My 340 getting 6 mpg

-
So I'll chime in on carb choice. The carb you have has mechanical secondaries. When you floor it the secondaries are wide open no matter what, plus a double shot from the accelerator pumps (they did that to cover the massive sudden vacuum drop in the carb). You could use a Holley with vacuum secondaries, or an Edelbrock AFB or AVS2. All those carbs have secondaries that are controlled by the demand for air/fuel by the engine. With them you can guess high on the size of the carb and the secondaries might not be all the way open until the top end rpms. I'd try an 800 AVS2.

If I can get 15 mpg out of my 340 with 2 Eddie AFB 500s, you can do better than you are doing! By the way I absolutely love your car!
DSC02942.JPG
 
Ill trade your 6 mpg for my 3mpg!
Look every time you hit that throttle you get maybe a fifth of gas mileage you will at cruze, that loud pedal comes with a price.
 
I would try another carb if you can. Even a factory carb. Anything. The carb you have may have some sort of internal fault. Fuel is pouring into the engine, almost literally. Have you checked for leaking needle & seats? Correct float level? Those are basics to carb set up. Tuning starts after the correct idle ign timing has been determined & set.
If someone advised you to use 10* initial timing, then never take their advice again because they have no clue.
 
Get rid of that carb.... try another
one.. the carb is dumping fuel. float adjustments . needle and seats pin hole in float . 6 mpg has nothing to do with timing or such in you case.
 
Harbor city, CA
Elevation 49ft
CylinderPressure, unspecified
transmission, unspecified
stall speed, unspecified
cruise-timing, unspecified
IDK how anyone can give you accurate advice.

But yeah, as I said earlier, 67PMJs are gonna be lean, requiring extra throttle to get to 65mph, and possibly to maintain it.
Put some 70s in there and 78s in the back, and a 10.5 PV. Sync the Transfer ports, reset your pumps, Modify your VA and Mechanical Timing Curve to, together, generate at least 48* of Cruise timing.

Here's how to set your cruise timing exactly right.
1) check your timing at cruise-rpm
2) rev your engine up to cruise rpm, Set your cruise timing to 48*, then
3) keep it there for the rest of this test.
4) without regard to the actual timing number, advance the timing a small amount. If the rpm goes up, bring it back to the reference rpm. Then repeat until additional timing produces no additional rpm.
5) but if additional timing from 48* does not produce additional rpm, then go the other way, taking out timing, looking for the whatever timing makes the rpm to peak.
6) after the max cruise timing is found; determine if the AFR is rich or lean, at that rpm, and fix it.
7) finally, take out 3 degrees of advance, to compensate for the lack of cruise load. Read the timing; Whatever you get now, at cruise rpm, that is what your engine combo needs and wants, and that is your target.
8) reset your cruise-timing to what it was in step one above; then return the engine to idle and let it cool before shutting it off.
9) now you gotta figure out how to get to that target.


Notes.
1) what you are hunting for is the magic timing number required at cruise-rpm, at the smallest throttle opening, that the engine combo is able to produce. Then lean it out to the minimum amount of fuel to maintain that rpm, at that throttle opening.
This is so easy, and it works for any cruise-rpm.

2) I once had a combo that cruised 75@ 1840 rpm, in double-overdrive. I used this method, and she gave me back 32 mpgUSg. I'm certain that if I had been cruising in direct at 3300, the results would have been very different.

3) Another thing I did was to, at cruise rpm/speed, put the trans into neutral and see how much distance it took to slow down to about 20 mph.
Then I checked the cars mechanicals to see what could be done to increase this distance. Things like adjusting the wheelbearings , the brakes, installing new U-joints, adjusting the front-end height, the attack-angle of the rear spoiler, and of course, the tire pressures and the alignment.

