mpg on my 340

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Too rich a mixture, not enough timing advance, brake drag, tire pressure, maybe thermostat running temp too low.
Worn rings, heavy oil.

Not answers, but possible considerations.
 
so when I am reading all those numbers.... why do I have such a bad milage ? 340.. 727 and 3.23... TQ carb..What is the secret ?? Greetings Juergen
And no...I don´t jump in the gaspedal hard !! the 11 mpgis with 55 -60 mph on the autobahn....
That's the million dollar question.
What Darthomas said, and
There are so many factors, it would be a book to try and answer that.
The biggest factors are RPM, and engine efficiency at that RPM, and load. It's pretty simple really. Light weight, low rpm and lean running. Trying to marry those three is when things go haywire for a performance oriented combo.
NO1) lighten the load, reduce friction, reduce wind-resistance..
NO2) Lower the rpm
NO3) Build a,small,efficient,lean-running engine.

Oh wait that's every manufacturers recipe for a modern EFI FWD econobox!
Well that's no good for a hot 340, in a performance E-body.
My guess is your engine is not as efficient as it could be. Perhaps your compression is down or the cam has long ramps, or the tune is just not in it yet.
The 3.23s and the TQ are keepers.As is the Chally, of course.
Loc-up TCs are usually good for about 200rpm at 60mph, and Manual trannys are usually good for an easy 10% better mileage, which is partly why I have an M/T.
 
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Our '69 Formula S FB has a stock 340, 727, P/S and manual drum brakes. The original owner had the stock rear gears changed by the dealer to either 2.91 or 2.76, but I have never checked to find out and think they are 2.91. When we first got it 20 years ago it would routinely get 20 mpg on the freeway at steady 60-65 mph and we were absolutely astonished. That was on pump premium before we had ethanol in the PNW. We don't drive it much on the freeway now, but when we do it gets about 18 mpg on the local 92 UL clear non ethanol gas. The change may be due to the different gas formulation now, I don't know.
 
No matter how much or how little alky is in your fuel it WILL DROP the mileage, because you must have more alky to make the same power. Ever seen an alky carb? They have HUGE jets compared to gasoline.

Retarding advance will drop mileage.

A change of camshafts is likely to, IE I bet it's hard to beat the original stockers for mileage.
 
sounds interessting...
my compression is 175 -180 psi on all cylinders.. brakes do not drag... AFR while cruising is around 14.1-14,4
The cam ?? Don´t know... and yes..my Ignition is probably...the weak point...because I can´t use the VC
If I use her... the engine is pinging... The CR is probably way to high ?

Greetings Juergen
 
sounds interessting...
my compression is 175 -180 psi on all cylinders.. brakes do not drag... AFR while cruising is around 14.1-14,4
The cam ?? Don´t know... and yes..my Ignition is probably...the weak point...because I can´t use the VC
If I use her... the engine is pinging... The CR is probably way to high ?

Greetings Juergen

No you probably just need to adjust the vacuum advance can, you can insert a small allen wrench (hex drive SAE, maybe 1/16"?) and turn the screw inside to change how much advance is put in for the vacuum; in your case counter-clockwise will reduce the advance until a higher vacuum is reached. 180 psi is totally in pump-gas territory. Also remember the vacuum advance line needs to be connected to ported vacuum (only works when throttle is open), not manifold vacuum (which is always working including at idle).

Also your A/F at cruise could be a bit leaner, you would pick up some MPG's getting it to 15-15.5:1 but with a TQ in Germany I'm not sure where you'll find replacement metering rods.
 
On highway (85 - 90 mph) I achieve about 15 mpg with my Duster, stock (except electronic ignition) 340 w. TQ, auto, 3,23 rear...
 
...I have a Carter Trick KIt... also jets from 95 -to 105
Rods..... so I can lean out the carb..
So the Carb is not the problem... the VC is the Issue...

