Good reason to run a 6.2 on premium fuel

[Geotrash]

Ran across this video while sitting on a Boeing 737, flying home from a work trip for the first time in more than a year.

Anyway, the guy does a teardown on a an auction-acquired 6.2 L92, and makes several comments about it that I did not know. Namely, that these engines apparently frequently suffer from cracked pistons. Seems another good reason to run them on premium fuel. Anyone have any more insight into this one?

 

[intheburbs]

I've never trusted the knock sensors to adjust the timing quick enough to prevent potential engine damage. Mine will never get regular gas. Even when gas was over $4. I never went cheap.

 

[Geotrash]

I've never trusted the knock sensors to adjust the timing quick enough to prevent potential engine damage. Mine will never get regular gas. Even when gas was over $4, as it will be again, I never went cheap.

I’m with you. Both of my 6.2s have only seen premium since I’ve owned them. Especially now since I’m running a black bear premium fuel tune.

 

[swathdiver]

Ran across this video while sitting on a Boeing 737, flying home from a work trip for the first time in more than a year.

Anyway, the guy does a teardown on a an auction-acquired 6.2 L92, and makes several comments about it that I did not know. Namely, that these engines apparently frequently suffer from cracked pistons. Seems another good reason to run them on premium fuel. Anyone have any more insight into this one?

And busted rings too. 6.2s are ten and a half to one compression motors. Running anything other than ethanol or 93 is asking for trouble. Those who frequent the forums see the results of folks saying they use 87 in them all the time. GM should have never said that they can use it because really, they cannot if want the motor to last.

The engines on gasoline do not run a separate set of tables like Ethanol does, they pull timing when knock is detected but advance it again and pull it again and so on. Some of the newer engines by Toyota or Nissan, detect the grade of fuel and adjust the timing and fuel accordingly which gives them different horsepower ratings.

 

[gooffeyguy]

Ran across this video while sitting on a Boeing 737, flying home from a work trip for the first time in more than a year.

Anyway, the guy does a teardown on a an auction-acquired 6.2 L92, and makes several comments about it that I did not know. Namely, that these engines apparently frequently suffer from cracked pistons. Seems another good reason to run them on premium fuel. Anyone have any more insight into this one?

This place is only 6 miles from me, lol.

 

[Geotrash]

And busted rings too. 6.2s are ten and a half to one compression motors. Running anything other than ethanol or 93 is asking for trouble. Those who frequent the forums see the results of folks saying they use 87 in them all the time. GM should have never said that they can use it because really, they cannot if want the motor to last.

The engines on gasoline do not run a separate set of tables like Ethanol does, they pull timing when knock is detected but advance it again and pull it again and so on. Some of the newer engines by Toyota or Nissan, detect the grade of fuel and adjust the timing and fuel accordingly which gives them different horsepower ratings.

That's the thing. I've been an almost daily participant here for the last year and a frequent visitor for years before that and never knew about the cracked piston issue.

Didn't know about not having different tables, but did know how the knock sensors work (or don't ;-)), so thanks for that.

 

[gooffeyguy]

Much like the heater T's at the firewall, I never knew they were a problem until getting on here a few years ago.

I've never had a problem with the ones on my 2001 that I've been driving for 15+ years and just replaced them for good measure 2 years ago when I was back-flushing the heater core.

Like everything, being on a forum like this makes us aware of the parts that are more prone to problems because we hear about it from a handful of the 69k members that are on here that are having a problem with a particular part. But that's just a drop in the bucket of the hundreds of thousands of GM trucks and suvs that have these same parts that have been sold over the years

 

[wsteele]

Kind of a fun business, at least until you have broken your nth engine down.

Also an interesting thread. After reading it and thinking about it, I checked the compression ratio of my LMG 5.3L and in my model year it is pretty darn close to 10:1. Might be 10:1 with as many miles as it has on it, who knows? I always assumed it likely was more like 9:1 or less, given the regular gas endorsement by GM

I have always run 87 Octane (regular) in it, but looking at the close to 10:1 compression ratio it really gives me pause. I was out and about running errands this morning, so I put my cheapo ODB scanner in live mode and watched the timing advance to see what GM does with it with regular gas stated as GTG. For the most part, under load with the throttle on it hard, the timing never got much above 25 degrees advanced, which was comforting. It would pop way up when I got off the throttle to well into the 50+ degree range, but dropped right back down when the throttle was opened again.

It would be really interesting to know how intelligent the timing curve is managed, based on things like knock sensor input, etc. If it is anything like the fuel pressure management in this first model year 2007, I might be disappointed with the answer.

 

[intheburbs]

And busted rings too. 6.2s are ten and a half to one compression motors. Running anything other than ethanol or 93 is asking for trouble. Those who frequent the forums see the results of folks saying they use 87 in them all the time. GM should have never said that they can use it because really, they cannot if want the motor to last.

