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Single Carb Intake, Dual Carb Intake, Triple Carb Intake, why not more ?

timkingsbury

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·       For Decades I have listened to people talk about Flathead Mopar 6 Cylinder Engines in terms of intakes, what is the best carb configuration for their particular situation.   

 

Discussions on putting two carbs and those who claim to be sure that is too much carburation or that it will use to much fuel. Then every once in a while the discussion of 3 carbs comes up, and that almost always sparks the debate on how it would take a race motor to need it, or how the engine will bog, or run poorly.   In the last 20 years with a good friend of the AoK boys coming across a huge stash of 2 barrel carter weber carbs which were designed for slant six engines, the discussion on utilizing a 2 barrel instead of two singles comes up.

 

I just smile, but then I know that when the stash of 2 barrel carter webers were found, its finder  put them on his website as a carb for a flathead mopar.  Its amazing how a market can be created and how quickly – “this is the way to go” spreads like rapid fire, without as much as any background check into something.

 

But 1st, let me go back to the 1st time I heard the discussion on multiple carbs vs a single multi-barrel carb, or  put another way, comparing that “old technology carter ball and ball vs a modern 4 barrel carb”..

 

It was about 45 Years ago, when I 1st  heard someone in a conversation with my Grandfather and my Dad, suggesting they knew a lot about Flathead Mopars and were  sporting a 4 barrel carb on a homemade intake.

This gentleman had played with flathead Ford v8s and had came across a Dodge 2 door sedan from the mid-50s.  He was suggesting he had built the ultimate flathead Chrysler Engine and he was one of those guys that whatever he had at the moment was just the best and the only way to go. 

Well after my Dad explained he had far from the ultimate flathead Chrysler, and that his wife’s daily driver (my Mom) was good enough to kick his ass, Dad pulled out my Mom's pickup.  It was sporting a bored out 265, with a cam, a factory dual intake and exhaust with a pair of carter ball and balls, and an a833 4 speed tranny.  After a little bit of fun that really wasn't much of a contest, licking his wounds sort of speak, Mr "Ultimate Flathead Chrysler" started down the road of excuses when Grandfather shook his head and cut him off at the pass.

 

 Grandfather like my Dad were automotive Engineers, and Grandfather literally knew more about Chrysler Flatheads than any person alive. Given he saw the very 1st flathead roll of the line in Windsor, Ontario Canada in 1935 and saw the last block cast in 1959, he had some pretty good credentials to give a lecture.

What is explained in a few minutes was not only how the flathead engine worked, but why the engine this gentleman had came with only 1 carb failed to perform.

Most think that 1 carb was put on the engine and that it has sufficient carburation for the engine, and if it needed more, Chrysler Engineers would have put more on.

 

On a basic level that is true, but what engineering was building was an engine to a specific HP, torque  and fuel consumption target and not to get the most out of the engine, make it as efficient as possible or even have it run to anything close to 100% optimum performance. 

By Optimum  performance I am not talking maximum  hp or maximum rpm or optimum fuel mileage on a vehicle.

 

Grandfather then explained that in fact when Chrysler was faced with the need to meet a 5 ton truck specification for dump/plow trucks asked for by Canadian Municipalities during the winter of 1950, that the requirement  had  filtered to engineering in late 1950. They  developed the 265 ci motor which was 3 7/16" bore and 4 3/4" stroke and have dual carbs and dual exhaust on them, which was what was in Mom’s pickup.

 Few realize that that engine actually had more hp than any other engine on the market.  I will attach the picture of the poster that was on Grandfathers office at the time.  I gave it to George Asche Jr years ago.   In any case you can see the hot v8 mopar had in 1952 was 133 hp and the flathead 6 had more hp. As an aside Grandfather with the cam grind out of the 1952 Chrysler that engine exceeded 150 hp at the time, but given the time, energy and money that have been invested in the new Hemi v8 that was never going to see the light of day on any marketing information.

That engine and the fact it had a factory intake, immediately became a stock car favorite in the 1952 season, when Mopar dominated stock car racing everywhere it landed.

