15MPG with a 460 anyone get better?

That is with 8 to 1 compression and a manuel 4spd and a motorcraft carb. 235/75 skins, 5:13 rear end.

Thinking of going to a higher compression head? and headers to try to get better MPG.

Greg
Eastern WA[IMG]http://[/IMG]

 

Let me know if anything helps you out I have a friend who has a 460 in a motor home and says he gets 7-8 mpg but also has a 8 to 1 motor and we were thinking maybe a set of closed chamber haeds would help.

 

I've owned a C350 (Centurion) with the 460 since 1989, and for the first ten years or so, I got 10mpg. Didnt matter if I was running to the store to get some milk, or hauling a 44ft. trailer. Its recently bumped up to about 12 (200K miles so the resistance in the cylinders doesnt hold it back as much). 15 sounds very impressive. I dont know what the compression ration in my 89 is.

 

I also have a 89 Centurion (460)
but it has a 6" inch lift
I have an avrage of 8-10 mpg

p.s.
I have a k&n filter setup&magna flows

how did you get better mpg after 200,000 miles

 

Hell, i wish i got 15 mpg, even when I first bought my truck and it was stock I was getting 8-10!! What's your secret?
-Jason-

 

I don't know how I get 15MPG. I don't need to drive over 55MPH and that is if I drive without pulling in the secondaries.

I am running the original mortorcraft carb and I understand it has very small jets on the primary. If I drive around town and put my foot to the floor I will drop to around 8 or 9 MPG.

This truck has alot of miles on it and every thing is "loose" and turns free. The alignment is good and the spark plugs, filters and distributer all are in good shape, also a standard trans.

Greg

 

The only way to get 15 would be to change the compression ratio (I think). But you would lose a lot of your torque and the truck would be worthless (in my opinion). Trust me, I checked into it. My truck gets about 7.3, but I have heard up to 10 and 12. Fifteen seems a tad high.

 

how exactly is a high compression ratio going to get you less torque, oh wise man?

 

I am not in the mood to start a flame war. I discussed this with a certified master mechanic. I told him that someone at school took a 454 and dumped it in a Corvette. The kid raised the compression ratio and rebuilt the engine etc. what do know - 580hp. Now, I got a 460 in my truck. I wanted racing type power (its a stage kids go through) and I asked him about it. He said raising the compression ratio kills torque (long story short, I didn't ask for details) He also said the truck would be completely worthless and wouldn't be able to haul (expletive) But this does depend on how much you change it/modify engine. If it is slight, then its not going to matter much. My 79 has a comp. of 8.2:1, my dads 78 has a 8:1. Not enough of a difference to give an (expletive) If you changed it to say, 12:1, then that is a race engine. Not good for towing a trailer. I am not an expert at this, nor did I admit to be one oh wise questioner.

 

74crwcb429hibPS4spd
how many rpms are you spinning on the freeway? With 5.13's it seems like you would be reving pretty darn high.
15 mpg, my neighboor was ready to hug me when we got 12 out of his 79 3/4 4X4 with 3.52 and 33's

 

MillerT,

I am reving very high on the HiWay. This truck used to do alot of hauling and towiing. I have not run this truck in over a month as I just threw a rod out the side of my oil pan.(I was not running over 5k revs at the time so I don't understand-- I assume whoever rebuilt the engine did not torque down the rods correctly.)
It seems I was over 3k at 45 MPH. I was thinking of going to 3.50 gears vs 4.10s but I hear guys say stay at least with the 4.10s(And taller/larger tires). As long as I have the engine out for a rebuild another option was going a ZF trans with OD, but I have not been able to find one at a ok price.

I get my heads back this week, hopefully and will get the engine back together next week. I went with a more aggressive cam and matching cam springs and significant polish(humps removed etc.) and port matched on some C9VE heads. I was running D3 heads before the thrown rod. Everything else is the same. I would have loved a Edelbroke carb, Stealth intake, roller rockers and Headman headers but $ is tight at the moment. I should have about $1500 into the engine with the rebuild(shortblock and head-- 9.3 to 9.5 cc when down.

We will see how my MPG is after these changes.

What do you think?

Greg

 

I think that is too bad, but at least you have the $ to take care of it. It seems like you would really want you motor to spin slower, but maybe that is the secret to your mileage, who knows. I would recommend 3.50 gears if you are keeping 33ish tires on it, but that is just me.

 

i really dont think raising compression will hurt torque actually i think it will help it. just dont get crazy and get it so high that you cant run it on pump gas.......as far as gears i personaly would stay with the 4 10's......i think 3 50's are getting pretty high for a truck/ tire combo like yours but if you do a lot of hi way traveling maybe 3 91's would be a better ratio.........

 

Wow, I had not heard of 3 91's

 

Hey...I have 4.22's in my truck
BTW...for whoever took me serious in the above post; joke's on you

-Jason-