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Link to a thread about a recipe for gas mileage [4.9L/300].

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1986F150six
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Link to a thread about a recipe for gas mileage [4.9L/300].

Post #1 by 1986F150six » Mon Sep 29, 2014 9:55 am

This is an ongoing project and maybe someone will be interested in a little reading:

http://www.ford-trucks.com/forums/13259 ... 300-a.html

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Re: Link to a thread about a recipe for gas mileage [4.9L/30

Post #2 by SuperMag » Mon Sep 29, 2014 4:53 pm

His experience is very similar to my own... The original feedback/ECM controlled fuel system was totally non-functional (9 mpg), so off it all came. My setup as dumbed down for mileage:

2x4 1986 Long bed, Np435 4 spd, start odo was 148K
Re-man'd Carb from a '72 vintage 300
Reman'd Points dist. from a '73 vintage 300 (I wanted to play around with dwell)
Stock cam, stock position, Cat converter left in place.
I tuned the carb to a bit on the lean side --at my altitude I can get away with that-- but left it with a decent pump shot and generous enrichment at higher RPMs.

My best highway mileage run for a tank of gas was 23.1 MPG (55-60 mph), but more typically 20-21. In town, 14-17 MPG.

From 2002 until just last year, this was my daily driver for 140K additional miles. It's mostly parked these days with an oil pressure problem an HV oil pump couldn't fix. The lifters stay quiet if I keep the revs up on the way out to the dump, but that doesn't do the mileage any favors.

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Re: Link to a thread about a recipe for gas mileage [4.9L/30

Post #3 by herosandwich » Fri Oct 03, 2014 7:40 pm

I'd be curious to know how he checks advance via vacuum (I know if you do the DSII conversion, it's a vacuum advance distributor, but how do you get timing from that? I only ask because the timing notches and marks on these engines suck pretty hard for location)

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Re: Link to a thread about a recipe for gas mileage [4.9L/30

Post #4 by mwilliamshs » Sat Oct 04, 2014 9:32 am

Marks can be improved cheap and easy with stick on tapes.

The indicator/marker/pointer/notch can be filed sharp and straight (careful not to take off a bunch of metal, you just want hard edges that are easy to distinguish) and then touched up with a paint marker. I use some metallic silver touchup paint from Wally World. A piston stop and some time could make this super accurate but I really just care about readability and repeatability and making my engine run its best, not making my timing "correct" by a spec in a book.

Measuring vacuum advance is done by disconnecting the distributor vacuum from the carb/manifold, plugging the hole left on the carb/manifold, and connecting the distributor vacuum to a handheld vacuum pump with a built-in gauge (mity-vac, etc). Run the engine at a steady speed, watch the timing marks with a light, and slowly apply vacuum via the pump. The timing will advance as vacuum increases. You can track the increase on the balancer and on the vacuum gauge and determine the curve pretty easily. Conversely, you can likewise disable the vacuum advance and track the mechanical advance by increasing rpm and checking timing along the way.
1989 E-150 Extended Body SuperVan Sportsmobile Camper Conversion 4.9L, C6, 3.08 R&P

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Re: Link to a thread about a recipe for gas mileage [4.9L/30

Post #5 by SuperMag » Sat Oct 04, 2014 12:43 pm

herosandwich wrote:I'd be curious to know how he checks advance via vacuum (I know if you do the DSII conversion, it's a vacuum advance distributor, but how do you get timing from that? I only ask because the timing notches and marks on these engines suck pretty hard for location)


Once you learn how to set timing with a vacuum gauge*, you'll never look at the marks again.

*Run engine to operating temperature. Disconnect dist vacuum and attach vacuum gauge to manifold vacuum (not ported carb vacuum). While idling, adjust timing to max vacuum, and then retard 1" of vacuum. Lock down the distributor because you're done. Don't forget to reattach the dist's vacuum line to the carb's ported vacuum.
Last edited by SuperMag on Mon Oct 06, 2014 10:43 am, edited 1 time in total.

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Re: Link to a thread about a recipe for gas mileage [4.9L/30

Post #6 by THE FRENCHTOWN FLYER » Sat Oct 04, 2014 3:45 pm

I've always wondered why people who use this method retard spark to reduce the intake vacuum by 1".
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Re: Link to a thread about a recipe for gas mileage [4.9L/30

Post #7 by SuperMag » Sun Oct 05, 2014 8:36 pm

When I first heard of this method, that's the first question that popped into my mind. So, renegade that I am, I tried it with full vacuum. Too much vacuum advance; I got ping at partial throttle/high vacuum.

The way I figure it, when you set the timing using the vacuum method, you're doing it idle in your driveway, a no-load situation. Going down the road, however, even at high vacuum/part throttle/no enrichment, there is a load. Hence the ping.

You could, I suppose, play with the vacuum advance curve, but I was never inclined to. Performance (such as it was) and mileage figures indicated to me that it wouldn't be worth the effort.

