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#47507 - 11/10/07 05:46 PM Super duper MPG 273/318 experiment ! NUMBERS!!!!!!!
HotRodDave Offline
master

Registered: 01/29/05
Posts: 9524
Loc: Kalispell Mt.
I have a 273 sitting out back seasoning and thought it would be fun to build it to get the best possible gas miledge and slide it in the 68 cuda for a while. Heres what I was thinking,

.060 over bore
cheap light weight I beam rods.
Cast crank, turned down to balance it.
Custom light weight pistons Zero decked
Coated on top and skirts
Stock Magnum heads
318 2bbl cam or shorter duration if some one knows one, mabey even custom.
Windage tray.
800 cfm Thermo-quad
Offy dual port intake
Screens over intake ports
195 t-stat
2.76 gears
A-500 trans

I think the heads will fit with no bore notches if I turn the valves to 1.88 diameter(the seat on these heads are way in from the edge of the valve) The one side will be shrouded but that should help swirl everything up.

The cam needs to be the shortest duration I can find to build tons of vaccume. And also the mag rockers 1.6 ratio will help the lift a hair to help it make a little bit of power any how.

I have TTI headers for the car any how so that should help.

Any one has any suggestions feel free to throw in your

It currently has a 318 low comp open chamber headed 2bbl and gets 22mpg high way and 18 intown. The goal would be ultimate miledge and any HP it can make without sacrificeing MPG would just be a nice bonus.

One more thing, I may bump the comp up a bunch and run it on e-85. Havent decided on that one yet, the other choice would be pump 93 octane.


Edited by hotroddave40 (01/29/08 09:37 PM)
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68 cuda 360 notchback SOLD

1996 Ram 2500 5.9 eddy intake EQ heads, mild cam upgrade great tow rig!


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#47508 - 11/10/07 07:46 PM Re: Super duper gas miledge 273 experiment !!! [Re: HotRodDave]
CudaMike Offline
super gas

Registered: 01/20/03
Posts: 1011
Loc: Kingston, TN
Dave, I'm thinking the Magnum heads may be a little big for a 273, since it is about 85% the size of a 318 (the smaller of the two Magnum headed engines). I'm thinking 302's with a good valve job and a little touchup blending. But, you would be giving up the 1.6 rockers. A custom cam could make up for that.
With the O.D. trans the 2.76's may be a little too tall, but maybe not.
Just thinking out loud

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#47509 - 11/10/07 07:47 PM Re: Super duper gas miledge 273 experiment !!! [Re: HotRodDave]
mopowergtx Offline
master

Registered: 06/18/06
Posts: 3075
Loc: Eastern Ohio
The E-85 would be going the wrong way to try and get better fuel mileage right? From what I read thats the way I understand it. Higher octane but lower mileage. Would a later model roller cam 318 be a better start evan though its got the extra cubic inch to feed? Thinking this because I wonder does the roller cam's reduced friction offer anything in the way of mileage benifit? I take it cast cranks are lighter than the stock forged 273 unit? Run the 273 full floater rods they should be lighter than the later model versions I believe. If you need a good stock set you can have the stock rods from my 67 318. What about 2.4 rear gears like in the late model 8 1/4. Man with an overdrive you could get that thing to idle at highway speeds. I know the KB Hyper pistons are almost 100 grams lighter than a stock piston so you'll shake some weight there too. Can you get a stock air cleaner for a 4 barrel Cordoba maybe and use the fresh air pipe and route it somehow on the Cuda to grap cool outside air for it? If you ran an old Edlebrock performer intake don't they have the correct choke well for a Thermoquad? Does reducing oil windage offer any mileage? Just some more thoughts. Sounds like a cool experiment.
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#47510 - 11/10/07 07:51 PM Re: Super duper gas miledge 273 experiment !!! [Re: mopowergtx]
mopowergtx Offline
master

Registered: 06/18/06
Posts: 3075
Loc: Eastern Ohio
Oh would running a twin electric fan setup with no engine fan make a difference?
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#47511 - 11/10/07 07:52 PM Re: Super duper gas miledge 273 experiment !!! [Re: CudaMike]
68Cbarge Offline
master

Registered: 01/14/06
Posts: 3131
Loc: Canuckville
Quote:

Dave, I'm thinking the Magnum heads may be a little big for a 273, since it is about 85% the size of a 318 (the smaller of the two Magnum headed engines). I'm thinking 302's with a good valve job and a little touchup blending. But, you would be giving up the 1.6 rockers. A custom cam could make up for that.
With the O.D. trans the 2.76's may be a little too tall, but maybe not.
Just thinking out loud



Yep.2.76's will be too tall with the O/D.
3.23's will be better.
Ditto on the 302 heads.
How about using a stock 360 2bbl grind cam? Just a thought.


