How much will a tired engine effect mileage

[CobraSix]

I've been trying to figure out when I lost my gas mileage. looked back over my records and it corresponds to when I put the new engine in, along with a 260 cam and a T5 tranny. I went from 25-30 MPG on the highway to 19-23 MPG.

So I started thinking...would a tire engine (one in need of a rebuild) cause that big of a lose in mileage? I need to just do a compression check to see where I'm at, but just curious.

Slade

 

[Lazy JW]

I think it would have to be REALLY tired to do that. Compression well under 100lbs. Lots of oil consumption, etc. I've driven a fair number of junkers that got decent mileage.
Joe

 

[xctasy]

You must read vlad's posts on how he tunned his 390 cfm carb on his 300 I6 truck.

What main jets and secondary metering plate and power valve are you running?

The 2V has H-U-G-E ports which drop the fuel in susspension, and its most likely the power valve is always on. You need a 6.5 or even 4.5 or 4.0 power valve. If its 8.5 or 10.5, fuel milleage is bound to be lousy! There is no need for enrichment untill the car is getting close to wide open throttle. It must criuse lean, and only go rick when its stepped on!

Check with Ricksmol on likely fuel figures. The 390 4V will always better a 350 2v on a open road cruise, because the rate of variance from lean to rich is wider than the 350 2-bbl, which is a compromise. Both are excellent econo carbs if the fuel is clean, the gaskets and ported vacuum is sound, and the jets and power valve are to tuned to spec.

 

[CobraSix]

Yeah...I don't think it is this set up though, I started dropping mileage as soon as I but this block in, running the old 1V set up with a 3 spd. I've got a leaking rear main on this block too (which is exactly why I pulled the old block), but other then that...my oil lose is generally from leaks...about 1 quart every 1000-1500 miles.

Slade

 

[Anonymous]

i STILL dont thinik I have ever gone above 18 mpg in any case even after rebuild (partial)

I am pedal heavy but still with these prices, I am thinking of squeezing more out of it