Optimum RPM for 305 MPGs

[RedBed]

Just curious if anyone knows the optimum RPM to get the best MPG out my 2BBL 305 with 4L60.

My guess is somewhere in the area of 2500rpm @ 65 ...?

[Tom]

Thats way too high. Lower is better. 65 should be more like 1900rpm.

[jkk]

Get a Prius???????

[Matt Man]

Originally Posted by RedBed

Just curious if anyone knows the optimum RPM to get the best MPG out my 2BBL 305 with 4L60.

My guess is somewhere in the area of 2500rpm @ 65 ...?

It depends on your camshaft, a stock 305 will not like 2000rpm as the power is not there too much. It says you live in Texas, so I'm assuming it is flat where you live. I think 2200-2500 would be better and won't be downshifting as much with a overdrive. 2,000 rpm or lower might be beneficial if you can keep your truck going the speed limit while going uphills and with a 2bbl carb and assuming stock 305 I don't think this will go well. Just my opinion.

[RedBed]

Here's the funny thing - now that I swapped in a 4L60, my MPGs went from about 12.5 (old 3-spd) down to 9.5 (4L60). Then last week I had a trailer with a heavy load, and stayed out of OD. My average jumped UP to over 10.5.

So I installed a tach. My current RPM are 1900 @ 65. And that is the spot where my MPGs s-u-c-k.

So this tank I am going to drive around without using OD at all. We'll see what happens to the MPGs. My guess is that they will jump up, and if so then I will need to swap out differential gears.

Using a calculator online It seems like my diff gears are possibly 3.73... I don't know what they are. But I have 29.1" tires, and using 3.73 as the gears, it comes in about right.

So if it happens like I think it will, I'll need to figure out what gears to swap to.

[RedBed]

Originally Posted by jkk

Get a Prius???????

Or... I could put on a skirt and ride a girls bike!

[nonstop]

I know it sounds counterproductive, but have you thought about putting a Quadrajet on? It will stay on the tiny primaries for mileage until you need it then tip into those huge secondaries. That swap would likely be easier and cheaper than a gear swap.

[RedBed]

Yes, have thought about Quadrajet. But That will be done once I get everything in line as far as gearing.

When I installed the 4L60, I knew that changing diff gears might be part of the deal, so not a problem.

[lilpoindexter]

I think your best mpg will be the slowest speed at which you go into 4th, and your converter locks up....your converter does lock up, right?

[Palf70Step]

Originally Posted by RedBed

Here's the funny thing - now that I swapped in a 4L60, my MPGs went from about 12.5 (old 3-spd) down to 9.5 (4L60). Then last week I had a trailer with a heavy load, and stayed out of OD. My average jumped UP to over 10.5.

So I installed a tach. My current RPM are 1900 @ 65. And that is the spot where my MPGs s-u-c-k.

So this tank I am going to drive around without using OD at all. We'll see what happens to the MPGs. My guess is that they will jump up, and if so then I will need to swap out differential gears.

Using a calculator online It seems like my diff gears are possibly 3.73... I don't know what they are. But I have 29.1" tires, and using 3.73 as the gears, it comes in about right.

So if it happens like I think it will, I'll need to figure out what gears to swap to.

Did you recalibrate your speedometer gears to match the new transmission. You may be getting better than you thing for MPG.

[RedBed]

Yes, it has lockup. Goes into OD about 65 and locks up about 68-70.

Yes, I did re-calibrate gears and checked it vs GPS.

[SunSoaked]

Remove the carb and replace everything underneath it with a 350. The added torque will do wonders.

[RedBed]

Originally Posted by SunSoaked

Remove the carb and replace everything underneath it with a 350. The added torque will do wonders.

I wish...

Shoulda never sold my '92 Dodge Cummins

[Rich84]

I'm no expert..But it should go into OD around 45MPH.
Maybe you have a heavy foot..LOL