More torque for my GMC Sierra 4.8?

[SDSeville]

Hi Everyone. My tow vehicle is a 2001 GMC Sierra 1500 Extra cab with a 4.8L engine and 35" tires. It does great towing my 19' Sea Ray for 95% of our trips. However, it struggles on our few long distance trips through the mountains. Even with tow/haul on, it struggles on the long steep inclines and has a hard time finding the right gear.

Any ideas on getting a little more torque without breaking the bank would be greatly appreciated.

 

[UncleWillie]

Manually force it into a lower gear.
Climbing hills at speed requires Power. Power is a product of Torque and RPM.
The higher the RPM, the lower the matching Torque to make the same Power.
That is why it keeps downshifting.
Rev it up a little for climb up the hills. The engine will thank you!

 

[Blind Date]

I suspect those big tires aren't doing you any favors towing with that little 4.8 unless you changed the gears in the front & back differentials. With the stock wheels/tires it would do a lot better.

 

[Starcraft5834]

I suspect those big tires aren't doing you any favors towing with that little 4.8 unless you changed the gears in the front & back differentials. With the stock wheels/tires it would do a lot better.

+1. Ive got an 08 Sierra 4.8 too, tow my 20 ft cuddy no problem,, those big tires are not doing you any favors.......... you have plenty of truck to tow that... what's the tow spec? mine's like 7500 lbs.. long bed.......would imagine your the same...that boats what 3K? just use your tow assist button...im sure it can handle it

 

[SDSeville]

Yeah, I know the tires make towing more difficult. I lifted it when I was 14 years younger than I am now. At this point, I would rather be minus the lift and tires in exchange for better towing and MPG. However, with the stock parts long gone, I am stuck with it like this (maybe slightly smaller tires next change). Even with the big tires, it does pretty well except for the real long inclines.

I like your idea Willie. It kept shifting up and down between 2nd to 3rd on the inclines. It seemed to go between 50 and 55 at around 3500 RPM and then shift to 3rd dropping the RPM to about 2000 and speed to the 40s. I guess I would have been much better off manually shifting to 2nd and leaving it there until I crest the hill. Is it safe to run around 3500+ RPM for 15 - 20 miles at a time?

 

[bruceb58]

If I am going up a hill, I always shift it down manually so it doesn't hunt back and forth. Worse thing you can let your transmission do.

 

[Silvertip]

As I tell folks it takes a lot of horsepower to make up for a bad axle ratio selection when towing. Tow/haul mode does not give you more torque. It merely raises shift points. And as everyone has told you, your 35 inch tires not only screwed up the speedometer it also screwed up the effective axle ratio. I just checked my 2001 Yukon with standard 16 inch wheels and the tires measure 29 inches. So your 35's represent an axle ratio change to roughly 2.90:1 if the vehicle actually has 3.53 gears. Even if you changed gears to 4.10's you would still be a bit short of the capability of the 3.53's and stock tires. You don't need more power. You need different gears. The situation is made even worse if the vehicle had less than 3.53 gears. You should not need to use 2nd gear unless you are climbing a steep mountain grade.

 

[bruceb58]

I have a 3.73 in my silverado and I am in 2nd all the time going up hills in CA. Going to Tahoe I am down to 30MPH right before the summit.

Is it safe to run around 3500+ RPM for 15 - 20 miles at a time?

Absolutely fine.

 

[UncleWillie]

People will argue torque all day. It is always about power. Always was!
To pull a 3000# boat up a 10% grade at 60mph (88ft/sec) requires 88 *.10 *3000 = 26,400 ft-lbs/sec = 48hp
48hp is just to lift the boat, not counting wind and tire resistance. In reality, closer to 60-75hp.
Now add the power to pull you and the truck up the hill, and you are talking close to 150hp. The engine has its job cut out for it.

Raising the rpms on the crankshaft, lowers the matching torque to generate the same power.
The faster the engine turns, the lower the torque generated, and the less force seen by the parts of the engine. Pistons, Rods, Bearings.
As long as you don't get close to Red Line, and the Radiator can keep up with the extra heat being generated, rev it up!
It might even run cooler at the higher rpms. Otherwise, just slow down, it isn't a race!

Changing the differential ratios is equivalent to a permanent downshift.
The tires will still turn at the same speed while the engine turns faster.

 

[SDSeville]

Thanks everyone. I think manually downshifting sounds more effective and way cheaper than throwing money at this motor. I just hope I didn't do any damage to the tranny last weekend.

 

[Mi duckdown]

also going down hills shift to lower gear as not having to use your brakes. trans braking.

 

[smokeonthewater]

If you aren't already my solution would be gas pedal closer to the floor... tiny engine big truck and bigger tires.. you need all the power you can get... floor it and let her sing..... IF it still hunts gears then manually downshift and ease up on the throttle enough to keep it below red line....


as for stock parts long gone.... put an add on craigslist.... someone will gladly pay labor at a shop of your choosing to have your lift put on their truck and yours returned to stock with their parts and trading your tires for stockers in better shape would be even easier

 

[Blind Date]

Racing the engine will be tougher on your transmission than the engine. If you don't have one already, I would suggest a trans. temp. gage. Holding 2nd gear and running up engine RPMs will cause your transmission to run noticeably hotter and you'll want to monitor that to make sure you aren't overheating it.

 

[bruceb58]

Racing the engine will be tougher on your transmission than the engine. If you don't have one already, I would suggest a trans. temp. gage. Holding 2nd gear and running up engine RPMs will cause your transmission to run noticeably hotter and you'll want to monitor that to make sure you aren't overheating it.

I notice the opposite. Running in a lower gear with higher RPM usually helps my temp.

 

[smokeonthewater]

Same here

 

[indy440]

Racing the engine will be tougher on your transmission than the engine. If you don't have one already, I would suggest a trans. temp. gage. Holding 2nd gear and running up engine RPMs will cause your transmission to run noticeably hotter and you'll want to monitor that to make sure you aren't overheating it.

thats 100% opposite of what happens.

 

[Captain Ollie West]

thats 100% opposite of what happens.

True statement. manually downshift hold a lower gear and keep the RPMs up. You do not want an auto shifting back and forth between gears. Be patient, if you want to go faster up hills, get a turbo diesel or a larger gas engine. Also, I agree with all of the other posts about the larger than stock tires. You have changed your final drive ratio which does not help.

 

[MTboatguy]

Have you checked with a performance shop to see what they would suggest? There are lots of little tuning tricks now a days that can boost performance for towing or cruising, they may be able to profile your ECM to meet your specific needs.

 

[Blind Date]

Not on my '04 GMC HD gasser.

 

[oldjeep]

Find a 16 year old with the same truck and offer to swap suspension and tires with him