Daughter needs Gas mileage from 273 commando

[one mile]

'65 Barracuda 273 Factory solid lift cam Commando. Bought "Basket Project" from friend, I am finishing it up for Daughter as Driver "Fun Car". motor and trans. He already built back to factory specs with hardened Valve seats as well as 904 Trans and converter that came with car from factory, "Think" it has a 2:96 Rear. 26" tall tire on 17's,"Tiger Grip" LSD rear. I have 600cfm Holley 62,65 jets Vac. secondary, dual line ,center hung float bowl conversion. (it's an Auto Cross thing, I use to "Road Race" when I was younger), edelbrock D4B intake , stock manifolds, x Pipe and Spin Tech Mufflers. D.U.I. ignition planned for combo(I Love them).
I love all of this but feel a camshaft change is in order with all the advancements made in this area. Also a hydaulic grind for when I am dead and gone for low maint. for her If she keeps it. Lots more "Stuff" done to the car but for now I am looking for the future and GAS MILAGE. Maybe Just Maybe, a little "Bump" for the old man (ME) and the car on idle,but Gas Mileage is first. Looking at 89 octane Gas. Come on and help an old Chevy Guy trying to make the transition and his Daughter happy ! One step at a time ! Seriously. Thanks, Tim (Dad)
:thumrigh:

 

[Abodybomber]

Basic Summit K 6900 ,cam & kit. 204/214@ .050 ,112 lobe centers(smooth idle ,lotsa.torque.( My advicelease leave the 2:94's,do all suspension ,safe.

 

[OldmanRick]

Congratulations to you and your Daughter, sounds like a great ride!

With the shortblock being put together at factory specs, i'm not sure if a cam swap will be worth the investment. Valve lash on a engine like that will usually hold for a long time. If your set on converting to a hydraulic, i'd consider the cam that "Abodybomber" suggested. Just remember that the adjustable rockers will still be part of the package unless you switch to stamped units at the same time.

I think I'd let her run as is and just give her as much initial timing as it will take with the hi compression on pump gas. Keep in mind that the best mileage on a combination like you have is from the tune and the right foot. Easy driving and keeping the rpm's down will do more for mileage then any component swaps with your current combination.

 

[2 Darts]

You'll have problems with a X pipe and a pre-67 A-body. The torsion bar cross member is only notched on the driver's side. Recommend a 3" single system.

Gas mileage + 273 Commando = LOL. Disconnect the secondary on the carburetor, Dad.

The 65 A-body had a 4" bolt pattern wheel. Sorry, there's not much in the way of wheel selection.

That being said, an easy way to improve fuel mileage is to fit a later model rear end to the car (they all interchange). If your car has not been converted to big bolt pattern axles, stick to 73 and later /6 cars. The gear ratio to look for is a 2.76:1

 

[Abodybomber]

Congratulations to you and your Daughter, sounds like a great ride!

With the shortblock being put together at factory specs, i'm not sure if a cam swap will be worth the investment. Valve lash on a engine like that will usually hold for a long time. If your set on converting to a hydraulic, i'd consider the cam that "Abodybomber" suggested. Just remember that the adjustable rockers will still be part of the package unless you switch to stamped units at the same time.

I think I'd let her run as is and just give her as much initial timing as it will take with the hi compression on pump gas. Keep in mind that the best mileage on a combination like you have is from the tune and the right foot. Easy driving and keeping the rpm's down will do more for mileage then any component swaps with your current combination.

Quite frankly,Rick.,you might be spot on.... I am aggressive on modification....

 

[Johnny Dart]

Gas mileage for the daughter....Corolla.