In any case Chrysler didn't just put on a second carb on it because they needed more carburation.  By then Chrysler already had Carter building Ball and Ball carbs from 85cfm -  425 cfm each and we now know they had a 625 cfm carter ball and ball single barrel carb if they needed it.

The reason for two was the basic issue, some would call flaw, but Grandfather  would call basic restriction to taking the engine to the next level.  I say that folding back to the earlier point that Chrysler was building engine to a spec of "x" hp, "y" torque and "z" fuel consumption.

 

The flathead 6 build by Chrysler has 3 Siamese intake ports,  each of which feed two cylinders.  Setting aside the exhaust for a second, and keeping in mind that an engine is really just a giant vacuum pump, putting 1 carb in the middle of the block, basically over the middle intake port feeding cylinders 3 and 4, means that if all cylinders are the same in compression ratio and ability to create vacuum and suck in a fuel mixture coming from the carb, then cylinder 3 and 4 are going to get more fuel than the intake ports feeding cylinders 1 and 2   or 5 and 6.   Yes Chrysler made intake modifications to help that, but they again were not trying to make the perfect engine, just have it meet specs required.

As  a little aside if your look at intakes from the 1930s through to the 50s you will notice Chrysler Engineers raised the level of the carb. With the Dual Carb truck intake it also was raised further with governors placed under the carbs.   The height of the carb mounting above the intake posts can easily be seen to rise from the 1930s to the 1950s. 

Its also why if your look at some of the aftermarket dual intakes made in the 30s and compare them to say the 3rd generation Edmunds in the 50s you will notice a huge difference in height. The raising of the carbs and providing a smoother run from carb to the intake ports saw huge benefits in performance. Of course maybe buried in the story is the fact that early intake was designed for a marine application where quick rev was far more the desired trait than was torque.   When the intake was moved to an automotive application you would find a quick rev with the clutch engaged, but disengaged there is a significant loss in torque and it will actually burn more fuel than a single carb.

 

But back to my story, if we now add the exhaust component into your stock Mopar flathead (or L-head)  which depending on what year engine and what vehicle,  has the single exhaust exiting at one of a few  different locations. For this discussion lets  say it exits at the back as does the post ww2 cars.     What you find is as the cylinders push out exhaust there is almost no restriction or back pressure at cylinders 5 and 6,  but there is a great deal of back pressure at cylinders 1 and 2.   

 

So here we have the most back pressure making it tough to push away the exhaust and actually the front intake port receiving the least amount of fuel. 

While the engine meets specs with no problem, its clear that if you can balance the exhaust, by having 3 exhaust cylinders exit through 1 exhaust pipe and the other three through a 2nd pipe, you can better balance the exhaust back pressure.  We sort of glossed over the fact that while there are only 3 intake ports, each cylinder does have its own exhaust port.   Something that changed with the introduction of the slant 6, which had  6 equal intake runners each feeding a cylinder.

 

Back to the flathead,  if we can better distribute fuel to balance the opportunity for each of the 3 Siamese ports to get fuel, then the engine will run more efficiently.   

So if you were to take a big block 25 1/2" engine, and anyone of them, not just the 265 and put the factory dual carb and dual exhaust setup on it and then put on the appropriate carter ball and ball carb on it, it will gain hp, torque and improved fuel mileage.  The reason is it runs more efficient.  The same takes place with the 23 1/2" USA small block which has the same intake and exhaust configuration, although slightly smaller ports.

 

If you take it one step further,  putting 1 carb on top of each intake port,  you can provide the optimum amount of fuel efficiency for the engine.

Back to our 4 barrel friend,  putting on a large carb  just  provides a further opportunity to over fuel the center siamese intake port.  When he hammered the throttle it was actually not able to burn all of the fuel in the middle two cylinders and was “bogging” ,until it could gain enough RPM to use some of the fuel.   

When he was running against Mom’s pickup which had more balanced back pressure, and a better distribution of fuel he had no chance even if the engines were internally the same. Of course they weren't but that is another story. 

