Moparts
Slant Six 2bbl Milage
Posted By: MoparJ
Slant Six 2bbl Milage - 11/26/08 10:53 PM
My 74 Duster with a 225 Slant has a two barrel intake and two barrel Holley off of a 318. It runs smooth. It usually gets 15-17 mpg on the hwy and 11-13 in the city. It has some miles on it and the valve seals may be needing to be replaced, but it runs smooth on all 6. The gearing is 2.76 behind a 904. Does this milage sound reasonable for a setup like this, or should it be a tad better? The valve lash seems alright, as there is no valvetrain noise. The exhaust manifold leaks a bit, as the idiot who had it prior to me did not put much of a gasket on, mostly RTV(
). I am going to fix that this weekend.
Posted By: DaytonaTurbo
Re: Slant Six 2bbl Milage - 11/26/08 11:03 PM
My old 74 Dart with a 225 with bad blowby would do low 20's us mpg on the highway in the summer.
Posted By: MoparJ
Re: Slant Six 2bbl Milage - 11/26/08 11:22 PM
I am beginning to think that the 318 carb is jetted too rich. The hwy milage may approach 20 at times, but the city is consistant 11-13.
Posted By: DaytonaTurbo
Re: Slant Six 2bbl Milage - 11/26/08 11:40 PM
Mine was pretty decent in the city as well, should be better than 11-13.
Posted By: In_The_Pink
Re: Slant Six 2bbl Milage - 11/26/08 11:42 PM
Quote:
My 74 Duster with a 225 Slant has a two barrel intake and two barrel Holley off of a 318. It runs smooth. It usually gets 15-17 mpg on the hwy and 11-13 in the city. It has some miles on it and the valve seals may be needing to be replaced, but it runs smooth on all 6. The gearing is 2.76 behind a 904. Does this milage sound reasonable for a setup like this, or should it be a tad better? The valve lash seems alright, as there is no valvetrain noise. The exhaust manifold leaks a bit, as the idiot who had it prior to me did not put much of a gasket on, mostly RTV( ). I am going to fix that this weekend.
It think those are typical numbers, and about what I get with my '77 Aspen wagon w/Super Six during normal driving. 
Posted By: 2Bad360sfromNC
Re: Slant Six 2bbl Milage - 11/26/08 11:58 PM
Quote:
I am beginning to think that the 318 carb is jetted too rich. The hwy milage may approach 20 at times, but the city is consistant 11-13.
You might be right, there. I had a BBD on my Valiant, and it got about 18-20 in town if i didn't kill it. I got into it too much usually, though. It was funny barking the right rear in 2nd. 
Posted By: RapidRobert
Re: Slant Six 2bbl Milage - 11/27/08 01:07 AM
whats hurting you the most is the 2.76 rear. With the low torque of the /6 & 74 A is heavy it makes you go too deep into the throttle. If you run into a good deal on a 3.23 rear in the bolt pattern you have(BBP I assume) which would probably be rare(in that ratio) You would gain alot. Or a set of dutra duals to attack the worst(restricted) area on the eng.
Posted By: Rug_Trucker
Re: Slant Six 2bbl Milage - 11/27/08 01:43 AM
I have 2 74 A bodies both with SBP wheels.
Posted By: RapidRobert
Re: Slant Six 2bbl Milage - 11/27/08 03:32 AM
A 3.23 in a sbp would be alot easier to come by. I just tossed several 7&1/4's because I got tired of tripping over them then I see 2 people who want them. ain't that how it always goes.
Posted By: ThermoQuad
Re: Slant Six 2bbl Milage - 11/27/08 04:33 AM
Your mileage is low, I also suspect a stretched timing chain. Those stock chains are good for maybe 50,000 miles...I have put a chain and gears in every /6 I owned. I have seen them stretched at much lower mileage as well.
As far as gears why not 2.94 instead of 3.23?. I have tried both with the /6 and I always found 2.94's worked best.
One /6er was a 69 coronet deluxe ferder [4dr] with no options...3 on the tree. I got 24 mpg on the interstate running 70's with 2.94's. Car had 3.23 when I bought it & got 19. The proverbial lol car, it was Grandma Websters car
Posted By: marklock
Re: Slant Six 2bbl Milage - 11/27/08 03:51 PM
My brother had a 78 Volare with the super six and said he got between 16-18 mpg overall. I do remember he cut the cat and adjusted the timing to get those numbers. This was 20 years ago and the car had 80k or so miles on it.
Posted By: 62maxwgn
Re: Slant Six 2bbl Milage - 11/27/08 04:06 PM
In its original condition (bottom pic) /6 it did 24/26 on a trip to North Bay,Canada.After the change to the 340,it would still do 18/20 with 3.23 rear.