 

[one mile]

All mods I could do to the suspension and Brakes have been done,Convertible sebring seats with shoulder harness, collapsible steering, full Firm Feei suspension ,Stage 3 power box, Right bore M/C, smaller W/C on rear to help with lock up, prop. valve , new run flat Michelin tires. Lets don't get into this...... I have driven myself nuts over this having to explain myself for letting a younger person drive an "Old Car". I say this just so "IT" does not rear it's ugly Head (Horse talk )and start running off....I love my child, it will be safe. LOL ! I just need your knowledge on better Gas milage....this is a new area for ME ! Ha Ha. Any more engine mods I can do to help? Thanks all for your replys, got to get back to work, Break is over......Tim

 

[one mile]

Abodybomber this was not directed at you ! LOL ! just wanted to stop it before it got started...Got Real Ugly on another Thread here about building a car for my Daughter.... See Ya ! Tim (Dad)

 

[pyrojim]

All mods I could do to the suspension and Brakes have been done,Convertible sebring seats with shoulder harness, collapsible steering, full Firm Feei suspension ,Stage 3 power box, Right bore M/C, smaller W/C on rear to help with lock up, prop. valve , new run flat Michelin tires. Lets don't get into this...... I have driven myself nuts over this having to explain myself for letting a younger person drive an "Old Car". I say this just so "IT" does not rear it's ugly Head (Horse talk )and start running off....I love my child, it will be safe. LOL ! I just need your knowledge on better Gas milage....this is a new area for ME ! Ha Ha. Any more engine mods I can do to help? Thanks all for your replys, got to get back to work, Break is over......Tim

You found like a pretty nice dad!

 

[moparlover]

I had a '68 340 dart with a .550 lift solid cam, x heads, large thermoquad carb (I built the engine from parts) 3:23:1 rear & I got 19mpg

the secret: 4 speed manual shift.

with a slop-a-matic trans forget it. 12mpg if you drive it easy, the camshaft will have very little effect I'm afraid.

you might be able to just do a torque converter change and get it up a little bit.
but before you invest tons of money into carbs/cams/marvel mystery oil/etc the best you could possibly do is swap to an OD manual trans. you will need pedal assy, bell housing, flywheel, pressure plate, etc. so it's not for the faint of heart

 

[toolmanmike]

Congratulations to you and your Daughter, sounds like a great ride!

With the shortblock being put together at factory specs, i'm not sure if a cam swap will be worth the investment. Valve lash on a engine like that will usually hold for a long time. If your set on converting to a hydraulic, i'd consider the cam that "Abodybomber" suggested. Just remember that the adjustable rockers will still be part of the package unless you switch to stamped units at the same time.

I think I'd let her run as is and just give her as much initial timing as it will take with the hi compression on pump gas. Keep in mind that the best mileage on a combination like you have is from the tune and the right foot. Easy driving and keeping the rpm's down will do more for mileage then any component swaps with your current combination.

I also agree,, Leave as is a and bump the initial timing up. Re curving the distributor will increase performance but depending how you drive it may not increase economy. I can get 18 on the highway with my Charger 273 but That's driving it real easy. 3.23 gear and a 4 speed. It would be interesting to leave everything else the same but install a od/4 speed. Anybody done this swap with mileage results? tmm

 

[GaryS]

Crappy fuel containing Ethanol is the biggest problem with old engines. I was working at a CP dealership in '64, and when brand new, a 273 with TorqueFlite and 3.23 gears would average 20 mpg and get 25 on trips, but not with today's government mandated fuel. My suggestion is to build it stock and teach her how to drive for mileage, and then just grin and bear 17-18 mpg with an occasional dip into the 20s. Without computers and fuel injection, that's the real world.

My current '64 slant six only averages 18 with a high of 22, but a '63 I had when it was only two years old averaged over 20 and fully loaded managed 27 on trips.

 

[toolmanmike]

Crappy fuel containing Ethanol is the biggest problem with old engines. I was working at a CP dealership in '64, and when brand new, a 273 with TorqueFlite and 3.23 gears would average 20 mpg and get 25 on trips, but not with today's government mandated fuel. My suggestion is to build it stock and teach her how to drive for mileage, and then just grin and bear 17-18 mpg with an occasional dip into the 20s. Without computers and fuel injection, that's the real world.

My current '64 slant six only averages 18 with a high of 22, but a '63 I had when it was only two years old averaged over 20 and fully loaded managed 27 on trips.