Years later when we created the AoK triple intake, we placed the first intake on  an almost rock stock 201 ci motor.  It had been rebuilt stock, although required to be bored out 10 thou to clean up cylinders. Beyond that it was a stock cam, intakes etc.  With 3 of the smallest CFM carter ball and ball carbs on board and headers made from a stock exhaust systems, the car ran smoother, had better acceleration and  got 6 miles per gallon better highway mileage over the single carb and single exhaust.    In the end, it is just a myth that you need some bored out, cammed up engine for 2 carbs and a full race motor for 3 carbs.

The reason why Chrysler didn't run 3 carbs was simple. 1) The cost of 3 carbs was no inconsequential  2) They could meet the HP, Torque and Fuel useage targets with 1 carb.  The exception was when there was a time window where the dual carb, dual exhaust 265 ci motor was released, but with overhead valve v8s and Hemi's coming shortly after the multiple carb flathead life-cycle was short lived.

 

There is a bit more it than that. I have glossed over a bunch of the engineering parts of why you don't just put a carb directly to each intake port with no equalization tube, but I am sure you get the drift.

Unlike a v8 where you might try and make carbs progressive because your feeding a intake plenum that equally or close to equally feeding all 8 cylinders, the flathead engine has 3 intake ports each feeding 2 cylinders so progressive carbs just are not effective.  On the flathead Mopar, with either 2 or 3 carbs you want them to produce the exact same fuel to feed each of the Siamese ports exactly the same. Its not progressive in terms of additional barrels or carbs, its progressive by pushing on the gas peddle.

 

 The key is making sure both or all three carbs are identical and that you have linkage that operates all of them exactly the same. 

 

Its a common misconception that they must be hard to keep synced. We have engines with tens of thousands of miles on them with multiple carbs and are never adjusted.  George Asche's 1929 Desoto that he has owned since 1950 likely has an unbelievable amount of miles on it and likely the  carbs were only touched when George has redone the engine.  I own vehicles with 100,000 + miles on them and the linkage for the dual carbs has never touched. That has a lot to do with just how good Carter Ball and Ball carbs are.. 

We also get asked  quite often about modifying the block to provide 6 intake ports, or using webers or other carbs, or running fuel injection.   Dad and Grandfather with too much time on their hands, as my Mother would say,  did modify a couple of engines to provide 6 intake ports. There were several  intakes made including one with an 18" runner set on it, one with 6 side draft webers and one with modified hilborn fuel injection.

At the end of the day, with various levels of success, nothing seems to outperform an Edmunds triple carb intake with riser blocks and 3 matched 1952-56 Truck carbs on them and maybe with some jetting changes.   Of course, since then we have developed a couple of new cam profiles and of course the AoK  triple which utilizes better and modern casting technology, as well as better flow bench testing and computer modelling that neither Chrysler or Eddy Edmunds had.    Have we thought about digging out the 6 intake port block that is still in Dad's shop, well yah we have, but that is another project and a blog entry for another time.

 

 

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Good blog entry there Tim. It seems what is old is new again or in other terms, the 45 year ago guy sounds a lot like a certain member of the forum, who fits the bill of what ever he has is clearly the best and the only way to go.  Sometimes I wonder if those people ever learn. Clearly the one on the forum hasn't.  I wonder if the  4 barrel dude learned his lesson ? 

Thank you for taking the time to explain multiple carbs and flathead mopar inner workings.  As usual I learn more on your blog in one entry, than I do from reading thousands of posts by the want-to-be experts on the open forum.

Barb

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Simply Fantastic, there it is in a nutshell, any of those who need this info, who ask in threads year after year, the answers are stated right here.

I posted for an experienced and professional answers on ,ulti carbs, the AoK Boyz will deliver with experience and knowledge to back it up, not just "Lip Service".

Thanx Tim for the excellent read, and look forward to more in the future......

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21 hours ago, maok said:

How would triple SU (1-1/2 or1-3/4) carbs work with the appropriate inlet manifold?

