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Wanderer1 · 10-23-2021, 03:02 PM

Hi all, I have a yukon xl with 8.1. I have an 11k camper...going up big hills/long grades I generally try not to hold the rpms past 4k (red line for the 8.1 big block is about 5k I think). 160k miles...engine is midly worked. Am I being overly cautious? I think on i70 in Colorado, I held it at 4k for like 30 minutes straight. Probably one of the more extreme examples. I'm not worried about overheating -- I'm worried about engine failure, especially the crank/rod bearings. I would like to push it 4500. At 4k in 2nd gear on the really big hills, I lose momentum. Perhaps at 4500 I could hold it. Idk. What do u guys think? How far do u Work Horse ppl push them?

donr103 · 10-23-2021, 03:06 PM

What is your trans temp?
As always good luck and let us know what you did and maybe better members then me will help

Wanderer1 · 10-23-2021, 03:48 PM

Engine/Trans temps are fine...monitored in real time with digital aftermarket guages.

Arch Hoagland · 10-23-2021, 05:41 PM

I don't run mine over 4,000 rpm. Max torque is around 3600 rpm.

I weigh in at 25,000 lb with my toad and climb lots of mountains.

At 95,000 miles now with no problems. I do change my oil about every 3,000 miles.

I like going slow up the mountains, gives me a chance to enjoy the scenery....lol

Wanderer1 · 10-23-2021, 05:47 PM

Thanks for your input arch.

tuffr2 · 10-23-2021, 07:32 PM

That engine is not designed to be a spinning engine like a 4 valve per cylinder with dual overhead cams.

I agree with 3,600 rpm as a better rpm to run that engine.

mfire1339 · 10-23-2021, 07:50 PM

3,800-4,000 my max.

Mike

kdauto · 10-23-2021, 09:14 PM

I can't speak much on the 8.1 as I have very little experience on them. As a general rule, you'd want to keep the engine running in the middle of it's max peak HO and max peak torque numbers. 4500 RPM for very long periods on an engine with heavy internals (pistons, rods and such) might be a lot.

I can run my 6.0 gas for 5 to 8 minutes at 5000 to 5500 RPM when climbing hills. Seriously though, unless you're trying to pierce the stratosphere I wonder why you'd be climbing at that speed for 30 minutes or more? As mentioned, the engine and trans would likely overheat at some point.

Bowtie Jim · 10-24-2021, 04:55 AM

You can run it at 4000-4500 rpm all day long .
As long as you have plenty of air to cool it down. And fresh oil.
These 8.1 big block Chevys are stout.
The only downside is they like to suck the gas tank dry.

Boogie_ · 10-24-2021, 06:26 AM

GM 8.1L Vortec L18 V-8 Specs and Information

NevadaNick · 10-24-2021, 06:29 AM

I never had an issue spinning mine that high for long grades other than what was just mentioned mpg. On one trip with a headwind i got 4mpg.

yeloduster · 10-24-2021, 07:26 AM

I live in Colorado and get a chance to do a horsepower check every time I go out!

I'm not shy to run it hard...but...on the up hill I leave the transmission in Drive and place the throttle on the floor and let the transmission, the grade and the engine decide what gear it should be in. On grades like Floyd Hill climbing out of Denver on I70 most of the time my speed is `~32-35 MPH and RPM is ~3500 RPM in 2nd gear. Some parts of the hill are steeper and the speed will fall to ~25 MPH and the transmission will shift to 1st and RPM's jump to ~4500 RPM. When the grade becomes a little less sleep RPM's climb to 4600 RPM and the transmission shifts back into 2nd gear. All the time the throttle is on the floor.

I think your Yukon with its 4L80E transmission is a different animal. 4L80E gear spacing is different than our Allisons. But I think I would do it the same way. You might go up the hill a little slower than holding the RPM's at 4500 but it will be easier on your engine. I wouldn't hesitate to let the engine RPM go to the transmission shift point but I wouldn't hold it there.

I had a Ford F250 with a built 390 CI engine. I didn't hesitate to take it up those mountains at 60 MPH and 5000 RPM in 2nd gear. I was younger then but I never broke it!

Wanderer1 · 10-24-2021, 07:39 AM

Quote:

Seriously though, unless you're trying to pierce the stratosphere I wonder why you'd be climbing at that speed for 30 minutes or more

...40mph for 30 mins is only 20 miles. That's not at all unusual for a mountain pass to be 15 or 20 miles long. And as fuel economy...yeah, I only average 5 or 6 mpg. 37 gallon tank though! So, some of u seem to be concerned about overheating. However, if cooling was not an issue, u still wouldnt recommend pinning it at redline for 30 mins, right? In other words, what else besides cooling/lubrication should be my concern? A friend of mine who had an 8.1 would just hold it to the floor over the mountain passes...no care in the world. Never had a problem. But then another friend said to be careful of spinning a rod bearing above 4k. To be honest, that's really the only thing I'm concerned about... that's why I started this tread. I'm really looking for technical specs of the 8.1 --with assumed perfect maintenance/cooling/lubrication, what breaks when and how under extreme conditions.

Wanderer1 · 10-24-2021, 08:00 AM

yeloduster, thanks...and yes, 4l80e. Wish I had the Allison! At 4k in first gear I'm about 40 mph. Back in the day when she was stock with 3.73's, I would be maxed out at 25mph on some of the passes too. I thought I was killing it. But after switching to 410's and the engine mods, I have been able to take it to redline in 1st gear on every grade so far...but I just can't get the upshift due the Trans spacing.