4) I don't run that combo any more. That cam lost lobes, and I replaced it with the next bigger size from the same manufacturer. This new cam lost bottom-end, big-time, relatively speaking, leading to a different transmission, and the loss of Second overdrive.
I took the engine apart, and increased the Scr some more, with slight loss of Quench.
The new combo cruises at 65=2240, and forget about 32mpgs. But it's still pretty good. But she now likes 56* or more, of cruize-timing. and I leaned her out a bit more, lol.
5) At cruise rpm the engine doesn't care about how many accelerator pumps are on the carb, and it doesn't care if it has vacuum-secondaries nor what size MJs are in it unless the PMJs are just too small, to even get to the desired cruising speed. It doesn't even care about the Transfer slot sync. unless the idle-mixture screws are cranked right out.
6) at cruize rpm, the engine only cares about maximum cruise-timing and minimum fueling, for the load it is pulling, which can change quite a bit with the engine's running temperature.
Addition concerns are; the inlet air temp, and of course the air density and humidity.
Some things cannot be easily compensated for, like the amount and strength of the overlap cycle, and most especially with the amount of power extraction degrees.
In your case I grossed your cam up to guess at the zero-lash numbers and the formula spit out just 106 degrees. This makes your compression degrees and your extraction degrees nearly identical to mine, with the exception that you overlap is about 67* to my 61*.
I see almost no reason that your combo, being roughly 600 pounds lighter than mine, couldn't out-perform mine in the fuel-economy arena, if we both ran at the same rpm. At that point, the only advantages that I might have is the 3.58 stroke, maybe a slipperier body, and the fact that I run a minimum coolant temp of 207, with fresh cold, above-the-hood inlet air.
And BTW, I run an ancient 750DP Holley that I bought used in about 1977. Notta chance would I, if I had your carb, give it up, no way.

7) Just to give you food for thought;
My previous cam was
276int/115comp/112Power/276 exh/53*o-lap
As you can see the extraction was 112* to your estimated by me, 106*
This cam was 223/230 @050; and it was way more fun than the cam that followed, namely,
276/114/105/286/61* overlap 230/237@050

Your 234/244 has at least 4* more exhaust duration than it needs, and for the lightweight car probably 8 or 10 too much. which at WOT is a maybe a good thing, but those extra degrees are stolen from the extraction cycle, which means, that at cruise rpm, a lotta pressure is going right out the tailpipe.

If I had your cam, I would retime it to 2* retarded, in at 110; But, this will reduce your CCP, which is why I asked for your current compression test results. If you are in at 104 now, going to 110, that represents a pressure loss of perhaps as much as 12psi, which with 3.91s and a 3500TC you won't hardly notice. But with 3.23s and a manual trans, I know is gonna suck.
However the 110 degrees of resulting Power extraction versus my estmated 106, is gonna make a huge difference in the potential to make fuel-economy, after the carb and timing is cleaned up.
I'm pretty sure your combo can't ever make 32mpgs, but I'll bet 20 in steady-state at 65=2400 is doable, and with any 750, and more with a spreadbore with triple boosters.
 
Last edited:
AJ/FormS said:
Harbor city, CA
Elevation 49ft
CCP unspecified
transmission, unspecified
stall speed, unspecified
cruise-timing unspecified
IDK how anyone can give you accurate advice.

But yeah, as I said earlier, 67PMJs are gonna be really lean, requiring a lotta throttle to get to 65mph, and also possibly to maintain it.
Put some 70s in there and 78s in the back, and a 10.5 PV. Sync the Transfer ports, reset your pumps, Modify your VA and Mechanical Timing Curve to, together, generate at least 52* of Cruise timing.

