Hey Guys, it's been awhile since I've posted so forgive me. I've got a 85 F350 4 door dually with a non catalyst 460. Next winter I plan on rebuilding the motor due to I've got a slight cooling leak in the heads (hopefully it makes it that long). My question is what can I do when rebuilding the motor to help the gas mileage? I use my truck to haul my 24 foot enclosed car trailer with my race car to the track. Here's what I have right now, the motor is stock. The only modification I've made is put an Edelbrock carburetor on it, which when not hauling it gets great gas mileage but since I installed it I think it gets worse gas mileage (I haven't had it on a long enough trip yet to check the mileage yet). I still have the original Holley/ Motorcraft carb that works great that I can put back on if needed. It has the original intake, exhaust manifolds, exhaust & so on it. It has 4:11 gears. Should I do a porting of the heads while there off because I've read they could use some help? Should I put in a towing cam? Should I put the original carb back on? What if anything can I do to help the gas mileage? Should I put in a towing converter? It still has the EGR valve on it that still works as well. I know these motors weren't made to get gas mileage & I'm not worried about what it's doing when not hauling because I don't really drive it but to haul the race car. I just thought while I was rebuilding it I would make some modifications if they would help the MPG! <!-- / message --><!-- BEGIN TEMPLATE: ad_showthread_firstpost_sig --><!-- END TEMPLATE: ad_showthread_firstpost_sig -->

 

Look into aluminum main & rod bearings. Run synthetic oil (afterbreak in). You could put stainless steel bolts in place of the mild steel carburetor & intake manifold bolts to keep your air/fuel charge slightly cooler. Air cleaners, pick what you want. Any aftermarket exhaust that flows more efficient than the stock logs is ALWAYS beneficial! If you do install the headers, you will have to retune your carburetor since the scavening will be improved. If the EGR works fine don't bother removing it IMO. Have fun with it and build a solid hauler without breaking the bank.

 

Thanks' 385seriesHemi! Thats a big help.

 

One other thing on the exhaust. Do not go with huge pipes. Just get a mandrel bent system that is headers-back close to stock diameter (a little larger maybe? I dont know the stock 460 exhaust diameter). Getting a more efficient exhaust flow with just bolting something up is alot easier than porting. You could put a carb spacer in also if you have the room to. Just shop around on pipe diameters etc and read testimonials if possible. Have fun.

 

I was looking at a 3" single system but since you said that I might go with a 2 1/2" dual system because that's what came om my truck stock was a single 2 1/2". The only problem I have is that the only thing I can find is the 3", I would have to have someone make a dual 2 1/2". I guess as far as a carb spacer I should probably go with a 4 hole since I'm towing with it, correct?

 

Yes, the 4 holed spacer would be best. You could try looking at 2-3/4" set of pipes too. Try to get the longest headers you can with your money though. Long tubes help in torque also. If you can only find 3" pipes off the shelf, maybe, thats the only size out there to bolt up to a set of headers for this big daddy engine in the aftermarket? But not everything is advertised too. Don't forget about the 3" pipes just yet. Keep looking around.

 

Thank's. I did a post in the exhaust section asking if anybody knew where there was an exhaust for it but nobody replied.

 

There's a reason that there are 3" pipes for your set-up. There are guys running pipes that big on 302's. Ever see a ricer tailpipe? Think of how much volume all those cylinders with all that stroke has.
Putting aside the fact that the low-end /small pipe torque theory is overemphasized at best , here's a link that lists 3" pipe for a smaller motor than yours by a company who's only business is custom exhaust: MagnaFlow Performance Exhaust
Where people get confused and go wrong with the small pipe/torque/ backpressure issue is that they are overlooking one major factor in the equation: headers. This is where almost all the scavenging and "backpressure" happens and where size (and length) matters most. After that bigger is better in most cases due to the restrictions in turns and cats and mufflers. Header and muffler choices are more important than pipe size. Here's a little more detail:
Exhaust Theory.

Bottom line- 3" is fine for your application.

 

DOUG1222556, so what your saying is use the 3" exhaust & a set of headers with it?

 

Yes, that is what he is saying MUSKRATT2. If you do not put a adequate pipe AFTER your headers that already flow ecceptionally more than the logs, you just created a restriction and excessive backpressure.

Btw, backpressure is something that happens because of the design(s). Its not wanted but its there. To me, backpressure holds hands with restriction, and reversion. I have not come to any conclusions yet on my theory but have read others theories along the way. But thats another topic in its own.

On the ricer tailpipes Doug mentions, are they turbocharged or not??? You MUSKRATT2 are dealing with a naturally aspirated engine remember. Inhaling and exhaling less volume of air than a force fed mill. With only having aftermarket exhaust and carburetor. The efficiency will rise a little, but, you still have the restrictive factory iron intake manifold.

Since you are pulling, which I should have said this to make it easier in the ifrst place, use the 3" pipes like Doug says. I just get a little carried away with tuning by components at times on every vehicle. OOps

 

Just some information for you. What I noticed a week ago in the chamber on my D3VEs I have been looking at (don't know what you have is the same or not) the exhaust valve is unshrouded. The clearance is pretty large which is great for your exhaust flow! I dont think this characteristic would differ since the valves are canted so your heads might very well have this also MUSKRATT2.Doug, I have a question for you. On the headers for the big displacement engines, say the engine in question right now. I know mentioned the use of a 2 3/4 pipe, but, I was thinking there would be a header collector diameter with that size also that might not be advertised up front. Is it pretty much a mandatory (that you have seen/heard) 3" header collector tube on all big CID components??

 

Yes, they are turbocharged, but they are less than 1/2 the engine of a V-8 460, but your point is well taken.
The links that I listed go into way more detail than I care to here, especially the exhaust theory link, which covers the real culprit mistakenly referred to as "backpressure" ( which does not exist), when it talks about waves. You will also notice that it says bigger is better is absolutely wrong, but then see what size pipes are recommended.
What I really liked about that article is the reference to the exhaust system as being a 5TH stroke on a 4 stroke motor.
I'm more of a small-block stroker guy, but when I searched 460 headers at Summit, every one I looked at had 3" collectors, including the ones with only 1 5/8" primaries, yet another clue that 3" pipes are they way to go.
I was basing my original recommendation on the fact that in my research, 2 3/4" pipes are none too small, and 3" would be an option on the slightly less than 400 ci. 351W stroker I'm building.

 

Ok guys, I've done a search & I can only find 2 exhaust for my truck. One is from Summit which is a 3" exhaust & the part number SUM-684012, I don't know what type muffler this is, but would it really matter? The other is a Flowmaster 3" exhaust for an 87 to I believe 96 , which my truck is an 85 ( I can't remember the exact ending year) with a 70 series muffler. Which one would you guy's chose? The Summit is a whole lot cheaper. I can't find anything else or do you guys know of anything else out there? Wouldn't the Flowmaster exhaust wouk on my truck?

 

Flowmasters are overrated and overpriced in my opinion. I've seen the Summit mufflers recommended by quite a few serious performance enthusiasts for the same reason.

 

Thanks Doug that's what I thought as well!