[edit] Before I happened onto that method, I would set timing by roaring up the road, foot to the floor, listening for knock. That always resulted in too much vacuum advance. Which, of course, indicates the need for some spring work. But as I spent only about 0.02% of my time with the go-pedal matted, I was back to the not-worth-the-effort frame of mind.

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Re: Link to a thread about a recipe for gas mileage [4.9L/30

Post #8 by THE FRENCHTOWN FLYER » Sun Oct 05, 2014 9:43 pm

So, as I understand it, one is retarding the spark advance to reduce MV by 1" not because that's where the engine is most efficient but as a band aid to compensate for the fact that that optimun advance is in the danger zone with the specified fuel that one is using with too low of an octane rating.

This, to me, seems way too arbitrary of a method to use as a general rule for tuning. Somebody else using a different grade of fuel could then concieveably come up with a different advance curve altogether.

FWIW, when we did spark tables for carbed engines we ran an extensive series of MSV (minimum spark advance for specified vacuum) dynomometer runs using "knock free fuel" (high octane). This is the surest way to determine what the engine truly needs for optimum spark advance at part throttle conditions.

Too often discusions on this forum center around raising the compression ratio on an engine to increase performance. Often that results in moving the safe knock free spark advance values even further away from true MSV values. At the very least it may mean losing some of the built in safety margin the factory tune up provides. If you want to live dangerously - and I admit I sometimes do - then at least you should understand the implications of doing so. Factory tune ups have to work in a miriad of climate conditions and not damage the engine. Ours don't necessarily have to. I'll end my coments by advising that there is also a condition called "incipient detonation" that may not be audible but can nevertheless still be injurious to one's engine.
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Re: Link to a thread about a recipe for gas mileage [4.9L/30

Post #9 by Econo4spd » Mon Oct 06, 2014 1:18 am

SuperMag wrote:Connect distributor and vacuum gauge to manifold vacuum (not ported carb vacuum).



I've read about setting timing with the vac gauge before ( I think F250 restorer had a good write up on it a couple years ago), but This is the first I've seen that the Distributor vacuum advance line is not plugged, but moved to a Manifold Vacuum source?

Please confirm my reading comprehension of your post. Thanks.
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Re: Link to a thread about a recipe for gas mileage [4.9L/30

Post #10 by SuperMag » Mon Oct 06, 2014 10:42 am

Econo4spd wrote:
SuperMag wrote:Connect distributor and vacuum gauge to manifold vacuum (not ported carb vacuum).



I've read about setting timing with the vac gauge before ( I think F250 restorer had a good write up on it a couple years ago), but This is the first I've seen that the Distributor vacuum advance line is not plugged, but moved to a Manifold Vacuum source?

Please confirm my reading comprehension of your post. Thanks.


You are correct. The gauge is connected to manifold vacuum. Not the dist. I've fixed my original post to reflect this.

That's what cut-n-paste editing does for ya if you're not paying attention. Thanks for the heads-up.

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Re: Link to a thread about a recipe for gas mileage [4.9L/30

Post #11 by SuperMag » Mon Oct 06, 2014 11:19 am

THE FRENCHTOWN FLYER wrote:So, as I understand it, one is retarding the spark advance to reduce MV by 1" not because that's where the engine is most efficient but as a band aid to compensate for the fact that that optimun advance is in the danger zone with the specified fuel that one is using with too low of an octane rating.

Exactly... But remember, we're talking about a carb-equipped daily driver pickup running fuel that may have an octane as low as 85, and may or may not contain 10% (or more) of alcohol and/or MTBE. It's not a carb-friendly world we live in these days, so we tune for the worst likely scenario.

And my situation is especially fraught with peril, as the altitude in which I drive can change from 3000 feet to 10,000 in just a few minutes, a tricky situation to tune for in and of itself... (It's pretty easy to spot the old-school mechanics around town these days-- they're the only ones driving pre-EFI vehicles. :lol: )

This, to me, seems way too arbitrary of a method to use as a general rule for tuning.

It is. But no less arbitrary than setting timing to the marks on a crank pulley. At least this way, the engine (and the fuel in the tank) is telling me what timing it wants, instead of me imposing my (ignorant) will on the engine.

Later in your post you mention incipient detonation... and it's that and those myriad climactic conditions that the 1" MV reduction is all about. It's the safety margin. And as arbitrary as it is, it seems to work.

For those interested, there's a nice article about tuning with the vacuum gauge here:
http://classicinlines.com/vacuum.asp

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Re: Link to a thread about a recipe for gas mileage [4.9L/30

Post #12 by motzingg » Mon Oct 06, 2014 1:13 pm

^ yeah thats a real good point... timing in degrees BTDC is more or less arbitrary, who is to say 15 degrees is 'optimal' in an engine, or something like that. At least with vacuum tuning you are listening to what the engine wants.

I typically get it close with vac tuning, then tune out all the detonation (that i can HEAR, good point!) and go a little bit on the safe side. If you are really good in all throttle conditions but have one spot where it always knocks, or a certain load condition, or something like that you can get tricky with adjusting the vac diaphragm and weights.

