the 64-66 273 has a slightly different intake bolt pattern, close enough you can wallow out the holes and make it work, on the other hand an SP2P ain't gonna make any noticeable difference in MPG, that's the reason few were made and sold. The area of the curve where it helps is such a low RPM you would need an even lower stall speed converter than stock or a manual and highish gear that can keep it at low RPM cuz even a 2.76 with no OD is spinning pretty good at 75 MPH without some very tall tires. If I had a 273 and was running a carb for MPG set up I would run a stock 318 dual plane intake and pre emissions carter BBD carb.

Did you do any testing with an sp2p with your previous combo?

hard to find since they moved it to epa archive

https://archive.epa.gov/otaq/technology/web/pdf/sae-2002-01-2743-v2.pdf

sample quote

The unique EPA engine used for this work is a turbocharged, PFI spark-ignited 1.9L, 4-cylinder engine with 19.5:1 compression ratio. The engine operates unthrottled using stoichiometric fueling from full power to near idle conditions, using exhaust gas recirculation (EGR) and intake manifold pressure to modulate engine load. As a result, the engine, operating on methanol fuel, demonstrates better than 40% brake thermal efficiency from 6.5 to 15 bar BMEP at speeds ranging from 1200 to 3500 rpm, while achieving low steady state emissions using conventional aftertreatment strategies. Similar emissions levels were realized with ethanol fuel, but with slightly higher BSFC due to reduced spark authority at this compression ratio.

end quote

What rings to use should be given serious thought.

Newest rings reduce friction.

I have read that just one compression ring, and one oil control ring, is not out of the question if max efficiency is the main goal.

LD4B performer, RPM, and even m1 single plane none of em made a hoot of difference, maybe 1 MPG from best to worst and I doubt the SP2P would be any better without a corresponding drop in RPM. I think the important action is in the heads where it gets mixed the most and burned. I am a firm believer that as the TQ range of the manifold (and entire combo) goes down the overall combo would improve by matching the TQ curve by reducing RPM of the engine at cruise speeds either by gearing with OD, LU or higher rear gear ratio, the reason I came up with that theory is because of the zero deck tight quench 318 magnum I ran in a 98 ram 1500 ex cab long bed, tight quench and high compression gave me a little bit improved MPG and TQ but when I switched from a 245-75-16 tire to a much taller 275-65-20 tire it really got good MPG and loafed along at 80 with very low RPM (I think it barely did 2000 RPM at 80MPH), doing 70 it would easily do 20 mpg, that's what makes me think I could do better in a much smaller dakota by running a really high rear gear to keep the RPM down along with building the engine to make more TQ down real low.

Zero decking my current block, running .028 head gaskets with a 2.94 gear almost don't even feel like an experiment to me at this point, I would almost bet on 22 MPG in this little truck. That's why I am really want to push the compression and gearing in this thing.

If anyone knows where I can get some aftermarket heads (not chinese) for a magnum that don't cost an arm and a leg please let me know.

I agree with the lower cruise rpm and it is the way the manufacturers have gone to help mileage with 1700-1800 cruise rpm on the highway .

Wouldn't whatever intake makes the best torque at cruise rpm be the one to help fuel mileage the most?

Didn't you run 302 heads on the first build? Maybe those ports were the limiting factor in the intakes not making much difference?

As far as the heads go could you just tube the push rod holes in the magnum heads and cut them open instead of spending a bunch on aftermarket stuff? Would moving the location/ angle of the injector boss work?

Just thinking out loud not trying to argue. I appreciate you sharing your experience with us.

The cuda engine I did use 302 heads, I used to subscribe to the theory that the smallest port made the most MPG because of velocity and such, I think all that did was hurt performance with no MPG improvement. I think the 920 head with 1.88 intake valves and a little porting would have been best for that engine, I think they are the best SB head for MPG unless you could really slow down your RPM.

The stock magnum head has no tube, just raw casting between port and pushrod. The EQ is made like this also but does have a slightly wider PR pinch. The Eddy, RHS, mopar aluminum and iron R/T all have a drilled PR tube but they also already have a much larger PR pinch, tubing them and opening it would really give a nice shot at the back of the valve I am just having a real hard time finding any much less a pair I can afford. The cheap chinese ones on fleabay have no tube and an even smaller pinch than stock heads, looking at the picture of jegs and others magnum replacements it looks like they are all selling the cheap chinese junk named as their own.

Awesome! thanks

Not a mopar but my 99 Corvette got 26-27 mpg. 6 speed and was turning 1300 @ 70. RPM does make a difference

back in the early 70's, i had a 64 barracuda with a 273 2bbl and a pushbutton 904. it had an open 7 1/4 rear, but i don't remember the gear in it.
running back and forth to work on the interstate at 65-70 [this was during the 55 mph speed limit time] that thing got around 26mpg.
was a really sweet running car until my old man clipped a phone pole............