The engines on gasoline do not run a separate set of tables like Ethanol does, they pull timing when knock is detected but advance it again and pull it again and so on. Some of the newer engines by Toyota or Nissan, detect the grade of fuel and adjust the timing and fuel accordingly which gives them different horsepower ratings.

The part I highlighted in red. I've always looked at my 6.2 as the "hot rod motor." I don't drive like a grandma, but I do treat the engine with kid gloves. The contrast is stark compared to my LY6. High compression aluminum block vs lower-compression iron block HD motor. I couldn't imagine stressing my L9H like I do my LY6, towing heavy and whatnot.

 

[Foggy]

With aluminum heads, compression ratio can be almost a point higher vs iron cylinder
heads given the same combo...
So 10:1 with alum heads is fine with 87 given modern engine controls, etc
Now in the old days about 10:1 is premium octane required with carb, dumb ignition, etc

I love aluminum !! So much lighter. My Small Block Chevy in my Monte SS is an all
alum block (aftermarket block) & alum heads.. It's 11:1 and I'll hit it with 175 nitrous
all on pump 91 octane fuel with no issues..

A lot of times it's the quality of the fuel, not just the octane rating... That's what is
******* engines. From my understanding the fuel around my area - Midwest/KC
is not the best quality. So I generally run some diff types of additional additives
when I know I'm towing hard with my Yukon or just running my stepside/corvette/monteSS
really hard. This hobby is expensive !!!!

 

[wsteele]

With aluminum heads, compression ratio can be almost a point higher vs iron cylinder
heads given the same combo...
So 10:1 with alum heads is fine with 87 given modern engine controls, etc
Now in the old days about 10:1 is premium octane required with carb, dumb ignition, etc

I love aluminum !! So much lighter. My Small Block Chevy in my Monte SS is an all
alum block (aftermarket block) & alum heads.. It's 11:1 and I'll hit it with 175 nitrous
all on pump 91 octane fuel with no issues..

A lot of times it's the quality of the fuel, not just the octane rating... That's what is
******* engines. From my understanding the fuel around my area - Midwest/KC
is not the best quality. So I generally run some diff types of additional additives
when I know I'm towing hard with my Yukon or just running my stepside/corvette/monteSS
really hard. This hobby is expensive !!!!

Ahso, I forgot about the AL heads.

OK, I will quit worrying again.

 

[iamdub]

Ran across this video while sitting on a Boeing 737, flying home from a work trip for the first time in more than a year.

Anyway, the guy does a teardown on a an auction-acquired 6.2 L92, and makes several comments about it that I did not know. Namely, that these engines apparently frequently suffer from cracked pistons. Seems another good reason to run them on premium fuel. Anyone have any more insight into this one?

Kind of a fun business, at least until you have broken your nth engine down.

Also an interesting thread. After reading it and thinking about it, I checked the compression ratio of my LMG 5.3L and in my model year it is pretty darn close to 10:1. Might be 10:1 with as many miles as it has on it, who knows? I always assumed it likely was more like 9:1 or less, given the regular gas endorsement by GM

I have always run 87 Octane (regular) in it, but looking at the close to 10:1 compression ratio it really gives me pause. I was out and about running errands this morning, so I put my cheapo ODB scanner in live mode and watched the timing advance to see what GM does with it with regular gas stated as GTG. For the most part, under load with the throttle on it hard, the timing never got much above 25 degrees advanced, which was comforting. It would pop way up when I got off the throttle to well into the 50+ degree range, but dropped right back down when the throttle was opened again.

It would be really interesting to know how intelligent the timing curve is managed, based on things like knock sensor input, etc. If it is anything like the fuel pressure management in this first model year 2007, I might be disappointed with the answer.

The LMG is advertised as having 9.9:1 SCR. But, GM's actual chamber volumes tend to be a few CCs larger than advertised. So, who knows?!

When my LMG and tune was completely stock, I'd get knock with hard throttle during hot weather on 87. It'd be noticeably less on 89 and non-existent on 91+ (93 is common here). There was a distinct improvement in power and MPG on 91+. I've only used top-tier fuels.

I thought that, back when a similar discussion arose, it was found in the user manual that 91 was recommended for the 6.2. Maybe I'm thinking of the GMT800 with the LQ9? It's "only" 10.1:1 CR, but a Gen3. Maybe it's because the timing control wasn't as strong and/or accurate for that generation. Or maybe I dreamed it all up.

 

[wsteele]

The LMG is advertised as having 9.9:1 SCR. But, GM's actual chamber volumes tend to be a few CCs larger than advertised. So, who knows?!

When my LMG and tune was completely stock, I'd get knock with hard throttle during hot weather on 87. It'd be noticeably less on 89 and non-existent on 91+ (93 is common here). There was a distinct improvement in power and MPG on 91+. I've only used top-tier fuels.

I thought that, back when a similar discussion arose, it was found in the user manual that 91 was recommended for the 6.2. Maybe I'm thinking of the GMT800 with the LQ9? It's "only" 10.1:1 CR, but a Gen3. Maybe it's because the timing control wasn't as strong and/or accurate for that generation. Or maybe I dreamed it all up.