I have a Mopar friend with a 42 PLymouth, stock built slant 6, od-833, 4.10 gears and tall tires that gets 26-27 highway. I think the od might be the key. tmm

 

[teringer]

my 78 aspen rt came with a 318 4speed od with a 2.96 gear(with the lean burn ign) it got a whole 15 mpg .took it back several times to dealer with fuel mileage complaints was to get 20mpg according to advertising .so after warranty was over I switched the intake to a ld4b/ 650 holly off a 429 ford truck/ 273 solid cam by trw with a .424 lift and 228 deg intake and exh. at .050/ put used 340 valve springs in dropped in a accell duel point race dist with no vacuum adv. and had the local exhaust shop put duels on it. to by surprise the first time I went on a road trip to oc md.( all flat ground) I started cussing at the wife because now the fuel gauge was broke the needle only moved a little off the over fill mark. so when I tried to fill the tank it only took 4 gals. in 120 miles so now I'm under the car trying to find out why I can't get more gas in it. so I get home and its 4 more gallons, so next thing I do is pull the tank to fix a problem . the tank was still full . this car never got less than 30 mpg after that the fuel savings made the car payment /so why didn't they just keep making them like this with the added fuel inj. would probably get 35 mpg. so hot rodding doesn't always hurt fuel mileage.

 

[66fs]

Your problem will be 89 octane gas and 10.5 pistons, 2 valve notches and a dome. You will be lucky if it will run on 93 octane. The cam is fine. If you adjust it 5,000 miles after you start it up they should go another 100,000 miles or more without any adjustment. You should get 20+ MPG on the highway. A Vacuum gage and teaching her to keep a steady pedal is the key to MPG. I assume you can tune that carb and distributor. Barracuda's, Aerodynamics, and 273's, efficiency, used to be mileage champs. And for Toolmanmike, The OD trans is sweet for mileage. You want to end up with a 2.76 or lower total ratio. Used to run mid 20's MPG with the Commando 273 and 833 OD. I put OD guts in a small bearing main case so I would not have to change anything else but the shifter rods and tabs. Hoping to be in Greenwood, SC. this year.

 

[67Dart273]

In my opinion, forget the 650 Holley.

 

[rumblefish360]

Does that ignition have a multiple spark ability?

This is a major key in seeking mileage IMO.

 

[nm9stheham]

You can get decent highway mileage with these engines even with an auto trans:
- High lift, limited duration, wide lobe spread cam; hydraulics or solids does not matter. So-called 'torque' cams will do this. (And this is not new cam tech; these torque grinds came out in the 70's with the 1st gas crisis.)
- Bump up compression to what will run on premium pump gas; 9.5:1 or 10:1. This will improve combustion efficiency and low end torque. (Don't limit yourself to regular! The higher compression you can do with premium will help you in so many ways!)
- Use quench dome pistons to improve mixture swirl in the cylinders and improve % of combustion; it will also suppress detonation better.
- Anything you can do to improve flow will help effieiency: single plane intake, headers; mild porting job, large valves.
- Better exhaust; 18" or 24" long 3" dia collectors on medium to largish tube headers will help a lot with torque and mileage. The long/large collectors will compensate for the low RPM torque loss that can occur with larger tube headers, but the large dia tubes will resonate at higher RPM and extend the useful RPM range. The large collectors is simlar to the H pipe but works better IMO.
- 600 cfm vaccum secondary 4 bbl; smaller primary venturi's; sounds like you have that.
- Get rid of any high stall torque converter

With the above combo you should get around 18-20 mpg with the auto (non-locking converter) and your tall rear axle gears on the interstate at 70 mph. Adding a locking converter would help more.