I know it's mentioned in here, and obv you've got some LA knowledge too, but I read all your posts in the Gen III section and think this is where you should be:

https://www.holley.com/products/eng...dge_dakota_gen_iii_hemi_swap_components/

My curiosity is getting to me. Back in the old days, when cars were cars and gas was gas, I had several 318 powered vehicles that would regularly pull 20-25 mpg on the highway. Gas isn't what it used to be. What kind of gas mileage are you expecting to get out of this super duper 318, and what is its expected cost to get that mpg? The port injected 96 318 in my 4x4 truck is only getting 10 mpg around town. and around 13 on the highway.

I agree with the above,
but would add that
- ignition timing is not what it used to be
- air to fuel ratio is not what it used to be

NOx pollution requirements have hurt fuel economy in a large way
Low fuel economy has pumped a lot of carbon dioxide into the air.
Low fuel economy have emptied a lot of money from wallets.
The money could have been spent on reducing water pollution, setting aside wilderness areas, etc

It keeps getting worse, NOx pollution equipment wise.

I telephoned my brother 2 days ago and asked if he had a minute.
He replied: I have an hour and 21 minutes
because I am sitting outside the KW dealership in Memphis waiting for the service department to open
because the check engine light is coming on and off on this new &#@ vacuum truck
and I know from experience I do not want it to go into de-rate.

Agree, my 01 360 van at best gets 14 maybe 15 going 70. The 69 Rt Charger 440 got 17 and I never.. put my foot thru the carb!

https://en.wikipedia.org/wiki/Shell_Eco-marathon

I certainly did not expect it,
but while playing for my 92 year mother
old black and white tv episodes of the Lawrence Welk Show from 1955-1964,
there are frequent Dodge commercials,
and some of those commercials say something like
“a totally stock Dodge model abc got xy mpg in the latest Shell Fuel Economy Marathon competition.”

Ethanol is the main culprit in the loss of fuel mileage. It is just a filler and a scam. Had a Honda Civic that would get 37mpg with mostly interstate driving. When I filled with ethanol free gas, it would get 41 mpg. Same hwys repeated over 50 trips with each.

It's not the ethanol, it burns, it produces power, at 10% there is no way it can cost you 10% MPG. Yes there is slightly less energy per gallon so in the same engine you would get very slightly lower MPG. On the other hand if the engine was not compromised to run on gasoline (yes they are compromised to run on gasoline) and was instead built with much higher compression, as much as double the compression than you could extract a lot more energy from an ethanol powered engine than you can from a gasoline engine. If we had e-85 around here I would be trying to run 16 to 1 compression and get much better MPG and TQ.

Cars got better MPG 30 or 40 years ago because we had lead in the gas permitting more MPG and we drove slower, you can get much better MPG in these modern cars if you set the cruise at 50MPG and could somehow keep the stupid 8 9 10 speed automatics from downshifting all the time, more compression would give the engine more TQ and require less of those down shifts.

As far as NOX costing MPG yes it costs a lot, almost every engine ever mass produced can tolerate at least one more point of compression that is generally considered to be worth about 5% improvement in MPG, imagine if every car suddenly got 5% better MPG how much cheaper fuel could be... and many engines can easily handle 2 points compression increase, the reason they can't do this is because NOX is formed with those much higher compression ratios and right now there is not a good enough and cheap enough catalyst to get rid of the NOX in the exhaust so lower than ideal compression ratios have been the go to answer for the manufacturers along with EGR that statistically reduces the chances of a fuel molecule from finding an oxygen molecule in a timely manner.

Close but ethanol does not make the same power as gas volume for volume 15% ethanol means maybe 10% less fuel millage.

Friday May 27, 2022
letters section of the Wall Street Journal
has a letter from
Andrew Randolph, ECR Engines, Welcome, North Carolina
titled
“E15 Gasoline can save you money at the pump”

He claims that E15 has 1.5% less energy than E10 but “should” cost 6 cents per gallon than E10

Since gasoline BTU per gallon varies both regionally and seasonally
and Ethanol depends on the
price of corn,
human labor,
and financial speculation,
(all rising sharply recently)
my gut tells me there is “wiggle room” to make a case either way.

Fuel mileage with ethanol v/s non ethanol gas in my Civic was tested over a long period of time with repeatable results. Only other difference in the gas that I am aware of was ethanol free was 90 octane and ethanol gas was 87. Maybe some emissions additive in the 87 had something to do with it? Stumbled on the mileage difference after I found a station near Gadsden AL that sold the ethanol free for the same price as other stations charged for the 87 swill. It was on my regular route I drove for work through that area twice per week for over a year.