RPM Fuel Mileage

[cobra20]

what do you guys think is a good rpm to turn to get some decent fuel mileage?

 

[shortboxchevy77]

between 2 and 2400 rpm at 70mph in my opinion. Any lower and you will burn more fuel working the engine outside of its power curve. I'm running 4.10's with 265/75R16 tires and with a 700R4 and turning 2500 at 75mph

 

[scottybaccus]

Not really. I'm getting 20 mpg turning mine about 1200 at 70 mph.
Simply put, fuel consumption is relative to rpm. Less rpm = less fuel. You may be cruising below your power band, but that's why we downshift.

 

[shortboxchevy77]

There is no way in hell his 4 wheel drive suburban with a 5.7 will pack itself efficiently at 70 spinning 1200rpm with a factory TBI unit. It's not as simple as lower rpm=less fuel consumption.

 

[cobra20]

no I asked this question because I'm building a 2wd K5 Blazer and the only thing set in stone is my rear gear ratio of 3.40 in the 12 bolt that is in the frame. I'm also wanting to put a 4L80E in it.

 

[Green79Scottsdale]

You can't nail it down that easy. Every combination is going to be different. You have to build your combo around that 3.40 (3.42?) ratio. Figure out if you are going to run the overdrive or not. From there figure out your tire height. Then you can get your rpm for your desired "cruise" mph. Build you engine to produce peak torque around that rpm. I have heard from multiple sources that is where your best mileage is, at peak torque.

 

[cobra20]

well right now I'm looking at getting a LQ4 and a 4L80E to put into the blazer. So really right now the only variable I can really play around with is the tire size.

 

[scottybaccus]

My truck is a 2wd swb, LQ4 & 4L80e with a 3.08 and 255/60r17 tires. A 3.42 swap is on my list.

 

[cobra20]

yeah according to the rear diff codes we have on here my rear end is listed as a 3.40

 

[cobra20]

I'm just hoping that I can get right around 20 mpg or so with the LQ4 and 4L80E

 

[fussfeld]

Read this:
http://www.oldsmobility.com/old/carlife_apr67.htm

 

[Rusty Nail]

Short duration / low overlap. That was the important part, along with 10.5:1 - good read.