Edited by 68Cbarge (11/10/07 07:54 PM)
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#47512 - 11/10/07 07:56 PM Re: Super duper gas miledge 273 experiment !!! [Re: HotRodDave]
JDMopar Offline
master

Registered: 01/19/03
Posts: 7789
Loc: Candler,NC / Myrtle Beach, SC
If you run an A500 OD with 2.76 gears,you're gonna have to drive about 95-100 mph to keep the motor in the sweet spot! 3.23 gears are about the bottom of the barrel to run with an OD tranny. I plan on trying an A999 lockup tranny with 2.45 rear gears in my wifes 69 Dart conv. The A999 will have the low first gear.I'd be interested to read what some of the good engine builders here have to say about what to do to a 273 to make it get good gas mileage.
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#47513 - 11/10/07 07:59 PM Re: Super duper gas miledge 273 experiment !!! [Re: mopowergtx]
DaytonaTurbo Offline


Registered: 02/26/03
Posts: 20446
Loc: Manitoba, Canada
Play with this

http://vexer.com/68rt/speed.html

You'll see an o/d with 2.x gears is just too low. You don't want to be under 2000rpm at 60 IMO. Too low of an rpm, even on a tiny cammed engine can drop it below it's power band too far and cost you fuel mileage. IIRC, for cruise rpm, ideally you want to be 100-200 rpm below your torq peak for best mileage.

What about a wideband o2 so you can actually tune the thing to get a nice lean a/f ratio? And a exhaust gas temp gauge to tune your ignition timing to optimal? Yeah where do you stop, lol.

I wonder if a roller teen would be better for mileage. A roller is easier to spin over so I could see it helping. However I did change to a roller in my 87 daytona and noticed no difference in mileage at all, although the roller was more aggressive of a grind than the stock cam.

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#47514 - 11/10/07 08:28 PM Re: Super duper gas miledge 273 experiment !!! [Re: DaytonaTurbo]
mopowergtx Offline
master

Registered: 06/18/06
Posts: 3075
Loc: Eastern Ohio
Quote:

You'll see an o/d with 2.x gears is just too low. You don't want to be under 2000rpm at 60 IMO.



Not knocking your opion of what you want for rpm versus mph but my stock 360 '01 1500 Ram 4x4 3.55 rear gear and stock 16" rims and tires with overdrive runs under 2000 rpm at 60 mph.
I get 15.5 mpg combo city/highway with it. Its been awhile since I drove my stock 77 Cordoba 400 thermoquad with 2.4 rear gears and it doesnt do much better than 2k at 60 as I remember. My thinking is if your cam(small) and engine combo makes good power starting at 1000rpm well what would hurt cruising at 1700-1800k in OD? Figuring the cam he'd probably run would be peaked at around 4000 to 4500 rpm. It doesnt take much power to maintain highway speeds. Correct me if I'm wrong I believe Chrysler evan offered a 2.2 gear set in 7 1/4 or 8 1/4. I think it was in the Diplomat body.
I think its all relitive to your setup.
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#47515 - 11/10/07 11:22 PM Re: Super duper gas miledge 273 experiment !!! [Re: mopowergtx]
da50r Offline
master

Registered: 05/07/05
Posts: 2613
Loc: Middle TN
You know what is funny... my wife and I took out 67 Dart 273, 2 bbl on a trip. We got 26 MPG real highway miles per the GPS which I think is accurate. Is that not amazing? I love that car.

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#47516 - 11/11/07 12:50 AM Re: Super duper gas miledge 273 experiment !!! [Re: mopowergtx]
DaytonaTurbo Offline


Registered: 02/26/03
Posts: 20446
Loc: Manitoba, Canada
Yes, however your ram has a lockup converter, as did the later 318 powered cars. Take a stock 60's 3sp trans, stick a 2.2 rear gear into it and at cruise speed on the highway your rpms will be so low that the converter is slipping.

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#47517 - 11/11/07 07:32 AM Re: Super duper gas miledge 273 experiment !!! [Re: HotRodDave]
feets Offline
Senior Management

Registered: 01/20/03
Posts: 26930
Loc: Irving, TX
After calculating the proper gearing, the next step will be driving habits.
After that, aerodynamic aids along with tire pressures and alignment will be key.
It's all in rolling resistance.

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#47518 - 11/11/07 09:18 AM Re: Super duper gas miledge 273 experiment !!! [Re: feets]
RodStRace Offline
I Live Here

Registered: 09/21/05
Posts: 12384
Loc: Chino Valley
I agree with the stuff posted. keyboard build the engine to make torque at 1800-3000, then set up the drivetrain to roll in that range.
I don't know if the magnum heads will work on those small bores.
a roller cam would allow you to keep the dynamic compression up, along with velocity. You will have to juggle that with mech. compression to keep it from pinging. I'd question the 60 over for that reason.
Low weights, good tolerances, high velocity, and max squeeze are the basic steps. I wonder if going with a smaller exhaust would help tune this combo (build torque down low)?

