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Fuel Efficient 460?

21K views 18 replies 9 participants last post by  PSIG 
#1 ·
I have my 390 engine in the shop right now trying to figure out why it wont start and if the cost get really high i have 2 options. 1.Buy another engine and possibly another tranny. 2.My grandfather has a 460 w/tanny with 30,000 miles on it that he'll let me have if i want it. The thing is, im building this car as a daily driver so i need to get decent mileage. I'm not expecting to get 22mpg with a big block engine, but would it be possible to build a 460 to get around 14-15mpg? The 460 puts out a lot of torque at low rpms and the car is light for this engine so i think its possible. Im willing to do machine work and use mods like cold air intakes, but no EFI, thats out of my price range.
 
#2 ·
my 69 429 (10.5~11:1) would get 17 mpg if you kept your foot out of it.
I had a 69 396 chevy (9:1) in a 81 dodge pickup, it averaged 17, drove that as my dd from '82 to '93. funny thing was I bought a 93 f150 w/300 I6, it only got 18 mpg.

problem you'll find with most 460s out there is 72-up were pathetically low compression- low as 7.6:1 if I remember right, only put out like 200 hp, and they were notorious for crappy mileage. if its a 68-71, it will be closer to 10:1 compression, and 370 hp- but then too, will require 93 octane+
guy I worked with had a late 70's 460 4x4 f250, 6-8 mpg highway- think that was the absolute worst mileage ive ever heard of...

my dream is to put a complete junkyard IFI/ignition setup off a 2005+ mustang on my 429...think with the new knock sensors the high compression can survive on todays gas- might need pistons with better quench distance, and making the hydraulic cam advance setup fit behind the water pump could get interesting, as would adding the extra butterflies to the intake manifold at the ports/adapting the mustang CMCC servo, adapting the crank trigger for the misfire detection in the pan or timing cover... but think it would be a fun project and dont think theres any reason -other than time- not to try it :)
 
#8 ·
my 69 429 (10.5~11:1) would get 17 mpg if you kept your foot out of it.

problem you'll find with most 460s out there is 72-up were pathetically low compression- low as 7.6:1 if I remember right, only put out like 200 hp, and they were notorious for crappy mileage. if its a 68-71, it will be closer to 10:1 compression, and 370 hp- :)
+1.....I had a 69 thunderjet in an 82 F100....It was the two barrel version(10.5:1 compression) but I swapped on a mid 70s 460 carb and 4V intake from a mid 70s lincoln..I also put on a set of headers and ground the bump out of the exhaust port..Other than that it was completely stock..I was able to get 17mpg highway cruising with that setup (C-6 and 2.75 rear gear)...It would ping very easily and was kinda gutless with that stock carb though..I installed a new holley 750 and the power increase was massive and the pinging went away...MPG dropped to between 12 and 14 but it was worth it....I think with proper tuning and an overdrive setup you could probably get low 20s with the right setup..
 
#3 ·
The 460 is free?

You're trying to do this project on the cheap... if you want to get the car going and start driving it, then put the 460 in. You can also consider hunting around locally for a used 5.0 or 4.6 with an overdrive transmission (I would do that over the 460).

Do you drive a lot as it is? It's one thing if you had a long commute, but the 460 will get you to school and back just fine. Of course, I don't know what would be needed to get the 460/tranny in your car.

If it was me, I'd find out for sure why the 390 won't start. I'd rather have the factory motor (or one that was a factory option) than something different, and if I was going to go the non-factory route, I'd look for a more modern motor.
 
#4 ·
While I have no issues with going 460 and cheap EFI or at least a WBO2 to get a sharp tune, I agree that a good mechanic should easily and cheaply find the issues with the 390 and go from there. The 390 should get mid to high teens for mileage if properly tuned and reasonably driven. You want decent mileage, but may spend all the difference getting the 460 to fit and work right. You can buy a lot of gas for the cost of a few conversion parts and labor.

I understand the reaction to EFI, but consider, it can cost from very little to under $500 for a fully tunable system, and you'll save more than the cost in a year. My work truck improved about 38% in mileage with fuel and ignition control, saving $900 in just the first year when gas was $3 a gallon. Note that I would only consider the EFI option if you can do DIY, or you're at the mercy of mechanics anyway. In that case you'll lose the savings in outsourced labor, or worse if it's poor outsource labor.

David
 
#5 ·
I think im going to go with the 460, the guy hasent figured out the main cause of the problem but he said im going to need new valve guides soon and possibly new valves as well. Will a 460 bolt up to an FE trans?
 
