Here is something interesting. A stock 340 4 speed cam (268/276) had 44 degrees of overlap. My roller cam has 41 degrees of overlap instead of 8. I used the wrong duration numbers to figure it. So this explains why I get 155 psi cranking compression with a 10.2 to 1 calculated compression ratio. Dave is right I'll be giving up some gas mileage, but hopefully not too much.I'll just have to drive faster to get the engine in it's efficiency range. Then the air drag will kill me Still it should give at least 20 MPG

http://en.wikipedia.org/wiki/Brake_specific_fuel_consumption

then read

http://www.prime-mover.org/Engines/GArticles/bsfc.html

somewhere i read a link about a company in Florida that runs classes for gasoline engine private airplane owners about how to set cruise at the 200 degrees F past the lean side of peak EGT in order to get to best BSFC...but I can't find the link in my bookmarks

someone ought to dig out this article and post it online:

http://www.sae.org/servlets/productDetail?PROD_TYP=PAPER&PROD_CD=933033

because I seem to remember it had a bsfc graph that would tell us the typical behavior of a Magnum engine like cylinder, but I am not certain of what is actually in the article because I looked at it so long ago

It has been a few weeks, has their been anymore data collected?

I am very interested in this since I currently am building a car and deciding which path to take.

Thanks, ROB

Haven't been driving it much lately. Last tank was strictly city driving, lots of cold starts and warming up, stop and go sort of thing and it got 19. That is the only tank since I broke a U-joint, where we also idled on the side of the road for probably an hour or more on that tank also. I figured it was a tainted test so didn't bother to post it.

I did try 87 octane this last time I filled up and it pings just a tad at higher rpm on full throttle blasts. I could probably retard the timing a couple degrees to fix it but it is not bad and I don't drive it at full throttle much so I am not concerned with it.

After this I would like to try the thin mopar head gaskets, I still think there is a little more MPG by switching to them. I might even try the screens over the ports when I do that.

I haven't had time to tinker with it lately though. I bought 74 a dart race car project and I am trying to put it together to sell.

After I get a little money from that project I still want to put in an A-500... that should help me on the highway to break 30mpg.

I had a bonestock, 100% stock, 1973 318 Duster that got around 16, and that was mainly hwy. Almost all hwy in fact. It was a bit disheartening.

I have really enjoyed the build and am contemplating something similar with one of my early A's.

Thanks for the update.

ROB

I would think that my single exhaust etc. weren't helping my situation. It was a one owner, and the guy told me that it got maybe 18 at best when new.

I was not real excited when I saw that 16 MPG. I was thinking that some headers and a mild cam etc. I could do that good.

It ran so well that I didn't have the heart to screw it up so I sold it. Should have kept it.

ROB

I just wanted to throw out an update on a couple things.

1. It has been warming up around here a little and it started pinging a little on heavy accel so I topped off the tank with about 5 gals of 93 and that made it quit. It had a mix of 89 and 87 in it. I think I will be useing 93 from here on out.

2. I have only driven strictly in town with this last half tank and it got 19 again.

I finally hooked up a vacume gauge to watch when driving and it's kinda interesting. I can keep the vaccume at 20 inches cruising at 70 on a flat road with no wind. It only pulls 25 idleing in park. I though it would be a little higher idleing and lower cruising. This still leads me to beleive it would love an OD gear. I bet in town it could go over 20 and I could easily knock down 30+ on the highway especially if it was a 5-spd manual OD

I got 23mpg with my /6 duster. That was with a a833od and the high geared rear with an automatic (i converted the auto to a manual). The car is in car heaven now . Still have all the parts for the convesion.

I thought about water injection but figured it would be a pain to keep up with and install compared to the mabey 1 mpg it would give me if that.

It is cheaper to operate now than before.

Conservitivly, under the same driving conditions I am getting 5 or more mpg better in town or highway so...

27 / 3.45 = about 12.7777 cents per mile

VS

22 / 3.25 = about 14.7727 cents per mile

On a 15 gallon fill-up I save about $9.58 over what it would have been before. Plus it makes a nice chunk of extra hp over the old motor so I don't mind the premium

On top of that I save a couple bucks on soda and candy bars because I fill up less often

Dave- Did I miss it? I can't recall seeing if you got a weight on that thing yet, as driven...

Have not got an exact weight, I am guessing around 3200 now. It was 3060 and I added an 8.75 and disc brakes but also put on a mini starter and aluminum intake as well as no mufflers at all now.

I am going to install a 68 273 in my 1950 Dodge pick up. I have a 67 Formula S 4 barrel intake. Would that be a good one to run with the mild cam and Electronic ignition. I am shooting for mileage too.

That would be a good intake. If you were going to run a thermoquad you would need an adapter though.

OK...I am losing sleep at night, and this is part of the reason. I have a 64 Valiant Signet. I am debating a mimic of sorts on Dave's idea here. I have 2 318's to choose from...one Mag and one 302 headed roller from the late 80's. Dave utilised the 273 solid cam. Will it hurt this project to run a roller? And if not, what kind of specs (duration, LSA, lift) should I be looking for? Target CR with quench? Will the benefit of a few less pounds also help? I can go wherever I want with this in some ways...and am seriously thinking that I will go 4-speed. 833 with 2.7-2.9's, or 833OD with 3.2-3.5's? Or chuck it all and do the same thing with a \6? I keep thinking that the theory of light recip assembly gets blown out the window with the 225, as that crank with it's 4.25" stroke ain't light, and it gets tougher to get a cam with specific specs, and exhaust becomes more costly to make it work efficiently (1 of Dutra's manifolds is the same price as Harold's Spitfires...) as well as carb/induction limitations. Just thinking out loud and looking for a bit of feedback before I start into it...

Thanks.

I built a 318 basically the same w/ KB 167s and 302 heads but I ran the pistons .002 out of the hole with .039 gakets. I ran it on a stand and it's really crispy. The cam is Comp 256XE. I am putting it in a 65 Valiant with stock manifolds, dual exhaust, 833 OD, and a 8-1/4 wih 3.21 gears. I have a few issues with the clutch, but hope to have it together by the summer. Am hoping for 25+ mpg on the highway too. This is a great thread. More real world results please!