I sent Moak a note to get clarification -      Maok said - "Hi Tim, SU (Skinner and Union) carbies are an old design  from England, clever in design in that they dynamically adjust the throttle bore. Used in many English cars from 8 cylinder Jaguars to 4 cylinder Minis. Popular here in Oz with inline 6 cylinder tuners, ie. Slant 6, etc.The SU's come in a variety of bore sizes from 1-1/4" to 2", single side draught throat only. Some call them the poor mans Webers."

Its not a carb I know anything about them. I see it was a early 1930s design listed as an updraft.    I looked up  the list of British cars they were used on and everyone notorious gas hogs.   They are an updraft hybrid from what I can see, and by the time Canada entered the second world war there were over 2500  patents for carbs in Canada and the USA and I know my Grandfather said the lineup of companies trying to sell carb and fuel delivery systems  was around the block in the late 30s.

In any case this would take a complete change in intake design to deal with the side/updraft delivery.   In any case sorry, I don't have any direct knowledge on them and this, like the webbers, fish  or about 50 different carb manufacturers that I do know tried to pitch Mopar  not anything Id invest time and money to develop an intake for.  Sorry

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21 hours ago, P15-D24 said:

What is the CFM rating of the B&B you use for the triple set up?

CFM or Cubic Feet Per Minute ranges widely in the Carter Ball and Ball family, with carbs at idle at less than 7 cfm and wide open at 38 cfm,  up to modified truck carbs with over 650 cfm per carb.  So it depends entirely what  engine, what cubic inch, what compression, what cam spec etc that your running. A stock 201 runs quite well with 3 earlier Plymouth carbs with smaller throttle bores and ventures   and my 1949 Plymouth which is a full race motor really is running 3 x 550 cfm carbs  and our Rear Engine Dragster is running 3 carbs with a total CFM  of very close to 2000 cfm and yes they are carter ball and ball carbs.

I do not have every carb and jet configuration spec'd by CFM but will put up some details of the common Plymouth and Dodge truck carbs shortly.  The Carter ball and ball has excellent throttle response and a great range of fuel delivery designed for manual transmission equipped engines.  For the Chrysler and Dodges whether Carter or Stromberg you have circuitry built into the carb to deal with the semi automatic/automatic transmission

 

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Here is my carter ball and ball cheat sheet.   Always keep in mind that it is very common to see people swapping tops, middle sections and bases so often looking at the marked part number on the carb bowl wing turns out to be foiled when someone has swapped around parts.  Add in different jetting and  carter ball and ball carbs give you an incredible range of carburation choices. This isn't a definitive list of every Carter Ball and Ball used, and some  I didn't list throttle bores and venture sizes, nor did I get into jetting.  You can literally wind up with paralysis by analysis with all the combinations an permutations there are available.

Carter ball and ball Carburetor  - Tim's cheat sheet

Plymouth -  

3 bolt – center section is 660 for Plymouth – starting 1950

2 bolt – center section is 635 -  1949 only

2 bolt – center section is 370 -  1939 – 1948

 

633s 1934-35 taxi base 395-4   (1 1/8 throttle bore 1 1/16 venturi)

 

1933 – 1938 – model 439s (1 7/16 throttle bore and 1 ¼ venturi)

 

1940 – 1942  -  “P9”  Carter Carb Ball and Ball  model # b6p1, b6r1 and b6s1 (2 hole base)

                          (1 5/32 throttle bore 1 3/32 venturi)

 

1942 (p14) and 1946-48 (p15)    Model d6g1 – (2 hole base)

                                                     (1 9/16 throttle bore 1 ¼ venturi)

 

* 1949 (p17 – p18) 1950 (p19-p20), 1951-52 (p22 – p23), 1952 (p24) and 1954 (P25) model d6h1, d6h2  

                                                                                ( 1 9/16 throttle bore 1 ¼ venturi)

  • there was a d6n1, d6n2  and d6r1 which are the same as the 1949-1954 carbs but have throttle restrictors

 

* 1953 – 1954 – P24-p25 Plymouth with overdrives – D6U1 (1 9/16 throttle bore and 1 ¼ venturi)

 

Dodge

Bolt pattern on base is 2 15/16”  and the center hole 1 11/16”

