New, to me, 2008 Silverado with tons of KR with 87 or 93 octane gas

[dr.mike]

Had this on an 02 6.0L. Turned out to be an air leak in the intake track between the throttle body and the MAF sensor.

[rel3rd]

Had this on an 02 6.0L. Turned out to be an air leak in the intake track between the throttle body and the MAF sensor.

Good find.
Unfortunately, mine did it with factory gigantic air intake "tube", as well as with the Airaid simple intake tube that replaced it.

[ChopperDoc]

i am going to follow this thread. i have a 05 with a bit more kr on 87 that you and more often. i did manage to blend some e85 and noticed a major decrease in kr ( down to a max of 2 deg and less often.

Lots of things cause knock. Obviously fuel is the primary culprit, because octane rating on gasoline is literally defined as that particular fuel's resistance to knock, in percent. 87 is 87% resistant to knock, and 100 is technically 100% resistant. Of course other real world factors contribute, so even fuels over 100 octane can knock if you have other things going on in the cylinder. Another consideration is the method the rating is reached. Has to do with the way it's tested. You have Research Octane (RON) and Motor Octane (MON). The motor octane test is more strenuous, because IAT of 300F is used. So that means even 93 could be just as volatile as say 89 IF the RON was high enough, and the MON was "equal." Moral of the story is fuel type is massively important.

So here is the list of things to be looking at...

1. Fuel type (duh)
2. AFR (try to keep it on the richer side, as this cools the cylinder surfaces)
3. Spark plug heat range and gap
4. Mechanical issues (vacuum leaks and oil leaks)
5. High IAT's
6. If it's real or not. False knock can drive you crazy. Look for stairsteps like his logs above, because that's real. False knock shows as "blips" and doesn't stick around more than a few milliseconds.

Easy tests are to simply put some good fuel in there, like 110 or 116 race gas and see if it's still registering. With stock"ish" internals, and conservative compression ratio/boost and timing, any knock you see on straight race gas can be considered false at that point, provided the other things are true.

Also, if possible, pull your plugs after a full throttle pull, if you can do this. To do it right, you want to get the engine off as soon as possible after full load pull, safest at track or on dyno. Then pull your plugs and look for the timing mark, and heat marks. Timing mark should be on the bend, and the heat mark should be right next to it. If the heat mark (discoloration) goes all the way to the base of the ground strap, then your plug is too hot. If the discoloration does not reach the bend, then the plug is too cold. If there is gray or silver shiny stuff on the porcelain, that's piston. If there's black stuff (specks typically), then it's oil. If there's both, then it's both. Make sure you use a magnifying glass and really have a look at them.

Plugs will tell you the real story if you are having issues figuring out if your sensors are lying to you. Not all of them are honest, so keep that in mind.

[rel3rd]

I run straight E85 now, using a sensor for ethanol content measurement. Still gets better MPGs than my old truck, and has zero knock under any load...even with all of the flex fuel added timing. So far, more cost effective than premium unleaded

Actually converted my Trans Am to E85 as well. For $2.25 gallon, better option than $3/gallon 93 pump, and 110 race gas mix.

[ChopperDoc]

I run straight E85 now, using a sensor for ethanol content measurement. Still gets better MPGs than my old truck, and has zero knock under any load...even with all of the flex fuel added timing. So far, more cost effective than premium unleaded

Actually converted my Trans Am to E85 as well. For $2.25 gallon, better option than $3/gallon 93 pump, and 110 race gas mix.

Really glad you got it figured out. E85 is very tempting to me for my own car. I don't have knock issues, but I'm just a hair under 12:1 SCR, so boost is kind of out of the question... well.... unless...LOL.

Don't think my wife would approve another parts list at this time, especially a blower of some kind, yet another fuel pump and even bigger injectors. Would still be pretty badass to throw 6 PSI at a 12:1 427 stroker on E85 LOL. Might have to add some heads to the list to get my compression back down, but it still sounds like a good time.

[rel3rd]

2 years ago, my car was a turbo car. Same engine now, so low on the compression for me, lol.

The E85 seems to make my car run more consistent as well. First time out, drove 45 miles to track, entered the "Street Legal" class and made it to the finals...then choked, lol.