Typically i find in tuning performance engines, that i need more advance but i need it later, so i mod the mechanical advance for lighter weights (grind them down) and grind down the limit tabs to let it travel more, then set initial timing as a compromise to ensure that final timing is in the right place.



Another good reason for 'retarding 1" from max vac' is that it makes starting easier, of course.


I'd like to play with that handy feature of 'start retard' (white wire) in my DS2 box, hook it up to a knock sensor or something? I dunno, it would require a circuit.

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Re: Link to a thread about a recipe for gas mileage [4.9L/30

Post #13 by Econo4spd » Tue Oct 07, 2014 1:06 am

Thanks for the clarification SuperM!
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Post #14 by Econo4spd » Tue Oct 07, 2014 1:07 am

oops, fat submit button...
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Re: Link to a thread about a recipe for gas mileage [4.9L/30

Post #15 by guhfluh » Tue Oct 07, 2014 10:22 am

I'll put my pennies in...

Setting timing at idle for best vacuum is good enough for a stock vehicle on a stock distributor to get close. It's too arbitrary to say it is the best timing for any other rpm or load other than idle. There's a reason the vacuum advance and mechanical advance curves are adjustable. Differences in fuel, VE and more differ from engine to engine too much to make it a blanket rule for everyone in every situation. In the end, setting idle advance by vacuum is just the first step to a long tuning process to get it right.

Just my opinion;)
1967 F-250 Crew Cab 2wd, 300 6cyl, T-170/RTS/TOD 4-speed overdrive
240 head, Offy C, EFI exhaust manifolds, Comp 268H, mandrel 2.5-3" exhaust, Edelbrock 500, Pertronix ignitor and coil, recurved dizzy. 200whp/300wtq

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Re: Link to a thread about a recipe for gas mileage [4.9L/30

Post #16 by THE FRENCHTOWN FLYER » Tue Oct 07, 2014 1:17 pm

guhfluh wrote:I'll put my pennies in...

Setting timing at idle for best vacuum is good enough for a stock vehicle on a stock distributor to get close. It's too arbitrary to say it is the best timing for any other rpm or load other than idle. There's a reason the vacuum advance and mechanical advance curves are adjustable. Differences in fuel, VE and more differ from engine to engine too much to make it a blanket rule for everyone in every situation. In the end, setting idle advance by vacuum is just the first step to a long tuning process to get it right.

Just my opinion;)


You said it better and more sucinctly than I did guhfluh.
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Re: Link to a thread about a recipe for gas mileage [4.9L/30

Post #17 by motzingg » Wed Oct 08, 2014 5:03 pm

so, then, what's the best way to measure timing when you're 'in it' high load, high rpm, WOT?

Would EGT be the best (aside from a dyno) measurement for max combustion efficiency? What would you be looking for?

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Re: Link to a thread about a recipe for gas mileage [4.9L/30

Post #18 by guhfluh » Wed Oct 08, 2014 6:56 pm

motzingg wrote:so, then, what's the best way to measure timing when you're 'in it' high load, high rpm, WOT?

Would EGT be the best (aside from a dyno) measurement for max combustion efficiency? What would you be looking for?

I'm not sure what you're asking. Do you mean how to find MTBT?

Besides a dyno or ion sensing, a drag strip would probably be the next best option. Finding MTBT for the whole curve isn't that easy though. Using a wideband, pyrometer and tuned knock sensor system is what tuners do everyday that don't have dyno access and tune for a particular fuel. They still like to use a dragstrip of sorts to measure gains or losses.

There's a lot more technical theory to it than I can explain or know, but that's pretty much the basics.
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240 head, Offy C, EFI exhaust manifolds, Comp 268H, mandrel 2.5-3" exhaust, Edelbrock 500, Pertronix ignitor and coil, recurved dizzy. 200whp/300wtq

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Re: Link to a thread about a recipe for gas mileage [4.9L/30

Post #19 by motzingg » Thu Oct 09, 2014 1:10 pm

yeah its more of a rhetorical or speculative question. I understand most of the theory, but practically speaking, driving around a 50 year old truck with no knock sensor, what's the best way to make sure you're on the safe side of perfect?

I have actually got a hookup on a open dyno, two hours for $100 but he's booked out past november last i talked to him.

No EGR, sensors or anything, just a mustang dyno and a guy there to turn it on and print you a chart, you supply all the jets, sensors, everything for whatever you want to do.

surprisingly tough to find that sort of thing, everyone i've talked to wants 180-200 for a 'tuning session' where they turn the screws and you just watch them.

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Re: Link to a thread about a recipe for gas mileage [4.9L/30

Post #20 by guhfluh » Thu Oct 09, 2014 9:24 pm

Instead of a knock sensor, you can look into "det cans".
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240 head, Offy C, EFI exhaust manifolds, Comp 268H, mandrel 2.5-3" exhaust, Edelbrock 500, Pertronix ignitor and coil, recurved dizzy. 200whp/300wtq

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