Here's how to set your cruise timing exactly right.
1) check your timing at cruise-rpm
2) Set your cruise timing to 48*
3) rev your engine up to cruise rpm, and keep it there for the rest of this test.
4) without regard to the actual timing number, advance the timing a small amount. If the rpm goes up, bring it back to the reference rpm. Then repeat until additional timing produces no additional rpm.
5) but if additional timing from 48* does not produce additional rpm, then go the other way, taking out timing, looking for the max rpm at whatever timing.
6) after the max cruise timing is found; determine if the AFR is rich or lean, at that rpm and fix it.
7) finally, take out 3 degrees of advance, to compensate for the lack of cruise load. Read the timing; Whatever you get at cruise rpm, that is what your engine combo needs and wants, and that is your target.
8) reset your cruise-timing to what it was in step one above; then return the engine to idle and let it cool before shutting it off.
9) now you gotta figure out how to get to that target.


Notes.
1) what you are hunting for is the magic timing number required at cruise-rpm, at the smallest throttle opening, that the engine combo is able to produce. Then lean it out to the minimum amount of fuel to maintain that rpm, at that throttle opening.
This is so easy, and it works for any cruise-rpm.

2) I once had a combo that cruised 75@ 1840 rpm, in double-overdrive. I used this method, and she gave me back 32 mpgUSg. I'm certain that if I had been cruising in direct at 3300, the results would have been very different.

3) Another thing I did was to, at cruise rpm/speed, put the trans into neutral and see how much distance it took to slow down to about 20 mph.
Then I checked the cars mechanicals to see what could be done to increase this distance. Things like adjusting the wheelbearings , the brakes, installing new U-joints, adjusting the front-end height, the attack-angle of the rear spoiler, and of course, the tire pressures and the alignment.

4) I don't run that combo any more. That cam lost lobes, and I replaced it with the next bigger size from the same manufacturer. This new cam lost bottom-end, big-time, relatively speaking, leading to a different transmission, and the loss of Second overdrive.
The new combo cruises at 65=2240, and forget about 32mpgs. But it's still pretty good. But she now likes 56* or more, of cruize-timing. and I leaned her out a bit more, lol.
Click to expand...
AJ, you are such a wealth of great info, thank you! I'll be applying some of your advice to my set up asap. Printing this one for my archives.
 
I think I am getting about 8 in my 64 dart with 340 3.55 gears 10.5 to 1 CR 750 vac sec 284 484 cam

one thing to consider is everytime you stop the gas in the Carb evaporates pretty quickly.
 
trapster said:
I think I am getting about 8 in my 64 dart with 340 3.55 gears 10.5 to 1 CR 750 vac sec 284 484 cam

one thing to consider is everytime you stop the gas in the Carb evaporates pretty quickly.
Click to expand...

Only if there's something wrong with your carburetor or you have a major heat soak issue.

I've never had that issue with my Holley double pumper, even in 110° temperatures. Even the Edelbrock I run on my truck takes several days.
 
AJ/FormS said:
Harbor city, CA
Elevation 49ft
CylinderPressure, unspecified
transmission, unspecified
stall speed, unspecified
cruise-timing, unspecified
IDK how anyone can give you accurate advice.

But yeah, as I said earlier, 67PMJs are gonna be lean, requiring extra throttle to get to 65mph, and possibly to maintain it.
Put some 70s in there and 78s in the back, and a 10.5 PV. Sync the Transfer ports, reset your pumps, Modify your VA and Mechanical Timing Curve to, together, generate at least 48* of Cruise timing.

Here's how to set your cruise timing exactly right.
1) check your timing at cruise-rpm
2) rev your engine up to cruise rpm, Set your cruise timing to 48*, then
3) keep it there for the rest of this test.
4) without regard to the actual timing number, advance the timing a small amount. If the rpm goes up, bring it back to the reference rpm. Then repeat until additional timing produces no additional rpm.
5) but if additional timing from 48* does not produce additional rpm, then go the other way, taking out timing, looking for the whatever timing makes the rpm to peak.
6) after the max cruise timing is found; determine if the AFR is rich or lean, at that rpm, and fix it.
7) finally, take out 3 degrees of advance, to compensate for the lack of cruise load. Read the timing; Whatever you get now, at cruise rpm, that is what your engine combo needs and wants, and that is your target.
8) reset your cruise-timing to what it was in step one above; then return the engine to idle and let it cool before shutting it off.
9) now you gotta figure out how to get to that target.


