Smallblock efficiency or How to have your cake and eat it too

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DemonK9 said:
When I had my '73 Duster 340/4 speed ('71 clone) I ran:
-Mopar replacement electronic dist from NAPA
-ThermoQuad 750
-GM HEI module conversion eliminating mopar ECM & ballast
-NGK plugs gapped to about .40-.42....initial timing at about 16 BTDC w vacuum advance.

I tested the fuel mileage a few times, under "normal muscle car" driving conditions = basic highway speed, with once or twice hammering it, opening the 4 BBL to pass with authority LOL
I would always get 26-28 MPG and thought that to be pretty good, considering an average new vehicle with all the sensor BS and EFI would struggle to get that!
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Nice,, I had a 73 Duster 318 auto with headers and a 500 cfm 4 bbl, crane economy cam. I was doing good if I got 22 mpg. Kept trying for more anyway.
 
I think a nice combination of vac advance for efficiency, HEI module for a hot reliable spark, good air flow (2 1/2" exhaust) and the TQuad lead to the good mileage.....but was no dog either when you wanted to give 'er.......lol.....or just lucky tuning.

 
DemonK9 said:
When I had my '73 Duster 340/4 speed
I would always get 26-28 MPG and thought that to be pretty good, considering an average new vehicle with all the sensor BS and EFI would struggle to get that!
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Not American miles...
 
One thing to consider is a god Thermoquad will generally get better mileage than an Edelbrock, or rebuilt AVS etc.

EFI no doubt has great A/F ratio, and that one item varies with the carb no doubt, but for the $ of EFI is high and a good rebuilt carb is pretty cheap.
 
DemonK9 said:
When I had my '73 Duster 340/4 speed ('71 clone) I ran:
-Mopar replacement electronic dist from NAPA
-ThermoQuad 750
-GM HEI module conversion eliminating mopar ECM & ballast
-NGK plugs gapped to about .40-.42....initial timing at about 16 BTDC w vacuum advance.

I tested the fuel mileage a few times, under "normal muscle car" driving conditions = basic highway speed, with once or twice hammering it, opening the 4 BBL to pass with authority LOL
I would always get 26-28 MPG and thought that to be pretty good, considering an average new vehicle with all the sensor BS and EFI would struggle to get that!
Click to expand...


A well tuned thermoquad is the best 4bbl carb choice if mileage is the main concern.
 
RAMM , thank you . thank you , thank you . Please write a book about your findings and publish the results . My next project is exactly that , a mileage engine . I need info about can selection ,carb , heads etc.. My idea is to reduce friction as much as possible , and of course , clean , clean , clean . Keep up the great work . later, Tom
 
i had just about that build stock 340 mahle pistons ede heads 11.4 compression ratio , 190 cyl pressure 670 holley 3:55 gears with gv overdrive that got 22-24 mpg on the highway cruising at 70- 75
 
Nat said:
i had just about that build stock 340 mahle pistons ede heads 11.4 compression ratio , 190 cyl pressure 670 holley 3:55 gears with gv overdrive that got 22-24 mpg on the highway cruising at 70- 75
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Impressive, what camshaft? J.Rob
 
RAMM said:
Impressive, what camshaft? J.Rob
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can't remember , was not a big cam , just on the edge for running power brakes . made 412 hp 435 tq ,I was the only one in our group not needing gas after 100 mile plus cruise . Ill try to find the specs on the cam , if i remember correctly it had 513 lift with 1.6 rockers other than that it's blank
 
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Planning on going for a cruise tomorrow.. 67 Fish, FiTech, 340, Edel heads, 222/.545 roller cam, 3.55 rear, 5 speed, 25.5" tires.. gonna check Canadian MPG.. just for fun!! Ill post results!!
 
so,, Im pleased with todays cruise results,,,148.9 km - 63.8km @115kph (72mph)and 84km @80kph (50mph) ...24.93 mpg imperial,,,20.7 mpg us... desktop dyno says the 340 makes 426 hp, just a number to put it in perspective. when i designed it i wanted 400 hp and 24 mpg...cake and eatin it too IMO..
 
