Best possible mileage?

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I tried for mpg with a slant in my 68 more door, fresh motor with milled head, 2bbl, hei, big exhaust... everything I could think of. Got 18 most of the time. One cylinders ate something and jammed the rings to the piston, put in a stock 318 with the same carb and hei and got 20 all the time.
 
My 93 318 dakota club cab got 22 over the road consistently after I converted it to a 5 speed stick.
Any 3.9 powered dakota I have ever had seemed to top out at 17, occasionally 18 but not very often. I'll take the v8 in that case.
Slant wise, my 79 D100 with the 3 on the tree manual steering and brakes and 3.55s was good for 22 over the road.
I have an 85 D150 right now, haven't driven it enough with the original engine in it to judge mileage, just got all the bugs out of it, and winter came. It's solid and want it to stay that way.
I have a 74 slant 6 that I'm building to play with in it, cam is at Oregon cams as we speak, block in machine shop, just finished porting the head as far as I dare (the band sawed one all over the forums has me scared, I may have already wrecked 2 heads, have 1 more I can experiment with) have an NOS BBD for it, hogged out exhaust manifold, have de-lean burned it already, factory 4 pin ECU.
Going for best I can get from it considering the 727 and 3.21s aren't going anywhere anytime soon.
 
I have a 84 D-100, slant six 833OD. I got the truck from the family of a friend that passed, and don't know what, if any thing was done inside the engine. It does have the super six two bbl, and a better exhaust. The rear has been changed to a 8 3/4 3.91 sg. Only checked the mileage once, from Florida to Ky, towing my race car. Truck was just the way I got it, except for a safety inspection, and oil change. Never even checked the timing. Got 13 MPG. Same trip with my 88 D-150, 360 4bbl/727 got about 9 mpg
 
Yup. Typical 360. Gas sucking pigs. I've had better overall service out of 318s vs 360s. And I've had 318s that were better on gas in the otherwise same vehicle, than either a slant 6 or a 360.
I've had this experience when compared to either a slant 6, or especially the 3.9.
I've also had a couple of gas sucking 318s, the worst of which was my 88 D-100 short bed, usually good for about 8 mpg, at 70 with a good tailwind I got a best of 12. And that was with ALOT of good money after bad in pursuit of making it improve from there. I'd have been money (and results) ahead but swapping intakes, putting a carb onto it and either a 4 pin ECU ignition or HEI than all the money I threw at the damn TBI that was on that truck. I've had 4wd. Ramchargers and pickups that were better than that turd.
I don't drive trucks for MPG but that's what I meant "Best it can be for what it is". And when I can get 19 out of a 3/4 ton B van with another 318 something is wrong when I got 8, out of a short bed 2wd pickup. With injection mind you.
I'm hoping for 18-20 out of the slant 6 I am building for my D150. We will see. That is alot of weight for such a small engine in a pick-up.
 
Take a look at the camshaft. Compare the duration on the compression and powerstrokes. IIRC the cams are (318 first then 360);
240/130/122/248/20 ; compared to
252/123/119/256/30 ;That's ;
intake/compression/power/exhaust/overlap
>Notice the 130 compression on the 318 versus 123 on the 360. This makes about the same pressure in each engine so that's a nevermind.
> but notice the 122 power on the 318 versus a slightly smaller 119 on the 360. Again, the slightly longer stroke of the 360 makes this to be about the same actual physical distance.
> Now look at the Induction duration; 240 versus 252. That is is 12* or nearly two more cam sizes. That's a lotta extra time to be pulling air thru the primaries. And that air always has fuel in it for the same amount of time. So if there is just a tiny bit too much fuel in it, it gets 12* extra time to pull it in.
But worse is if the peak cylinder pressure does not occur in the 25 to 28 degree ATDC window, cuz the piston, with the longer stroke is rapidly accelerating away from TDC, and past the optimum window.

If your vehicle takes 50 hp to cruise at 65 mph, then it should make no difference what size engine you use, 50 hp is 50 hp.But it does make a difference; why? Because we are talking about 50 hp NET,off the back of the crank.
So if the 318 pistons and valve gear sucks 10 hp and the 360 sucks 15 (I mean I'm just throwing numbers at the wall to illustrate the point), that in an increase of 1/3 or 33% more internal friction. So the 360 HAS to use more gas just to spin itself.
Then consider that a 318 usually comes with a 904, versus a 727 with a 360, and the 318 will have a 7.25 versus an 8.25 with the 360, So again, the 360 has to drive thru those handicaps.