Notes.
1) what you are hunting for is the magic timing number required at cruise-rpm, at the smallest throttle opening, that the engine combo is able to produce. Then lean it out to the minimum amount of fuel to maintain that rpm, at that throttle opening.
This is so easy, and it works for any cruise-rpm.

2) I once had a combo that cruised 75@ 1840 rpm, in double-overdrive. I used this method, and she gave me back 32 mpgUSg. I'm certain that if I had been cruising in direct at 3300, the results would have been very different.

3) Another thing I did was to, at cruise rpm/speed, put the trans into neutral and see how much distance it took to slow down to about 20 mph.
Then I checked the cars mechanicals to see what could be done to increase this distance. Things like adjusting the wheelbearings , the brakes, installing new U-joints, adjusting the front-end height, the attack-angle of the rear spoiler, and of course, the tire pressures and the alignment.

4) I don't run that combo any more. That cam lost lobes, and I replaced it with the next bigger size from the same manufacturer. This new cam lost bottom-end, big-time, relatively speaking, leading to a different transmission, and the loss of Second overdrive.
I took the engine apart, and increased the Scr some more, with slight loss of Quench.
The new combo cruises at 65=2240, and forget about 32mpgs. But it's still pretty good. But she now likes 56* or more, of cruize-timing. and I leaned her out a bit more, lol.
5) At cruise rpm the engine doesn't care about how many accelerator pumps are on the carb, and it doesn't care if it has vacuum-secondaries nor what size MJs are in it unless the PMJs are just too small, to even get to the desired cruising speed. It doesn't even care about the Transfer slot sync. unless the idle-mixture screws are cranked right out.
6) at cruize rpm, the engine only cares about maximum cruise-timing and minimum fueling, for the load it is pulling, which can change quite a bit with the engine's running temperature.
Addition concerns are; the inlet air temp, and of course the air density and humidity.
Some things cannot be easily compensated for, like the amount and strength of the overlap cycle, and most especially with the amount of power extraction degrees.
In your case I grossed your cam up to guess at the zero-lash numbers and the formula spit out just 106 degrees. This makes your compression degrees and your extraction degrees nearly identical to mine, with the exception that you overlap is about 67* to my 61*.
I see almost no reason that your combo, being roughly 600 pounds lighter than mine, couldn't out-perform mine in the fuel-economy arena, if we both ran at the same rpm. At that point, the only advantages that I might have is the 3.58 stroke, maybe a slipperier body, and the fact that I run a minimum coolant temp of 207, with fresh cold, above-the-hood inlet air.
And BTW, I run an ancient 750DP Holley that I bought used in about 1977. Notta chance would I, if I had your carb, give it up, no way.

7) Just to give you food for thought;
My previous cam was
276int/115comp/112Power/276 exh/53*o-lap
As you can see the extraction was 112* to your estimated by me, 106*
This cam was 223/230 @050; and it was way more fun than the cam that followed, namely,
276/114/105/286/61* overlap 230/237@050

Your 234/244 has at least 4* more exhaust duration than it needs, and for the lightweight car probably 8 or 10 too much. which at WOT is a maybe a good thing, but those extra degrees are stolen from the extraction cycle, which means, that at cruise rpm, a lotta pressure is going right out the tailpipe.

If I had your cam, I would retime it to 2* retarded, in at 110; But, this will reduce your CCP, which is why I asked for your current compression test results. If you are in at 104 now, going to 110, that represents a pressure loss of perhaps as much as 12psi, which with 3.91s and a 3500TC you won't hardly notice. But with 3.23s and a manual trans, I know is gonna suck.
However the 110 degrees of resulting Power extraction versus my estmated 106, is gonna make a huge difference in the potential to make fuel-economy, after the carb and timing is cleaned up.
I'm pretty sure your combo can't ever make 32mpgs, but I'll bet 20 in steady-state at 65=2400 is doable, and with any 750, and more with a spreadbore with triple boosters.
Click to expand...
Please stfu
 
I'm heading to his place to tune the carb sat or sunday... and will change the adv bushing ,increase the initial timing by 10 degrees and then see what it gets.

