there is no way to do that. without accurate reading of what your doing its just a crap shoot. also tuning every engine is slightly different, so what works for one won't generally work for another when trying to run the most power , the best fuel efficiency, etc. getting an average state of tune you can use the same settings as you'll be close. what carb do you have?

And sometimes running as lean as possible does not yield the best gas mileage. I have richened the the jets in some carbs and have actually increased my gas mileage

I have a Mopar Q-jet. The carb and intake came off an 80's non-computer controlled pick-up truck. I'm guessing the basic procedure for tuning for max mileage would be similar with other carbs also.(obviously the details would differ though)

Seems like I read years ago that the lean burn system Mopar used in the 1970's leaned the mixture out to a 16:1 or 17:1 ratio of air to gas. Is this approximately as lean a mixture which can be used and still maintian drivability? If drivability is acceptable, does this mean the mixture is not lean enough to harm the engine?

For what it's worth, I just did a valve job on a 79 Volare with lean burn. It had 2 cylinders with no compression. Took it apart and two exhaust valves looked like they had a cutting torch taken to them. When will a super lean condition cause driveability problems? Depends on alot of things!
I think alot of the cracked head problems are due to running the engines on the ragged edge of driveability

I think the main problem running lean is for high HP motors. The lower power motors will take longer to be affected by a lean condition, less overall heat. I also think by getting a really good homogenius mixture will allow you to run leaner with less problems because you eliminate hot spots during combustion, or at least reduce them. I left the exhaust valve rotators on this motor to help keep them more even tempertures. The area between the seats is where these heads like to crack so I polished that area to reduce stress risers and hot spots there. I have a list of stuff I would like to do to it still but I am broke and I think I have snatched up the simplest improvements, everything else is going to be like pulling hens teeth, cept mabey the OD trans.

A friend is offering to pay my way to the Chrysler classic in BG for my 30th bday so I might get to run in the 1/4 and see how fast it is. I am torn bout them lettin the brand Xrs in though.

I did the same thing on my magnum heads. I don't know why they leave that sharp edge between the valves. I filed mine down nice and round. I don't think I'll have any problems with cracking.

Would installing valves made from a more heat resistant material help to reduce the chance of burning the valves by running a lean mixture? Seems like a logical solution, but what kind of valve(s) would be more heat resistant?

Hotroddave40, do you mind telling us some more details about your ignition system. I know you posted earlier that it is an electronic ignition system. Can you give us some details on the advance curve? What do you have the base timing set at? (since changing to electronic ignition) Are you running a factory coil and spark plug gaps?

I have a chrome accel coil. Mopar electronic ign dist and harness with a autozone box. The distributer is the new adjustable mallory one. I set the idle for the most vacume then drove it with the vacume unhooked and adjusted the mechanica, it didn't need much taken out from factory, till it quit knocking at any throttle. Then I hooked up the vacume advance and did the same thing, drive adjust drive adjust till the knocking just went away. I would have to check again but I think the initial ended up about 16btdc and the total mechanical was around 32 btdc.

Just had it weighed at bowling green,

#3077 and it had a full tank of gas.

BTW the miledge seems to be pretty consistant 17 in town if I am real hard on it and 29 on the highway if I am real easy, like a steady 65mph. Most of my tanks are mixed driving and get about 25. If I am real easy on it in town it will still get around 20-21

I can't seem to get over 30 with it though

I wonder what a set of Magnum heads with dished pistons and quench would do? I'd bet money you'd be over 30 then!

no, for mileage you want efficiency, which means lots of cylinder pressure, so you want as high of compression as possible with as little overlap....if you wanted to really boost mileage, I'd use mag or 302 heads milled down to about 55cc w/flat tops, run a short duration cam like dave is, and water inject it (like a lot of turbo guys do) for detonation resistance.

Slow to 60 mph for a tank.

If I might chime in for a second....

There are a few factors you need to take a long hard look at.

#1 is your ignition timing as it relates to burning efficiency. If you map out piston velocity relative to crankshaft position you'll see a sine wave pattern. In order to make the most power and waste the least fuel you want all of your fuel to burn as quickly as possible when the piston has the most mechanical advantage. But you can't let the chamber exceed a particular temperature or you'll have auto-ignition (knocking).