But if you make those considerations, as I have, when I installed a 318 top-end and cam on a 340, then you get the 318-type fuel-mileage out of it.
Or if you slow the piston speed down of the 360 to match the 318, again you get 318 type of economy.

But what of the 225 with it's 4.125 stroke? Yeah, there it is . Compared to the 3.315 of the 318, that is a lot of ringtravel
In a 318 the total ring travel over two revolutions of just one cylinder is 3.315 from top to bottom to top to bottom is 13.26 inches versus 16.5 for the slanty. When all eight are considered, that comes to 106 versus 99, so the 318 is only 7% more. It wouldn't take much frictional difference to put them on par, even considering the bore difference of 15%.
The point is this; Sometimes,more is less. Sometimes 318 cubes, over 225, uses less fuel per mile

The one single fuel waster is not having peak cylinder pressure occur in the window of 25 to 28 degrees AFTER TDC. Put yours there and see what happens.
I would like to tell you that I once did, and gearing my reasonably shaped 68 Barracuda to 85=2100 rpm(see edit1) with a manual trans, she returned to me 32 mpg. But nobody believes that so it must be impossible. And this with a 360 and a 223/230/110 cam yet....... so you didn't hear that from me.
My cruise timing? set to 2100 =45* in the distributor plus up to 15 more on the dash-mounted dial-back, spark-delay box, so 54* on this trip. That's what it took to put the peak pressure inside the window.

Edit one . I geared the car to go 85 mph at 2100 rpm. That was with an A833 overdrive box, ( .71od) and a GearVenders Overdrive (.78) behind that, and 3.55s out the back, so a final drive of 3.55 x.71 x.78=1.966 in double-overdrive or Second overdrive; same thing. This would be like running 2.84s with an A500 in loc-up.
 
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AJ/FormS said:
The one single fuel waster is not having peak cylinder pressure occur in the window of 25 to 28 degrees AFTER TDC. Put yours there and see what happens.
I would like to tell you that I once did, and gearing my reasonably shaped 68 Barracuda to 85=2100 rpm with a manual trans, she returned to me 32 mpg. But nobody believes that so it must be impossible. And this with a 360 and a 223/230/110 cam yet....... so you didn't hear that from me.
My cruise timing? set to 2100 =45* in the distributor plus up to 15 more on the dash-mounted dial-back, spark-delay box, so 54* on this trip. That's what it took to put the peak pressure inside the window.
Click to expand...

I don't get 85=2100 rpm... what do you mean?
and I put a 252 cam (stock 360-2bbl) into an 83 D250's 318 and its difference was huge in power and mileage improved too. Never touched distributor advance curve (juust advanced it til it pinged and then backed it up 2*, stock original 83 distributor) but along with that cam, I
didnt degree it, just put it dot to dot with new Edelbrock True Roller chain
swapped from 2 bbl Holley 2280 and stock cast iron intake to Performer (not RPM) and 600 CFM CarterBrock carb
put on a set of EQ Magnum heads- bought new as bare castings and cherry picked best hardware from 3 sets of stock cracked Magnum heads, no porting done besides how they came out of the box
and a set of Hooker Super Comp headers, 2-1/2" true duals all teh way to the bumper from the collectors.....

How would I go about "putting peak pressure at 25-28*ATDC"? and is this a universal figure?
 
also most of my 318s have had 727s even if I have had to put said 727 in there....my 360s except for 1 came to me with 904s. (the exception was an NP435)
most were 8-1/4 rears.
saying this for "friction" reasons which sap power....
 
volaredon said:
I don't get 85=2100 rpm... what do you mean?
Click to expand...
I geared my Barracuda to go
85 mph =2100rpm, I'll go fix it.
AJ/FormS said:
Edit one . I geared the car to go 85 mph at 2100 rpm. That was with an A833 overdrive box, ( .71od) and a GearVenders Overdrive (.78) behind that, and 3.55s out the back, so a final drive of 3.55 x.71 x.78=1.966 in double-overdrive or Second overdrive; same thing. This would be like running 2.84s with an A500 in loc-up.
Click to expand...

At these low-rpms it is almost impossible to get the timing right with the factory timing controls. When you throw away the LB timing computer, you throw away all that timing. Assuming the dang thing still works.
 
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ok, so i wanted peak mpg's w/78 b100 van, has /6 od 4 speed. because of of hilly ny highways makes for alot of down shifting. at 4500 lbs takes some pushing. getting 16 mpg. i feel there's more to get. wondering should of went 318? figured w/6 it'd be better and last longer wise. i will try aj's timing trick,and get back. also putting 2-1/4 exhaust n free up so flow.
 
