6.5 block , 6.2 heads

[GOEHILL]

I had an engine built a 6.5 engine block with 1o- 10 crank and new 6.2 heads. this is NA I am only getting 18MPG . I have 1/2 to sub with 700r4. 342 gears 4x4. what speed in O/D will produce 1800 RPM.

[Robyn]

Hi there
Well now lets see here.
The 6.2 heads generally have slightly smaller precups with smaller ports to better swirl the fule air mix as it burns. This results in better mileage, usually
What IP are you using, DB2 C or J pump settings or DS4 (electronic)
depending on how the pump is set up can really change the fuel economy.
Are you using 6.2 injectors or 6.5 ?????????
There are several factors that will come into play here.
Generally with the combination of 3.42 gears and a 700R one would expect to see 22-24 highway mileage.
Tire size, vehicle weight and such and driving habits can all play a big part too.
Let us know more info.
Robyn

[MPrichard]

As the fuel economy articles started coming out while I'm in the middle of a 6.5 rebuild, I wanted to do whatever I could to squeeze as much mileage out of my k2500 Sub as I could. I'm replacing the 454 (375k and still going) with a 6.5TD out of a '94 C3500 (with harnesses, computer, etc.). I've also picked up a used 5521 pump to replace the 5068 and have been trying to get GM to tell me which chip I need to get (no EGR, auto) to make the computer compatible with the updated pump, but that's for another thread.

I'm having my heads done with 6.2 (or single dot) pre-cups. I'm wondering, since you asked if he'd used 6.2 or 6.5 injectors, are these interchangeable? Would there be a potential fuel economy advantage to the 6.2 injectors? I'd originally thought that in 6.2 heads, the injectors came out at a different angle and were a different length.

[jjmoore]

Hi there
Well now lets see here.
The 6.2 heads generally have slightly smaller precups with smaller ports to better swirl the fule air mix as it burns. This results in better mileage, usually
What IP are you using, DB2 C or J pump settings or DS4 (electronic)
depending on how the pump is set up can really change the fuel economy.
Are you using 6.2 injectors or 6.5 ?????????
There are several factors that will come into play here.
Generally with the combination of 3.42 gears and a 700R one would expect to see 22-24 highway mileage.
Tire size, vehicle weight and such and driving habits can all play a big part too.
Let us know more info.
Robyn tires are BFG 9.5x30 r15. the IP is a stock 6.5 NA pump that I was told to detune 1/4 turn ccw, I am using the short injectors.