454 engine improvements for better mileage

[garym]

I am planning on a cam change and intake/carb change on my 84 C30 crew cab truck.I haual a 38 ft GN trailer and the gas mileage is not good.I was planning on the Edelbrock cam #2162 cam .500 lift on int&ex 218 deg int&228ex @.050 114 deg lobe sep.
Comp has two cams 260H .475 lift on int&ex 212 dur@.050 on int&ex lobe sep 110 deg
Comp 268H .485 lift on int&ex 218 dur@.050 lobe sep 110 deg.
The comp cams above are towing cams, but the 268H cam "IS GREAT FOR HEAVY TOWING IN 454" So what would be the best cam for my truck? The rear gear is 4.10 and I do not know if changing to a 3.73 rear gear would be better o r not.As far as carbs go I was going to maybe go with the Edelbrock # 1411 750 carb with the electric choke on the Edelbrock Per former 2-0 #2161 intake. Planning on removing the smog/air pump and cast iron exhaust as well. I also would like any other advice/input on the above cams, as I know the mileage is not going to be great but I want to improve what I have a little bit.Fuel injection is something I do not want or considering. THANKS garym

[travis]

If your towing heavy loads, taller gears will make it worse. I’ve done a couple of trucks with similar mods...a ‘77 C30 dually, 454/TH400/4.10’s and a ‘78 C30 454/TH400/3.73’s. Mods were rejetted stock q-jet, performer intake, recurved HEI, 2 1/2” duals with free flowing mufflers and stock iron manifolds and no cats, and a generic 214/224@.050 hft cam on a 112 lsa (probably not optimal but cheap and available at the time). Both were a lot stronger from idle up, and seen 2-3 mpg increases. Synthetic oils and fluids help too, as well as some sort of cold air induction. High inflation pressure highway tires and driving a bit slower also helps a lot.

[Truckedup]

Do you know what intake vacuum the engine has when cruising with a load? For a carburetor gas engine to get decent fuel mileage at normal road speeds you need higher vacuum and lower RPM's...A higher rear axle gear often puts more load on the engine and lowers the vacuum and it may go into the power circuit more often.High vacuum also helps to vaporize fuel..You probably have only three forward gears? In my opinion , you'll get better results from a transmission set up giving 5 or 6 useful gears...Some sort of secondary transmission, or a main trans with more speeds... This works well if you drive in hilly areas...

[FC-Pilot]

My old 454 crew cab Dually picked up 1.5 MPG when I put small diameter long tube headers on and another 1 MPG when I then when from dual 2" exhaust to 2.5" dual exhaust. I also had a vacuum gauge mounted in the dash and I drove by that. I tried not to have the vacuum drop too low while accelerating and cruising. I would love to have played with the heads and cam to get better performance at the same time.

Paul

[garym]

Thanks for the replies.So I have not decided on a camshaft, but the ERSON CAM grind #RV 15 H has the following specs
LIFT int .495 ex .495 dur @.050 214 on int&ex. lobe sep 112+4 OR the other cams in my first post. THANKS garym

[F-BIRD'88]

Slow down or get a smaller trailer..
The vaccum guage is the best tip yet.

Improve wind drag.. Big front spoiler.
Roof spoiler. areodynamic towing mirrors.

Make the truck and trailer pair more areo at speed.

Increase tire pressure.

[Geoff2]

Remove two cylinders...

[Alan Roehrich]

How much work are you willing to do?

How much money are you willing to spend?

How serious are you about modifying and tuning it?

What is your skill level?

I can tell you with certainty that the greatest impediment to efficiency in those old engines is an abysmal compression ratio, it is actually down around 7.5:1, which kills both torque and fuel economy.

[gnicholson]

A pair of 96 and later l29 heads would be a big improvement

[Truckedup]

How much work are you willing to do?

How much money are you willing to spend?

How serious are you about modifying and tuning it?

What is your skill level?

I can tell you with certainty that the greatest impediment to efficiency in those old engines is an abysmal compression ratio, it is actually down around 7.5:1, which kills both torque and fuel economy.

Gas truck engines designed for hauling loads always have lower compression ratios. Keeping up with traffic in a loaded gas engine truck means relatively high rpm's with deep throttle openings and low intake vacuum..By loaded I mean at least 12000 pounds gross...Cruising along at 55 on flat ground is a different story..

[Brian P]

Transmission?

Lock-up torque converter ... that is strong enough to stay locked in top gear? A lot of the older ones weren't designed to handle full engine torque.

I don't know what your tire OD is so I will guess 28" (feel free to provide the actual number). With 3.73 it will be turning around 2700 rpm at 60 mph in direct drive with no torque converter slippage. With 4.10 it will be around 3000 rpm.

If you can't do a lock-up torque converter then use the lowest stall speed torque converter that you can find. It needs to have minimum possible slippage in coupling mode (higher speeds). With these old transmissions this is why taller final drive doesn't necessarily mean better mileage. Taller final drive brings the revs lower and required torque higher and then torque converter slippage increases and converter efficiency goes down the crapper.

A manual transmission might be a better choice. It needs to be a wide-ratio one so that you have a hope of pulling away from a stop and having a decent choice of ratios at highway speed.

There's a reason that everyone is going to 6 - 8 - 10 speed transmissions nowadays - and torque converters that are capable of staying locked at full engine output torque and lower revs.

[dfarr67]

Better heads
cam
headers
Rochester quad properly tuned, prefer efi
4L80E

[PackardV8]

Do some math, but mine always comes out, unless you're rebuilding anyway, new cam, headers, heads, intake, transmission swaps, never pay out from the increase in fuel mileage. So yes, if a refresh is in the works, a new cam and lifters doesn't cost extra, but problem is, there's little to be gained in fuel economy in aftermarket cam timing.

[Truckedup]

Do some math, but mine always comes out, unless you're rebuilding anyway, new cam, headers, heads, intake, transmission swaps, never pay out from the increase in fuel mileage. So yes, if a refresh is in the works, a new cam and lifters doesn't cost extra, but problem is, there's little to be gained in fuel economy in aftermarket cam timing.

I agree....And a working truck engine is not going to exceed 4000 rpm in normal operation...Most of heavy work like pulling a long grade at 60 mph will be around 3000-3500 rpm in an intermediate gear with 75 percent throttle opening....I see the need for a mild cam and exhaust flow improvements.. But saying better heads do you mean to concentrate power in the most used RPM range? And how big of a carb is needed for best power at less than 4000 rpm ? Again, I'm assuming here the truck and trailer gross of at least 12.000 pounds......

[MadBill]

For what it's worth (ignoring power enrichment, which may or may not tilt the scales) an engine is more efficient at WOT than at any part throttle %, due to reduced pumping losses. This is the physics behind cylinder deactivation, small engines with turbos and Hypermilers who accelerate at WOT from very low to low/medium RPM and then coast.