Puzzling MPG returns....

[dynamutt]

OK- i got a '69 A100 stick van, w/ a new reman. 318. stock 2bbl.... this was a running but hardly sorted out project when i bought it. I got a petronix ignition, got the timing set to full mech advance @36 btdc, (close, anyway- tough as hell to get a clear line on the timing marker),, idle at 10 btdc. (degree tape on balancer) ..... plugs are clean, no soot in tailpipe. runs and accellerates smoothly, quite perky.Im rolling along at 17 inhg or better.
dosnt bog. 3.55 rear, tall 15 in lt truck tires at 55 psi. Im getting a bit over 10 MPG, the last run mostly highway under 65. TEN MPG. this dosnt compute.

[PwrWgnDrvr]

U need to go downhill with a tailwind.

[sledgehammer]

mpg does seem a little low but those vans are definitely not aero dynamic

[dynamutt]

Well.... the 318 was touted as economical. And drag really starts to stack up over 60mph. Previous to this van, i ran a 80 econo w/ a stick & 300 inline six i did a lot of mods on and was getting way more power than stock, and 25-30% better mileage...... did a lot of long runs with it, and always have a vac. gauge hooked up- its handy. you can see the vacuum really start to drop above 55-60. ANYWAY, a long way of saying that 80 MPH mileage. Not 55-60. ........sumpthin aint right. I got a GPS speedo in it, so the miles are accurate....... im just finishing an adaptor i made to mate the brand new ($85!) motocraft 2150 2bbl with about 20% bigger venturis on it, see how that goes. I had one on the 300 ford.... real soild kit. you can tune the dumper jet to come on at a specific inhg.... so thats next. its a breathing/comopression issue, i gather, reading a lot of 318 articles on the net. it would seem, in order of logic, i need to put a better breathing, higher lift cam in there..... im not top end oriented, its mid range grunt i like- besides, how fast ya wanna go in a 69 van?- any recommendatiuons for whats called a "RV cam"- thats some work, but not diffucult. i gotta get better mileage outta the beast.... increasing volumetric efficiency that way might ne a noticeable bump......... and i read all factory pistons offer a deck heieght thats .050 up to .090, but KB has a set that brings it up to 15 or so- reasonable $, and a lotta work but compression is bang for the buck. the third major thing would be a set of the "302" heads- casting numbers, 80's autos) but thats at the tail end of this..... im not building an engine that sees 5K, it will rarely see 4 k, so bigger ports isnt as much a consideration....

[PwrWgnDrvr]

Having driven 318's, 360's, 383's, 440's since the early 70's, close to a million miles, including more than a dozen freshly rebuilt 318's, Ive NEVER seen a 318 beat 10 mpg, except on a couple occasions when long distance highway driving in favorable conditions blessedly allowed 12.
Spending $$$ to get a couple extra mpg takes a damn lot of miles to break even.

But I sure do love the 25 mpg in my 66 D100 SWB with the CTD!

[Txas2step]

Having driven 318's, 360's, 383's, 440's since the early 70's, close to a million miles, including more than a dozen freshly rebuilt 318's, Ive NEVER seen a 318 beat 10 mpg, except on a couple occasions when long distance highway driving in favorable conditions blessedly allowed 12.
Spending $$$ to get a couple extra mpg takes a damn lot of miles to break even.

But I sure do love the 25 mpg in my 66 D100 SWB with the CTD!

Hey Terry, have broken even, in gas savings, on that beauty yet, for what you paid ?

[PwrWgnDrvr]

I actually made money Chris. I kept charging the client the 80c/mile the W100 383 was costing me for the 100+ miles a day I was driving to do their service work. That work lasted 3 yrs. The CTd truck dropped that to 30c/mile, so after 30,000 miles it was paid for
I love those fillups - it only has a 16 gal tank and every 300 miles I put in about 12 gal

[Wildergarten]

I actually made money Chris. I kept charging the client the 80c/mile the W100 383 was costing me for the 100+ miles a day I was driving to do their service work. That work lasted 3 yrs. The CTd truck dropped that to 30c/mile, so after 30,000 miles it was paid for
I love those fillups - it only has a 16 gal tank and every 300 miles I put in about 12 gal

Back when I was working on boats, I was told in no uncertain terms not to use a galvanized fuel tank for diesel.

The concern is small particulates that may form in the diesel fuel due to the interaction between the zinc and fuel occurring within the tank. These particulates may end up clogging injectors or filters when the stored fuel is used in diesel engines. However, this problem does not seem to be too alarming and is only noticeable with smaller tanks. When large tanks typical of what is used in practice are used, the clogging problem becomes negligible. This is due to the weight of the particulates. Heavier than the fuel, they tend to rest undisturbed near the bottom of the tank. Regular cleaning of an in-line fuel filter may also be an option if the clogging problem seems to persist.
https://galvanizeit.org/knowledgebase/a ... rage-tanks

Did you etch it off the inside or did you just ignore that?