I did a lot of towing in the first 60K miles of its life with an enclosed 5,000 lb trailer. It was all out west (lots of mountains) and while I have always been a "baby it" kind of guy with my Yukon, there were times when I was hauling up a steep grade where I was pretty close to or at WOT, passing a slow moving truck, etc. I never noticed any knocking and I think I am pretty sensitive to those kinds of things, but I can't say for sure. I think for the first 100K this truck only saw Chevron 87 (or whatever the "regular" grade was for that location), so obviously Top Tier, but nothing special I think.

As soon as I get the nerve up to do some runs with the analog fuel pressure gauge taped to my windscreen, I will see how it looks at WOT on a pretty steep grade. It has been hot as hell here lately and for the foreseeable future, so I likely will get a chance at an acid test.

 

[swathdiver]

The 2007-2009 5.3 trio had flat top pistons and a 9.95:1 CR. The 2010-2014 5.3 duo had valve reliefs in their pistons and a 9.6:1 CR.

I used to be able to hear knocking and pinging in my Buicks but cannot hear a thing in the Yukon, can't hear much anyway anymore with tinnitus. So, when checking for such, I use my instruments, err Tech-2 and or Torque Pro app. Been drooling over Banks I-Dash with air density mouse...

 

[1BADI5]

What's more common to break or go wrong with the L94 and LY6 is not the pistons (ring lands) but the cylinder heads.

The issue is how tight the intake and exhaust valves are on the rec port heads; they like to crack between the valve seats. It in turn make them junk or not cost effective to repair.

Bottomline though, if you can't afford to feed it the right fuel......you might want to rethink the purchase.

 

[swathdiver]

What's more common to break or go wrong with the L94 and LY6 is not the pistons (ring lands) but the cylinder heads.

The issue is how tight the intake and exhaust valves are on the rec port heads; they like to crack between the valve seats. It in turn make them junk or not cost effective to repair.

Bottomline though, if you can't afford to feed it the right fuel......you might want to rethink the purchase.

Didn't know this, thanks!

 

[iamdub]

What's more common to break or go wrong with the L94 and LY6 is not the pistons (ring lands) but the cylinder heads.

The issue is how tight the intake and exhaust valves are on the rec port heads; they like to crack between the valve seats. It in turn make them junk or not cost effective to repair.

Bottomline though, if you can't afford to feed it the right fuel......you might want to rethink the purchase.

Isn't this what happened to @mikeyss? I know a valve seat dropped, but maybe it was because the head cracked between them.

 

[Just Fishing]

Kind of a fun business, at least until you have broken your nth engine down.

Also an interesting thread. After reading it and thinking about it, I checked the compression ratio of my LMG 5.3L and in my model year it is pretty darn close to 10:1. Might be 10:1 with as many miles as it has on it, who knows? I always assumed it likely was more like 9:1 or less, given the regular gas endorsement by GM

I have always run 87 Octane (regular) in it, but looking at the close to 10:1 compression ratio it really gives me pause. I was out and about running errands this morning, so I put my cheapo ODB scanner in live mode and watched the timing advance to see what GM does with it with regular gas stated as GTG. For the most part, under load with the throttle on it hard, the timing never got much above 25 degrees advanced, which was comforting. It would pop way up when I got off the throttle to well into the 50+ degree range, but dropped right back down when the throttle was opened again.

It would be really interesting to know how intelligent the timing curve is managed, based on things like knock sensor input, etc. If it is anything like the fuel pressure management in this first model year 2007, I might be disappointed with the answer.

Looking at a stock tune from my old 5.3, its not 100% clear since it's referencing voltages.

[ECM] 12970 - Knock Sensor Threshold Init: Initial learned threshold for knock detection. If knock sensor exceeds this learned value then the engine is considered knocking..

[ECM] 12971 - Knock Sensor Threshold Min: Minimum learned threshold for knock detection. If knock sensor exceeds this learned value then the engine is considered knocking..

[ECM] 2958 - Knock Sensor Transient Mode Airmass: Minimum airmass required for knock sensor transient operation.

Bunch of other tables that reference how sensitive the knock sensors are from there.
This is mostly gibberish to me.

 

[FrankU]

Isn't this what happened to @mikeyss? I know a valve seat dropped, but maybe it was because the head cracked between them.

Dropped valve seats are usually the result of overheating with square port heads.

 

[wsteele]

The 2007-2009 5.3 trio had flat top pistons and a 9.95:1 CR. The 2010-2014 5.3 duo had valve reliefs in their pistons and a 9.6:1 CR.

I used to be able to hear knocking and pinging in my Buicks but cannot hear a thing in the Yukon, can't hear much anyway anymore with tinnitus. So, when checking for such, I use my instruments, err Tech-2 and or Torque Pro app. Been drooling over Banks I-Dash with air density mouse...

Great thought, I will bring along the Tech 2. Lots to look at anyway.