340 Gets Terrible Gas Mileage

[MopaR&D]

I would like to find one that will stay on the damper. Two have flown off my new damper....

I think he means to use it just for the sake of figuring out the cam timing events turning the engine over by hand, not necessarily leave it on the damper permanently to use when the engine is running. It would save the hassle of removing the pulleys and crank bolt to attach a degree wheel.

If I need to work with a stock damper and I'm trying to figure out my full ignition advance curve I'll use a tiny Dremel cutoff wheel and carefully mark the damper in 10-degree increments up to 50 or 60 degrees BTDC. Totally permanent and costs nothing.

 

[Jeremiah (jd)]

Years ago a friend of mine installled a 2800-3000rpm converter and it killed his low speed fuel economy. It did not lock up around town.

Probably your best course of action would be converting it to a 4-speed.

: D

Beautiful car btw!

I am an NGK man but have had success and failures with all of them. Like a friends brand new set of ngk r plugs that lost 100whp because of a bad plug in #7...new out of the box, installed by me. I was shocked.

 

[MopaR&D]

Years ago a friend of mine installled a 2800-3000rpm converter and it killed his low speed fuel economy. It did not lock up around town.

Probably your best course of action would be converting it to a 4-speed.

: D

Beautiful car btw!

I am an NGK man but have had success and failures with all of them. Like a friends brand new set of ngk r plugs that lost 100whp because of a bad plug in #7...new out of the box, installed by me. I was shocked.

I have a cheap unknown-brand converter in my Duster that stalls around 2600 RPM and is pretty loose in street driving but I still average 14-16 MPG with a 450 HP 360 although I do have 2.94 gears. Still I think even if I had 3.55s it wouldn't be much worse. Loose converters definitely kill fuel economy though, engine is always spinning faster than it needs to to push the car around.

Good to know about the plugs too I'm about to get a set of 8 to put in my truck with a wider gap after installing a Pertronix Digital HP CD box and Flamethrower III coil, hopefully I don't get a bunk one.

 

[512Stroker]

I would like to find one that will stay on the damper. Two have flown off my new damper....

Same here lost 2 of them.
Just recently I had the balancer off so I cleaned it really well applied a new timing tape and shot 2 coats of clear engine enamel over the whole thing.
I defy it to come off now.

 

[Mattax]

I would like to find one that will stay on the damper. Two have flown off my new damper....

The one from mopar perfromance stayed on pretty good. That was in 1990 or so. The black background made it easier to read.
The current engine has a non-mopar diameter damper so I had to try different brand. It didn't stay on that long. I don't know if the difference was the prep or the adhesive. I have a couple more to try - when I get 'round to it.

 

[Mattax]

I think he means to use it just for the sake of figuring out the cam timing events turning the engine over by hand, not necessarily leave it on the damper permanently to use when the engine is running. It would save the hassle of removing the pulleys and crank bolt to attach a degree wheel.

yes. Exactly.

I have a cheap unknown-brand converter in my Duster that stalls around 2600 RPM and is pretty loose in street driving but I still average 14-16 MPG with a 450 HP 360 although I do have 2.94 gears. Still I think even if I had 3.55s it wouldn't be much worse.

Yup. I had 3000 brake stall setup and had T/A adjust it down a few hundred rpm. But regardless, higher stall speeds do not directly equate to slipping for normal driving. Under light throttle there's no slippage worth worrying about. Its under full throttle that it slips up to the stall speed. More power can drive the stall speed up. Less power drops it down.

FWIW that car got 14.0 mpg in normal mixed driving. With recreational use, 1 autocross per tankful, usually around 9 mpg. City only driving, its more about gallons per minute. When a car's not moving fuel use is all about time running.

I've got to say that I don't believe spark plug brand is going to make a noticible fraction of a difference to power or mpg. If a plug is cracked or damaged, then its bad. If its fouled, its fouled. Sure NKG's quality may be better than Champion's. But if someone wants to buy me a set, I'll run them back to back against the Champions at the track. If the MPH goes up in a meaningful way, I'll pay for them. Cecil, maple Grove, or even ATCO if we could somehow be sure of getting more than 1 run in 4 hours. Need at least 2 runs on each set.

 

[Jeremiah (jd)]

That may be true with your cars IDK. I was simply relating my experience from 20 years ago.

All of my cars have manual transmissions and a power adder so these slow automatic cars are out of my wheelhouse. : D