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#47519 - 11/11/07 09:42 AM Re: Super duper gas miledge 273 experiment !!! [Re: HotRodDave]
TC@HP2 Offline
master

Registered: 01/23/03
Posts: 4773
Loc: Pikes Peak Country
To get the engine working efficiently and loaded up on torque, you need as much cylinder pressure as possible. This means small duration cam to keep the sweet spot low and as much compression as your local gas supply will allow.

Yes, going to E-85 will cost you in mileage as it takes 30% more alcohol to make the same power as gasoline, so your burning more of it. But, total cost involved may also be a factor. In my flex fuel vehicle, 04 Suburban, it is a wash cost wise when gas is $2.95 and E-85 is $2.35. If the price spread gets greater than that, then E-85 becomes more economical from a financial stand point. Below that price point gas is better.

I also agree that you don't want to spin the engine to low. To cruise down the highway only takes 50-60 horsepower. So you want to have the maximum amount of torque at the smallest possible throttle opening regardless of rpm, within reason. This will be much more efficient than spinning the engine slower just to keep the rpm down.

Everything that applies to performance engine building applies to mileage engine building. It is just that the return is greatly diminished. Sure, roller cams may provide less friction across the rpm range and at peak power are worth an extra 12 lb ft and 10 hp. That same set up in a mileage build may still have reduced friction and increased power, but only have an extra 2 lb ft and 2 hp. Also, total cost involved is a determinate of what you want to do. You could easily spend $20k building a trick motor that will only get 3-5 more mpg that a good solid blueprinted and balanced build up that costs $7-8 grand.

For the car, you want to lighten it as much as possible. An A body is already kind of small, so you punching a much smaller hole in the air than a E body. Not much you can do for aero as a dart is a brick no matter how you look at it. Skinny high pressure tires, synthetic grease and fluids to reduce resistance, a whole bunch of little tricks can gain you a lot.

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#47520 - 11/11/07 10:33 AM Re: Super duper gas miledge 273 experiment !!! [Re: TC@HP2]
Θάνατος Offline
supercuda

Registered: 09/04/07
Posts: 12836
Loc: betwixt the land of the living...
The least aerodynamic part of a car is the stuff under it.

A belly pan woud be a fairly cheap and effective addition. Just remember to allow for air to flow out of the engine compartment, the radiator will thank you.

Back when I had my Diplomat 318 powered I could turn mid 20's on the highway. That was with 2.24 gears and an aerodynamic package at least as brick like as yours. City mileage was horrible though, even with the low first gear trans adn a lock up converter.

I later put in a 360, an A833 and a set of 2.94 gears and would turn low 20's with that combo. City mileage wasn't too bad then.

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#47521 - 11/11/07 01:42 PM Re: Super duper gas miledge 273 experiment !!! [Re: Θάνατος]
HotRodDave Offline
master

Registered: 01/29/05
Posts: 9524
Loc: Kalispell Mt.
The reason I would mabey use the E-85 is I can bump compression up a bunch and with increased compression comes increased efficency and it should offset a bunch of the differance. Flex fuel vehicles will always suck a bunch more ethenol than gas.

I have driven the 80s cars with 2.20 gears and they were fast enough for this experiment and my engine should be more efficent at low rpms with a good tight quench and small bore. I have an 8.75 rear with 2.76 gears and going 80 mph it could already stand another gear shift. I can find no higher gear for the 8.75. Lots of newer cars are under 2000 at 60 even 70. The A-500 has the low gears in it and I want one in there any how.

I was thinking of the offy dual port intake because the small primary runners should really keep velocity up at the low rpm cruise range. I don't have one of these yet though. I do have a street dominator, and LD4B and a factory single plane 2bbl.

The 302 head would be a good idea, any one want to throw a set my way? I'll trade for a set of cracked mags!

I was thinking the mags also because I had them. I have seen 1.88s on a .030 bore 273 and they were almost touching the bore, that is why I was thinking .060 over.

I have a cast crank and they are lighter, thats why I thought I'd use it.

The only rods I have are factory magnums, hence the thought of useing chinese I beams.

I don't have a spare 318 block sitting around but people should be able to use one for a clone with similar results.

I think the tq peak of 273 and 318 2bbls were both around 2000. I would be attempting to bring it down a hair from there.

I think HP will be livable I am not woried about that, the HP will take care of itself. I don't expect it to be a fast ride with this motor.