[dynamutt]

PwrWgnDrviver, thats exactly the kinds empiracle knowledge im looking for. OK, now i know this 10MPG is a feature, not a bug. Theres nothing wrong. Thats good to know,
So, my googling "318 dodge tech" & such brings me to some idea why these offer such low MPG. Breathing is a big part of it. I cant help but think improving the breathing on the 300 got me good gains. So... the cams on these things are minimalist, to say the least. and gioven the flat piston and low deck height, its not much to add more lift. Bang for the buck is important, & Summit has three cams, all under 130 w/ lifters. https://www.summitracing.com/parts/sum-k6901/make/dodge https://www.summitracing.com/parts/sum-k6900/make/dodge as im planning on putting a clutch on the fan, i figure to pull the radiator. And im a tinkerer. it works. i can get better than 10 mpg out of it. I got dual 2.5 exhast thru cherrybombs, so even w/ the crappy log manifolds, its gotta be good for what im working towards. This will let the larger motorcraft carb do its job. more volumetric efficiency, more bang for the buck..... third leg of the stool, after ignition setup and breathing, is compression.....im gonna see what some of these carb and cam changes offer up. I mean- from 10 to 12.5 mpg is a 25% increase. i gotta be able to squeeze 15 outta this thing.... the 300 was only 8.3-1cr. im an old guy, wrenched all my life, retired, the labor is free, as it were.

[PwrWgnDrvr]

I actually made money Chris. I kept charging the client the 80c/mile the W100 383 was costing me for the 100+ miles a day I was driving to do their service work. That work lasted 3 yrs. The CTd truck dropped that to 30c/mile, so after 30,000 miles it was paid for
I love those fillups - it only has a 16 gal tank and every 300 miles I put in about 12 gal

Back when I was working on boats, I was told in no uncertain terms not to use a galvanized fuel tank for diesel.

The concern is small particulates that may form in the diesel fuel due to the interaction between the zinc and fuel occurring within the tank. These particulates may end up clogging injectors or filters when the stored fuel is used in diesel engines. However, this problem does not seem to be too alarming and is only noticeable with smaller tanks. When large tanks typical of what is used in practice are used, the clogging problem becomes negligible. This is due to the weight of the particulates. Heavier than the fuel, they tend to rest undisturbed near the bottom of the tank. Regular cleaning of an in-line fuel filter may also be an option if the clogging problem seems to persist.
https://galvanizeit.org/knowledgebase/a ... rage-tanks

Did you etch it off the inside or did you just ignore that?

Didn't build the truck Mark and didn't know that tech detail until now. Its a factory tank. Had the truck 15 yrs now and over 50,000 miles since I got it. Have never had a plugged fuel prob.....

[Txas2step]

I actually made money Chris. I kept charging the client the 80c/mile the W100 383 was costing me for the 100+ miles a day I was driving to do their service work. That work lasted 3 yrs. The CTd truck dropped that to 30c/mile, so after 30,000 miles it was paid for
I love those fillups - it only has a 16 gal tank and every 300 miles I put in about 12 gal

You need to post some pictures of it.

[Red383]

"But I sure do love the 25 mpg in my 66 D100 SWB with the CTD!"

We need to see some details on this!

Aaron

[sledgehammer]

I have a ‘75 Dodge van, 318, automatic, 3.23 (3.21?) rear gears, headers, 600cfm Edelbrock carb and I got 15.5 mpg on a trip I took from my place to Oregon and back. Not great but not horrible either. It was freeway driving so speeds varied between 60-70

[dynamutt]

OK. Got the https://www.summitracing.com/parts/sum-k6901/make/dodge cam installed, and adaptors made to get the brand new motocraft 2150 2bbl ($67!) for a 351 ford onto the cast iron stock manifold. Havent done any mileage runs but my two test drives had me barely needing to crack the throttle at 55-60, keeping 16-18 inHg, at about 2700 rpm @60. cant figure how to post a pic.....

[dynamutt]

Stock, fresh rebuild of unknown comprtession: 10.3 MPG, over a hundred miles at under 65. After the cam/ carb swap: 14.7, a FORTY SEVEN % improvement... that over the same hundred miles of highway, but i admit it goosed it a few times. Took it over the San Marcos Pass- rt 154- steep & twisty. ..... never got near to dropping out of third. never got near to flooring it. was able to keep 10onHg or better.... id come on a steep turmn and just goose it and it would acellerate the whole way.... i put a power valve of 5inHg, in it, so i never lit it off.

[sledgehammer]

That’s a very good increase

[dynamutt]

Replicated it. another hundred miles or so- it has a gps speedo, so its accurate- and taking the mountain pass on the way back- it just floated up the san marcos pass, i never really had to floor it, just goose it.... and i didnt need to downshift once. mileage was 14.3.

[dynamutt]

HA! Some fine tuning- a hair over 15MPG. thats a 50% improvement over stock. I KNEW this was possible. Next: i got a spare distributor i shortened the mech advance on w/ a Pertronix pickup in it.... trying for 16mpg..... this cam https://www.summitracing.com/parts/sum-k6901?rrec=true this carb https://www.ebay.com/i/142624440253?chn ... rxEALw_wcB and a lot of elbow grease.....