3 bolt – center section is 661 for Dodge truck 

2 bolt -  center section 404 – from early 1941  to 1947

 

1937 – 1940 truck   - etr1r (2 hole base)

 

1940 – 1948 cabover is a 6c1, 6c2, 6d1, 6dir, 6e1, 6f1, 6g1, 6m1 (updraft carb)

 

1941, 42, 46, 47 truck  etr1r, b6s1, dta2, dtb1-dtb1r, dtb2-dtb2r, dtb3-dtb3r, etp2, etr1-etr1r

 

1942 – 1949 trucks – model dtc1 (1 9/16 throttle bore and 1 ¼ venturi) or

                             model ett1 (1 11/16 bore and 1 11/32 venturi)

 

* 1946-1947 carbs with velocity governors – eyb1, eyb4, eyc1, eyc3, et1, et2, et4, e7b1, e7c1, e7f1, e7s1

 

* 1950-1954 ½ and ¾ ton and 1952 1 ton – dte1 and dte2 (1 9/16 throttle bore and 1 ¼ venturi)

 

* 1950 – 1956 1 ½ - 3 ton – e7t1 and e7t2 (1 11/16 throttle bore 1 11/32 venturi)

 

1950-1954 cabover is 6n1 and 6n2 (updraft)

 

** 1952 2 ¾ - 4ton with dual carburetors – e7u1 and e7u2  1 11/16 throttle bore amd 1 11/32 venturi)

    E7t10-1533 center

 

* Dodge d46 and d47 – 1953  - model d6h2 1 – 9/16 throttle bore and 1 ¼ venturi

                                                  * Same thing but with overdrive – model d6u1 (same bore and venturi)

 

** 1953-1956 2 ½ ton truck with 2 carbs – model e9k1 and 39y1 (1 11/16 throttle bore and 1 11/32 venturi)

    (this is the 265 ci motor carbs)

 

*1953-1955 2 ¾ ton – 3 ½ ton or 1953-56 4 ton – model e9g1 (1 11/16 throttle bore and 1 ¼ venturi)

  (this was the 331-377-413 big block motor with dual carbs)

 

* 1953-1955 1 and 1 ½ ton truck (route van) e9h1 (1 11/16 throttle bore and 1 11/32 venturi)

   (this is the 331-377-413 big block – single carb)

 

* 1954 d51 and d52 – e9n1 or e9t1 (1 11/16 throttle bore and 1 11/32 venturi)

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4 hours ago, Rockwood said:

Simply Fantastic, there it is in a nutshell, any of those who need this info, who ask in threads year after year, the answers are stated right here.

I posted for an experienced and professional answers on ,ulti carbs, the AoK Boyz will deliver with experience and knowledge to back it up, not just "Lip Service".

Thanx Tim for the excellent read, and look forward to more in the future......

Your very welcome. I hope it helps clarify a few long standing fallacies and takes away some of the mysteries on flathead 6 carburation.   The carter ball and ball really is quite a carb design, with great throttle response and terrific fuel atomization and delivery over wide ranges of torque and rpm ranges.  There is no doubt with enough time and money a computerize fuel injection system could outperform our AoK triple carb intake equipped with carter ball and balls, but I don't see a line up of guys putting their money where there mouths are for that challenge.  Whether rock stock smallest cubic inch flathead mopar or bored out 125 thou 265 big block, stroked with a wild cam, high compression and all kinds of tricks it doesn't matter.   The engine with two equally split carbs and dual exhaust runs better, has more power and gets better fuel economy if driven the same as a single carb configuration  and all factors are better with 3 carbs and dual exhaust, no matter which flathead 6 engine with 3 Siamese intake ports.  Going to 3 carbs does have consequences in terms of air cleaners  and air boxes under hoods so it isn't without some compromises.   

But the often heard comment that you need some performance engine to handle two carbs and need some full race motors for 3 carbs is just absolutely incorrect or flawed engineering logic... lol.. or a lack of engineering logic and a lack of understanding how a flathead mopar with 3 Siamese intake ports actually work.

