Tuning Ignition for Economy

[BIGREDRASA]

I debated about posting in the Small Six section, but hopefully we can generate info for a general Sticky.

I'm running a DS II Dizzy with DS I cap and GM HEI Module. I've seen plenty of discussion on how to recurve the dizzy for more power. What I want is best fuel economy in the 2000-3500 RPM range. I already know I should be getting a bit more power from the few mods I've made, but my goal is economical high speed cruising. I want to go up and down mountains without having to floor it and downshift. I definitely won't try to run my convert for more than short stretches at over 90 MPH (the wife would freak out). You there, Bort62?

 

[TeddyXY71]

What about the thermostat temperature? If I remember correctly, running the motor at a higher temperature will give you better economy. You will lose a slight amount of power though. But if the slight power loss is acceptable, the pay-off is more miles from the same amount of fuel. Couldn't give any firm numbers on what the gains would be like, its just the theory I know about.

Teddy

 

[BIGREDRASA]

This is true, but not the way I want to go. I've done what I could to reduce heat, so I can hammer down or sit in traffic on the hottest days without worry.

 

[66 Fastback]

I am not sure I follow what your question. The most power and economy is going to be the most advance that your motor can handle at all rpm's without pinging. For economy, a properly functioning vacuum advance is required. For best economy / performance, use the manifold vacuum source. To be honest though, I can't tell you how much if any change in economy will be seen if you add a couple of degrees of timing advance.
Doug

 

[BIGREDRASA]

We've had several posts on changing the advance curve on the DS II distributor for max acceleration. I'm curious to know if the same curve also renders the best MPG, provided one uses discretion in applying the gas. Where's Bort62 when I need him?

 

[XPC66]

What about the thermostat temperature? If I remember correctly, running the motor at a higher temperature will give you better economy. You will lose a slight amount of power though. But if the slight power loss is acceptable, the pay-off is more miles from the same amount of fuel. Couldn't give any firm numbers on what the gains would be like, its just the theory I know about.

Teddy

The engine runs hotter because advancing the spark increases the cyilnder temperature and in the process increases heat transfer into the water jacket, but the EGT consequently drops because there is less residual heat on blowdown.

The idea is with any engine is to increase compression while retarding spark until the fuel can no longer keep things cool.

Seeing as the compression is fixed the first pass is to set the fueling. To do this you start of running rich and lean out to when either the power starts dropping or EGT stops rising and starts dropping.

 

[66 Fastback]

But leaner jetting requires more spark advance since th combustion is slower in a lean mixture. Retarded timing increases the EGT. Seems to me that dumping hotter gases into the exhaust is not going to improve any efficiency. Maybe I am overlooking something. If so, talk slow, I'm an Aggie!
Doug

 

[XPC66]

Yes lean mixtures require earlier spark. I was taking about making sure the engine is properly tuned, before going down the track of advancing timing, which would require leaning the mixture.

You can't just leave the fueling as it is and advance timing hoping to get better economy. This is one of the advantages of ECUs; where you can easily manipulate AFRs and timing for low load conditions, whereas carbies are always a best fit solution, regardless of whether they have a fancy name or not. Likewise the dizzy only has the centrifugal governor and a rough approximation of engine load via vacuum reading to determine what advance is required.

 

[BIGREDRASA]

I'm looking for possible differences in adjusting dizzy for economy rather than power. I do imagine that the timing set perfectly for the target cruising speeds of 65-80 MPH will render the best MPG on a road trip.

 

[Bobscoupe]

Big Red,

This is a great post for discussion. I am reworking my build now to a budget minded economy cruiser.

I do most of my driving in mixed city/highway.

I have a 5200 direct mounted, with an MSD 6a, MSD coil, and Clifford exhaust through 2" duals with Dyno Max mufflers. I have 320 gears and a 4 cyl T-5.

Looking at modifing my DSII and installing cam for best mileage. Anyone have a suggestion on a cam profile? Has anyone done the DS II modification per the sticky and achieved good results?

Thanks
Bob

 

[BIGREDRASA]

I PM'd Bort62, he's a great advocate of DS IIs. should hear from him shortly.