Today I checked my timing.. ( after I changed the set up in the Distributor)
12 deg @ idle... 17 deg @ 1500 rpm 24 deg @ 2000
29 deg @ 2500 and 33 deg. @ 3000 rpm.. ( without the VC ! )
With VC... the timing goes up to 46 deg. @ 3000

But if I use the VC,,,I always have this klicking /pinging sound when I drive steady in the 50 to 60 mph range...
60 mph ...in my case equals 2650 rpm... more or less close to the peak of the timingcurve...with /or without VC... The engine accepts 33 deg... of timing...but the 13 deg from the VC... are too much...
The VC is connected to the Ported vacuum btw.
so perhaps I need to reduce the VC a bit more.. but then
I will end up with 42 deg.. all in..incl VC.
Greetings Juergen
 
Either you have a combustion chamber problem, like carbon build up or oil getting into the cylinder, or a serious cam timing problem, or a combination of way too much compression or not good enough fuel octane. The last "in the mix" is engine running temperature.
 
...I have a Carter Trick KIt... also jets from 95 -to 105
Rods..... so I can lean out the carb..
So the Carb is not the problem... the VC is the Issue...

Today I checked my timing.. ( after I changed the set up in the Distributor)
12 deg @ idle... 17 deg @ 1500 rpm 24 deg @ 2000
29 deg @ 2500 and 33 deg. @ 3000 rpm.. ( without the VC ! )
With VC... the timing goes up to 46 deg. @ 3000

But if I use the VC,,,I always have this klicking /pinging sound when I drive steady in the 50 to 60 mph range...
60 mph ...in my case equals 2650 rpm... more or less close to the peak of the timingcurve...with /or without VC... The engine accepts 33 deg... of timing...but the 13 deg from the VC... are too much...
The VC is connected to the Ported vacuum btw.
so perhaps I need to reduce the VC a bit more.. but then
I will end up with 42 deg.. all in..incl VC.
Greetings Juergen

Sounds like you know what's going on, thanks for the details... I think adjusting the vacuum advance can is all you really need to do. It won't reduce the total degrees from the VC but will make it so the advance doesn't come in until you have more vacuum. Does it ping all the time even on a flat road with the VC hooked up or is it more when you come to a hill and you give it a little more gas pedal to maintain speed?

Regarding the thread topic FWIW I average 16 mpg about 60/40 city/hwy with my 10.5:1 360 w/ Mag heads, 904 auto and 2.94 gears. Highway is probably closer to 19-20, city prob around 14-15. I'm expecting it to go down when I swap in a bigger cam and 3.55 gears, how much I'll have to wait to see.
 
.... the pinging occurs in two different situations....
When I accelerate FULL ( but not the first lets say 2500 prm ) The AFR is RICH under this condition.. around 10.5 -11.0 ...
The other Pinging ( just a bit......very very silent ) is under steady load.... i.e not accelerating...but also not going slower... also around 2500 rpm ....more or less some revs...
Carbon built up doesn´t exist... and the engine also don´t uses oil.. less than a 1/4 of a quart / 1000 miles
About the camshaft timing... I installed a new chain set
including a chain tensioner...but the Timing issues existed before the chainset change... also...
Engine Temp is 200 °F all the time...I use a 195°F thermostat.... perhaps I need to go down to a 180°F
Thermostat..?? The 340 came from the factory with a 195° F as far as I know...

Greetings Juergen
 
i would think the airgap style intake would be the worst possible choice for mileage.
so hard to vaporize the cool gas.You need the heat.There is currently
another thread about 383 mileage
 
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Best tricks for mileage are timing setup - and run the vacuum can; and tire pressure/alignment. Pump the tires up tto the "maxpressure" noted ont eh sidewall. Make sure the car's alignment is good. And tune the timing first with the vacuum can, then tweak the carb. I've gotten 17 in a 383 C body with 3.55s, a customer's 496 is getting 13 on the highway and makes just shy of 600hp, another with a small block 422 has over 20K on it and gets over 17. It's all in the parts choices and tuning.
 