Posted By: Magnumguy
Re: Slant Six 2bbl Milage - 11/27/08 07:05 PM
I would suggest 2.94's also. Probably find it in the newer 80's models, such as G-Furys, etc.
Once upon a time, a friend of mine's folks had a 63 Dart, with 170 and 3 speed. It would get, on the interstate, just under 30mpg's!!!! They repeated these numbers every trip north on the interstate.
Posted By: RapidRobert
Re: Slant Six 2bbl Milage - 11/27/08 07:14 PM
3.23's would be perfect around town but would be terrible on an interstate trip. If your not a traveling salesman most people are going to be mostly going stoplight to stoplight.
Posted By: B5 Bee
Re: Slant Six 2bbl Milage - 11/27/08 09:45 PM
'84 D100, 833OD, 225 with 2bbl added, gets 20mpg HWY at 65mph. Only got 18mpg with the original 3.21 gear and a 235x15 tire, 20mpg came with a swap to an older 8.75 rear with 3.91SG.
'79 Aspen, 904 LU, 225 Super Six, don't know the gear, gets 24mpg HWY at 65mph.
'68 Signet, 904, 225 with 2 bbl added, header, don't know gear, still has 13" tires, gets 19-20mpg CITY driving it easy.
Posted By: Rug_Trucker
Re: Slant Six 2bbl Milage - 11/28/08 03:04 AM
Quote:
3.23's would be perfect around town but would be terrible on an interstate trip. If your not a traveling salesman most people are going to be mostly going stoplight to stoplight.
I will beg to differ on that 3:23. I have ran my 198 3 speed 1bbl to Oklahoma and back at 25+ mpg. 65-70 mph. Cracked exhaust manifold, duals
With a BBD or a 318 sized Holley 2280 with a ported head .090 off it Hooker headers, H pipe and same duals 80-82mph 21.8-22mpg on 93 octane.
Maybe the gear works with the short stroke 198?
Posted By: 70Valiant
Re: Slant Six 2bbl Milage - 11/29/08 09:12 PM
On the way back from Pittsburgh this summer running 65-70mph I got 23.4mpg with a 225/, Lock up 904, 3.23's and 24" tires. I'm running 9.8:1 compression, 465cfm Holley 4bbl, electric fan, manual steering, clifford shortie headers and a 2 1/2" single exhaust. Going by the mile markers on the road I am off 1 mile per hundred, or one percent so my net was just over 23 mpg. I get 15-16 around town and I like to hear that cherry bomb
Posted By: MoparJ
Re: Slant Six 2bbl Milage - 12/03/08 08:45 PM
The motor is definately on the loser side; it does not knock, but the valve seals are worn and it sounds loose when it is being shut down. My nose can pick out the scent of some blowby.
The chain probably is going south. The carb is a Holley 2bbl of a stock 75 318 dart. It is an OE piece. The exhaust is 2" from the manifold, through a Flowmaster muffler (does not sound great on a slant).
I dont think the lash is too far off and I have timing at a good setting, which would be as aggressive as I can go before detonation sets in.
The rear tires are 215/70/14s.
Posted By: njmopar
Re: Slant Six 2bbl Milage - 12/04/08 03:06 AM
2bbl here with 2.76 (and 13" wheels). I can get into low to mid 20's no problem on the highway.
Posted By: mopowergtx
Re: Slant Six 2bbl Milage - 12/04/08 11:42 PM
1979 Aspen 2dr - Super Six - 2.76 gears - 215/70-14 tires - rebuilt lockup converter. 22mpg driving to work everyday. 13 miles state highways and 2 miles through town then 10 miles on the Interstate one way. Had a wore out Super Six before that one setup the same way and it got the same kinda milage. Alot town driving would pull it down to 18-20mpg.
Posted By: moparguy
Re: Slant Six 2bbl Milage - 12/05/08 02:33 AM
in my old 76 dodge aspen i would get about 24-26 on the highway. it was the super 6 and I drove it like an old lady, i wasnt gonna get anywhere fast anyways. if i got about 70 mph though the mpgs sank like a rock to around the 15-17 range
Posted By: gts340swinger
Re: Slant Six 2bbl Milage - 12/05/08 03:02 AM
From my experience, the more worn out your /6 is, the better the mileage will be.
Posted By: MoparJ
Re: Slant Six 2bbl Milage - 12/05/08 08:27 PM
I guess I should mention that the 904 is in need of a rebuild and a shift kit. It shifts very soft and the front seal is leaking a bit. Never slips gears, though. The tc may be shot too.