I am considering getting a slant six'd plymouth and I am wanting to achieve the best fuel economy I can..

It needs a head, so I figure I should have them shave the head down to bump the compression up, but how much compression can these motors take on regular gas?

And is there a paticular cam that does the best with economy?

It'll be sporting an automatic but I have a OD 4-speed sitting in the garage that will go in later.

Thanks!

Travis

I don't know about the build, but a '76 Feather Duster got 24 MPG!
I think it had a special carb.
If you take off .045 from the head, You should be just under 9 to 1 comp. I think that is OK for reg gas.
I have a Comp 252s cam. It is advertised as "better economy". It is quite mild, just a step above stock.
Some also say that if you go to the factory 2 bbl (super six), your MPG increases.
Hope that helps.

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"Nothing in all creation is hidden from God's sight. Everything is uncovered and laid bare before the eyes of Him to whom we must give account."

Feather dusters with a 4 speed got 30+ mpg. My brother in law sold his at carlisle last summer. His had an automatic and got 28MPG on the way out there.

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70Valiant,,,
I see in your signature, that your slant head is shaved .100

Do you run regular gas with no problem ?
Or do you need higher octane ?

Nope I have to run premium(92 octane minimum) That stuff aint cheap either.

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Here's some food (fuel?) for thought..

On my truck, when I installed a performance computer I had to use 93 octane, which sucked, but..I did pick up about 1-2 MPG on the highway. I blame it on spark advance.

Would I gain enough with higher compression and/or timing to make it worth while to buy 93? Heck, I'm used to it now. And when you average 12-14 MPG, that takes a while! LOL.

BTW I started this thread but apparently wasn't logged in when I posted. Oops.

Travis

You will not see big differences with cam changes, although you want to make sure it is "degreed in," whatever you use. The COMP 252 or MP 244 cams will be very good for driveability and economy, and will be not too much better than the stock 71-up mechanical cam.

Carb/induction, ignition advance, and drivetrain are the areas to focus most on. A 600 CFM 4bbl will get the same or better mileage than a stock 1bbl if set up right. I like the Edelbrock 500 myself.

The biggest single change in mileage I got was by putting in a manual trans (5spd with 3.91 axle ratio). Second biggest was by looking directly at air/fuel ratio with an O2 sensor and tuning jetting to run a little lean at cruise (once with EFI, once with a 2bbl carb so far). You must also make sure vac advance is working.

Lou

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Home of Slant6-powered fun machines since 1988

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I think EFI might offer a noticeable improvement for an
inline six. I think the stock slant six manifold is pretty
good for fuel distribution but multi-port EFI ought to make
it a little better. I agree with what Dart270 said, dialing
in with an O2 sensor might make a noticeable difference.

That made me smile.

Gas is three times cheaper In USA than here in finland.
That makes me cry

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Sorry, my english is not very good

Around here, gas cost $6 or so, for 95 octane(which is not the same octanes you use, probably 92) 10 norwegian kroner/ litre
And it sucks...

I agree on the O2 sensor, for about $80(to get guage and a heated sensor), or $60(to get guage and a non-heated sensor) you can get a setup which makes tuning a breeze. It also is helpful for tuning to fuel economy, or if you're in the mood to go quicker.

As a side note the only location that I could easily stick the O2 sensor in rendered a non-heated sensor useless, you can try going the non-heated route but you will have to keep the sensor very close to the exhaust manifold(or in it, I hear some manifolds were made to accept O2 sensors, never have seen it personally).

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My car may be slow to sixty, but at least it's been reliably slow to sixty for more than thirty years.

I have a non heated o2 3" or so after the manifold, and it doesn´t work good
at idle, and I wonder how accurate it is above idle too.

Maybe you need to talk to local politician and find how much of that is taxes to fuel their need to spend...

The gas stations had stickers last year, and they said about 75-80% is taxes
I really want to move somewhere else, but I can not afford that either.
We also have a lot of other taxes for using/owning cars, and almost none of that money goes back to build roads and stuff, like they said they would be, when they started the "road tax" thing...
Everything just goes in their big moneysack, and they probably dont know what they use it for themself...