 

[XPC66]

I've always been an advocate of electronic dizzies, but I've never seen one improve economy. They do give better torque delivery at low revs and don't misfire like points, but apart from that. Maybe the Durapsark II has something extra?

 

[BIGREDRASA]

I've always been an advocate of electronic dizzies, but I've never seen one improve economy. They do give better torque delivery at low revs and don't misfire like points, but apart from that. Maybe the Durapsark II has something extra?

This was the topic I had looked at before: http://fordsix.com/forum/viewtopic.php?t=30894&highlight=
It started off on the topic of MPG improvement, but drifted more into power. I like power, but MPGs are very important on road trips.

 

[XPC66]

OK the basics fundamentals of advancing the ignition is to make sure the fuel is near as damnit completly burned by the time the blowdown event happens.

But the more you move away from TDC the more cylinder area is exposed. This has two main effects: the fuel mixture coming in robs heat from the coolant which reduces the total liberated heat for work and the pressure on the upstroke increases while the pressure on the downstroke decreases (this is why the spark retards under load= to provide more pressure on the downstroke).

Because the combustion is starting earlier the piston will see pressure acting against it earlier, which will load the crank and draw energy from the flywheel. It will also create losses through sidewall loading because of the angle of the rod, the bigend bearings will wear more and more oil will be burned because it is being delivered for longer into the combustion process.

So you really need to weigh up the pros and cons of advancing without regard to flame speed i.e AFR

 

[Bort62]

IMHO:

The fundamental concept behind optimum ignition advance is the same independent of the goal. Optimum power and optimum efficiency are going to be one in the same.

Generally this is true when it comes to an engine - it is always a question of efficiency. It is just a question of relative to what -

MPG is a question of efficiency relative to consumption of fuel. You want to get the most power (to the wheels) out of the least amount of fuel consumed.

Making the most power you can (performance) is efficiency relative to engine displacement - You want to generate as much power as you can within the physical restrictions of your motor.

Achieving the first is key to achieving the second.

The goal of ignition advance is to ignite the fuel/air mixture at such a time that the maximum force is exerted on the piston on it's down stroke. To a first order approximation, this means that you want combustion to conclude very near TDC. Too early, and your engine is fighting against the pressure caused by combustion (detonation, pinging, loss of power, etc). Too late, and the mixture combusts worthlessly while the chamber is rapidly expanding (downstroke) - yielding little to no force on the piston.

In a micro sense, this is a simple thing. You can measure power output (which is going to be equivalent to efficiency) and adjust until you find the maximum.

The problem is, your engine operates in many drastically different environments, and the "perfect" ignition advance for one environment is going to be very different than that for another.

So you need a way to set it differently for different environments.

I will spare everyone the diarrhea of the keyboard that it would take me to explain how a distributor, and it's different types of advance, work - because you all know that already. I will just supplant that by saying really the only way that **I** have the patience to try and tune ideal advance across all environments (and hence achieve max efficiency in all of them, leading to the best MPG performance in every day driving) is with EFI. The variables w/ a traditional distributor are just way too dependent for my tastes. I much prefer the independent interaction of EFI spark tables. (Ie, I can have 40* of advance at 3500 RPM and 15* @ 3600 RPM if I want to, same load). You just can't do that with a distributor and so, as a result, you end up having to make compromises.

Compromise = inefficiency

 

[wsa111]