my compression is 175 -180 psi on all cylinders. AFR while cruising is around 14.1-14,4
The cam ?? Don´t know... and yes..my Ignition is probably...the weak point...because I can´t use the VC If I use her... the engine is pinging... The CR is probably way to high
...I have a Carter Trick KIt... also jets from 95 -to 105
Rods..... so I can lean out the carb..
So the Carb is not the problem... the VC is the Issue...
Today I checked my timing.. ( after I changed the set up in the Distributor)
12 deg @ idle... 17 deg @ 1500 rpm 24 deg @ 2000
29 deg @ 2500 and 33 deg. @ 3000 rpm.. ( without the VC ! )
With VC... the timing goes up to 46 deg. @ 3000
But if I use the VC,,,I always have this klicking /pinging sound when I drive steady in the 50 to 60 mph range...
60 mph ...in my case equals 2650 rpm... more or less close to the peak of the timingcurve...with /or without VC... The engine accepts 33 deg... of timing...but the 13 deg from the VC... are too much...
The VC is connected to the Ported vacuum btw.
so perhaps I need to reduce the VC a bit more.. but then will end up with 42 deg.. all in..incl VC.Greetings Juergen

-This post is, for me, very hard to read; are you saying that with the Vcan disconnected, you are having NO detonation issues while cruising?
-So I'm gonna reduce all this to one line: 12/33@3000 plus 13ported, no detonation on the mechanical curve. Is that right?
Well then it seems obvious to me;
-Detonation is caused mostly by too high a temperature in the chamber.
It might be due to; excessive timing,or too high a cooling system temperature, or a restrictive exhaust, or the carb sucking hot underhood air. I leave the timing for last, cuz you can lose a fair amount of driveability when sacrificing timing.And you can gain power with fresh cold air and a free-flowing exhaust.I also try not to sacrifice the minimum running temp.
-Someone mentioned running a lower temperature. This is an option; just remember that the thermostat sets the minimum running temp. If you are running 200*F at highway speed with a 180*stat, you will be running the same with a 160*. If you want to run a cooler highway speed, you will have to figure out how to shed heat faster.

But if you are now down to timing;
-Here's what you need to do; map your mechanical advance against rpm, on a graph paper, and you will instantly see the issue. Run advance up the left vertical axis and rpm along the horizontal.In your case it is a straight line running up very steeply.This curve won't work with your cylinder pressure, and your available fuel. OK let me rephrase that; it didn't work on my combo which is very similar to yours. You have two choices;1) reduce your cylinder pressure, and 2) delay your timings
-Your curve is putting too much timings in for a 2650 rpm cruise.
All your mechanical advance is not allowing the Vcan to function as it is intended too.
- Your curve works out to be 1*/100rpm, beginning at about 1000rpm; so at 2650 your all-in mechanical might be 16.5 +12=28.5 And you have 46 -33 =13* in the can, so TOTAL cruise timing @2650,should be 28.5 + 13= 41.5, and you say this is too much.You also say that the 28.5 by itself is ok. So, the solution is to find out exactly what she wants, between those two.And then redesign the curves to provide it. And the easiest way to find out,is to just rev the engine up to 2850 and set the total(with vacuum advance) to some arbitrary number between 28.5 and 41.5 and see what sticks.When you find it, deduct the 13 and you will be left with the mechanical target to hit.
-Example; let's say you found that 37* was accepted by the engine at 2650 while cruising. Then 37 less the 13 in the can, Equals 24* so you will have to build a curve that makes 24* at 2650 rpm.Bada-Boom!
-At this point you will be thinking that you are gonna have to make a choice between power and economy.I tell you what if you can tell the difference between 28.5 and 24 at 2650 at WOT, your but-dyno is a heck of a lot more sensitive than mine.You are only ever at WOT and 2650 when you are on your way to some higher rpm. And if you have something like a 2400TC, then you are talking maybe,one or two seconds in the zone from 2400 to 3300(depending on your power to weight ratio). At most non-WOT throttle settings you will probably be on the primaries, and the power difference will be un-noticed; so give the engine what it wants for cruising, and forget about any powerloss.
-You might be able satisfy the cruise timing requirement with a single stage curve, by delaying full mechanical timing to some higher rpm, than where it comes in now. I'll guess 3600 or perhaps even a little higher.When you build your own engine, you kindof have to throw out the timing book and let the engine tell you what it wants.But if not;
-I gotta warn you,a two-stage curve is not easy to build. The curve needs to have a kink in it. (At 180psi, my combo needed it's power-timing to be slowed down from 2800 and on.The max mine will accept at 2800 is 28*, but from 3400 on it will accept up to 36*).I suspect yours will want a similar curve. The dizzy will need two different kinds of springs. One of them has to have a long-loop that basically does nothing, for the longest time, and when it finally comes into play it slows down the other spring.The second spring will be doing all the work while the long-looper is on vacation. Since it is now doing the work of two springs, it needs to be twice as strong. I have only ever set up factory dizzys this way.I doubt you will find a spring-pair to work exactly as your engine needs. When I get close, I start lightening up the flyweights to dial it in.The positioning of the kink needs to be done by you, experimentally. I can't tell you where to put it, but;
-But putting the kink at 2800 worked for me.I run about .78*/100rpm(below 2800). So at my cruise rpm,(2200); I run 14idle plus 10centrifugal plus 22 in the can equals 46 total cruise-timing.. The engine is fine with 7/8 more from my dash-mounted dial-back timing gizmo.But it really makes not much difference, so I just leave it at 46*@2200. So my timing works out to 14/34@3400,plus 22ported
 
