Sturmcrow

I am driving from Orange County up to Las Vegas this weekend to do some wheeling with my brother. This is the first long trip I have taken my truck on, so plan to use it to dial in the timing advance.

I plan to set the timing to 10 degrees advance, fill up the tank, drive 67 miles.

Set timing to 12 degrees advance, fill up tank, drive 67 miles.

Set timing to 15 degrees advance, fill up tank, finish drive, fill tank again.

I know that 67 miles is not really a super-long trip distance, but I only have 240 miles and want to try at least 3 settings. I also want to do it all on the same leg, not part on the way there and part on the way back.

I am posting this here to ask if you guys think my plan sounds good or if I am making an obvious mistake without realizing it.

I am also curious about how the ECM/ECU handles spark advance. I read once that we should run 91 octane fuel because our engines will advance the spark until knocking is sensed and then retard it a bit. If that is true, then why does the base timing even matter? On the other hand, does the ECM only retard timing so that setting the base timing more advanced helps in some cases?

a51young

sub'd, interested in your findings

snobdds

So every 67 miles your going to stop, pull the dizzy and rotate the engine 2* and put the dizzy back in?

Remember cam and ignition timing have a direct relationship and that must be maintained. By turning the dizzy, that is just moving the timing "advance" number, not actually moving the ignition timing by 2 or 3*.

You may want to rethink this...Do you want to move the ignition advance or actually put 2* or 3* extra degrees of timing in?

Sturmcrow

I have to admit I am not really sure what you are asking. Or at least, from what I understand I do not agree with you. I think you are saying that I will move the distributor 2 degrees. In reality, I will move the distributor whatever amount it takes to advance the spark 2 degrees as measured at the crank.

I plan to stop every 67 +/- miles, fill up the tank to get an idea of fuel economy, and then adjust the base timing by loosening the 12mm bolt on the side of the distributor and using my nifty timing light to set a given advance. My digital timing light allows me to plug in whatever advance I like, to a tenth of a degree.

This seems to be a pretty common practice. Factory timing is 10 degrees advance for best emissions or whatnot, lots of folk run theirs at 15 degrees or more for better power, others run theirs at 12 degrees because they don't want to blow up the engine.

snobdds

Your only changing the advance...not the actual ignition timing. For what your doing, you need to change the ignition timing.

Slight difference...

MudHippy

There's a kernel of truth in what you're saying. Albeit a small one...

What you're doing by setting the base ignition timing is setting the MINIMUM ignition advance angle. Which is why it's done at idle. When the MINIMUM ignition advance angle is required. The ECU will then be unable to allow for less advance than the set base timing. Since it never retards ignition timing, it only advances it beyond the base timing when required for higher than idle rpms and/or higher octane fuels(due to physical limitation set by the clocking of the distributor, when base timing is set, which it cannot override electronically).

So, the higher you can set the MINIMUM advance angle, the closer it will be to the MAXIMUM advance angle. And the engine's peak power output occurs when the MAXIMUM ignition timing angle is being applied. Therefore, if you start out(at idle rpm) with the MINUMUM ignition advance angle CLOSER(than stock setting) to the MAXIMUM ignition advance angle, you will be making more power at those rpm that don't require the MAXIMUM advance angle(idle through low to mid rpm). Causing the effective powerband of the engine to be widened significantly. Resulting in more low to mid rpm range torque, with no effect on high rpm, and/or peak, torque output(since that's always going to be during the application of MAXIMUM ignition advance angle, regardless of the base timing setting).

If none of that makes much sense. Let me cut right to the chase...

1. Advancing the base timing as far as it will go isn't going to get you much, if at all, better MPG(unless you do a lot of low rpm driving, then it might).

2. Running higher octane fuel more than likely will though, since the effects of that will occur at higher rpm(like say cruising on the highway, when the advance angle will be slightly less than the MAXIMUM, giving the ECU headroom to advance it further than it would be able to without the knocking running a lower octane grade with that much advance causes). Unless you do a lot of low rpm driving, then it might not.

