Is there a "replacement for displacement"? 8.1 vs �6.2

davefr · August 6, 2015

My '06 Sierra 2500HD was the last year of the big block 8.1's w/Allison. I love the truck and it's low mileage and in great shape. I don't care about the 12.3 MPG because it's not a daily driver. My 8.1 does have a tune.

I'd kind of like some of the new '15/'16 creature comforts and improvements and don't really need the 3/4T payload.

Does the 6.2 with 8 speed A/T approach the 8.1 in "butt dyno" performance? I'm not reading very favorable reviews here. (at least w/o a tune)

Has anyone owned both?

TIA

bdbake01 · August 6, 2015

The accuracy and repeatability of butt dynos is highly questionable.

Also, some are larger than others.

TJay74 · August 6, 2015

So you are asking if a 330hp 8.1L is going to feel faster than the 430hp 6.2L? I am pretty sure the 5.3L would walk the 8.1L with no issues, the 6.2L would be a walk in the park. BB or not, the 6.2L make more HP and TQ than the 8.1 all day long.

smrr1 · August 6, 2015

the 6.2 will kill the 8.1 on acceleration but if you like your torque from idle you will be very disappointed. the new motors make great power and get great mpg but don't make power until they get on up in the rpms.

fondupot · August 7, 2015

the 6.2 in the 1/2 ton bill blow the doors off an 8.1 3/4 ton all day long.

Robert.jean1 · August 7, 2015

I think the Butt method you speak of concerns feeling torque. Your truck stock has 330 HP but 450 lbs torque. The new 6.2 has 420 HP and 460 lbs torque. So my opinion is your butt dyno will read close to the same except for the 1500 obviously being way lighter than your heavy 2500 but must consider your gear ratio as well.

TJay74 · August 7, 2015

the 6.2 will kill the 8.1 on acceleration but if you like your torque from idle you will be very disappointed. the new motors make great power and get great mpg but don't make power until they get on up in the rpms.

This is not even remotely correct, the new 6.2L makes the max 460ft lbs of torque at 4100rpm, but it has a good majority of the torque ready from 2100rpms and up. Now the LT1 in the Vette makes its torque a little higher, but not much. By design the big small blocks tend to make a good amount of power and torque well into the area under the curve.

crushNchowda · August 7, 2015

your truck probably weighs solid 1200 lbs more and is down almost 100hp and has less torque, doesn't have direct injection or the snappy shifting of a new 8 speed auto

You should already know the answer

I would imagine a 5.3 truck that has the 3.42 gears is quicker, I KNOW a 5.3 truck guzzling E85 w/ 3.42 gears is quicker, and a 5.3 chugging E85 w/ max tow 3.73's may actually be dark horse/sleeper fastest 1/2 ton gasser GM makes period.

I am not even sure an iron block 7200 lb HD w/ the 8.1 would be quicker than one of the new 4.3 trucks. I'm not being a jerk I'm just being realistic

BBRU · August 7, 2015

The accuracy and repeatability of butt dynos is highly questionable.

Also, some are larger than others.

LOL

davefr · August 7, 2015

the 6.2 will kill the 8.1 on acceleration but if you like your torque from idle you will be very disappointed. the new motors make great power and get great mpg but don't make power until they get on up in the rpms.

That's really my concern. The 8.1 comes on real strong right after idle but is not a high reving engine. I don't care if the torque curve on the 6.2 is at the high end because that's not where you spend a lot of time driving. (unless the new 8 speed gets you in that band quickly). Torque between idle to 2500 RPM is really what you feel the most in all around driving.

That's also why I hated the Duramax. They're wonderful on the highway but feel like slugs in all around driving.

Just curious how the 6.2 performs and I know there's also the weight advantage to take into account going from 3/4T to 1/2T.

crushNchowda · August 7, 2015

That's really my concern. The 8.1 comes on real strong right after idle but is not a high reving engine. I don't care if the torque curve on the 6.2 is at the high end because that's not where you spend a lot of time driving. (unless the new 8 speed gets you in that band quickly). Torque between idle to 2500 RPM is really what you feel the most in all around driving.