WHEN IS part B oing to be posted . very interested as I want to rebuild one of my 340 for maximum mileage and around 450 or more hp . I'm just wondering if a lightweight crank ,. rods and pistons would help . Can't wait to see your final build . Wish mopar had the parts available that fprd and gm have
 
Nat said:
WHEN IS part B oing to be posted . very interested as I want to rebuild one of my 340 for maximum mileage and around 450 or more hp . I'm just wondering if a lightweight crank ,. rods and pistons would help . Can't wait to see your final build . Wish mopar had the parts available that fprd and gm have
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Soon! I am going to cheat a bit and tie it in with my Masters of Motors build. That engine will be the ultimate effort towards power and efficiency so it should acheive 20+mpg with a considerable effort on the tune. J.Rob
 
RAMM said:
Soon! I am going to cheat a bit and tie it in with my Masters of Motors build. That engine will be the ultimate effort towards power and efficiency so it should acheive 20+mpg with a considerable effort on the tune. J.Rob
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Any updates to share?
 
RAMM said:
Not really with the competition being cancelled 'cuz pandemic. I have amassed a good amount of parts and plan to make some progress this winter. J.Rob
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I'd like to pick the collective brain about my build. Building a stock stroke 340 forged arias flat top pistons zero decked, stock 340 rods, magnum style heads, probably RHS X, but have EQ's and and Eddies already as well. So 10.5 to one with iron or 11.0 or so with Eddies. Magnum style air gap, thermoquad w/ adapter, and magnum accessories inc serpentine. I have a set of Doug's already. Maybe 3.91 gear or 4.10 8 3/4 have not decided yet. Using a A500. Yes, I am married to an automatic with my bad back and knees. This is going in my 3700lb Challenger. I was thinking of running a fast ramp cam in the .230 @50 range, and maybe a 2400-2600 lock up converter. This will be a street car. Priorities in descending order are
1. 100k plus reliability
2. Efficiency - 20mpg hwy
3. Ease of maintenance (again with the bad back)
4. Idles well enough to run A/C and enough vacuum for power brakes.
5. Fun and quick as hell light to light on the street.
Loose goals of 425hp and 425 torque with a nice flat torque curve, and 12.5 or so 1/4.


Questions:
1. EQ's and RHS heads now have 1.92 valves. Will clean up ports to flow 250-260 or so. 1.92 ok or upgrade to 2.02?
2. What specific cam choice(s) would you recommend?
3. Converter stall?

Any and all advice is appreciated. Thanks ahead guys.
 
mgoblue9798 said:
I'd like to pick the collective brain about my build. Building a stock stroke 340 forged arias pistons zero decked, stock 340 rods, magnum style heads, probably RHS X, but have EQ's and and Eddies already as well. So 10.5 to one with iron or 11.0 or so with Eddies. Magnum style air gap, thermoquad w/ adapter, and magnum accessories inc serpentine. I have a set of Doug's already. Maybe 3.91 gear or 4.10 8 3/4 have not decided yet. Using a A500. Yes, I am married to an automatic with my bad back and knees. This is going in my 3700lb Challenger. I was thinking of running a fast ramp cam in the .230 @50 range, and maybe a 2400-2600 lock up converter. This will be a street car. Priorities in descending order are
1. 100k plus reliability
2. Efficiency - 20mpg hwy
3. Ease of maintenance (again with the bad back)
4. Idles well enough to run A/C and enough vacuum for power brakes.
5. Fun and quick as hell light to light on the street.
Loose goals of 425hp and 425 torque with a nice flat torque curve, and 12.5 or so 1/4.


Questions:
1. EQ's and RHS heads now have 1.92 valves. Will clean up ports to flow 250-260 or so. 1.92 ok or upgrade to 2.02?
2. What specific cam choice(s) would you recommend?
3. Converter stall?

