390 mpg help

One thing guaranteed, most of us will never drive a truck long enough for the fuel economy increase from a cam, intake, carburetor, headers, higher compression, five-speed trans and so on to pay off. Do the math; the payoff just isn't there. Build what you want, just don't expect to pay for it with fuel savings.

Real world, the old 390" Ford truck is a 12-15 MPG rig. I once won a case of beer proving another Ford truck didn't get 20 MPG on the highway. Just looking at it, I knew those chromies and little car tires, which made it look racy, were making the odometer turn faster. A quick check of the odometer showed it was off by 20% and thus made the long division fuel mileage show 20 MPG, but when the odometer was corrected, it was getting 16 MPG at best with a 302".

thnx, jack vines


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You will never see the payoff UNLESS, and here's the big unless, you're doing a rebuild already (like he is) then the cost increase of parts is only slight if any at all and the only difference is in the planning stage.

Replacing a perfect engine with another one 95% of the time will not pay itself off though.

Sorry I didn't get to this DynoSim earlier, I love doing them but have been busy.

OK, agree with most everybody on here about what this motor needs to operate with high torque at low rpm's. I built it with an 8.9:1 static compression ratio using 74cc chambers and KB150 pistons having a 20cc dish. Used large-tube, equal-length headers through the mufflers for these pulls.

Standard FE iron dual-plane intake, 600 cfm carb, this cam...
HYDRAULIC-Great for vans, trucks and 4WD. Excellent for towing, mid-range torque, smooth idle. Hyd. 1200 to 5200 33-222-3, 260H, 260/260 212/212 .484/.484 110°. Installed 3 degrees advanced to make max low end torque. Makes 8.07:1 dynamic compression ratio....
1000 73 382
1500 123 432
2000 174 458
2500 216 455
3000 260 456
3500 311 467
4000 342 450
4500 357 416
5000 355 373

I used the same cam on this build, but switched to an Edelbrock Streetmaster intake manifold. The software liked it so much that I relaxed the cam timing back to straight up to build some hp and torque higher up the rpm scale. The new cam timing gives an 8.00:1 dynamic compression ratio.
RPM HP TQ
1000 86 453
1500 146 512
2000 207 543
2500 254 534
3000 301 526
3500 335 502
4000 365 479
4500 380 443
5000 373 392

I used the Edelbrock 60069/60079 flow figures for this Dyno
Sim. The .400 flow figures and below were within 5 cfm of a decent set of FE iron heads, but the .500 and .600 figures were more optimistic. We use a lift limit of 0.484" on these pulls anyway, so never did make it to 0.500", much less 0.600". Anyway, for those of you who are playing along at home, here are the e-brock figures....
.100 88 64
.200 153 113
.300 195 148
.400 233 171
.500 265 183
.600 270 200

Now, if a guy has the components and the expertise to put one of these together, then he, like Bogey said, needs to do whatever is necessary to set the squish for this motor to operate on pump gas.

Getting to this static compression ratio includes 809.85 cc's in the cylinder (0.030" over) and 102.51 in the combustion space. This 102.51 cc figure includes chamber, piston, gasket, piston deck height.