milage, the more effcient and faster you can make the fuel mix burn, the less total timing you can run to make the same peak torque which further reduces the pumping losses as the pistons approaches TDC.

So ... in short, I should keep it at 10* and go back to 87 octane, right?

Run some seafoam through your brake booster check valve. It sounds like you have some mad carbon buildup leading to hotspots in the CC and higher CR's. Throwing octane at it may help with pinging issues...but those issues exist for a reason.

Already Seafoamed it last fall. Surprisingly, I didn't get very much smoke out of it. It was kinda disappointing ... nothing at all like the '86 GT 'vert that I had. But it didn't hurt anything, either. I didn't drive it much at all during the first 6 months I had the car because it had so many cooling problems that I had to iron out first. I think I've only put on about 4k miles since it became my DD, so I very much doubt that it's due for another Seafoam treatment just yet.

But yeah, the pinging is there for a reason - too much timing, probably. Although it should be noted that the CFI setup wasn't exactly the best thing Ford ever came up with. I read somewhere that because the butterfly in the TB doesn't open up 100% at WOT, and because the injectors are ahead of the TB butterfly in the airflow, it runs the front two cylinders a little lean - the SSP cars that had CFI back in '84 supposedly had a slightly modified TB that would open up 100% and they didn't have this problem, but I'm not sure why they insisted upon keeping this "feature" in the civilian cars. If I knew if some way to modify the TB to open fully at WOT, I'd try that, but really it's not just at WOT that it pings ... usually more like on hills at cruise when you have to dip into the throttle a little more but you're still keeping it in the same gear (basically it pings a bit under an increased load at cruising RPM's).

Guess I'll roll it back to 10* today and switch back to cheap gas. Sucks, though, because there was a noticeable improvement with the added timing, especially when taking off from a stop - felt a little more torquey than before. Meh ... oh well. It's my DD, not a go-fast weekend toy, so I'm not too worried about setting any records or anything. At this point, I'm actually thinking of swapping 2.73's into it to see just how good the mileage can get.

 

[Darkwriter77]

Just went out and adjusted the timing. It was set about at 14*. I rolled it back to about 12* ... actually closer to 11*, just to be safe. Only thing is, now that I've got the A/C working again, it's gonna be hard to resist the urge to use it so I can get an accurate comparison of whether or not my gas mileage improved.

But either way, 14* was probably more than this car wanted, so I guess 11 or 12* is what it's gonna have to be happy running. I'll try running 87 octane in it from now on and see if I get any pinging with less timing advance.

 

[gmachou]

Hey, you just want to see his exhaust pour white smoke for 20 minmutes!!!

All joking aside, the sea foam does work at cleaning the cylinders.

Now to add to the mix. I was told to run higher octange as well when I bumped up to 14* because it burned more slowly allowing the piston to get closer to the top before full burn.

[Actually differing octane fuels burn at the same speed, the flash point-(tempature/compression) needed to ignite it or start the burn process. For example 87 needs a lower flash point to ignite, and 93 has a higher flash point... so the 87 starts it burn faster, but they both take the same amount of time complete the burn. The 87 got a head start] with this in mind there are instances where 93 octane "could/would" reduce hp-Torque particularly without advanced time to match...] tons of people get into 93 octane has more power? Or they advance the timing then delay the burn paying extra for higher octane? Same rusult as 87 set at less timing advance... put it on 87 and advance it as far as you can without pre ignition (pinging). Keep your money in your pocket! Higher compression motors on the other hand will require the higher octane no way out of it!] X 2 on the Seafoam (mechanic in a can!)

 

[Noobz347]

[Actually differing octane fuels burn at the same speed, the flash point-(tempature/compression) needed to ignite it or start the burn process. For example 87 needs a lower flash point to ignite, and 93 has a higher flash point... so the 87 starts it burn faster, but they both take the same amount of time complete the burn. The 87 got a head start] with this in mind there are instances where 93 octane "could/would" reduce hp-Torque particularly without advanced time to match...] tons of people get into 93 octane has more power? Or they advance the timing then delay the burn paying extra for higher octane? Same rusult as 87 set at less timing advance... put it on 87 and advance it as far as you can without pre ignition (pinging). Keep your money in your pocket! Higher compression motors on the other hand will require the higher octane no way out of it!] X 2 on the Seafoam (mechanic in a can!)

This is close but octane has nothing to do with the flash point of fuel other than as single variable used to help determine flash point. Octane has to do with the fuel's resistance to ignition during compression [before] an ignition spark is introduced and more specifically, how well it conducts heat between its own molecules.

93 octane fuel resists being detonated by compression better than 87. All other burn properties are determined by the regional and seasonal mixes of pump fuel additive packages.