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A pretty ingenious idea I got from a book I have on tuning Holley carbs by David Vizard, you can use a hand-held vacuum pump (Mity-vac) hooked up to the vacuum advance can to help dial-in the needed advance. It allows you to manually adjust the timing in the car while driving.
 
Not to contaminate this thread with non-Mopar stuff... but even my 68 El Camino SS with a slightly warmed over 396 got 17-ish mpg on the german highway. Other car was a 70 Challenger with a lowly 318 that used more. :)
Both are long gone...
 
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Once again I'll post my 2000 Dakota R/T 5.9 CC Mileage.

At 60 MPH 2000 RPM through the O/D effective final drive of 2.8x (3.92x.73) EVIC says 17 MPG.

At 50 MPH 1650 RPM EVIC says 23 MPG.

EVIC verified by actual math to be within .5 MPG over three full tanks.

So no, peak torque is not peak MPG.
 
My last trip my 410ci stroker got 14mpg cruising 80mph at 3200rpm.
28" tires with 3.23 gears.
 
Once again I'll post my 2000 Dakota R/T 5.9 CC Mileage.
At 60 MPH 2000 RPM through the O/D effective final drive of 2.8x (3.92x.73) EVIC says 17 MPG.
At 50 MPH 1650 RPM EVIC says 23 MPG.
EVIC verified by actual math to be within .5 MPG over three full tanks.

So no, peak torque is not peak MPG.
If peak torque was the place to cruise at,our powerful street sbms would be cruising at between 3700ish and 4500ish,I think.And you have proved the Mpg to Rpm relationship.
Peak torque is more important for your rotor tiller.

I have had good results with gearing for peak vacuum when in neutral. If it vacuum-peaks at 2200, I would consider that about the lowest fuel-efficient cruise rpm. A similar engine that vacuum-peaks at 1400 will usually get better fuel mileage than the one that peaks at 2200. I proved this with my engine, by having run it with 3 different cams from 270 to 292 advertised durations. The Scr was adjusted with each, to keep the Dcr within about a quarter point. The final drive ratios were adjusted with each, to work with the peak-vacuum. The cruise fuel-mileage varied widely. Of course the 292 was the worst, and the 270 was the best.The AirGap, and Eddies, stayed on all of them.As to cruising,Nothing else was changed except the cams and the final drives, and occasionally the carb. With the 270cam,I also experimented with many different final drives. At one point I was down to 1.53 (2.76 x .71 x .78). this made 85mph = 1700, and 65 = 1300. This cam could pull phenomenal mpgs.It also had a ton of torque. More than the other two,especially the 292. This 270cam was pretty happy with a starter gear around 10.0/1. It loved 11/1. Now, 12/1 was just too low,and the 13.28 (3.09 x 4.30s) was wild and ridiculously low and that rear was not in there very long. And while 9/1 was acceptable in most cases, the 11/1 was the favorite.
In case you are wondering, these are the chunks I tried;2.73/2.94/3.23/3.55/3.91/4.10/4.30/4.86/5.13. Eventually; the 5.13s spit out two teeth,the 4.10s I traded away for the 3.55s,the 3.91s got noisy and I was unable to re-adjust it quieter so I junked 'em,and the 4.30s are now sold.This is now going on 17 years since I started. (I still have the 4.86s;any takers?) The various engines have also been tried with trannys having lows of 2.47/2.66/3.09.
--My favorite will always be the 270cam with the 3.09-o/d box,3.55s, and the GearVendor splitter. This was an extremely nice combo, for every conceivable driving circumstance..This thing vacuum-peaked very low,and was quite happy with; a 1.97 final drive,and a 10.97 starter.It cruised at about 1600Rs, having vacuum-peaked a little earlier.
--I would still be driving this combo, except the cam dropped 2 lobes when they took the ZDDP out of the oil.It would be most excellent with my final gearing as it is today; 3.09-1.92-1.40-1.09-.78od, and split %s of 62-73-78-71 into od.
 