The proper advance curve depends on many variables.
Cam,compression,transmission,octane of fuel & even differential.
Mr. Gasket markets an advance spring kit #925D
Borg Warner offers several vacuum advance cans. The short travel is V398 & the long travel can is the V397.
A rich mixture requires more advance & a lean mixture less advanve.
Also more advance in cooler weather & less advance on hot days.
Even humidity can be factored into the equation.
An engine with a wild camshaft with a 1000 rpm idle might require brazing up the advance slot on its beginning part of the travel so you don't have centrifigul advance when setting the initial timing.
You need to check your air fuel ratio using a wideband tester. Cruise 14.5-14.8 is ideal. Air fuel ratio at WOT should be in the 12.8-13.1 area.
On a holley carb you don't want a power valve opening too early & too late to cause a lean hole in the air fuel mixture at part throttle acceration.
The vacuum advance can is adjustable & can be adjusted with an allen wrench with the aid of a hand held vacuum pump.
My engine has 10.3 compression, 190# cranking compression.274 cam.
I run the centrifigul advance @ 20 degrees+16-18 initial=36-38 degrees mechanical with the advance in by 2800 rpms.
I run the short travel V398 can with the advance at max @ 14" of vacuum & have it go to 0 at 5" of vacuum. Yes i have to run 93 octane fuel.
Every combination is different.
A sun machine makes all the adjustments much easier.
Performance distributors with Classic Inlines as a dealer can tailor a curve necessary for your engine.
But you will need a windband A/F tester to get your air fuel ratio correct for best power & ecomomy as previously mentioned by Ian.
If you nail your adjustments on the money you will have more power & better fuel economy, Bill

 

[MustangSix]

Gotta agree with Ian. Electronics is the only way to optimize for efficiency.

ANY curve kits, modulators, springs, etc., will only ever be a compromise and cannot be tuned to meet specific mapped requirements. Without going to a full on EFI Engine management system, a good choice would be to adapt a Ford EDIS system to the engine via a Megajolt board. All the parts are available and relatively cheap.

http://www.bgsoflex.com/mjl/mjl_edis.html

 

[Bort62]

Tuning spark tables is quite likely the best place to "find" power and efficiency in a car.

 

[XPC66]

The proper advance curve depends on many variables.
Cam,compression,transmission,octane of fuel & even differential.
Mr. Gasket markets an advance spring kit #925D
Borg Warner offers several vacuum advance cans. The short travel is V398 & the long travel can is the V397.
A rich mixture requires more advance & a lean mixture less advanve.
Also more advance in cooler weather & less advance on hot days.
Even humidity can be factored into the equation.
An engine with a wild camshaft with a 1000 rpm idle might require brazing up the advance slot on its beginning part of the travel so you don't have centrifigul advance when setting the initial timing.
You need to check your air fuel ratio using a wideband tester. Cruise 14.5-14.8 is ideal. Air fuel ratio at WOT should be in the 12.8-13.1 area.
On a holley carb you don't want a power valve opening too early & too late to cause a lean hole in the air fuel mixture at part throttle acceration.
The vacuum advance can is adjustable & can be adjusted with an allen wrench with the aid of a hand held vacuum pump.
My engine has 10.3 compression, 190# cranking compression.274 cam.
I run the centrifigul advance @ 20 degrees+16-18 initial=36-38 degrees mechanical with the advance in by 2800 rpms.
I run the short travel V398 can with the advance at max @ 14" of vacuum & have it go to 0 at 5" of vacuum. Yes i have to run 93 octane fuel.
Every combination is different.
A sun machine makes all the adjustments much easier.
Performance distributors with Classic Inlines as a dealer can tailor a curve necessary for your engine.
But you will need a windband A/F tester to get your air fuel ratio correct for best power & ecomomy as previously mentioned by Ian.
If you nail your adjustments on the money you will have more power & better fuel economy, Bill

Where do you get those wild cams that allow you to run 1000rpm?

Just to take you task on a couple of things:

a lean mixture burns slower than a rich one, so typicallythe spark is advanced, although with the higher cylinder temps it can cause det and may need retarding a tad;

for cruise economy I would have said ~15.5 is ideal @ 10" or more vacuum (low EGT, high CHT) and 12.8 is ideal (high EGT, high CHT) for max power, unless it was a turbo and then I would say around 11.0 ish (lower EGT, lower CHT)

 

[wsa111]

XPC66, any camshaft with more duration & overlap are going to need a higher curb idle to obtain a cleaner idle, especially with an automatic trans.
Whats the big deal with a 1000 rpm idle, you must be used to very mild cams which will idle at a much lower rpm.
Richen up you advance, lean it & retard.
When you burn a hole in a piston you learn real fast.
I shift at 6200 rpms to take full advantage of the camshafts power range.
Yes with fuel injection you can burn a leaner mixture at cruise than the ideal carb ratio of 14.5-14.7.
In your combination you might need different specs. bill