#9 ·
You'll have ten times the amount of time and as much money invested in the project if you install the 460. (Exhaust system, engine mounts, transmission crossmember, shortened driveshaft, transmission linkage, different radiator, different transmission coolant lines, different vacuum system, throttle control etc. etc. etc. Get my drift.)
That's counting getting a 390 engine completely rebuilt. Good gas mileage comes from gearing, not less horsepower. Jim
 
#10 ·
I've decided to go with the 460. I'm going to have to have new piston rings, valves, valve guides, and pushrods for the 390. The 460 is in very good shape, it only has 20,000 miles on it and if i can get it unstuck, it should crank right up. There was nothing wrong with the 460 when my grandfather pulled it, he just wanted to get rid of the motor home. As for the drive line and engine mounts, there is a place not too far from here that can shorten my driveline for $25-$65; and a freind of my father is a real 460 nut and has alot of spare parts he sells real cheap to people looking to build their first 460. It wont take near as much time or money to get the 460 going in my galaxie so im going with it. I may have a low buget, but i have the advantage of a really friendly, old community. So back to the topic at hand, I want ideas on how to get good gas milage out of this thing. The tranny is a 3-speed C6 (not sure if it has an overdrive), and since it came out of a motor home i believe it has a better cam, stronger crank, ect. and i think it has HEI on it but im not sure of that either. I'm going to get another look at the engine in a few days and try to get the rest of my questions on it answered.

P.S. The debate on 390 vs. 460 is over. Serious answers and suggestions only please. Thank you.
 
#12 ·
Would any fuel injection components from a more modern 460? Or heck, besides the EFI, would any of the electronic ignition from a newer 460 work on that motor? I'm just thinking it might be easier to dial in an EFI motor for fuel mileage than one with a carburetor.

Someone can correct me if I'm wrong, but I didn't think the C6 had overdrive? I've also heard that you have to have a C6 from a car, not a truck- I don't know what the difference is?

Also... if your car has a 390 in it, shouldn't it already have a C6? What might need changed so you could use your existing tranny?

Sounds to me like you've got about 100 things to do before worrying about the fuel efficiency of the 460.
 
#14 · (Edited)
It looks like things are quickly getting complicated here...If the motor is "stuck" from sitting it may need some serious work to get it running regardless of how many miles are on it..Even if it does eventually turn over and run it may have damage due to rusty cylinder walls or rings depending on why it is stuck..It may even have to be rebuilt..
I think it would be pretty difficult to adapt an EFI system into your galaxie if the motor is indeed fuel injected in the motorhome..For your sake I hope it isn't as the late model EFI 460s were way down in power compared to the older late 60s and early 70s models....The C-6 is a 3 speed non overdrive trans as was mentioned..The trans from your 390 will not bolt up to the 460 so make sure you keep the trans from the motorhome..

Basically nothing between the 390 and 460 will interchange so be sure to get all of the brackets.pulleys etc from the motorhome....If you are swapping based on the thought that you have a mint low mileage 460 I would really check out that "stuck" engine before you get too far into this..I would hate to see you spend money on the swap parts only to find out the 460 is in no better or even worse shape than your 390...
 
#15 ·
Many C6 trannys had GV overdrive. I was surprised at how common the C6 OD is, after seeing how many members here have them as a factory option on their cars. Very strong, too. Not so sure if a motorhome would have one though. Certainly easy to check, as it is rather obvious!

David
 
#16 ·
I understand that im running a risk with the 460 being stuck. i was planning on tearing it down and rebuilding it anyway because if it has dish top pistons those have to go. The C6 from the MH will bolt up to the car, but i may have to have the driveline shortened. This isn't the first time i ran this risk. The 302 Boss in my F-100 sat up for 10 years and was locked up tight, but we tore it down and cleaned out the cylinder walls and it's a real monster now, so i know what im getting into. It's a 4bbl also, not an EFI, however, i want to say that it does have HEI on it. I'm going to look at it right now and get some pictures. I'll post back soon. Also, the local machine shop has a dyno cart so ill have it running before it goes in the car.
 
#17 ·
... i want to say that it does have HEI on it. I'm going to look at it right now and get some pictures.
It likely has the big distributor cap, indicating a Duraspark II electronic ignition. That's fine for what you're looking to do. If it is missing the fender-mounted module, you have an opportunity to upgrade to the DS-I HEI equivalent box and coil.
:tup:
David
 
#18 ·
I have a 460 out of a one ton van that has the fuel injection set up on it and I can tell you first hand that is will not fit into an early Galaxie without some modifications. These EFI systems use a big snorkel looking thing that makes the system to tall. I put this engine in my 60 Starliner and with the motor pan setting on the floor and the car at ride height the hood would not close. I could use a large scoop but just did not care to do that.

My engine also has an AOD on it and I will have to remove and alter the firewall/floor area to make it all fit. It was so much work I have now decided to use the 4 cam 4.6 with an AODE I also have setting here.

Scott...
 
#19 ·
Yeah, most truck and van EFIs (except Explorer 5.0L) have taller intake setups. Normally, they are swapped for lower 4v-style throttle bodies during conversion, or the upper plenum swapped for a plenum 'box' with front intake - sorta-like the GM setups. The 460 EFI manifold is one example where a 4v throttle body will bolt right on to the lower manifold. That said, the lower manifold is nothing to scream about for flow above 4k rpm or so. A swap to a more typical altered dual-plane or EFI single-plane is the usual route for any performance. If you're going to deal with the cubic mpg, you might as well have some power to go with it.

David
 
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