Fuel injection and fuel economy

[Ziegelsteinfaust]

On my truck I can get 18 maybe 19 mpg cruising the highway at 75-80 with a constant afr between 13.3 to 14.0. The last few weeks I have had to make quite a few 200 mile drives to go get stuff, and visit family. All in the high desert so I have to go over the Cajon pass, or the one on the 14.

My truck in a smog legal built 383 LT1, with a .500 lift 206 duration cam roughly, 10.7-1 cr, afr 195 heads, and backed by a TH700r4. My truck is a C10 rcsb stepside with 30x9.50r15 AT tires, and 4.88 gears in the 12 bolt.

So I was quite surprised by the highway mileage. When before hand I would of bet the farm on 12-13 mpg.

What really got me was my 5 maybe 8 mpg city. I have tried several different tunes to try to get it up more. Yes that is what she said. Although currently I am stopped by pinging at 2250 rpm due to load on the engine with its high dynamic compression ratio. So I leave it rich to keep the engine happier. I know of I could lean the carb out another jet or two. It would improve, but not by that much as I am basically still on the idle circuit buzzing around town. Where my highway afr is good, and everything is happy. Namely me at $5 a gallon 91 octane.

My job is 7 miles from where I live, and it is alot easier to take streets. I only idle the engine 30 seconds to build a oil pressure then I go on my way. Besides the crap mpg city. This truck runs awesome for what I do.

So would fuel injection. Either something like Holleys stealth tbi, or some sort of custom port set up add up to better mpg?

I am seriously reconsidering this as I want a 4L80e to back my engine, and why not have a complete package.

As I plan to keep my truck till I die as I feel 35 again when I drive it. Plus I would like a bit better afr control.

[Tom]

Highway I doubt you'll do much better but in town should be a few mpg gain at least.

[Ziegelsteinfaust]

My thought is the city should be around 12+ since my gear ratio provides so little resistance to acceleration. How much in reality I don't know. As I am not able to do A-B testing.

On my fresher LT1 I just picked up that will get a comp 306 cam to help with dynamic compression. Along with a bunch of gasket replacements. I am thinking of trying a 650 vacuum secondary to see if more signal helps out city mpg. Currently I have a 750 vacuum secondary.

Highway any increases would be just margin of error gains. Since part throttle the carb is pretty damn close, and the manifold hopefully won't have to be changed.

[Rickysnickers]

I think you are doing pretty well with the mileage you have! I don't think it's going to increase much, if any at all, with fuel injection. You most likely will get better cold start and maybe a smoother idle. Fuel injection kits are a little expensive and you would have to burn through a lot of gas before you were to pay it off. I also believe the only FI kit that is CA legal is the Atomic EFI.

[Ziegelsteinfaust]

I am pre smog or 75 and earlier. So I can run what I want with very very very little real life chance of having to change my set up.

So if my truck burns cleaner then what I would be required too. It's a non starter in the real world. 15-20 years ago they had mobile smog trucks parked on the side of the highway. In theory they would flag you if you were running dirty. I seen others get pulled, but I never did. As I fully tuned my vehicles to my limits atleast. Have not seen one in atleast 15 years. I would usually see them by pick a parts.

I would seriously consider fuel injection when I get a 4L80e. At that point I will look at my finances, and really decide. Right now I am looking to trade a 750 Holley vs for a 650 VS to modify.

It was more of a concept question. I never had a vehicle do this bad on the street with out a big cam. Like a Duntov 30-30 or a modern version of sorts.

My light duty C20 rclb with a dead 350, th350, and 4.11 gears would do 8-12 typically. Although highway was 12-13 at 60/65. So I find it odd with all my engines advantages it gets worse. The advantages a deeper gears, higher compression, slightly better tires for mpg, and lower over all weight.

I just find it weird. Maybe there is some detail I am unable to see at this point.

[MySons68C20]

Originally Posted by Ziegelsteinfaust

On my truck I can get 18 maybe 19 mpg cruising the highway at 75-80 with a constant afr between 13.3 to 14.0. The last few weeks I have had to make quite a few 200 mile drives to go get stuff, and visit family. All in the high desert so I have to go over the Cajon pass, or the one on the 14.

My truck in a smog legal built 383 LT1, with a .500 lift 206 duration cam roughly, 10.7-1 cr, afr 195 heads, and backed by a TH700r4. My truck is a C10 rcsb stepside with 30x9.50r15 AT tires, and 4.88 gears in the 12 bolt.

So I was quite surprised by the highway mileage. When before hand I would of bet the farm on 12-13 mpg.

What really got me was my 5 maybe 8 mpg city. I have tried several different tunes to try to get it up more. Yes that is what she said. Although currently I am stopped by pinging at 2250 rpm due to load on the engine with its high dynamic compression ratio. So I leave it rich to keep the engine happier. I know of I could lean the carb out another jet or two. It would improve, but not by that much as I am basically still on the idle circuit buzzing around town. Where my highway afr is good, and everything is happy. Namely me at $5 a gallon 91 octane.

My job is 7 miles from where I live, and it is alot easier to take streets. I only idle the engine 30 seconds to build a oil pressure then I go on my way. Besides the crap mpg city. This truck runs awesome for what I do.

So would fuel injection. Either something like Holleys stealth tbi, or some sort of custom port set up add up to better mpg?

I am seriously reconsidering this as I want a 4L80e to back my engine, and why not have a complete package.

As I plan to keep my truck till I die as I feel 35 again when I drive it. Plus I would like a bit better afr control.

Have you considered a wide band 02 sensor to see what your town driving afr is?

[Ziegelsteinfaust]

Originally Posted by MySons68C20

Have you considered a wide band 02 sensor to see what your town driving afr is?

I have one installed, and had my vacuum guage in the cab on a long piece of hose for tuning. As I knew I had to becareful with tuning a higher compression motor.

Around town it is about 12.5 to 13-1 afr. On the freeway or in 3rd instead of fourth on the street it is between 13.5-13.8-1 mostly.

It has ran fine at 14-14.5 on the freeway, but that's tip way to lean on me right now. My soon to be newer engine will get a cam swap to help out

I quit taken out more jets due to detonation issues, and just adjusted to ping less.

[MySons68C20]

Originally Posted by Ziegelsteinfaust

I have one installed, and had my vacuum guage in the cab on a long piece of hose for tuning. As I knew I had to becareful with tuning a higher compression motor.

Around town it is about 12.5 to 13-1 afr. On the freeway or in 3rd instead of fourth on the street it is between 13.5-13.8-1 mostly.

It has ran fine at 14-14.5 on the freeway, but that's tip way to lean on me right now. My soon to be newer engine will get a cam swap to help out

I quit taken out more jets due to detonation issues, and just adjusted to ping less.

Oops sorry I re read your orig post regarding your afr. 5 to 8 mpg is quite a swing.
I believe Tom is right on this..... if it's 8 ish I don't think you will do much better efi or not.