The Stovebolt Site Forums The Shop Area Engine Shop motor advise?

hi anybody give me some idea on what a 283 /305 or 350 will give in mileage and whats a good cam choice
auto box and also need advise on suitable rear end ratio

not a race car just an everyday wich will pull well and have good mileage

Kind of a loaded question.

Here's some (but not all) things to consider.

MPG will be affected by:
1. Transmission gearing -- the 200R4 I'm using has a .68 4th.

2. Rear end ratio

3. Diameter of rear tires

Figure out what you have versus what you want and gather up the pieces.

Once you know, trans gearing, rear end gearing, drive tire diameter and weight of vehicle call a cam munufacturer and get their recommendations.

I'll go along with that "loaded question" statement.

Before making any specific recommendations, I'll ask ya a couple of questions.

What year truck?

Will it be a daily driver or a weekend cruiser?

Is mileage the most important criteria?

With those questions remaining unknowns, I'll give you my opinion (and that's all it is, just an opinion...and everybody's got one.) First, I'd go with a 350 motor. Any increase in mileage you'd get over a 283 or especially a 305 would be marginal at best. And the additional torque of the 350 would (again, in my opinion) make it worthwhile.

Second, if you want the best optimization of torque ("pull well") and mileage, a stock setup is probably the best compromise. Either that or a mild "RV" cam that has something like 210 degrees of duration on both exhaust and intake and a lift of around .450. Lobe separation is kinda academic on a mild cam like this. 110 degrees or thereabouts is the normal LSA and has worked well on the cams that I've used.

Third, the carburetion issue will have a lot to do with the end result. Some folks are fine with a 2-barrel carb for economy...I prefer a 4-barrel with small primaries and larger secondaries so that I have power on tap when I need it, but can get acceptable mileage if I keep my foot out of it. I prefer AFB (Carter or Edelbrock) carbs, but others prefer Quadrajets for this type of application.

Predicting mileage without knowing some of the variables is almost impossible, but I'll just mention that for my truck (64 C10, 282 I6, Carter 4-barrel, headers, 4-speed and 4.10 gears) 15 mpg is about what I get in a combination of city and highway driving. It doesn't seem to vary much one way or another from that figure.

If I had my way, I'd prefer to have a lower numerical rear gear...something like 3.08...but not for the sake of mileage, but rather the ability to cruise on the highway without spinning that long-stroke motor at high speeds for long periods of time.

If you're asking about which transmission to use, the TH200-4R or TH700R4 are good choices because of the overdrive top gear. Tha would allow you to run a steeper gear (3.73 or 4.10) and still have a decent top end.

The summation of all of this is that the components all have to work as a package to get optimal performance, whether that means mileage or power. And if you want both, you'll probably have to make some concessions in both areas. It's hard to get real good mileage and have a real powerful motor/transmission and rear end package all at the same time.

I dunno if this has answered your questions, but it's given me a few minutes to avoid doing any real work.

Torque -vs- cubic inch
Mileage -vs- cubic inch
Shoe size -vs- mileage

Easy answer how big of a shoe do you have ?
7 -vs-15 mpg
10 -vs- 6 mpg

Now determine if this is a grocery getter that the wife is going to drive size 7 shoe = 15 mpg

Rusthater drives to the local parts store and smokes the tires out of the parking lot in front of a 69 Chevy short box big block truck shoe size 10 = 6 mpg

Sorry Rusthater I had to throw that one in there .There is not a good equation it just depends on what you are building.Give us a little more information and we will try and give you some good advise.Welcome to the Stovebolt Forum

ok guys thanks for the input let me try to make iot a little clearer
i am in england gas is $10 a gallon!
lpg (propane) is about £4/5
diesel is about the same as petrol ($10)
truck is a 49 stepside to use everyday
so i need either a good torquey petrol (hopefully a v8)
wich with the right combination of rear end/tyres/right foot/transmission will do maybe 20 mpg??? a cam and headers may help this i can then run lpg through an impco 425 propane carb
and as lpg is half the cost of petrol should then equate to 40 mpg wich is fine

OR
i need a lazy reliable diesel wich will do maybe 30/40 mpg BUT i then wouldnt have the ,,noise,, and the fun of the v8 when i wanted it + i would have the stinking rattling noise ,,but,, they are super reliable and very very torquey

another option i thought was a english gm straight 6 these are bulletproof in a car these do 20 -30 mpg have a bit over 200hp are very cheap but theers the electronics issue no big deal but stil another job
+ car mpg is not truck mpg

at the mo i ,,think,, its a 216 but with gmc on valve cover i would imagine this is just thirsty and slow but torquey?

whaddya think guys?

Ok...with a little more info, the idea of the British I6 with EFI and an OD trans makes sense.

The V8 LPG option might also work, but I don't know enought about it to have an opinion.

20 mpg in a 49 with a V8 is possible, but it wouldn't be easy. I still think that 15 mpg is more realistic with a carbureted V8 unless most of the miles are highway with an OD trans.

Most aftermarket cams are made with performance in mind, rather than mileage. A stock cam will probably be the best bet for a mileage setup. Remember: most performance parts are designed to improve the flow of air and fuel thru the motor which generally means using more fuel. While the motor might run more efficiently from an airflow standoint, it won't necessarily decrease the amount that's used.

Another "outside the box" option might be a Vortec TPI V6 from a 96 or so Blazer along with the transmission and rear end. You'd have to do the computer thing, but it's been done before. Get the whole package from a wrecked one (They might not be all that common in the UK, tho) and use the whole thing. My wife has had 2 Blazers like this (she currently has a 2004 and loves it) and consistently gets around 20 mpg, although she doesn't keep track of her exact mileage. Most of her driving is in town.

Just some more thoughts.