I am also thinking since this will be a highway truck lowering it a couple inches will help too! Thoughts?

Cley
 
moparblood said:
i will try aj's timing trick,and get back
Click to expand...
When you do this,
and after you have discovered the perfect timing
Then you can simultaneously twiddle the mixture screws to find the highest rpm for that cruise timing.
Be advised, that not every combo can be made to cruise at those settings..... because
it is sometimes physically impossible to either;
A) achieve that number with the parts you have, or
B) the engine might not have enough power to get to the cruise rpm and still be on the low-speed circuit, or
C) if it does, it might want to detonate the whole way, or
D) the rpm is just too low.

The method I detailed just tells you what the engine wants. Sometimes you cannot give it to her, because of the limits of the parts.

Furthermore;
You really need to work out your timings in the following order
1) establish the Power-Timing first. How much and how soon, without detonation.then
2) the Idle-Timing, then.
3) the rate of advance, then finally,
4) The Vcan tuning is last on the list because; if you change any of the first three, that will automatically change your Max V-can timing.

You can do things in any order you want to, but if you want optimum, you will be doing things multiple times.

If your cruise rpm is less than 2200 rpm, it becomes extremely difficult to get the cruise timing she wants. If you are serious, you will have to get an adjustable spark-delay box. Mine is in the cabin where I can reach it. This will reduce your learning curve very substantially.

I'll give you an example;
1) Say your power-timing (that's at WOT) works just fine without detonation at 36* at 4000 rpm.
But at 3600, it will only tolerate 32*. So you can figure out that the timing curve cannot be faster than 4* per 400 rpm which is 1* per 100.
But suppose that at 2800rpm she detonates with anything more than 22*. So then from 2800 to 3600 your rate of advance cannot be more than .75* per 100.
And at idle, she likes 12*, so from say 800 to 2800, you can dial in at the rate of .50* per 100.
Such a curve is impossible to build. At the very most, factory parts will only support ONE change in the rate of advance. So which one will you sacrifice? Put that on hold
2) Now lets say, your .73 overdrive and 3.23s cruise at 65=1900, your mechanical timing with the above curve will be 1900 less say 800) x.5*=5.5, plus the Idle-timing of 12=17.5. But Suppose the engine wants 40m degrees to get the peak pressure to occur in the window of 25 to 28 degrees ATDC. So then the Vcan has to bring in 40 less 17.5=22.5. This is just barely doable if you mod your Vcan But if the slanty wants more than 42* she's sol.
Now. the slanty still has to get to 1900! And if that Vcan modification cannot be slowed down enough to keep her out of detonation.... Yur gonna have to sacrifice something; what will it be this time?
Sometimes, the lowest cruise rpm is not the right answer. By 2200, optimum timing targets may be a lil easier to attain; and will get you better fuel economy than crappy timing at 1900.
By 2400, optimum cruise timing should be doable with the factory parts.
From 1900 to 2400 is plus 26%, which is the difference from 3.23s to almost 4.10s
But 4.10s with a 3.09 low and small tires like 26.7s(84"rollout), is brutally low. You will be reaching for to shift into second before having crossed the intersection. I highly advise against 4.10s with 26.7" tires,lol. But with 235/75-15 (92" rollout), 4.10s would be fine.
 
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AJ/FormS said:
Martinsville..... yur only 8.5 hours from me.
As to the engine; Do this:
Get the thing tuned up and running right. Put a 195 stat in it.If it overheats fix it, but make it work with the 195 stat. If it has flat tappets, set them at that temp to .013/.022.
Next; you have to make sure the engine gets the maximum amount of CRUISE-Timing possible, that it tells you it WANTS, not what you might think it wants.
So, Make sure the V-can is working.
IMO, you can leave all the pollution junk on there for now. If it has a lean-burn, make sure the Vacuum pod is functioning. Make sure the Vcan works in Neutral.
Ok next you will need a timing lite and a tachometer.
I'm guessing your combo will cruise at or near 65= 2200.
So at running temperature; in neutral, put it up on the fast idle cam at around 2200 rpm. Then just pull in timing until it stops picking up rpm; don't even put the lite on yet. Then reduce the rpm back to 2200. Next, RETARD the timing some until the rpm peaks again. But if the engine loses rpm, then advance it again, until it stops picking up rpm. And repeat until you find the max timing that makes 2200 rpm.
When the rpm peaks at around 2200 rpm NOW read the timing.
Then retard it three degrees and write the number down. Then return the engine to idle.
Now, if you run outta slot on the distributor before the rpm peaks; modify the slots! for more advance. How will you know ? IDK, I'll guess your slanty will TOLERATE about 42* or more at 2200 in Neutral.
What you have just done, is obtain the maximum advance that your particular combo, WANTS or TOLERATES, at 2200rpm.
Now you just gotta figure out how to make it happen. ( A new post or thread)

