the 7.25" in my '76 duster uses a sealed roller bearing w/o adjustment, so it has to be a straight roller or ball bearing...I can't remember which at the moment.

You guys with your Magnums and 302's. Nothing wrong with the stock 273 head. You can get some good flow numbers out of those heads not to mention port velocity. He can also play around with head gasket thickness to fine tune the CR.

Manual trans is out of the question unless someone wants to donate a complete set up. I think with this low powerd motor the early dakota 5spd should fit and work best. The a-500 has a higher OD ratio and the trucks with them don't seem to get much if any worse miledge than the 5spds, but I would prefer the 5 spd personaly they are more fun to drive.

The original 273 heads are not hardened seats. The 302 has more swirl and velocity in it also. I am torn between the 302 and MAG right now.

I am in the process of moveing right now so I have not started yet, just gives me more time to plan. Keep the ideas flowing.

I have flow number that show the 273 heads will outflow the 302. As far as hardened seats, unless you are towing and running that 273 hard and lean you don't need hardened seats. Pulled the heads off my 273 with 75,000 miles and no valve recession. 67 Dart, 273/Carter 625, electronic ignition, duel exhaust with Flowmasters, Comp 268 cam with 904 and 3:23's drove from NW to LA and back with an average of 22 MPG at average 64 MPH.

My 273 headed 318 was getting 22MPG with 2.94 gears in my Duster. The early closed chamber 273 heads are a good choice for a gas mizer set up.

rig it up to go nuclear!!would last a lifetime.......

I'll skip quoting all the "Prince Valiant" stuff but I do have to take exception with it.
He did lots of work with numbers to show his theories. The real world blows a great big hole in it because torque production is not linear. Efficiencies of individual parts vary greatly with engine speed. The whole package will swing widely as the engine accelerates through the rpm range.

As for super stupid-low gearsets, you're killing your mileage.
How many of you have a 2.2 or 2.4 geared M-body that gets better than 15 mpg in the city? It doesn't happen because the car has to work so hard to overcome the lack of torque multiplication during acceleration.
Seteady state cruising is great but you've got to get up to speed first.

I had a 318 87 150 longbed pickup with 2.94 gears and I got 16 in town. It had taller tires so it was more like a car would with 2.20 or 2.45 gears and more weight. And for the highway it would get 19-20 and it only had a 3spd 904 and worse aerodynamics. With a more optimized engine and drivetrain I really don't think 20 in town and even 30+ on the highway is too much to ask for(with sane driving habits and a few other car tricks).

This discussion has been interesting but increasing fuel economy is very difficult.
There are only two things to do to reduce fuel consumption:
1) reduce the work you are asking the engine to do
2) make the eninge more efficient

So all of the ideas to reduce the work of the engine; lighter wheels, reduced aero drag, manual trans or lock-up TQ are good ideas and will result in improved fuel consumption no matter what is done to the engine.

The real problem is that actual fuel economy may not be effected even if the engine is more "efficient". This is because most of the time the engine is operated in a part throttle mode. It is very difficult to improve part throttle fuel economy because as the engine is made more "efficient" the throttle position changes (closes) which causes the engine to overcome more pumping work (the work the engine needs to overcome to suck air past a partially closed throttle plate). It's one of those things that you take 3 steps forward with say compression ratio and 2.5 steps beck due to an increase in the pumping work, so the 10% efficieny improvement becomes 2% or less and this is just not seen when driving the car.

Idle fuel consumption is pretty much based on engine speed with fuel/air ratio also a part, so the lower the idle RPM and the leaner the lower the fuel consumption will be.

Engine-wise I suggest keeping it simple; use a high compression ratio for thermal efficiency and a low overlap cam for good idle at a low RPM with a lean idle carb setting, with this you might be able to see an improvement with fuel economy.
Any other thing you can do to reduce the engines work should also show an improvement in fuel economy.

Question Prince,

If the engine is using EXACTLY the same mass flow rate of fuel,(more fuel per cycle at lower rpms), how does RPM really make any difference???

In your over generalized 440 example at either 2800rpm or 1800rpm it still consumes about 14 lb/hr of gas. Correct?? You stated: "Doesn't matter if that's 30HP @ 3000 rpm or 30HP @ 2000rpm. It's just 30HP.....I will move ~ same amount of air and fuel within a given time period." So to make 30hp, you need 14lb/hr of fuel, wether you have a 440, 318, 2.2l, or 600cc. If gas weighs 6 lb/gal, your gas tank is STILL draining by at least 2.3 gal/hr regardless of the engine or its rpm.

Answer: By your arguments engine RPM(or even engine displacment) doesn't affect the rate of fuel consumption. You've talked yourself in circles because neither is actually true.

imo, you either really don't know what you're talking about or you're over generalizing and simplifing to the point of confusing yourself and others. I honestly think its the latter. Mainly because i agree with your general conclusions, but your reasoning and rational for them barely hold water. i suggest more work with the caculator before typing.

I've said it before and now agree with feets, torque vs VE isn't a straight line. Your VE example/argument is worthless.

BTW mechanical eff(friction)is a much greater % of total engine eff as rpm drop. So the thermal eff and ve both usually have to rise to maintain the same output, which is usually very unlikely given your argument for static throttle position. At a constant load friction doesn't rise nearly as quickly with rpms as VE and TE

One more thing, regardless if you're right or not, no one will respect your opinion of you're being a jerk.

PV... What's the deal? Wy get all fussy about what I wrote when you didn't even address it in your post?

I said that VE is not linear. That remains true.
I didn't knock your work. Instead, I pointed out a simple flaw.
You've got lots of info but when one little thing goes awry, it throws out everything related to it. Think of it as working a 6 page math problem then dividing by zero. OOPSIE! There goes all that work.

Please guys don't get my thread locked! Focus on the subject, you guys are all thought provokeing and I apreciate every ones thoughts and input.

The 273 heads will have less velocity because they have a slightly larger port volume. Not that they would be a bad choice for that reason, they would make less pumping losses. That is also a reason for me to consider the magnums, I have a set of them and the 273 heads but no 302s...

you could probably find someone on here to swap you a set of Mags for 302's. They'd probably jump on it!

At what point does good swirl/tumble/mix become more important than just velocity? If we're talking a couple % faster in a 44-year old head vs. a 24-year old head, I choose the newer one every time.

Clair