An idea for better mpg on a 454 BB

[lostcause06]

Ok so here's the ordeal. I am rebuilding my 454 BB on my suburban. So here's the idea.

My 454 has 300hp and about 280lbs of tq, a weak BB by any standard and I get about 12-15 MPG which is good for me... BUT... Seeing how I have some extra money to throw in the block... What if I did some upgrades (cam,heads,rollers) which would bring me to 460HP....

So would that extra 160hp kill my mpg or make it better? Now I know the usuals "tranni type, gearing, ease of gas pedals, etc.." Let's forget about all that. Assuming everything is the same on the truck (exhaust headers gearing etc) but the BB is torqued up would it improve mpg!? Let the nonsense begin.

[lostcause06]

Anyone ?

[whitels1]

I'm not sure anything making 460hp is going to get good gas mileage, unless it's an LS with a turbo.

[lostcause06]

That's not the question here.

[lostcause06]

The idea is with more hp, it should be easier for the BB to pull that heavy ass around compared to having it underpowered and having to work harder to pull it.

[Average Joe]

280 on torque? Is this from a chassis dyno? Even the weekest smog era 454's made 380 ftlb at the flywheel with 230 hp.
Regardless, you want more power. Depending on what year the BB in question is you may be below 8 to 1 on compression. Upping this to 9 to 1 with cast iron heads or 9.5 to 1 with aluminum heads will improve efficiency and power.
Adding a higher lift cam with conservative duration should also help with power without comprimising milage. Keep duration at .050 less than 220 degrees and lift around .500. A split duration cam favoring the exhaust would be wise.
Id run a Performer intake with a Qjet for induction or better yet spend your money on a aftermarket stand alone tbi like Fitech or Holleys equivalent due out in March.
You wont see 460 HP with these mods but I doubt you will lose any mpg either. 12-15 mpg in a BB 'Burb is pretty darn good.

[lostcause06]

It's 380 torque sorry about that. The BB is out of a 85 suburban so I know they changed the compression on those terribly. So far so good then, sounds like it's worth upping the hp. 12-15 is awesome for a BB that's why i am hesitant to up it up but it makes sense that if it can breath easier and run easier which means it doesn't have to work as hard to carry its own weight the mpg should stay the same (which is great) or improve (even better)

[notchbackgta]

You will get more MPG by adding an overdrive. I get about 10-12 with mine and a TH400 and I think I am going to put in the NV4500 sooner than I expected, should put me up 1 or 2 MPG on the highway with the 454, I also put on Holley TBI, that should get me another 1 or so around town too, but it was mostly to, hopefully, pass emissions here in NJ since mine should have a SBC

[HO455]

To improve milege you are really looking to improve your efficiency in a specific rpm range. That range is is going to be determined by your intended speed and gear ratio. Some modifications will help across the board and some will limit the engine in other rpm ranges. Think like diesel engines. Raising your compression ratio as far as reasonable will increase efficiency. With aluminum heads and proper combustion chamber prep 10:1 or slightly above is possible pump gas. With valve grinds and porting that increases low lift flow past the valve you can get more fuel air mixture into the cylinders at lower rpms a with less valve overlap. These are mods that many people know nothing about as very few people request them, and most of the aftermarket is not interested in providing. Look at big cars of the late sixties. Those 4000+ lb 450+ cubic inch cars were able to get 15 to 18 mpg on the highway with carbs and iron heads. I had a 74 Bonniville that got 15 with a well worn 455. Find a head porter who knows what low lift flow is and is interested in your kind of project. Get with a cam company that the porter is happy with so that the project can go forward as a team. These kind of mods are also great for making low end torque (always a plus off road). Don't forget aerodynamics. I know these things are bricks but narrower tires and little air dams can make help. General motors doesn't put them on for show they are using them to get their average CAFE mileage up. Look to salt flat racers for ideas on how to make the front end more areo friendly. Get a wide band A/F meter to help tune the fuel ratio. The $450.00 I spent on mine has long been recouped in gas savings. The hypermilage web sites have some very good information posted by some really smart folks, if your willing to wade through all rest of the garbage there's money to be found. Good luck and as always your results may vary.