If anyone in the area wants to come with and see what I'm doing, message me.
 
Last edited:
AJ/FormS said:
Not a lot to go one, but
I can guess with the best of them.

My questions are;
>at what speed were you driving to get that 6mpg, or by tach, what rpm? or was it combined city/hiway?
Then
>At what elevation are you operating at; cuz 67s at sealevel are way too lean.
>What's your Cylinder Pressure? Cuz that combo wants at least 10/1 true Scr, /or 160/165psi..
At 140 psi, the fuel-economy will tank.
>iron heads?
>Who told you the power peak on that cam was 6800? My guess is more like 5300.

>With 3.73s, a manual trans, and 24" tires; 65mph calculates to 3400rpm. For cruising and to get optimum fuel economy your timing is gonna want to be about 56* advanced.
with an auto-trans your rpm
might be/should be, within +/- 3 %.

What I imagine; and/or am afraid of;
> is that cylinder pressure is lower than optimum, and the
> for cruising;
> the cruise timing is way short of the mark, and
the idle-mixture screws are set way too rich, and 67 MJs are way too lean
and the the throttles are way too far open, in an attempt to compensate for all those short-comings.
> and I'll bet you are trying to run a 160* thermostat, with the carb sucking hot underhood air.

I mean your cam is not that far from mine, and my car comes in at 3650/me in it, runs 3.55s, with a 360 even!, burns 87E10 with PMJs in the 70/72 window, and in my wildest dreams I could never get it down to 6mpgs on the hiway. notta chance. If it wasn't at least 3 or more times that, I'd worry.
Oh sorry, I run at 65=2240 rpm in overdrive lol.
And BTW
Your car requires a certain amount of fuel to make a specific amount of cruising horsepower. Lets say your particular car requires 40 hp to maintain 65 mph. Doing the math on that, I get 16.7mpg. Because your engine is spinning at about double the rpm it would require to make 40 hp, a bunch of fuel is getting burned up and/or wasted in just making the rpm, and the cylinder pressure, and fighting ring-drag, etc. So while I agree with everyone that 6mpg is insane, lol, Yur combo is never gonna be that great, and I can tell you, that one of the reasons, is the very short extraction period of that cam.
By my guess, that comes to around 106*@ zero lash, probably less, which means that your pistons are down just a tic over halfway, when the exhaust valve opens, allowing the still expanding hot exhaust gasses to escape the cylinders and heat up whatever they come into contact with. Are you having overheat issues? this could be part of it.
And another thing;
By my guess, that cam of yours has around 67* of overlap. Which, with headers, and screaming down the hiway at 3400 rpm, is gonna put a major yank on the plenum, pulling raw gas right across the piston-tops and into the headers. Imagine what that does to your fuel-economy.
BTW-2
The 750 double-pumper is the right carb for that combo.
1) the accelerator pumps only operate while the throttle valves are moving, and after the shot is delivered, you won't get another shot until you close the throttle valves first. So; at a steady speed, neither of the pumps are doing anything.
And you can adjust those pumps about three ways, to work on your combo. Not every combo needs them to run at max.
BTW-3
I did not read every post, so by now, surely somebody talked about synchronizing the Transfer slots to the Idle-mixture screws.
If that carb does NOT have a 4-corner idle system,
then IMO, the primary throttle valves will need to be drilled, to give the engine the air that it wants without jamming extra gas into it. If this is not done, then the mixture screws will end up wrong, usually too rich at off-idle but low throttle openings. ie a rich cruise condition.
BTW-4
>you are running a PCV right? this is NOT an option.
> I've never had an unheated O2-sensor read right at idle.

