I know this is an older thread, and it has some pretty good info in it.
I will add this much. For a street use truck FE engine, I always recommend going with 9.5-10:1 comp ratio, and a cam that specs out in the 260-270 "advertised" duration, with around a .500 total valve lift. Top it off with a decent dual plane 4V intake, like the edelbrock performer/performer RPM and a carb in 600-650 CFM range.
These specs will give you an engine that makes plenty of torque & HP compared to stock, yet the fuel mileage (when driven with some level of restraint) will be about the same as a totally stock engine.
Granted, this formula is mainly intended for a vehicle that will be driven on the street, not for all-out "race-like" conditions.
Lets face it, anything that came factory-equipped with an FE, isn't going to be a great MPG vehicle no matter what. They all have the aerodynamics of a brick wall (maybe the wall has an advantage?) and are made with REAL steel (heavy curb weight).
As my dad always said, there's not much you can do to improve the MPG of an FE powered vehicle. There's also not a lot you can do that will hurt either, so you might as well make that SOB run good....... I tend to agree.

 

i ran some stock fe specs thru desktop dyno 5 , numbers came out only a little high.
i also ran some fte members specs and on average came out 25-50 hp high and trq was just ridiculous .

 

GREAT RECIPE - thanks!!

I'll be building one from this recipe this winter!

 

I just got done with my F100 390 project, and in 300 mi., my mileage has varied from 14.04 to 10.8 on 91 octane, 4100# with a full tank and me in it. Here's the specs:

Edelbrock 1404, 500CFM:
Jets, .086/.095
Nozzle, .28
Springs, Pink
Metering Rods, 65x47
Performer Intake
2 1/2" x 14" Air Cleaner

Hyd. Flat Tappet Cam (Melling MTF-4):
204/214 @ .050
.486/.512 Lift
104/120 Lobe Ctr.
107 Lobe Sep.

Hedman Headers
Dual 2 1/4" Exhaust, Behind Tire Exit
Delta Flow Mufflers

OEM 1974 Breakerless Electronic Ignition
11 Degrees Initial, 36 Degrees Total Timing
Autolite 45 .036 Gap

C6 Auto
Stock Converter
3.00:1 Rear Gear
31" Tire

 

All these recommendations for 9.5:1 to 10:1 cr surprises me with todays low quality fuels. If you plan on doing any towing with a high DCR; watch out for detonation. These are iron head engines involved in this post. I'm surprised at the lack of mention about the importance of recurving the FE dizzy. I run 16* initial and 36* total mechanical all in by 2600 rpm. Also; aren't you guys concerned about steel shim head gasket leaks? I know some get lucky but it is a big gamble. JMHO

My current build utilizes a single pattern cam which seems to work well with FE's and helps with torque. Thanks to the guys at the FE Forum for their advice.

390 bored .060
Ported C8AE-H heads with stock sized replacement valves
One piece retainers and valve guides machined for viton posi loc seals
#70 Holley jets installed in head oil passages to restrict oil flow to heads.
Factory adjustable rockers
Comp 270S solid cam and lifters
Stock 390 stroke
Sealed Power H304P pistons
ARP rod bolts
Ported Edelbrock F427 intake
Undecided on carb....looking at Summit 600CFM carb
Balanced and blue printed
Melling HV oil pump and ARP drive rod
Recurved stock dizzy with Pertronix one

 

Yes, care must be taken in regards to timing when dealing with a comp ratio this high. However, it's not really high, considering where it was in the 60's.
Properly timed, 9.5-10:1 CR is fine with most of the fuel available today. Newer vehicles are running these same comp ratios, or even higher in some cases, without issues, since they have a knock sensor and computer to handle the timing. I've seen as high as 13:1 CR for for some the newest engines on the market (Mazda's newest "SKYactive-G" engine has 13:1 US market, 14:1 elsewhere, and runs on gasoline. Will be out very soon in the 3 and CX-5 models).....

 

Engines could get away with it in the 60's with better quality fuel. As you elludedto; newer vehicles can run higher CR due to being computer controlled. We are comparing apples to oranges here. What's the point of building in higher CR's if the timing has to be retarded to prevent detonation. To look at the larger picture; one really needs to calculate their DCR to see what grade of fuel they have to run. 10:1 nowadays with pump gas and an old tech engine is getting very difficult to pull off without aluminum heads. Not saying it can't be done but builder beware.

 

First, I didn't reread this whole thing so some of this may have been covered already. But here goes..
The new stuff almost always has aluminum heads, and now has variable valve timing so they can get away with much higher CRs than was previously possible without it being some huge cammed drag car. Lot's of FEs run high CR (11:1+) on pump gas, but they also have huge cams and 4500 stall converters.. Not exactly the recipe for a street truck.

In our old tech engines we have to know what DCR a given cam will give in your setup. I have a static CR of 9.8:1 and with the XE274H cam have a DCR of 8:1. Which is just right for a heavy vehicle that tows. DCR isn't all there is when determining what cam is right, but it's a very major component when figuring what gas you can run on.

I'm guessing someone mentioned steel shim head gaskets. It's all in the prep here. I haven't had a problem with leaks when both surfaces have been milled flat. If you try to throw the steel shims on something that this hasn't been done to then you're much more likely to have sealing problems. There's no reason to use steel shim gaskets on a 9-10:1 390 anyway though (which I agree is not a very high CR). If you are rebuilding it, just get the right pistons and use the standard size gasket. Maybe someone was trying to get some more CR from a 360?

Also as said timing is very important. Especially if you're trying to flirt with the edge of what your available fuel will allow. A recurved dizzy is a must.

 

I'm running 91 octane in my 428cj at 10.6:1 cr with no problem. My Mach 1 however doesn't tow.