A belly pan is a good idea, I think I can figure that out.

I recently put an electric fan on the car but have not checked miledge since. It really suprised me how little I have to run it to keep the current motor cool.

Keep the sugestions comeing you guys are throwing out some good ideas.
_________________________
I am not causing global warming, I am just trying to hold off a impending Ice Age!

68 cuda 360 notchback SOLD

1996 Ram 2500 5.9 eddy intake EQ heads, mild cam upgrade great tow rig!


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#47522 - 11/11/07 03:51 PM Re: Super duper gas miledge 273 experiment !!! [Re: DaytonaTurbo]
mopowergtx Offline
master

Registered: 06/18/06
Posts: 3075
Loc: Eastern Ohio

Quote:

Yes, however your ram has a lockup converter, as did the later 318 powered cars. Take a stock 60's 3sp trans, stick a 2.2 rear gear into it and at cruise speed on the highway your rpms will be so low that the converter is slipping.



He said he was going to use a
Quote:

A-500 trans


Thats a lock up torque converter trans same as my Ram. Dave I messed around with my Ram today watching the tach and my speed in OD with a load of firewood in the back. 10-15% uphill grade at 1800 rpm in OD at around 57 mph and it was fine. Wasn't losing any speed. Was pulling fine. I like the consesus here that you need to put it between 1800-2000 at your normal cruising speed. Dave if you could get your hands on a 7 1/4 or 8 1/4 that would bolt in it that would be instant mpg bonus versus the heavier 8 3/4. Lightweight aluminium wheels sounds like a good idea too. What year did the Dippys and 5th Aves get roller cam motors? Theres a 86 I believe here next to my house I been thinking about getting for the K-member on the cheap. I need to come down to Tenn anyhow and see Defeo, guy owes me twenty bucks!
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#47523 - 11/11/07 04:52 PM Re: Super duper gas miledge 273 experiment !!! [Re: mopowergtx]
HotRodDave Offline
master

Registered: 01/29/05
Posts: 9524
Loc: Kalispell Mt.
I would have a final drive ratio of 1.904 and it is not much more than a 2.20 for steady speed cruising and I would have a better take off gear. With a 27 inch tire it would do 2000 right at 80 mph. I am planning to move out west with even higher speed limits so I think this should work out fine.

Just for fun I figured a 2.20 and OD would make a 1.52 final drive ratio and put 2000 right at 100 mph

I agree the roller cam would probably get a couple more hp because of friction loss but a flat tappet can get more lift at those real short duration numbers. I think with the magnums 1.6 or mabey even some 1.7 rockers and a custom short duration cam I could still open the valves a good amount to get some more tq.
_________________________
I am not causing global warming, I am just trying to hold off a impending Ice Age!

68 cuda 360 notchback SOLD

1996 Ram 2500 5.9 eddy intake EQ heads, mild cam upgrade great tow rig!


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#47524 - 11/11/07 04:58 PM Re: Super duper gas miledge 273 experiment !!! [Re: da50r]
rbstroker Offline
super stock

Registered: 09/24/06
Posts: 1139
Loc: West Tennessee
da50r, what trans, gear, and tire size are you running. I am putting a '65 273 Dart together hoping for some good mileage and a prostreet look. My Coronet stroker is fun until it comes time to fill it up which is pretty often.
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#47525 - 11/11/07 06:58 PM Re: Super duper gas miledge 273 experiment !!! [Re: HotRodDave]
RichV Offline
top fuel

Registered: 01/20/03
Posts: 1671
Loc: Seattle WA
Fuel Inject it. That way you can use lean cruise.


Another idea, turn it into a Aktinson cycle engine (not the diet craze). You do this my using a high mechanical compression ratio around 12 to 1 then have the intake valve held open until after BDC so some of the intake gases are bled off. This will result in higher mechanical efficiency, but low power. Aktinson cycle engine are very popular in hybrid applications.

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#47526 - 11/11/07 07:33 PM Re: Super duper gas miledge 273 experiment !!! [Re: HotRodDave]
Prince_Valiant Offline
top fuel

Registered: 02/10/03
Posts: 1665
Loc: Milwaukee, WI
For an auto, I'd probably run 3.21's in a 8 1/4 or 3.23's in a 7 1/4 rear.

Look to getting the lightest parts possible.

I ran a 360, fresh but mild build, with 2.94 gears and the OD 4speed manual...did GREAT with mileage (best trip, 55mph was 26mpg...tended to average high teens and low 20's). The large torquey engine did fine with the super tall gearing, wide ratio's. This was in an A-bod, with an 8 1/4 rear. Stock compression, MP .450 cam, performer intake, holley 600, hedman headers, MP ignition in a 76 valiant 4 door.

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