Power Plant Suggestions

[dodge freak 2]

With 3.91 gears-no OD, 26 1/2 tall tires and a "tight" 10 inch 3,000 stall TC in the 904 trans, my 340 can pull 13--14 mpg going 65's mph-if I went 60 it be a tad better. Driven hard it gets me 10 mpg.

I've heard of 7 mpg rides with 440's and same gears..with $5 a gallon gas  in the next few years--IMO, a few more MPG might matter

Now I could be wrong and gas prices could hold steady or even drop a bit ? Hard to believe gas in the USA was under $2 a gallon 4 years ago but it was-for a couple of months.

People sometimes say, oh I'm not going to worry about MPG, its a muscle car but then when $20 of gas is gone in 30 mins, the car sits more then its driven.

[brads70]

Here is a link to my engine build . You can have both power and economy if you chose the right parts.
http://www.cuda-challenger.com/cc/index.php?topic=78386.msg883819#new
I never dyno'ed it but an engine builder friend of mine says close to 600 HP I figure about 540 and I still get 17 MPG ( with an OD )

[HP2]

The motor and transmission (440/727) which is currently in the car is aimed for drag racing with a very high compression ratio (previous owner said 13:1) and requires using 110 octane gas. So that's not gonna fly for my purposes, it also has a small 5 gallon fuel cell - that needs to be replaced by a stock tank.

I am wary about trying to adapt the existing motor to EFI because I don't have all the details and don't feel like dealing with a Frankenstein combination or discovering things along the way. I already know I don't want 13:1 compression so it's gotta be torn apart.

Since I have a spare 440 block I might as well sell the existing powertrain and build it anew with components I want and are proven to work with each other with minimal fuss, also building a 440 v.s. a 340 can't be much different in cost which is why I am leaning towards the 440.

Did the previous own give you any reciepts on the engine components that could help you dial in what exactly you have, such as machine operations performed, piston manufacturer and part number, cam specs, etc, or do you know what shop did teh work on it? Details like this are critical to an engine build and someone must have these records. Have you done a cylinder pressure test to see how much cranking pressue you actually have?  The pressure test is a key answer to have before proceding. The reason why it is important is that just becasue the engine is claimed to be 13:1 and is supposed to run on 110 race gas, it doesn' necessarily mean it has to if the cylinder pressue isn't there to justify it. Dynamic cylinder pressure is what necessitates octane requirements. It is entirely possible for someone to put 13:1 pistons in a block that has excessive deck height with open chamber heads and a large cam that only has 180psi in cranking pressure. With a fine tuned ignition and fuel curve, you can get any pressure under 200 psi to live on the street. This is why I say it may be possible to avoid the whole rebuild step and go straight to efi. FWIW, compression ratio not only makes more power, but it makes that power because it is using the fuel charge more efficiently. Higher compression extracts more power out of the available fuel which means you can burn less of it to produce the same power compared to a lower compression set up.

Selling intact but used engines, especially race engine, is a touchy proposition. It may take you some time to get maximum return out of it, especially if you are unfamiliar of the exact details of whats inside. If you are selling one to fund the other, you could find yoursef upside down in the build very quickly.

[Srtviperjr]

Lots of solid advice there, I am not planning on making a dime on the existing motor and transmission, what I get for it is just bonus.

I'd rather just start with a clean slate and am willing to pay that price.

Transmission is going to be replaced with a modern 5 speed so it's gotta come out, motor has to come out to repair the inner fenders, might as well just build a new motor.

Gas prices? lol.... It's like $5.70 a gallon for 94 octane gas here. I shouldn't be driving a car period for that price. haha

[dodge freak 2]

Lots of solid advice there, I am not planning on making a dime on the existing motor and transmission, what I get for it is just bonus.

I'd rather just start with a clean slate and am willing to pay that price.

Transmission is going to be replaced with a modern 5 speed so it's gotta come out, motor has to come out to repair the inner fenders, might as well just build a new motor. Gas prices? lol.... It's like $5.70 a gallon for 94 octane gas here. I shouldn't be driving a car period for that price. haha 

So you should be trying to save dollars when you can--more funds for gas so you can drive it more often ! I hate going on long trips and leaving my favorite ride home and taking the smaller-newer-less safe car since it gets 24 mpg but money comes first for me. 

A different cam-maybe cylinder heads might all it need. Some mid 70's heads might drop the compression more then you think--that is IF its a true 13 to 1 motor.

Why replace those nice pistons if you don't have to ? Chances are they are good strong forge units install/machined by a pro  builder. Plus some cams are made to bleed off some compression or a custom cam can be order.

Back around 1980, Crower cams had a  sbc V8 getting 30 mpg with 13 to 1 compression but the cam closed the intake valves very late, they claim it ran on pump gasoline. 

I would think twice before just junking those pistons, best to find out just what you have and then talk to some cam grinders--there is still a few left.

[Rolling_Thunder]

I'll go against the grain and suggest a new gen Hemi -  You can find a 6.1L for <$4000 these days - throw on headers, cam, CAI and a tune you're well over 500hp. They give you affordable option for EFI, respind well to modifications, and are proven engines...    why throw the same amount of money into a 40+ year old style engine?    The 6.1L comes with aluminum heads, EFI, and makes 425hp stock...      Building a 425hp BB with aluminum heads and EFI will cost you almost double what you would be into a 6.1L for....       

[dodge freak 2]

Yeah but in 40 years will these new Hemi's today be worth building up ? My thoughts were not, that the castings are so thin and cheap the motors will all be junk in 40 years time. Some older machinist  shook his head and agreed with me.

These old Mopar's engines 40 years on are still in great shape, the iron used was good quality and the bores were made for more then just a .005 clean up. Aluminum warps,  cracks and corrodes over time.   

Maybe it doesn't really matter since most of us will be gone with in 40 years--live today, forget about tomorrow, lol
 

[HP2]

Oh, I don't know about that.  The iron castings are not any worse than the old stuff, at least with what I've seen, and the aluminum parts can be easily repaired. Once you shatter an iron block, its a throw away. Break an aluminum one and you can weld it up and remachine it to be good again.