I did the above combo on a 351C years ago and that was what I put in a '70 Ranchero with a 3.0 rear and C4 auto, stock conveter. The compression, breathing improvements, and long collectors to compesate for the large tube headers and torque cam, made it a stump puller at 1500 rpm that would still rev smoothly up to 6500 rpm (honest!). The better combustion efficiency of the higher compression and swirl of the quench-dome pistons made up for the smaller carb at higher rpms; the quench domes allow for more timing advance too. The 1-2 shift point of this combo was at 55 mph and the 2-3 shift point was at 85 mph! It would kill anything else on the street due to the torque off the line and the wide rev range expcept for highly modded engines (I could outrun 440 Satellites and Coronets all the time; can I say that on this site!?!), yet give good mileage. The 351C was a good intake breather out of the box, so working on valves and porting on the Chrylser small block may be a key thing to do for this combo to work well.

BTW, my son needs a wife; you daughter sounds 'well equipped' with the Barracuda; PM me if you are interested in an arranged marriage.... LOL !!

 

[one mile]

looks like I will have to dial in what I have the best I can then start changing one thing at a time to see what works best. Thanks for everybody's input ! dial in, diall in.... we shall see!!!! Tim (Dad)

 

[rumblefish360]

I would so NOT use a sine plane intake. Stick with the dual plane. Trade for a Edel. Performer if anything.

Open air element cleaner
2-1/4 exhaust pipe with an H pipe

You should so well on the Hwy.

 

[67Dart273]

I would so NOT use a sine plane intake. .

He mentioned D4B which is the early 273 dual plane, I guess the forerunner (no pun) of the Performer

http://www.forabodiesonly.com/mopar/showthread.php?t=116751

 

[toolmanmike]

Your problem will be 89 octane gas and 10.5 pistons, 2 valve notches and a dome. You will be lucky if it will run on 93 octane. The cam is fine. If you adjust it 5,000 miles after you start it up they should go another 100,000 miles or more without any adjustment. You should get 20+ MPG on the highway. A Vacuum gage and teaching her to keep a steady pedal is the key to MPG. I assume you can tune that carb and distributor. Barracuda's, Aerodynamics, and 273's, efficiency, used to be mileage champs. And for Toolmanmike, The OD trans is sweet for mileage. You want to end up with a 2.76 or lower total ratio. Used to run mid 20's MPG with the Commando 273 and 833 OD. I put OD guts in a small bearing main case so I would not have to change anything else but the shifter rods and tabs. Hoping to be in Greenwood, SC. this year.

Good to hear about the o/d 833

In my opinion, forget the 650 Holley.

I agree, Use a 550-600 Edelbrock with your intake. The smaller the primaries the better. Thermoquads got good mileage if you could keep your right foot under control.

Does that ignition have a multiple spark ability?

This is a major key in seeking mileage IMO.

Great idea!
Multi spark is great for low to mid rpm efficiency.

I would so NOT use a sine plane intake. Stick with the dual plane. Trade for a Edel. Performer if anything.

Open air element cleaner
2-1/4 exhaust pipe with an H pipe

You should so well on the Hwy.

Yep! dual plane for efficiency. Not many choices for the 65 273's though because of the different intake bolt angle. The D4B works well with a small vac. secondary Holley or small Edelbrock.

 

[goldduster318]

I would change the heads to the 88-91 318 heads 4323302...the fast burn, swirl combustion chambers will help burn efficiency immensely. My friend had an '88 Diplomat with a high mileage engine and these and it easily got 15mpg city with 2.76 gears, a 999 Torqueflite and a very heavy foot.

 

[replicaracer43]

I would change the heads to the 88-91 318 heads 4323302...the fast burn, swirl combustion chambers will help burn efficiency immensely. My friend had an '88 Diplomat with a high mileage engine and these and it easily got 15mpg city with 2.76 gears, a 999 Torqueflite and a very heavy foot.

Probally not gonna work with a dome piston.....

 

[67Dart273]

my 78 aspen rt came with a 318 4speed od ............................ this car never got less than 30 mpg after that the fuel savings made the car payment /so why didn't they just keep making them like this with the added fuel inj. would probably get 35 mpg. so hot rodding doesn't always hurt fuel mileage.

Let me be the first to say this