If you're at 16 degrees BEFORE TOP DEAD CENTER that means you're starting the burn way way in advance of it's maximum mechanical advantage. This indicates either (A) Your fuel is not ideal for your goal -OR- (B) Your combustion process is slow and inefficient. There's not much you can do about A but B you can change.

#2 EGT (Exhaust Gas Temperature) Again relating to efficiency of burn. Whereas previously we're seeking maximum use of our mechanical force, EGT dictates maximum use of your CHEMICAL "force".

When the fuel burns and does what it does, heat is generated. Heat is energy. Wasted energy is wasted fuel. A VERY HOT EGT INDICATES ENERGY WASTED. A hot EGT is also caused by a lean mixture. Lean out the mixture and the EGT goes up. Makes no sense?

That's because the burn cycle is taking longer than the duration of the power stroke. You're wasting power by dumping it out the exhaust. Again, shorten the burn time.

One of my grandfather's favorite sayings was:

"Every job is easy if you have the right Tools"

to really do what you want to do
you need
EGT,
wide band oxygen sensor
at minimum
and in the ideal case.....
a set of eight spark plugs with fast reading pressure sensors embedded in them

Before using stock cast Magnum heads on a high compression and lean air-fuel engine set-up I would "temper" them in an non-oxidizing atmosphere oven at 520 degrees F for 24 hours, and then polish over the sharp edges in the combustion chamber.

Any new numbers from this 318?

Im looking to start a project like this but with a 170cui slantsix or a 273

I have been driving it a lot and it always falls right in range with previous postings. Tennessee has started putting %10 ethenol in all the gas but it didn't seem to make any differance. As a matter of fact I topped it off with 5 gallons of E-85 the other day to fill the tank, didn't seem to affect the way it drives any I will post how it affects the MPG when I finish off that tank. It was about 50 cents cheaper than 93 octane and Tn does not subsidize it. I would not be afraid to run another point or 2 compression with it to bring back some of the suposed eficiency loss

I would recomend the 273 over the slant because the only custom thing you need is pistons. With the slant you need a ton of milling to get closed chambers and zero deck. If you did all that milling I bet you would still need a custom piston to get valve clearance and low enough compression unless you want to make it run on e-85. If you could go this way though I bet a 170 would get better mpg on e-85 than a 273 on 93 octane. However if you threw an a-500 behind the 273 it might be close. I do beleive based on what I have learned: a 273 built with custom pistons and custom cam and a performer intake and OD that 35 mpg is reasonable. Also if I was running a motor that small that slow I would get some smaller headers like 1-5/8 and mabey add in an extra 12 inches to the primaries to boost low rpm tq. A narrower wheel would probably be good also, mine are 7.5 wide but have a very low profile tire to lower rolling resistance.

If I built it for e-85 I would open the heat crosover to gain some bit of efficency that it suposedly loses. It burns cooler so it should still not ping. Mine is blocked and I think it would knock if I opened it.

I mention all the e-85 stuff because I am thinking of switching it over with thinner head gaskets and some head milling.

Wow so much info out there...

My goal is to SAVE money so $$custom$$ parts are out. Anything I do is going to be done with off the shelf parts.

Also running on 87 is a must. The higher grades jump 10 or 15 cents between the grades here.

Im leaning more to the 170. Mainly because I already have 1, 2, and 4bbl intakes to play with and 2 diff sets of headers. As well as a ported, milled head with the MP oversized valves.

My plan so far is to put the better head on my original 225 thats in the car with a supersix (carter BBD) intake/exst manifold and run 2.25" exst.

Drop the front of the car to match the sagging rear springs

Clutch fan (already have)

Multi-spark MSD box. (already have)
And some type of belly pan to blend the front bumper to under the K-member. There is kinda a big gap there and it looks like the K-member is just hooking the air.


I'll keep my goal low at 25highway. I already get 18-22 with the messed up 225 thats in there. Since i already have most of this crap kicking around i'll see how it works out. If it goes well ill spend the money on doing up a(still looking for one) 170short block.