This crate 89, non-HO (not a 351 firing order) with small heads, & 9 something compression is new/used?

 

If you have the rpm manifold, with a mild/stock flat tappet cam you are losing lowend torque. That will be part of the issue. So pending you being attached to that intake, your next step is to get a carb kit and recalibrate the carb. Also get a vacuum gauge and some hose. Hook it up to the manifold and see what you have at idle, and during various driving conditions that will help clue in what your engine is doing and needs

 

My '89 with a carbed 351 and Edelbrock 1806 gets 9-10 MPG in mixed driving but it is a 4x4 with a C6 and 3.55 gears.

 

thx, I figure it may have been the wrong choice in manifolds. I’m getting a solid 20 for vac.

 

brand new. Well a full rebuild from Canada engines

 

Like mentioned above, a vac gauge (mounted) & carb tuning should get the mileage higher.

It's just that with this small of engine (stock heads/cam) & all the weight of a 4 by can never be offset with a carb over functioning efi.

I'd put a roller cam in it in a heartbeat, heads if affordable. Then it might live up to the carb/intake.

 

You're truck is right inline with mine on fuel consumption. Around town I get about 200km per tank, even now with it only running on seven. I just filled up the other day and that tank was 9 mpg(imp), which would be slightly better than 7 mpg(US). It has been fairly consistent over the 20 years I've had it, but the engine is very tired and in need of replacement now. When I find a good replacement I hope it'll do a little better on fuel. I was getting 220km per tank when I ran E3 spark plugs, I was very pleased with that.

 

Also what brand crate engine is it? A cheapo rebuilt one may not be up to snuff on clearances. A generic piston may be down the hole and you may only have 7.5:1 compression which will kill mileage

 

I'd still look into a wideband and a carb tuning kit.

This e10 doesnt do like the old gasoline did with plug colors. It will change but it's got to be way off rich. This is a big discussion with the old hats on my carb tuning forum.
Do you know anyone that has a different carb you can borrow to see if you get different results?

 

I have an 1806 Edelbrock, it’s 650 Thunder series and was about the same. But on my previous 5.0

 

If you truly want better mileage, why not just go back to the EFI? It's not a complicated system. Lots of parts in the Pick N Pulls.

 

A wideband would let you tune safely, without grenading your motor. At highway cruise in high gear or low load condition about 16 to 1 AFR is typical for any OHV carbureted engine. EFI runs much more, but this isn't possible with a carburetor. When an economical cruise jetting is selected, then you will almost certainly have to modify the power circuit AFR to avoid going too lean when under load or acceleration. This is when valves start burning, under power accelerstion or load the AFR will need to be very rich in the 12 to 13 range.

What kind of distributor is in that? When carburetors ruled the scene, and dinosaurs roamed the earth they were mechanical/centrifugal + load based vacuum advance.

14 degrees timing just tells you what the timing is at idle, you'll have to plot it out at increments out to 3000 RPM or so. Should be in the mid 30s when spooled up, and somewhere around 50 degrees BTDC when cruising down the highway on flat ground.

The CFM calculators are mostly designed or used for drag racing, and to sell carbs, near as I can tell. You want a smaller carb than something designed for high RPM and top speed. Ford often supplied a carburetor with something less in CFM terms than the engine cubic inch size if that tells you anything.

 

I have a 1994 351w 2wd with tuned SpeedDensity EFI getting 300km per tank (70l, 19gal), driving nicely. Truck is a Flareside, weighs 400lbs more than regular short box, and a canopy.
So that's about 9.8mpg.
I would expect less if it was a 4x4.