The car rolls on 205 70 15 michelins, is bone stock except for the distributor. I replaced the factory heavy spring in the distributor with a factory light spring to make the timing come in quicker, and bumped the initial timing from 2 BTDC to about 8 BTDC at 750-800 rpm. With the vacuum advance hooked up the total timing is around 50 degrees at 3000 rpm, disconnected its about 33-35 degrees at 3000 rpm. The motor has 60K original miles and is in an excellent state of tune - fresh carb rebuild of the 1945, valves adjusted, 10 / 30 w oil. The distributor changes only improved the highway mileage maybe 1 mpg. EGR and other pollution stuff is disconnected. Motor has 18 inches of vacuum at idle.
What would you do to bring the mileage up to 25 mpg? Skinnier tires? Remove the catalytic converter? Would like to take it on some long road trips this summer but w/o increasing the mileage that isn't going to happen.

Add more initial timing, at least 10 degrees if not more. I run 16 degrees initial. You can go with a longer throw can to get it up a little higher by 2500 rpm. I would have used a longer looped spring and rotated the spring post for max throw. Tighten up the primary spring by rotating the post out to keep the light spring tighter.

Make sure the can is not engaged at idle. Pull off the vacuum line to see if the rpms change.

Where does your rig cruise at 2500 rpm?

You can swap out that #60 jet in the 1945 back down to a #58. Your bone stock motor will run with a #58 which is approximately 8% leaner.

Since your down south, run a cold ram air intake to your snorkel. If you want pictures on how to do this for about $20.00 send me your email.

Run 2.25" exhaust pipe at least the first 6 feet if not more.

Tires should be fine, just keep them at 35 pounds.

Drive slower, 60 mph. You will hit 25 mpg, no problem.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

When you rebult the carb, what jet did it have in it? You might save another MPG by swapping to 1 jet size smaller (but no smaller than a #59...)... also changing the exhaust pipe to a 2.25" from manifold to the muffler, then stock out the muffler is good for another 1-2 mpg depending on tune... I got bux to bets that your 1975 monolith catalytic convertor is pretty much 'used up' and needs replaced (if required by your area), or eliminated (if you don't have to get inspected...)

Skinnier tires might help rolling resistance but not totally necessary, but with a larger diameter tire you may have slightly changed the 'actual rear ratio' compared to the stock rear ratio and tire size, and that might change your power band and cruise a bit...

Also unless you swapped out your speedo gear to correct for your tires being almost 1" in diameter bigger your speedo/odo will be off 1-2 teeth worth of speedo gear compared to stock... (that might help get your mileage back!)


Good luck

-D.Idiot

Good point DI!

Get your speedo checked and change the gear if needed for a accurate reading.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Before posting a lot of stuff, just take a second to look at what's going on... 'what has changed?'... good mechanics always check the basic items and changes to see what's 'not right' then goes from there...

In this case tire size isn't stock and that can change the speedo/odo reading (2 teeth per rpm is a fair amount)...



-D.Idiot

What is the rear end gear ratio? 2.76?
Is it a disc brake car?
DD

Yes its a 2.76 7 1/4 rear and is a disc brake car. It's all big bolt pattern stuff. Steel rims 15 x 6 off a 77 Chrysler New Yorker so I can run the better tires. I do have 195 75 14's on stock 5 inch rims to throw back on it, but it handles way better with the 15's.

Instead of using the odometer for the mileage, I filled up, did a test run with the miles calculated off of mapquest and re-filled up at the exact same pump, to come up with my 20 mpg.

I'm not sure on the jet size - will have to check it. Is that 1945 jet the same as a 4150 or 4160 4 barrel holley? I have tons of that stuff. If not, any good source donor cars that that jet might be in?

I tend to agree that the cat is probably used up, as back in the 'bad old days' there was still a lot of zinc in motor oil which probably polluted the cat a long time ago.

Is there a stock /6 that came with a 2.25" exhaust manifold pipe that will fit an a body - maybe a super six volare or pickup truck? I still find a lot of slant six cars in yards down here in Florida.

Looks like the gear calc you need with the 205 tyre is 27.52. Makes that a 28 tooth gear needed in the trans.

Not too sure how accurate MapQuest is. Others with more info may be able to chime in there. Keep in mind that the 28 tooth gear will not have your speedo right on the money, but close enough. If I've got my thinking the right direction the speedo will show slightly faster than you are actually going. As such the miles it shows will be slightly higher than actual also.

Someone please correct me there if I've got that backwards.

Speedo gear swap is super simple to do. One of the first things I'd do so you can see closer to where you really are on it.

_________________
From Mopars to classic Minis and back to Mopars in 19 years flat!

Will work for roast chicken crisps!!

Sixpack,

Yes, the jets are interchangeable.