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66/72 sounds kindof lean, I can barely hit 60mph with 66's, and there's nothing left over for PT acceleration.But if you can make it work, hey, MorePowerToYa. 10/16 is pretty good spread.
Our A's only take between 40 and 50 hp to maintain 60 mph, so if I estimate 45hp, that would be 3.75 gallonsUS per hour. Of course 60 mpg is a mile a minute, so those 3.75 gallons will move you 60 miles. That then looks like 60 miles per 3.75 gallons which reduces to 16mpgUs. So you are right on target.
Mind you this is for an A/F more suited to WOT,So I would expect this to be a minimum mpg.



I bet you can. 16 should not be hard, at steady-state cruise


150/40=3.75 km/liter.Times that by 4.55 to convert from liters to Canadian gallons, and times .62 to convert to miles is 10.58 mpgImp. To convert that to Usg, times it by .8, equals 8.46 mpgUS, as already said. I just love the math exercise


Yeah you are probly a little off-tune too.


I believe that could be possible




Here's my recipe;
So, take one 10.9 aluminum headed 360 with a 223* cam, headers and AirGap. Install a 600Vac Secondary.Get the timing right, and leannnnnnnnnnnn out the low speed circuit. Then put a teensy bit back in for safety sake. With a stick and wicked highway gears, expect into the 30s mpgUS@80mph. Easy recipe.Just leannnnnnnnn her out.
And a wagon load of timing.Just pour it in, and pour it in. I gave her 50 then 55 then 57,60,&62, then I ran out. She still was taking it.( For those that are curious; I have a dash-mounted, Dial-Back Timing Gizmo. Best tool I ever bought.The range is 15 degrees) .
How is that possible you ask? Ok,Ok, I'll tell you.
I was using the GV .78overdrive behind an A833-O/D and 3.55s, so my final drive ratio, in double O/D, was 1.97, and 80mph was 1999 rpm calculated.And I had modded the carb to accept wire restrictors in the idle wells. And I had several wire-sets with various cross-sections. I was not yet running on the edge.

Fast forward a few years.
Gone are; the 223*, the double O/D, and the 600.
Swapped in are ; a 230*, .78 O/D, and a 750DP.
I get about 10 USg combined; no more long trips........


Thanks for the detailed response AJ, I did mention that I have a power valve in the front primary, I always jet up 8 sizes when I remove one, whats your opion?
 
My best combo was always 12 degree static timing, plus 12 degrees mechanical, plus 12 degrees vacuum advance.
I always limited the max mech advance with fixed stops in the slots where the dist weights swing out, to about half of the maximi
 
My best combo was always 12 degree static timing, plus 12 degrees mechanical, plus 12 degrees vacuum advance.
I always limited the max mech advance with fixed stops in the slots where the dist weights swing out, to about half of the maximi

Surely you mistyped that. 24 degrees? THIRTY four, maybe. "In the day" my factory stock 71, I used to run a lot closer to 38-40 "total" with vacuum on top of that. This was a hi compression 71 engine, "allegedly" 10.X :1.

The old 70RR with the 340 in it would "run right with" a stocker 383 RR
 
I followed the recommendations of the typewritten ancient "yellow cover" Direct Connection racing notes shop bible that said
"Thou shalt attempt to always provide 36 degrees total advance at the desired efficiency application."
 
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