What is the sweet spot for the best mileage at highway speed?I had a 12 valve, that was 1600 rpm's.Now I have a 24valve.

 

Mine seems to be around 1900 RPM's...

 

Hoss, thanks for the come back.

 

With mine seems if I stay at 70MPH or less. That is right around 2000rpm.

 

A 'sweet spot'?? That would indicate that, if you were to graph mileage vs speed (same thing as rpm) there would be peak in the curve and it would fall off on either side of that peak. I have my doubts about that.

So, if 1900 rpm works out to 70mph, when you slow down to 60 you get worse mileage?

 

1900 RPM's is about 65 mph in my truck...not 70 mph. I was simply answering the man's question. On my truck, it seems to get the best highway mileage around 1900 RPM's. Going up from there and it drops. Going down it doesn't really change unless you let the RPM's get TOO low. Lighten up. The man is just asking a question.

 

[quote author=Hoss link=board=20;threadid=18317;start=0#msg171814 date=1060743849]
1900 RPM's is about 65 mph in my truck...not 70 mph. I was simply answering the man's question. On my truck, it seems to get the best highway mileage around 1900 RPM's. Going up from there and it drops. Going down it doesn't really change unless you let the RPM's get TOO low. Lighten up. The man is just asking a question.
[/quote]

Lighten up yourself. I understand he was 'just asking a question.' I was just trying to get at something resembling a correct answer to his question. There is no such thing as a 'sweet spot' unless there is enough of a bucket in the specific fuel consumption (sfc) curve for the engine to make up for the exponentially increasing aerodynamic drag, and most sfc 'curves' are essentially flat.

 

cp, sorry to disagree, but there is such a thing as a "sweet spot". Doubt if you will find it in any technical manual. For a rough definition, this is the rpm that the everything (engine, tranni etc) seems to be in syc and the vehicle appears to run smoother and quieter. As Hoss said, the fuel consumption above that rpm does appear to drop off. So don't go looking for a sweet spot in charts or curves because you will not find it. Just drive any vehicle and experiment until you find the speed or rpm where everything appears to be the "happiest".

 

What Stan the ole Canuck said.

;D

There is definately a sweet spot on all trucks...its that place where all runs well and sounds great. Not a technical or analytical thing, just a place where all meshes and feels fine.
My 01 loves 2000 rpm. Everything rolls along real nice at that speed/rpm. At 1900 rpm it just don't sound SWEET.

For fast cruising I found 2300 RPM is nice too.

 

If I stay below 70, I get great milage. When I start putting my foot into it more than that, I start dropping more and more the faster I go.

 

I agree, my truck seems to be happy between 65-70mph.

MikeyB

 

'I' am the sweet spot... ;D :-*

My truck seems to be just a tad under 2000 it runs and sounds best. Seem to get best fuel mileage just under the 2g mark also.

 

If run at 70/71 exactly and get 20-22 mpg (calculated by tankful), if I let it drop just a little under maybe 68-69 there is a notable drop in exhaust sound- I'm straight piped and sound like a freightliner- also it is slightly smoother and I have exceeded 23 mpg (by actual tankful calculation). That is probably at 1900 on mine. Also the trans sounds just slightly quieter at 1900 rpms. There is no calculable sweet spot but it is notable by sound on a straight piped truck, no doubt in my mind. It also seems to hit another quiet point right near 80 mph. 72-78 seems pretty loud. I have never run more than a tankful at 80 though and I averaged about 18 mpg on that trip. Now at 80 if the tailgate is up it is MUCH louder than if I put it down, I think I'll look-into a box cover.

 

[quote author=cp link=board=20;threadid=18317;start=0#msg171827 date=1060745208]Lighten up yourself. [/quote]

I AM lightened up you red necked, yellow bellied, ring tailed, sap suckin', snow blowin' egg head!!!! ;D

There....now I feel better. ;D :P

 

I agree with the "sweet spot". If I try and decipher those pointless marks on the tach, I think it's about 1750 RPM, around 68 mph, and about 22 mpg on the flats. And "Yes", if I drop below this speed, the mileage doesn't improve until I drop below 60. I define a "sweet spot" as a combination of speed,mpg, and a little engine noise. Commuting back and forth from work (40 each way), I like to run around 1600 rpm as it's much quieter in the cab as well as being easy on the nerves but my fuel effeciency suffers a little.