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Another great blog entry Tim.  It make so much sense when you explain the intake and intake ports technology in lay terms. I know in the early 60s I built and engine and put the competitions valves in the engine hoping to get more fuel. It seemed to hold the engine back. I then carved away at the block trying to improve the flow. That was marginally successful. I then got a triple carb log intake from an old stock car racer and the engine seemed to come alive. I don't even think all of the carbs were identical although I can see the benefits there. The engine idled better. You just had to touch the throttle and it was amazing. I think this was asked before; do you make triple intakes for the 230 ci Plymouth Motors ?

Super fan of the AoK boys. Thanks for everything you guys do for the hobby!

Paul

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I agree, OMG this is great stuff.  Finally someone explained in lay terms how the flatheads really work. I must confess I was one of those thinking that my stock engine couldn't handle dual carbs. Now I see why some many of the guys with stock engines pull this off.   Thank you so much for that carb cheat sheet. I have a pile of carter ball and ball carbs around that I haven't a clue what they are from or sizing. This really helps me to separate the wheat from the chaff ! 

Thanks

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Great info Tim. I am in need of some help. I have a offey dual carb manifold that I thought my stock 1937 ply carbs would fit but didn't know there was an economy carb back then which my 201 stock motor has.The offey manifold stud center to center 2 bolt is 2.925. Would have info on wher I might get a couple of carbs for this fix ?  Thanks again for the info and help.  Dave Dowdell aka t-bag

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Hi Dave -  I think  you will find that 1938 and older carbs the mounting bolt pattern are about 1/2" smaller than 1939 and newer. I don't know the exact measurement. I am sure Tim can get it for you.   Your offy intake I expect take the bigger carbs.  The only aftermarket intake I saw that took the smaller carbs was a nicson.  You will need 1939 and newer carbs for that intake, or you have to enlargen the holes on the carb based by 1/4"on each side to give you the 1/2".  All that being said Tim likely wont say it but I will.  Sell the offfy and by an Edmunds or one of the new ones Tim and George Asche are making.  The offy has the carbs too low and you loose torque. For an older engine like your 1937 you really see it where you are already a little light on hp and torque verses the post ww2 cars.

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Interesting. We have seen this concept quite a bit actually. On  the exhaust pipe,  cool factor is definitely there, although performance wise it will be little better than

stock and it may even have a bigger back pressure imbalance.  On the Intake again cool factor right up there. Performance wise  carbs are too low, no effective balance tube or sufficient atomization  area in the intake. My guess, having never seen it, is it has a bit more rev, looses a bunch of torque and likely tosses out raw fuel on a regular bases.

 

So super cool to look at, but after that, it looses it for me pretty quick.  Definitely appreciate seeing it just the same.

 

Tim

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I thought I would add this one to show you an example made "Down Under"  by Andrew. He actually races this car and you can also see the handy work evident  elsewhere under that engine compartment.     Over the next few months we should have a  comparison for you as in the next couple of weeks I will be boxing up an AoK triple to send to Australia.  Its not the 1st  that headed down under, but will be the 1st that replaces a home made triple on a full race motor.

Of course as I said earlier 3 carbs on a rock stock original 1936 201 ci motor, with the right sized carbs way out performs both in power/torque and fuel economy, but in this case Andrew is chasing the  edge of the envelope.

 

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You know Tim I have read your post several times on muti carbs.  Its brilliant. What a great explanation and I for one can testify that when I moved to multiple carbs I got better fuel mileage. Actually almost 20% better. Keep up the awesome work........ please!

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On ‎12‎/‎13‎/‎2017 at 2:40 PM, oldasdirt said:

You know Tim I have read your post several times on muti carbs.  Its brilliant. What a great explanation and I for one can testify that when I moved to multiple carbs I got better fuel mileage. Actually almost 20% better. Keep up the awesome work........ please!

I'm curious to know what your mileage numbers were, and in what car? The  bone stock (and well worn ) 218 in my 52 Plymouth sedan got around 22 mpg on the highway, and I'm wondering if expecting another 20% in fuel efficiency is even practical. Excellent post all around. 

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