On the head pipe, yes, trucks and vans had 2.25". That's how I got my first one.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

So I pulled open the carb today and the jet is stamped 611. I assume thats close to a 61 Holley 4 barrel jet. Only problem is my Holley Jet Set starts at 62. So what's a good boneyard yehicle to find a # 58 or 59 jet in a 1945 carb? There are still a few older mid 80's slant sixes down here in the boneyards...will probably grab a factory air cleaner set up with the cold air hose too, and look for a 2.25 header pipe....

Aggressive Ted - are you saying that a 2.25 inch header pipe off a van or truck has the correct bends and such to work for an A body? If so, cool...

Forget about mapquest. Get on the interstate with a stopwatch, do 60 as steady as you can on flat land, and use the watch to time the green mile markers. You should exactly pass one after 60 seconds - they are pretty accuratly planted. After a few whacks at it, you should be able to get a pretty good idea of what 60 on your speedo actually means.

Try again at 75mpg, which should take 48 seconds. I don't know why, but most speedos I've calibrated this way are non-linear. So take a few different readings at different speeds and try to get a feel for how far off the speedo is at different speeds. Express that error as a percentage, then mulitply that percentage by the odometer reading between tank toppings, and you should get a fairly accurate idea of what your actual mileage is.

Resist the temptation to just use the same gas pump and let it shut itself off - this is regularly inaccurate. Cram as much fuel as you can into the tank. Till it won't take another drop. Then when you refuel, do the same. That's a bit more accurate. To be truly accurate, you need to be able to sight the fuel level in the tank with accuracy, but that's hard to do without getting all fancy. Maybe a tank dipstick?

Kip on truckin'

_________________
1965 Valiant wagon Turbo slant (work in progress)
2000 Chevy 155" cargo van - The Abductor
1970 Newport convertible
1996 Buick Roadmaster Wagon
1966 CruiseAire motor home
1990 Toyota 1 ton box truck TURBO slant (scraped)

Forget about mapquest. Get on the interstate with a stopwatch, do 60 as steady as you can on flat land, and use the watch to time the green mile markers. You should exactly pass one after 60 seconds - they are pretty accuratly planted. After a few whacks at it, you should be able to get a pretty good idea of what 60 on your speedo actually means.

Try again at 75mpg, which should take 48 seconds. I don't know why, but most speedos I've calibrated this way are non-linear. So take a few different readings at different speeds and try to get a feel for how far off the speedo is at different speeds. Express that error as a percentage, then mulitply that percentage by the odometer reading between tank toppings, and you should get a fairly accurate idea of what your actual mileage is.

Resist the temptation to just use the same gas pump and let it shut itself off - this is regularly inaccurate. Cram as much fuel as you can into the tank. Till it won't take another drop. Then when you refuel, do the same. That's a bit more accurate. To be truly accurate, you need to be able to sight the fuel level in the tank with accuracy, but that's hard to do without getting all fancy. Maybe a tank dipstick?

Kip on truckin'

_________________
1965 Valiant wagon Turbo slant (work in progress)
2000 Chevy 155" cargo van - The Abductor
1970 Newport convertible
1996 Buick Roadmaster Wagon
1966 CruiseAire motor home
1990 Toyota 1 ton box truck TURBO slant (scraped)

Sixpack,

Yes, that is what I was saying however, look out for those that head over to the passenger side. Thats great if your going to run duals, but try and find one that goes straight back, if not you can use the other one, you just have to cut it and add more pipe. Either will get you started in a pinch. I did that to get me by and later bought some super thick flanges and had them put all new mandrel bent 2.25" pipe on.

Older 1920 Holley's had the smaller jets. All the 1945's I have seen from 1974 on had 612 jets in them. I just order the jets I need from our local Black Diamond Auto Parts. All the Holley gas jets are interchangeable in the one, two and four barrel carbs.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

got the part numbers, sure their not remans? I have about 5 oem 1945's spilled apart in bins in the garage for reconditioning and the 1974 models have #58's in them, the 1975 and 1976 models have 612's... and a truck 1979 model has a #62 in it... I also have the 1920's apart and find that the OEM 1973 carb came with a #56, the 1960's carbs came with a smattering of #54,#55... and even a #56'H'...


-D.Idiot

Swapped in a # 60 jet (smallest I can scrounge from the boneyard so far, still looking for a 58 or 59) from a 78 slant six pick up Holley 1920. Original jet was a 603. Timing is 10 ' initial BTC - 19-20 inches of vacuum at idle, 35 ' total mechanical at 3000, 49 total at 3000 with vac advance hooked up. Pumped up the Michelins to 35 and took it for a ride. Pulled down around 21 - 22 mpg at 55-60 mph.
Was inquiring on Moparts and someone mentioned their lock up trans Volare would get 3 - 4 more mpg than an older non lock up A body. Wondering if a swap would be worth doing, if those mileage numbers are true. Any guesses? A lockup trans can be id'ed by pulling the pan and seeing a crossover tube, correct? What are good candidates for a lockup car 904?