BTW, I run mine at ~23° BTDC all the time. AND I run 92 octane. With good reason for both.

Sturmcrow

Ok, I think I get what you're saying. I gather that the minimum timing set at the factory really only affects the emissions at idle then.

I have to admit that I noticed no difference in power or anything when I previously had my idle timing set 15 degrees advanced. Granted, that was only using my butt dynometer.

I do not have ready access to 92 octane fuel, but I did start using 91 octane on Mudhippy's advice in a different thread.

snobdds, To change the actual timing, I assume I would need to change settings in the ECM? I apologize for not understanding what you meant in your first post.

scope103

Don't forget that you won't pass smog with the timing mis-set.

While I really admire someone who is willing to run an experiment like this, you may not have enough data. 67 miles is only going to be 3-3.5 gallons of gas, so you're trying to tease out a result depending on +/- a few tenths of a gallon when the pump shuts off. Also, air resistance makes an easily perceptible difference in mileage. So while you'll do your best to drive at the same speed, the wind could be different at different times of day.

But some data is almost always better than no data, so if you're willing to try the experiment we'd all be glad to hear what you come up with.

ksti

It would seem like, and I just speculating
there are many variables to this experiment to get a true finding or as close as possible.
How accurate is the fuel gauge?
67 miles seems inadequate to get a true reading.
Wouldn't a full tank of fuel be the best, more accurate test?
Or am I just over thinking?
Just trying to get a bead on this experiment.

Sturmcrow

I do agree that a longer, flatter course would work better for this experiment. Anyone planning to drive across Nebraska or Kansas anytime soon?

I also just got an email from work that the Santa Ana winds are supposed to pick up this weekend, which will also throw me off.

andlours

iTrader: (1)

Oddly enough, I'll be driving from Oklahoma City to Denver, straight through Kansas...

4runrjunkie

The fuel gauge issue wont be a problem, because my assumption is he will fill the tank back to full at the end end of each section, so he will have an 'exact' measurement of how much fuel was used on each section. It is almost impossible to track fuel mileage by using the fuel gauge haha.

ksti

Can you enlighten me on how it's almost impossible to track fuel mileage by using the fuel gauge?.

a51young

really?? A difference of one tenth of a gallon makes quite a difference, unless you are fine with an large error. Say 100 miles with 5 gallons vs 100 miles with 5.1 gallons is a difference of .4 miles per gallon. Can you calculate the fuel consumption closer than a tenth based only on the fuel gauge and tank capacity? I know I can't, but then again my fuel gauge is all shifty for the first half tank.

4runrjunkie

This basically sums it up, but to clarify, lets say you fill your tank up and drive it around for a while, and then notice the gauge is dropping faster than you expected, so now you are left with a gauge that reads a three quarters of a tank, and want to figure out what kind of gas mileage you are getting. You have no way of knowing exactly how much fuel is left in the tank. You could easily be off by 1 or 2, or even more gallons if your gauge is as inaccurate as mine. The only way to accurately track your mileage is to track how much fuel is going in vs how much you are driving. The gauge itself is useless for mileage tracking.

ksti

Well thanks for the clarification, wasn't trying to split hairs for an exact fuel mileage reading (ie the fuel gauge)
I was probably lacking common sense
I have no excuse, except for being old.
Probably a lack of roughage in the diet.

willyt4r

On my recent trip to Mammoth Lakes California. I experaimneted with 91 octane gas. the difference is significant . My previous trips going up the mountain i got 15.8 to 16.2 mpg , Using the 91 octane the MPG was 17.8 uphill. Going downhill was even better went from 17.4 to 20.5 MPG. The load was same cruise control set at 65. Oh what a !difference

MudHippy

It's practically a guaranteed result. Which is why I always run the highest octane I can get in ALL my vehicles. And since they're all fuel injected, there's no tuning required to see a performance increase. The ECU takes care of it automatically.

Inu

My first car positivly hated 91. Havnt ran it in the runner, next fillupi guess Ill try it

bone collector

results??