That's also why I hated the Duramax. They're wonderful on the highway but feel like slugs in all around driving.

Just curious how the 6.2 performs and I know there's also the weight advantage to take into account going from 3/4T to 1/2T.

weight is HUGE - take a look at the camaro SS, it weighs nearly 4000 lbs (like 3800 i think) and compare it to an old LS1 Z28 or WS6 firebird - the new camaro has 430HP the old ones had 350 HP and best stock 1/4 times are nearly identical - high 12's - reason? The LS1 cars have a 4-500 lb weight advantage

Even more extreme is my C5 Z06 which is a high 11 second car stock w/ only "405hp" (granted it may be more like 425) - but it only weighs 3100 lbs

The torque curve for the new LT1 is pretty damn flat, I haven't seen results for the truck platform, but in vettes it makes over 360 to the wheels @ idle, and peak torque hits around 4000rpm, but its not much higher - like 400-410 @ the wheels dropping off around 5300 rpm

I would imagine in the trucks the torque hits @ least as early and probably looks even flatter

kstruckcountry · August 7, 2015

I'm betting a tuned 8.1 with the 6 speed Ally will feel more powerful than the new 6.2. Will it be? Not necessarily. But the 8.1 will out tow a 6.2 hands down.

gone_fishing · August 7, 2015

I think both the new 5.3 and 6.2 have good torque "down low" but it's so dampened by the computers torque management that you would never know. I bet a new 6.2 with a tune would feel as snappy and possibly even snappier then 8.1 big block.

smrr1 · August 7, 2015

This is not even remotely correct, the new 6.2L makes the max 460ft lbs of torque at 4100rpm, but it has a good majority of the torque ready from 2100rpms and up. Now the LT1 in the Vette makes its torque a little higher, but not much. By design the big small blocks tend to make a good amount of power and torque well into the area under the curve.

His question comcerns the "butt dyno". Have you driven both? I have. Owned a 14 6.2 for a year. The 8.1 feels like it will blow the tires off or up root a large tree idle-2,000 rpm. The new 6.2 while very powerful is a dog below 2,000 rpm. All the new trucks are thanks to torque management. Old school vs new school. While i miss the old V8 style power delivery i have gotten used to the new motors. Just don't be affraid to wrap up the rpms if you want to get in to the power. GM might publish certain numbers but those are absolutely useless if the computer will not allow you to put it to the ground.

The 6.2 is more powerful, has more torque, and will out run the 8.1. My post is referring to how you feel the power being delivered and at what rpms. Don't think everyone is running around at 4,000 rpm to be able to utilize all the torque of the new motors. However i think we all use idle-2,000 rpm all the time.

Jon A · August 7, 2015

But the 8.1 will out tow a 6.2 hands down.

No, not even close. While the impressive torque right off idle, lack of torque management, etc, will certainly make the 8.1 feel better at low speeds, if you charge up a really steep hill with a really heavy trailer the 6.2 will blow the 8.1 away. You just can't fake 100 extra HP.

Now if you're just talking about "feel" at part throttle, yes the 8.1 will probably feel better as it does have the torque advantage up to 3500 RPM or so. It will pull things at 1/2 throttle more easily, staying in a higher gear at lower RPM and seem to get the job done more easily. But when tested in the extreme, the 6.2 will be able to maintain a higher speed up a hill with a heavy trailer.

To the OP: Even with a tune, don't expect the 6.2 to feel like the 8.1 right off idle. It'll feel good, but not quite that torquey. However, how it feels on your "butt dyno" will mainly depend on how long you keep your foot to the floor. The first 1/2 second or so and/or initially spinning the tires might go to the 8.1...but after that it's all 6.2. It'll keep you pinned in your seat long after the 8.1 feels like it has run out of gas.