I have a 2004 33' Class A Ford stripped chassis RV with the 2 valve V10, 310 HP. It has a 5.375 rear end.
A couple of times I've driven 60-65 mph and "seem" to get the same MPG as at 55 I drive most of the time. I usually get 8.8-9.3 MPG. That is about 2200 RPM.
1. What RPM are these engines at for best fuel consumption ie BSFC.
2. Is there a curve I can see?

 

Peak torque is 425tq @ 3,250rpm however it makes 80% of the peak torque not much above idle. The engine just starts getting into the meat of the torque curve and closer to the peak around 2200+rpm which is probably why you you have experienced around the same mpg even though you are driving faster. The increase in torque does not require as much throttle input to maintain speed. I have noticed it with my truck as well.

 

Great question Fiesta. Thanks for the input DKF. I have had diesel SD's and this is my first V10 SD. I was always told with the diesels to keep them under 2k. Now with the V10 on this last trip we took I was doing the same thing, but it seemed to up shift a lot. Now I will try the 2200 to see how it responds.

 

I've never seen a chart for the engines when used in vehicles, but there are charts showing BSFC for V10's used in generators. I have no idea what differences there are in the engines/controls for them, and most of them show the specs only for LP or natural gas, but I have seen versions showing the specs for gasoline, too, like this, http://www.edi-dist.com/images/pdf/f...pec%20RevB.pdf . Obviously the power ratings are different, so the BSFC and curve may be, too, but its the closest I've come across.

 

On our setup the difference between 55 & 65 isn't very noticeable unless we are in a heavy wind. We normally run between 60 and 62 on good wind days and the tachometer in our truck runs 22 to 24 but they aren't all the accurate. If we can't hold it in OD because of wind then we back it down to around 55 and it runs closer to 3000.

Denny

 

Isn't the internet great!
The pdf file was very helpful. It has a gas BSFC chart I've been looking for, for a year. It is nearly flat like the torque curve. The difference at higher speeds will only be the additional air drag not engine fuel consumption. In calm and tail wind days I should get about the same MPG going 5-10 more MPH. On headwind days several times (with my improved freer flowing intake) I experienced only a drop of .5 MPG. Before my forward facing intake with gauze air filter was installed I lost 3 MPG in heavy headwinds. (Try 6 MPG on a 75 gallon tank!!!)