Any and all advice is appreciated. Thanks ahead guys.
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If you are married to the TQ I’d find a different intake manifold. Running an adapter is a guaranteed power killer and distribution nightmare.

If you want a good selection of .904 lobes, Howard’s has the most I’ve found. Like a couple of other cam grinders, getting them to use them is near impossible, especially if you tell them it’s a “street” car.

I think 3000 is the lowest stall you should use.

Select your gears and figure out what you CRUISE RPM will be and pick your cam based on that. 3.91’s and an OD still might not get you 20 MPG. If you are married to that number you need to rethink your gearing and cam timing.
 
Well I hope Howards are "all that & a bag of chips" cause I ordered a cam in June & I'm still waiting. Apparently Covid caused problems at foundries too. Or so they say.
 
yellow rose said:
If you are married to the TQ I’d find a different intake manifold. Running an adapter is a guaranteed power killer and distribution nightmare.

If you want a good selection of .904 lobes, Howard’s has the most I’ve found. Like a couple of other cam grinders, getting them to use them is near impossible, especially if you tell them it’s a “street” car.

I think 3000 is the lowest stall you should use.

Select your gears and figure out what you CRUISE RPM will be and pick your cam based on that. 3.91’s and an OD still might not get you 20 MPG. If you are married to that number you need to rethink your gearing and cam timing.
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thanks for the input

On the intake I am limited what I can run using all magnum stuff. Might be able to open the intake up and do some welding if needed. I'll have to measure.

Cruise rpm with 26.5 tall tire, 3.91 gear, .69od is 2400 at 70mph or 2700 at 80mph. I plan to drive it quite a bit on longer trips. 4-8 hrs at a time. Would like to keep rpms somewhat in that range for that reason.
 
I would go with 3.55s for that combo and a 2.74 1st gear ratio . That drops your cruise rpms with out sacrificing launch power.
And if your area is anything like out here in Idaho its common to get passed while doing 80 mph .
 
mgoblue9798 said:
I'd like to pick the collective brain about my build. Building a stock stroke 340 forged arias flat top pistons zero decked, stock 340 rods, magnum style heads, probably RHS X, but have EQ's and and Eddies already as well. So 10.5 to one with iron or 11.0 or so with Eddies. Magnum style air gap, thermoquad w/ adapter, and magnum accessories inc serpentine. I have a set of Doug's already. Maybe 3.91 gear or 4.10 8 3/4 have not decided yet. Using a A500. Yes, I am married to an automatic with my bad back and knees. This is going in my 3700lb Challenger. I was thinking of running a fast ramp cam in the .230 @50 range, and maybe a 2400-2600 lock up converter. This will be a street car. Priorities in descending order are
1. 100k plus reliability
2. Efficiency - 20mpg hwy
3. Ease of maintenance (again with the bad back)
4. Idles well enough to run A/C and enough vacuum for power brakes.
5. Fun and quick as hell light to light on the street.
Loose goals of 425hp and 425 torque with a nice flat torque curve, and 12.5 or so 1/4.


Questions:
1. EQ's and RHS heads now have 1.92 valves. Will clean up ports to flow 250-260 or so. 1.92 ok or upgrade to 2.02?
2. What specific cam choice(s) would you recommend?
3. Converter stall?

Any and all advice is appreciated. Thanks ahead guys.
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Well you could have just p.m'd him instead of hijacking the thread. A lot of people are here reading for what RAM is sharing and its annoying to have to skip through a bunch of bumps and side tracking questions that should be in there own thread.
 
MOPAROFFICIAL said:
Well you could have just p.m'd him instead of hijacking the thread. A lot of people are here reading for what RAM is sharing and its annoying to have to skip through a bunch of bumps and side tracking questions that should be in there own thread.
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So sorry to have wasted your valuable time by inquiring about an engine build that is both high performance and efficient. The exact topic that RAMM originally posted about. I would have just PM'd RAMM if I was only seeking his opinion, but I was looking for input from others as well. If you only want to hear from RAMM, I suggest you follow your own advice and PM him.
 
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