Still havent gotten a handle on the Nitrous/E85 tuning yet, but have finally caved in to tuning with Lambda instead of AFR. WOT commanded lambda advice is all over the place, both N/A and Nitroused, so have some dyno time coming up to figure it out myself. It seems to like 1.20 PE (.80-.82 lambda) on motor, and as rich as .72 lambda on a 150 shot so far street tuning it...

So far am loving "race gas" for $2.25/gallon.

Curious to see how the truck tows this Saturday, since I'll be hauling the car to the track for the 1st time since converting.

Using a GM sensor on both, FWIW.

[GrannySShifting]

I run straight E85 now, using a sensor for ethanol content measurement. Still gets better MPGs than my old truck, and has zero knock under any load...even with all of the flex fuel added timing. So far, more cost effective than premium unleaded

Actually converted my Trans Am to E85 as well. For $2.25 gallon, better option than $3/gallon 93 pump, and 110 race gas mix.

Hello, and welcome to 2010 Bob haha

The newer 5.3s make a good bit more than the old ones, have higher static compression etc They will not take 28-30 degrees timing like some of the old ones will. Oil consumption definitely hurts too

Its a wash in cost running 93 vs e85, with fuel mileage factored in your spending more than if you just put 93 in it likely but alot wider tuning window at least. Run it optimal on e85 and do whatever you have to do with timing on 87 to keep it from knocking and call it a day (obvoiusly it was knocking since it went away with better fuel)

[rel3rd]

Hello, and welcome to 2010 Bob haha

The newer 5.3s make a good bit more than the old ones, have higher static compression etc They will not take 28-30 degrees timing like some of the old ones will. Oil consumption definitely hurts too

Its a wash in cost running 93 vs e85, with fuel mileage factored in your spending more than if you just put 93 in it likely but alot wider tuning window at least. Run it optimal on e85 and do whatever you have to do with timing on 87 to keep it from knocking and call it a day (obvoiusly it was knocking since it went away with better fuel)

Thanks Pal...LOL.
If I didn't literally just have a RoFo open up at the end of my street that sells Flex Fuel, I'd still be back in 2009...lol.
I got rid of my 8-71 blown big block Chevelle because it made no sense to drive 45 minutes away to get fuel for a turd that gets 3 mpg's on E. Now it is local for me...whole new ball game.

On the truck, I think I'm going to try running 1/2 unleaded 87, and 1/2 Flex.
E-40-ish "should" command a low 12:1 afr, which should gain a little mpg back, but still have enough combined octane to keep it happy.

For it to not get any KR, with 87 only, I had to take a ton of timing out, which pretty much negated using it because then I needed to give it a ton more throttle to get and keep it moving.

I did install a catch can on it, but still haven't done the SeaFoam smoke show to clean out the intake.

I wasn't too worried about it because I thought any residual oil/carbon buildup inside the engine (post injectors) would be easily handled by the E-85?

[GrannySShifting]

Thanks Pal...LOL.
If I didn't literally just have a RoFo open up at the end of my street that sells Flex Fuel, I'd still be back in 2009...lol.
I got rid of my 8-71 blown big block Chevelle because it made no sense to drive 45 minutes away to get fuel for a turd that gets 3 mpg's on E. Now it is local for me...whole new ball game.

On the truck, I think I'm going to try running 1/2 unleaded 87, and 1/2 Flex.
E-40-ish "should" command a low 12:1 afr, which should gain a little mpg back, but still have enough combined octane to keep it happy.

For it to not get any KR, with 87 only, I had to take a ton of timing out, which pretty much negated using it because then I needed to give it a ton more throttle to get and keep it moving.

I did install a catch can on it, but still haven't done the SeaFoam smoke show to clean out the intake.

I wasn't too worried about it because I thought any residual oil/carbon buildup inside the engine (post injectors) would be easily handled by the E-85?

I dont think running e85 will clean it up anything like seafoaming it will

That prob what Id do split it 87 and ethanol.

[5FDP]

E85 will clean it up more than you think. It does wonders for cleaning up intake runners and piston tops.