Crap, I'm falling asleep, I gotta go lie down
Click to expand...
I’ve said it before listen to this man or pay him to ck it out and tune it. Ahh yes the Almighty cylinder. Pressure.
 
str12-340 said:
So I'll chime in on carb choice. The carb you have has mechanical secondaries. When you floor it the secondaries are wide open no matter what, plus a double shot from the accelerator pumps (they did that to cover the massive sudden vacuum drop in the carb). You could use a Holley with vacuum secondaries, or an Edelbrock AFB or AVS2. All those carbs have secondaries that are controlled by the demand for air/fuel by the engine. With them you can guess high on the size of the carb and the secondaries might not be all the way open until the top end rpms. I'd try an 800 AVS2.

If I can get 15 mpg out of my 340 with 2 Eddie AFB 500s, you can do better than you are doing! By the way I absolutely love your car!
View attachment 1716243998
Click to expand...
Thank you for your response!

I will take your suggestions into consideration. At this point ive spent the money on this carb. Mopar official will be coming this Saturday to tune it for me. And we will see what we get. But i have been told by multiple people about the edelbrock AVS. I will keep an eye out and most likely snatch one when it comes up. Just to have it

Secondly. Thank you for your words about my car. If your on instagram. You can see more pictures on the cars profile @64whiteghost

20240327_164140.jpg
 
AJ/FormS said:
Harbor city, CA
Elevation 49ft
CylinderPressure, unspecified
transmission, unspecified
stall speed, unspecified
cruise-timing, unspecified
IDK how anyone can give you accurate advice.

But yeah, as I said earlier, 67PMJs are gonna be lean, requiring extra throttle to get to 65mph, and possibly to maintain it.
Put some 70s in there and 78s in the back, and a 10.5 PV. Sync the Transfer ports, reset your pumps, Modify your VA and Mechanical Timing Curve to, together, generate at least 48* of Cruise timing.

Here's how to set your cruise timing exactly right.
1) check your timing at cruise-rpm
2) rev your engine up to cruise rpm, Set your cruise timing to 48*, then
3) keep it there for the rest of this test.
4) without regard to the actual timing number, advance the timing a small amount. If the rpm goes up, bring it back to the reference rpm. Then repeat until additional timing produces no additional rpm.
5) but if additional timing from 48* does not produce additional rpm, then go the other way, taking out timing, looking for the whatever timing makes the rpm to peak.
6) after the max cruise timing is found; determine if the AFR is rich or lean, at that rpm, and fix it.
7) finally, take out 3 degrees of advance, to compensate for the lack of cruise load. Read the timing; Whatever you get now, at cruise rpm, that is what your engine combo needs and wants, and that is your target.
8) reset your cruise-timing to what it was in step one above; then return the engine to idle and let it cool before shutting it off.
9) now you gotta figure out how to get to that target.


Notes.
1) what you are hunting for is the magic timing number required at cruise-rpm, at the smallest throttle opening, that the engine combo is able to produce. Then lean it out to the minimum amount of fuel to maintain that rpm, at that throttle opening.
This is so easy, and it works for any cruise-rpm.

2) I once had a combo that cruised 75@ 1840 rpm, in double-overdrive. I used this method, and she gave me back 32 mpgUSg. I'm certain that if I had been cruising in direct at 3300, the results would have been very different.

3) Another thing I did was to, at cruise rpm/speed, put the trans into neutral and see how much distance it took to slow down to about 20 mph.
Then I checked the cars mechanicals to see what could be done to increase this distance. Things like adjusting the wheelbearings , the brakes, installing new U-joints, adjusting the front-end height, the attack-angle of the rear spoiler, and of course, the tire pressures and the alignment.

