Optimum RPMs

[doby48]

After having the gears, engine, tranny, tires, etc replaced. I need to try and dialin my truck. Currently the mileage and towing power are both horrible. I'm a bit at a loss as to where to start other than with the RPMs. Currently I'm running at 2100 RPMs at 65mph which sounds awfully low to me but before I start messing aruond with tire sizes, etc I wanted to get thoughts from some of the others. Anyone know the sweet spot, or RPMs from the factory on a 1994 Chevy C1500?

Just to give you all an idea I am getting about 9mpg for mileage and get stuck on grommed dirt roads when it rains (and my truck has POSI as well).

[maxwedge]

You really need to include some info, gearing, engine mods, truck size and weight, engine size, tire size, intended usage, how else can anyone suggest an answer to your "questions".

[doby48]

I had done an earlier post and didn't realize I ommited some of this information in this post.

I bought the truck used and the previous owner had changed out the gears, I don't know what they were changed to but was told the he changed them out for towing an RV. I got some tips from some guys as to how to figure out the gears based on turns of tire vs axle. The engine was installed about 20 months ago and is a 2004 5.7L Chevy Silverado Crate Engine with no additional mods.

Truck is a 1994 Chevy C1500 4x2 with POSI, Extended Cab, Long Bed. Current tires are P235/75R15. No topper on the truck but during hunting season there is a topper with no change in gas mileage or towing power. I have a 21ft Bass Boat that I need to tow and I am able to tow without issue when going down roadways, however, I have had difficulty pulling the boat out of boat landings, going up hills, etc (and have had to use a 1993 v6 Chevy Corsica to pull the boat out of the lake when the truck gets stuck). I have also had difficulty drivin down groomed dirt roads by getting stuck (and these are roads that compact front wheel drive vehicles don't have any issues driving down).

I would expect to be getting either decent power or decent mileage, but the place that I'm stumped is to why both my mileage is horrible and my towing power as well. If I failed to provide any needed information, let me know.

Thanks for any help anyone can provide.

[doby48]

The information I provided on the engine was not entirely accurate... It is not a Vortec engine, its a 2004 engine thats a 350, 5.7L.

[maxwedge]

At those rpms, probably a 3.73, your poor mileage is driving habits or obviously something is wrong. have it scanned for sensor inputs. Many things cause power loss, timing, fuel mixture, blocked cat and so on.

[doby48]

Thanks for the feedback maxwedge.

Driving habits are good expecially since I've been trying to get the best mileage possible. Slow acceleration and deceleration, I live in the country so most driving is rural (55 mph with infrequent stops), and limited city and freeway driving. I dont do short trips since it is 30 miles into the closest city and its not much of a city so when I drive into town I definatly combine trips.

I had a sensor scan done and everything came back fine. The timing was recently checked as well. I have tried differnt grades of gasoline and stuck with differnet stations and have seen some minor differences (from 9mpg to 11mpg without towing anything).

However, I hadnt thought about the cat though. The truck has 310,000 miles on the original cat so I'm sure thats a problem. I will look into that as the next repair for this truck

Thanks for your help on this.