I'd like to preface this by saying that I don't have recent first-hand experience here -- this question stems from "complaints" from my wife. We have a 1999 Suburban with the Vortec 7400 big block. This is a 3/4 ton truck, towing capacity is 10k lbs and it has transmission cooler, power steering cooler, etc. It's our tow vehicle for a 2 horse trailer -- it's got plenty of capacity for what we're towing. I'm think it's got a 4.10 rear for the benefit of towing too.
We live near a pretty big hill, about 3 miles of 7% grade, and she's gotta tow up that hill in order to get to one spot she goes riding. She feels like the truck doesn't have enough power. Now, I'm sure it is a little worn out given it has almost 170k miles on it (we've only had it for a few years and 10k miles or so though) but I think it just sounds like it's working because of the low gearing, 4 speed transmission, and lack of sound deadening.
Given the 4 speed, there aren't that many choices if you want to move at freeway speed. Not a problem on the flat, but on the grade this can be annoying. She doesn't want to drive up at 35 mph if it can be avoided. I told her if it doesn't want to pull in 3rd gear, just to drop it 2nd and drive up at 50-55 mph at 3500 RPM. But then, I'm used to cars with small, revvy engines. Is this appropriate treatment for a big block or should I just tell her to take it easier and go up at whatever speed 3rd gear will allow? There's no redline marked on the tach but under heavy throttle it will shift at around 5000 RPM IIRC. Torque peak is around 3200 RPM.
Is this working the truck too hard?
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yep 3500 rpms is fine. they put these engines in boats and run them at 5000rpm
55-60 should be at least 3rd if not 4th w/o od
For only 3 miles I'd let it sing at 3500 rpm. Your right at max torque and with the shift point at 5k your more than likely safe. In a gasser it's usually better to rev than lug, especially in today's newer engines. Also leaving it in second might save the tranny from shifting a lot on the hill.
Originally Posted By: volk06
For only 3 miles I'd let it sing at 3500 rpm. Your right at max torque and with the shift point at 5k your more than likely safe. In a gasser it's usually better to rev than lug, especially in today's newer engines. Also leaving it in second might save the tranny from shifting a lot on the hill.
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Let her rip. I ran my old 89 big block for lots of years towing over the rockies at 4 grand for miles, never missed a beat. The guy who owned it before me towed 12,000 lbs with it for the first 56,000 thousands miles of it's life. the remaing 124,000 miles I put on it was about 90 percent towing a 8000 lbs 5th wheel.
Vantage in Washington is 10 miles of 4 to 8 percent grades. I used to do that one pedal to floor BBC screaming and the 3 speed hitting right around 200 degress with the huge tranny cooler. Sometimes I miss that sound.
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You are not working it at all...
I run my 7.4L in my boat for 30+ minutes at a time at full throttle at 4400 RPM...no worries at all. Its still an under-stressed engine at that power level, and can do that all day long.
Get a Scangauge to monitor critical temps if it worries you. I don't think 3500 RPM will be doing any damage.
Sometimes when towing with my truck I have to let the engine run at around 3000-3500 RPM because I don't want to use OD when towing. Even though the engine makes a lot more noise at that RPM, the Scan Gauge indicates it's perfectly happy running at that speed. Engine temps don't go above 200* and the transmission temp is the same as it would be with no load.
"...about 3 miles of 7% grade"
At 35mph that boils down to a little more than 5 minutes, 15 seconds...
Pulling a two horse trailer up the hill.
Sounds about right to me. What is her problem specifically with this? Are people behind her honking to get her out of the way?
Have her give them the "1-fingered Salute". Are you supposed to buy a new 1-ton Diesel @ $40K to go 55 mph?
In no way is this "working the truck too hard". It is what it is designed for. I bet it has no problem going down the hill.
Cheers!
So it won't hold speed up the hill?
How fast would you like to go?
Is there really something wrong?
I don't think there's anything wrong with it -- it pulls up the hill fine and will pull up in top gear at the right speed when it's not loaded or towing. Honestly it probably will pull up most of the hill in 3rd but I bet it would hunt a bit and IMO locking it in gear is better than that.
This is partially impatience but also partially just about getting up the hill with a minimum of trouble. If you don't want to go 35 with the semis, then it's nice to go fast enough to not have to slow people down when you pass the semis -- which requires at least 55 or so most of the time. 35 mph would be fine w/ me but if the truck's OK with 55 then it's easier just to give that my blessing than try to convince the wife to go slower 
Good to hear it's not a problem though.
Good to hear it's not a problem though.
Originally Posted By: Norm Olt
"...about 3 miles of 7% grade"
At 35mph that boils down to a little more than 5 minutes, 15 seconds...
Pulling a two horse trailer up the hill.
Sounds about right to me. What is her problem specifically with this? Are people behind her honking to get her out of the way?
Have her give them the "1-fingered Salute". Are you supposed to buy a new 1-ton Diesel @ $40K to go 55 mph?
In no way is this "working the truck too hard". It is what it is designed for. I bet it has no problem going down the hill.
Cheers!
This brings up a question; some vehicle lose speed going up the grade but others do not or lose very little. This is when the throttle is held steady and there is no up shift. Does that depend upon the vehicle weight and the available engine torque at that particular rpm/speed?
3500 is nothing, in boats you run 454's at that or 1k rpm more all day long.
Boats work engines much harder than any truck can. Well maybe if you hooked 10k pounds up to it, blasted the AC, and ran it up a 10% grade all day at 4k RPM. That's about how they run on the water. That's also why gas marine engines are shot at 2k hours or less.
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we run a BBC stroker that started out at 572 CI at much higher speeds than that.
Not going to hurt anything. probably good for it as long as everything is sound.
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