4) I don't run that combo any more. That cam lost lobes, and I replaced it with the next bigger size from the same manufacturer. This new cam lost bottom-end, big-time, relatively speaking, leading to a different transmission, and the loss of Second overdrive.
I took the engine apart, and increased the Scr some more, with slight loss of Quench.
The new combo cruises at 65=2240, and forget about 32mpgs. But it's still pretty good. But she now likes 56* or more, of cruize-timing. and I leaned her out a bit more, lol.
5) At cruise rpm the engine doesn't care about how many accelerator pumps are on the carb, and it doesn't care if it has vacuum-secondaries nor what size MJs are in it unless the PMJs are just too small, to even get to the desired cruising speed. It doesn't even care about the Transfer slot sync. unless the idle-mixture screws are cranked right out.
6) at cruize rpm, the engine only cares about maximum cruise-timing and minimum fueling, for the load it is pulling, which can change quite a bit with the engine's running temperature.
Addition concerns are; the inlet air temp, and of course the air density and humidity.
Some things cannot be easily compensated for, like the amount and strength of the overlap cycle, and most especially with the amount of power extraction degrees.
In your case I grossed your cam up to guess at the zero-lash numbers and the formula spit out just 106 degrees. This makes your compression degrees and your extraction degrees nearly identical to mine, with the exception that you overlap is about 67* to my 61*.
I see almost no reason that your combo, being roughly 600 pounds lighter than mine, couldn't out-perform mine in the fuel-economy arena, if we both ran at the same rpm. At that point, the only advantages that I might have is the 3.58 stroke, maybe a slipperier body, and the fact that I run a minimum coolant temp of 207, with fresh cold, above-the-hood inlet air.
And BTW, I run an ancient 750DP Holley that I bought used in about 1977. Notta chance would I, if I had your carb, give it up, no way.

7) Just to give you food for thought;
My previous cam was
276int/115comp/112Power/276 exh/53*o-lap
As you can see the extraction was 112* to your estimated by me, 106*
This cam was 223/230 @050; and it was way more fun than the cam that followed, namely,
276/114/105/286/61* overlap 230/237@050

Your 234/244 has at least 4* more exhaust duration than it needs, and for the lightweight car probably 8 or 10 too much. which at WOT is a maybe a good thing, but those extra degrees are stolen from the extraction cycle, which means, that at cruise rpm, a lotta pressure is going right out the tailpipe.

If I had your cam, I would retime it to 2* retarded, in at 110; But, this will reduce your CCP, which is why I asked for your current compression test results. If you are in at 104 now, going to 110, that represents a pressure loss of perhaps as much as 12psi, which with 3.91s and a 3500TC you won't hardly notice. But with 3.23s and a manual trans, I know is gonna suck.
However the 110 degrees of resulting Power extraction versus my estmated 106, is gonna make a huge difference in the potential to make fuel-economy, after the carb and timing is cleaned up.
I'm pretty sure your combo can't ever make 32mpgs, but I'll bet 20 in steady-state at 65=2400 is doable, and with any 750, and more with a spreadbore with triple boosters.
Click to expand...
Thank you man ! I truly appreciate your information !! I will work on this and get back to you.

Btw alot of guys keep recommending the edelbrock 800 AvS2. Thoughts?

I havent tested cylinder psi. Will do this saturday

I have a 4 speed A833

Where are you located?
 
64whiteghost said:
Thank you for your response!

I will take your suggestions into consideration. At this point ive spent the money on this carb. Mopar official will be coming this Saturday to tune it for me. And we will see what we get. But i have been told by multiple people about the edelbrock AVS. I will keep an eye out and most likely snatch one when it comes up. Just to have it

Secondly. Thank you for your words about my car. If your on instagram. You can see more pictures on the cars profile @64whiteghost

View attachment 1716244476
Click to expand...
Even though Justin and I do not fully agree on the approach to setting up the timing, having him come and help you is IMO the hands down BEST decision.

