I am musing about the effects installing a bigger cam (specifically the MP 244 cam), bigger valves (1.7 and 1.4 roughly), and doing porting on a head will have on the fuel efficiency of a slant six. All other things being equal, will the larger valves and lift simply result in more gas being sucked into the bores and therefore equal poorer mileage? Or will the increased power translate to a smaller thottle opening to maintain the same speed and potentially increased fuel economy?

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Casually looking for a Clifford hyperpak intake for cheap.

If it were me, with that cam, and valves, I would do a little pocket porting, mill the head to get a comp ratio of about 9 to 1, and use a valve seat angle of 30 degrees to enhance low lift flow.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

I agree with Charlie, also at the same time matching in a good timing curve will keep the power up and mileage up also...all you are trying to do is get the stock mill out of the poor efficiency range...into the "better" efficiency range...

You're going to mate this to a super six right? or are you keeping the 1 barrel?

-D.Idiot

Okay, thanks for the tips. This is a motor that will be going into my old 72 Satellite four door sedan, so I am not trying to build a race car. Just get a little more power and hopefully better gas mileage.

I plan to do just little upgrades using parts I already have, so I figure a .060 overbore with the bigger valves, MP 244 cam, MP double roller timing set, mild porting and compression ratio increases, exiting through dual exhaust and breathing through Holley 2305 staged 350 CFM two barrel carb ought to be a pretty good street motor for fuel economy.

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Casually looking for a Clifford hyperpak intake for cheap.

That sounds good to me. You are going to degree in the cam, RIGHT?

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

With the cam in, bigger valves, street porting, that cam, the Holley....and if you have a set of Dutra Duals...the slant might make a possible 180 street HP or so....

Heck the HPak duster isn't too different from what you're trying to do (other than I have stock valves, and the torquey Hpak with the baby 4 barrel)...and it's pretty close to 200 hp or so...

That boat with some better rear gears would be fun to drive for sure!

-D.Idiot

nobody answered the original question. he asked what the effects would be on fuel economy. as far as i know an engine is basically an inefficent air pump. the more efficent you can make it the better it will run, the more power it will make and the better mpg you will get. obviously, if you are making more power, you will consume more fuel, and if you are making less power, you will consume less fuel. the trick is to land in the middle of those two.

the rest of the componets used with the engine will help determine what kind of mpg you will get. also the car that engine goes into will also help determine mpg. a small engine in a large(heavy) vehicle will not get good mpg because the engine will be working too hard to get the car moving.

using the staged carb is a good idea. that way you get the best of both worlds. as was stated, the timing curve is very important in this kind of build. i don't know what it should be, but someone here should be able to point you in the right direction. another thing you should do is port match the manifolds to the head. that will also help in air pump efficency.

zedpapa

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1970 dodge dart w/225 /6 bored .040" over, holley 390cfm w/vac. sec., compcams 252s, clifford shorty headers w/2.5" exhaust w/flowmaster, f-body 11" front discs, aluminum A-833OD, 8 1/4 w/3.21 SG
soon to have 5 gears!!!

The cam will be degreed, I am going to run an Offy intake, and I will definitely be playing with the advance curve. I don't have Dutras, but I do have a set of home-made dual exhaust manifolds. Eric W has tuned his 72 Satellite sedan with the factory slant and one barrel with single exhaust to get around 19 MPG on the highway cruising at 65. I am hoping to mooch of his knowledge and experience.

As far as rear gears go, I can't remember what the stock ones are, but I am probable not going to change them.

I want to run the cheapest pump gas possible, so I don't know if I will be upping the compression ratio.

I'm hoping to pick the car up next week and spend the rest of the summer getting it slanted and cleaned up. I will have to pull the 318/727 in it now and figure out a way to mount the 225 on the v-8 k-frame, but I will make something work.

Thanks for the tips guys!

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Casually looking for a Clifford hyperpak intake for cheap.

Reed, I definatly recommend a compression ratio increase. I will garutee, the stock head with an aftermarket gasket will not even get to 8 to 1. Also the increase in cam will reduce your dynamic CR. Compression ratio will give you the best of both worlds, power and economy.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Okay, you convinced me. I will have to CC the heads and figure out how much I need to mill them (I have a stock 74 head and my "big valve head" and I want to try a big to small valve comparison).

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Casually looking for a Clifford hyperpak intake for cheap.

Even if you have to go up a grade of gasoline it only amounts to a couple bucks a tankful and with improved efficiency you should see an improvement in fuel mileage which would offset the fifference.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

Actually, I get around 22mpg. Carefull tuning baby!

The mods you are talking about can only improve gas mileage, BUT bigger factors in mileage will be timing curve and carburetion adjustments. Cam timing needs to be right too. That cam is basically stock, and the head will be more efficient with some minor porting.

Lou

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