I know I'm not the only one grinding my teeth over $3 gas, so I was playing with Excel to try and calculate if and when an improvement to increase mileage would pay off, and came up with the following.

Let's say gas is $3/gal and I'm now getting 10mpg, it costs me $0.30/mile for gas. I put a free flowing exhaust in - new muffler and headers (assume the cat is ok) for $800. I now get 12mpg, a 2 mpg improvement and it now costs me $0.25/mile for gas. It'll take me 16,000 miles for the $0.05/mile gas savings to pay for itself, and in 32,000 miles I'll have saved $800 in gas.

Of course this all depends on the assumptions being true and remaining constant.

Is an 'average' increase from 10 to 12 mpg reasonable in this scenario?

Thanks

 

If your running a EFI 460 the exhaust looks to be thge same as what is used on a 5.8 and or 5.0. My 86 has 2 1/2 inch head pipes going into a single muffler with the ends squeezed down to 2" into the muffler then 3 inch to the rear but muffler is squeezed down to 2 1/4 before it goes into the 3" pipe. The muffler has about 7 inches of back pressure. Figure its the same muffler used on the 5.8.

Tremendous power increases can be had on the EFI 460s by converting to a 5.0 HO throttle body (approx 40 lbs of torq) and a cat back system(tremendous increase in torq) but realy needs a complete exhaust change. 2 1/2 to 3" works well a Walker 21309 reduces back pressure to 1 inch.

 

with nothing more than an exhaust change no I don't thing expecting 2mpg increase is a reasonable expectation I would expect at best maybe a .5mpg increase with no other changers.

 

Monsterbaby ... 'm pleased to have you chime in, very much. What other changes would you recommend? I was thinking more spark and open up the intake side, too. But I don't know how to do those on a 460 yet, especially this 91 I have.

The 2 mpg increase was optimistic swag, mostly to put some sort of number on the spreadsheet, as well as the 10mpg and $3 gas.

 

Well I will try but if you notice I don't usually chim in on EFI stuff expecially on upgrades I am trained to repair them but I don't use it for high HP engines.
one thing I do know the efi 460s have a very restrictive intake tubing if you look at he hoses going from the air box you will find a hard platic coupler take the hoses off, and you will see airhorn type restrictors I have found that removing those helps with the power some, and have heard that some guys go with an open air airfilter arrangement never tried that one myself but is supposed to really help.
Another thought is one of the power tuners or chips I have heard but don't have personal experience on these engine with them but have heard that some guys get as much as 3mpg with them (once again I personally don't know from my own experience)
Some other suggestions i would have are basically just some maintance type of things.
First you have 24 yr old injectors, and they are probably dirty, adn not spraying a nice cone which will cause fuel to puddle in the intake, and is not effiecent combustion causing poor fuel economy, so since new injectors are pretty expensive I would look on evilbay and see if someone is selling some they took out of a car that has few miles on it to upgrade just try, and find some with about the same delivery rate as the 460 (I think it's 24lb/hr but not for sure, and my book doesn't list it maybe someone else can chime in with that) I have seen takeout sets with low mileage go for less than $100. Or if that doesn't pan out find a shop that still does injector cleaning, andhave them done if you can't find one buy the strongest injector cleaner you can find, and run a couple of tanks with it in it that will help at least
Another thought is cap, and rotor if they are original replace them, same things with plug wires replace them with a good set I prefer Taylors myself other might have other preferences but that is mine, and I run them on almost everything i own.
Also replace the plugs, and stay away from platinum just run normal plugs platinum do not improve performance or fuel economy just longevity (actually will hurt perfornce) and they cost a lot more. once again everyone has a preference mine happens to be autolite in Fords.
Another thing to play with is every engine even within the same year, and model have a "sweet" spot for timing so do some experimenting with it get a base figure and without changing other things bump it up a couple of degrees, and recheck if it goes up then bump it again until either the mileage doesn't go up anymore or you start ot get detonation, at which time back it off a couple an leave it.
Also if your going to get into the engine maybe look at a little bigger computor compatable cam, and make sure it's degreed in (and even if you leave the stock cam setting it straight up is a good idea) Also one area of these engines that I feel is way over looked by everyone is the pushrods. All canted valve engines push the push rod sideways which causes flex and you loose as much as .015" of lift, and some duration of the cam so going with a 4340 moly .080 pushrod will reduce that and if your into the engine I would look into replacing those, but proably not worth tearing into the engine just to do it.
on the heads the restrictive port is the exhaust and if you have them off porting the exhaust is a good thing atleast clean them up some this will help a little also.
Ignition I am not a fan of the TFI ignition system but it's probaly ok just failure prone, I do know MSD makes a replacement for it, and have heard it improves things I once again don't personally know on that since whenever Ihave had one fail I went to a different dist, and replaced it with a MSD box but most of my stuff is built for performance.
You didn't mention how many miles on this engine or what oil you are running but 2 possiblilities here first go with a lighter weight oil, or if you don't have seals leaking now, and not too many miles on it switch to a full synthetic doing either one of these will help with economy by reducing drag on teh engine, and reducing friction.
I am sure I could come up with others but hopefully someone else will chime in thats had some more experience with the EFI system to give you some tips on getting more out if it.

 

Get yourself some good quality headers and a good single 3" exhaust and put a straight pipe through the catalist. Also like monsterbaby said cut off the horn like intake muffler. This will help if you can keep your foot out of it. I did this to my "96 and it helped quite a bit.

 

hey whats the fun in that.

 

Hey there Turbo 2256, you said something about a torque increase with a 5.0 H.O throttle body on a 7.5 L.Can I trouble you for a bit more info on this please? If this was addressed on a previous post I apologize, I don't get to this electronic box as much as I would like.

 

I have never done the swap at least on a 460 other stuff. Bottom line the 460 is the only engine that Ford converted to FI that never did better on economy over the carbed version. Two things become readliy apparent the throttle body is smaller than what is used on a 5.0 Mustang the other is the exhaust at best it is sized for a 302 low performance. Looking at other parts the intake manifold look at whats on a Mustang. Wat did a 460 get a 4 barrel carb intake with fuelinector bosses and an elbow adapting a throttle body to it. Cylinder heads were also douwn graded over earlier carbed versions. Any way you just need to come up with an adapter or a larger dual throttle body adaprter. Might need an adjustable fuell pressure regulator and up the system pressure a tad.

 

will a 5.0HO TB bolt right up??? How about a 1st gen LIghtning TB?? I was considering doing a TB upgrade and after reading this board tonight, definetly considering headers and getting rid of the cat that cones down to a 2.5" outlet.

 

I have seen pictures on this site of a 460 with a 5.4 lightning / 6.8 V10 throttle body. I know that the TPS plug is different but that can be adapted. It was the oval throttlebody used on later model lightnings. It looks like it will bolt right up to the "goose neck" looking throttle body adaptor. Check out this guys pictures. BBK makes larger throttle bodies for these applications.
http://homepage.mac.com/m715/rigs/PhotoAlbum34.html