You will not see an immediate MPG boost because tuning burns up fuel. But with the following tankfuls you will see improvements. The more time and effort you are willing to put in, the better it will get. Change a major item like a carb, expect there may be a setback until it is tuned to at least the same level.
 
I have a vac advance distributor I'll bring for fun, I'll have to shorten the slots 1st.
I'll be check plugs for spark lines placement just at the bend on both ends.
The carb is my main concern.
The plugs were black when it had 65's in it to begin with... so I'll be into that pos top of the list.
 
64whiteghost said:
Thank you man ! I truly appreciate your information !! I will work on this and get back to you.

Btw alot of guys keep recommending the edelbrock 800 AvS2. Thoughts?

I havent tested cylinder psi. Will do this saturday

I have a 4 speed A833

Where are you located?
Click to expand...
1) I have a bit of trouble with big metering-rod carbs, and late-closing intake valves. I find Holley carbs easier.
Except, for strictly cruising, then the M-rod system is hard to beat. And so, my favorite is and will always be, the Thermoquads.
When the Airgaps began to show up at the local speedshop, they were all Chevys. I ordered one for my 360LA, only available in square-bore, and waited. Had they been available in Spreadbores, I would for sure have bought one.

2) yeah I'm real interested to see the results of the compression test.

3) Manual trans/3.73s is good for a 340.

4) Avatar says south-Central Manitoba/Canada; elevation 900ft which is why I have a 360. It offers a lil more punch off the line.
 
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In my experience, once the A/F ratio is set correctly at ~13:1 full throttle and near 14.5:1 cruise, timing is the most important tuning issue for FE. 340's like about 34° mechanical advance and as much vacuum advance as the fuel will allow which is typically about 51°. These are crank degrees, not distributor degrees. A timing tape or marked damper are a must to set up total timing correctly.
My preferred setup is to use an 11° (distributor degree) advance plate (FBO works) and set initial timing at 12° (engine) advance for a total of 34°. (2*11+12). Then use a vacuum advance unit that is market for about 15° (Dist) advance. The vacuum point at which vacuum advance starts is adjusted by the Allen head screw in the vacuum canister accessed through the nipple.

Granted, I was using a mild cam during the '70's fuel economy crisis, but with tuning and an electric cooling fan and desert cooler radiator, I got my 340 to get 22-24 on the highway (2.94 rear gears). Here in Denver area, my current 340 with a 284/484 cam and 10.25:1 CR gets 16-17 MPG using the tune above. And it produced 300 rear wheel HP on the Mile High chassis dyno.
Let us know the distributor configuration when you get things checked out.
 
TT5.9mag said:
Learn how to tune the carb and if you’re not running ported vacuum advance with around 45-48 degrees of cruise timing you should be.
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Maybe, just maybe you should watch some David Vizard and Unity Motorsports Garage videos. There are a bunch of others also that speak to ported or manifold vacuum. The short speech; manifold vacuum with an adjustable vacuum advance so you can dial it in.
 
Dale Davies said:
Maybe, just maybe you should watch some David Vizard and Unity Motorsports Garage videos. There are a bunch of others also that speak to ported or manifold vacuum. The short speech; manifold vacuum with an adjustable vacuum advance so you can dial it in.
Click to expand...
I have. I do not put Vizard on a pedestal and regard him as the all knowing, all encompassing wonder man that some people do. David is a smart guy for sure but he speaks in absolutes and there are plenty of ways to get things done.
 
maybe power valve is ruptured burning more fuel. 10 initial with big carb and cam imo isn't enough. my dart is a 318 with 600 holley and 480 lift cam initial is 20 degrees and I don't plan on changing the timing because it runs really good at 20. I do run high test fuel.
 
Back in the day my Formula S got 14mpg combined with 3:23's. It was a 511"RB. The trick is 2bbl's get better MPG. Mine had 3 of them! I suggest going that route with yours.

Combined MPG = 7 in the city, 7 on the highway :p
 
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