tinbender59

With fuel prices going up most of us truck owners are becoming more concerned about MPG. last week I put $50 worth of gas in my truck, 12.6 gallons, that is absolutely nuts!!!!

The following is my theory on engine/toy building;

First off, a bigger cam, larger valves,Larger intake runners, and larger exhaust will not help MPG, in fact these will kill MPG. each of these are designed to improve horsepower; HP is high RPM. look at a generic dyno chart, torque dies off around 5200, then HP really takes off around the same. Everybody asks how much HP you got, or states their HP numbers proudly. as they should!! But as you push the HP numbers up, you also increase the amount of fuel needed to achieve those numbers; thus lower MPG. it takes BTU to make Horse Power.

I know all of the "experts" talk all of the latest new larger port heads, new cam designs...... but THEY also have unlimited funds. and are paid to sell these new products.

I am no expert, I just know that my tried and true methods work for me. I once had a 1986 3/4 ton 2wd with a 500 Cadillac, reworked distributor, 270H cam, Holly 850 double pumper, and duels, that achieved 18.5 MPG consistently. and 12ish pulling a 24 foot 3 axle GN loaded with 6k.

My WS6 LT1 powered 1997 K1500, is getting 17 consistently "now". and I have seen 20 once, it had a timing issue, that I had to chase down.
when I prepair to build a project, I think "real world" not "Pie in the sky dreams" what is the actual use of the build. As in ; daily driver? quarter mile terror? mud thrower, or a combination ?? A daily driver for me is 2200 rpm at 70MPH. since 80% of my driving is Highway "100 mile round trip daily" I need to build for that RPM/,then I look at the available "parts" that will help to build the power band of my RPM window. 2200 RPM is smack dab in the middle of the torque band, so I need to build torque instead of HP. which is not talked about very much in today's environment.

wow what a can of worms?? this is in no way a complete concise documentary, just a starter thread.

OK Lets start at the top; if you are looking for MPG, and reliability; loose the carb, go fuel injection. EFI can deliver performance, but it's biggest advantage is fuel management AKA MPG. EFI also has crisp, and clean throttle response, which I like a lot. the Throttle body has little effect on an EFI system, other than limiting upper rpm by limiting the amount of air flow. But Most EFI intake manifolds systems are designed to run out of air by 5500 to 7k and most stock TB's "the butter flys" run out about 6k. A very small gain for a $300 investment?? stock injectors in my opinion are at the very least a bare minim of what is needed. I like to increase the injectors on an average of 25%, plus update to the design 3's, better atomization of the fuel at the moment of injection. MPFI is Better than TB, SPFI is better than MPFI... mine is running in SPFI mode.

next is the distributor; you have got to get it set in correctly, and good parts.
you need to be running above 30 degrees of advance at your "window" rpm, At 42 degrees you will start to knock pretty good.

Heads??? oh my, that is wide open, you will get 25 different answers from 17 different people. head design is very arbitrary in my opinion. I have ran 1.84/150 small chamber on a 350, got descent MPG, and excellent torque, but it ran out of air at 5k, the best I ever ran were, 1.94/1.60 68cc cambered heads.

Exhaust; LOL this is going to start a urinating match, You can go too large!!!!
Just as you can go too small.

My rule of thumb up to 300ci 2 inch exhaust, up to 400ci SB 2.25 inch, larger motors 2.50 inch, all to the back of the car (sonic tuning) for torque.
For HP as big as you can go, and as short as you can stand the noise.

I run small tube shortie headers on the stock header pipes 2" (scaveng or expansion chamber theory ) to the cats, then 2.25 out the back through Flowmaster copycat mufflers.

last but not least, gear ratio's Vs tires. if you jump over 2 inches in height on your tires, then you need to change gear ratios. SB Chevy's do not do to well under 2k, trust me I have been trying to figure that one out for years. the only place it works is in an aerodynamic car like the Vette, they do get 30MPG consistently.

This I a quick and dirty run down of my philosophies, not intended to cause a fight. just Me and how I work out my builds
I can explain each subject in detail later as needed

tjjack10

I have a chevy c10 with a 307 , am presently getting 16 mpg and pay $2.25 per gallon for propane. I am hesitant to publish this as they will surely tax away all advantage. Do the math, I am getting equivalent of 28 mpg village-hiway combination driving with my v8. I am interested in building this engine to achieve a higher compression ratio. Any tips I will welcome.