As to the chassis:
It is a brick!
I got an 84 with a 318, and the faster I drive it the more gas it sucks....... cuz it has to punch a pretty big hole in the air. So you can't do much about that. But there are some things you can do.
> Hard tire pressures as mentioned
> alignment
> make sure brakes are not dragging and wheelbearing grease ain't turned to soap.
> install new U-joints and repack them before installing, with Moly grease
Install 75/90Gear oil in the rear and STRAIGHT Dextron-II in the trans.
> some say leave the tailgate at home.
> turn the A/C off, keep the windows rolled up. If you have to make a choice, use the A/C
> that's about all I can think of. There are more things you can do, but none are cheap. These will get to to 80 or 90%

Once you have this baselined, then you can map out your timing curves, and see if there's a lil more left in the tune.
Or I'll sell you my 84 and you can steal parts,lol.
Click to expand...

Old thread, new info to me. :popcorn: I finally had time to begin applying your advice to my '64 Dart. /6 with fresh valve job, Holey 1920, stock exhaust, rebuilt 4 spd, 8 1/4" 2.45 rear end with, I think 25" tall tires. 70 MPH at 2,500 RPM. 1) Swapped out the 180-degree thermostat with a 195-degree unit. The temp needle on the dash is one needle width inside the "Normal" range now (and its wintertime!). I can't say if the antique temp guage is accurate, but a needle that close to the ragged edge is a realistic distraction! 2) Resetting the rocker arm / valve gap from 10 and 20 to 13 and 22 increased my compression by 5 PSI to 165.

Cruised from Tacoma to LA two years ago and averaged 17 1/2 - 18 MPG. Put 25 miles on it today in commute stop and go, along with 70 miles cruising between 70 and 80. The little Dart made 20 1/2 MPG for the first time since I've had it! :D Now where is that thread on how to make a red neck timing tape, and my 40 year old Cornwell timing light!? :rolleyes:
 
Most full size truck applications I've seen seem to be a wash between the 225 and the 318 on MPG.
As noted earlier, the 318 is the win as there's more power.
 
I got 18 in my 70 Dart bringing it back from Reno, all interstate at 80 mph with 2.76 gears
 
My 66 Dart, 273-4 get's 18 hwy. if I drive it nice. My 70 318 Swinger get's 18 hwy. pretty consistently. It has dual exhaust and the stock 2 barrel. I am curious how much mileage may change and in what direction with a LD4B and a 650 AVS2. Both are 3.23 SG cars but I run taller 15" tires.
 
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Fuel economy is often lost, just in the getting up to speed.
A half a dozen accelerations from a dead stop with a hiway-geared, 3500# combo, is gonna drop your mileage significantly; no matter how lean you make the cruise circuit.
And if you saw on the throttle, the Accelerator pump is not helping

In the quest for fuel-economy, in a given combo; a dash-mounted, dial-back, timing box, coupled with a distributor that has serious adjustability, will be your best friend, and a high-amperage ignition system or Multi-spark, is your second best friend.
 
A vacuum gauge doesn't hurt, either.
 
AJ/FormS said:
Fuel economy is often lost, just in the getting up to speed.
A half a dozen accelerations from a dead stop with a hiway-geared, 3500# combo, is gonna drop your mileage significantly; no matter how lean you make the cruise circuit.
And if you saw on the throttle, the Accelerator pump is not helping

In the quest for fuel-economy, in a given combo; a dash-mounted, dial-back, timing box, coupled with a distributor that has serious adjustability, will be your best friend, and a high-amperage ignition system or Multi-spark, is your second best friend.
Click to expand...
I was a service writer at a Gm dealer back in the late 70's- 80's ( pre to obd1). I got a big charge out of how most people don't know how to figure mileage.
 
yep.

Even some folks you think surely ought to.
 
I have one friend who, whenever asked, says- "I get *** miles out a of a tank".

While technically part of the equation, it's not the answer, especially since he never volunteers the size of the tank.
 
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