Need a little help here. I live in Alaska and we only have as high as 90 octane for sale up here. My original plan was to get stage 2, but am scared I might experience quite a bit of knock not being able to run 93. I would think that would also take a even smaller (2.9,2.85) pulley out of the equation. Our air up here is a lot colder, but don't want to risk going kaboom since I can't run 93 octane. Any advice? We don't have much of anything for tuning shops up here, so if anything, I'd be looking at a pre-tuned pcm if I didn't do stage 2. Is it possible to have a tune for 90 octane, or am i just being dumb. What else can be done to reduce knock? Need some help here. Thanks.

 

i know some guys here that have stage 2 and running midgrade (89 octane) fuel with no problems.

 

By no problems, do they have any way to monitor knock?
because my car, with stage 2, intake/exhaust, knocks even with 91 octane
94 is the only fuel that doesnt cause knock in stage 2 IMO.

different with every car obviously....but thats just my experience.

 

Do you have any knowledge with tuning or know anyone (person, shop) that does.

If I were you, I would taylor my car to the environment that it runs in. Seeing as you can't get 93, you can tune to be safe with 90 and then concentrate on other important aspects of power.

My recommendation is flow. Buy a spare head, find a machine shop and either save up and build all at once or build a little bit at a time when money makes it possible. Getting a 3 angle valve job and port and polish on the head will make gobs of power on this engine. Along with a solid intake and 2.5"-3" exhaust, depending on how crazy you want to get, that should make for a strong car.

If you don't want to delve into the inerts of the engine. I still highly recommend having it tuned to run on 90 by someone that knows what they're doing. It's just good practice...

 

Thanks, but I would rather go in the direction of simple power adders. I am a complete noob when it comes to tuning, but there is one shop here that can tune, but has no dyno, so I'm assuming that's more of a guessing game. I was wondering if maybe intense could tune a pcm for 90 octane to run gm stage 2. That way, I keep some aspects of my warranty.

 

You're much better off having a tune done for your exact car. Canned tunes are unspecific and can be potentially dangerous. Not having a dyno is only a safety issue because to log you have to run through all of third gear putting you above 100. I'm sure in Alaska you can safely find a road to wind the car out and not danger yourself and others or get in trouble...

 

WERD! Stage 2 makes about 3-4 degrees (2 if you are lucky) of KR on 91 octane. At 3-4* you can actually hear the knock.

 

I hear ya, but wouldn't running a "canned" tune for 90 octane be safer than running the gm "canned" tune for 93? Thanks for your help. +1 rep.

 

I'm not going to knock any vendors on here, but I'm pretty sure GM has a bigger budget. My point with all of this is that you need to tune for low temperatures/low octane. Something Intense could do for you, but not as well as someone who can sit in your car and log your AFR and KR. It's definately a test-and-tune style, but I'm confident if the guy has any experience with HPT on newer vehicles, he can tune you much safer than a "canned" tune and for probably around the same price as Intense would charge you...

 

So would it be possible to run stage 2 with the gm tune, then monitor a/f and kr with a scan gauge. And since IAT temps will most likely be lower than most states, will that reduce some of the knock? How does elevation factor in, cause we are practically at sea level? Just curious, cause I read that it has an effect as well.

 

Don't the stage 1 & 2 kits come with a label for the gas door to use 91 octane minimum? The stock LSJ seems to run on 87 at least reasonably and there is no requirement from GM to run higher.

That said your best bet is stay with a 3.0" pulley or larger. The 90 octane will be fine for Daily Driving. Get some race gas and throw in a couple of gallons for spirited driving.

 

GM does require Premium, it's in the owners manual. That "loss in power" they describe in the Manual from not running Premium, is the result of knock.

 

So, the pcm can sense knock and will retard timing, correct? So, is the risk loss of power, or damage to the motor? After reading some stuff, it seems like water/meth injection could solve this problem. Is this true? Is it possible to have a low enough IAT in order to make up for lack of octane? Some have said maybe a dual pass setup with a heat exchanger would help also. It really sounds like the key to reducing knock is to reduce heat, so is this a possibilty?

 

KR will result in damage to your motor, and a loss in horsepower.


Please don't rely on Water/Meth.

Yes reducing IAT2 temps will reduce knock, since knock is the motors tendnecy to detonate gas before the spark, as a result of heat.

 

The owners manual says "use 91 or higher for best performance. You may also use middle grade or regular unleaded gasoline rated at 87 octane or higher, but your vehicles acceleration may be slightly reduced."

87 octane is required 91 or more is recomended. The low octane advance tables in the ECM are capable of compensating for 87 octane in the stock tune.

Pierre

 

KR does NOT cause engine damage- KNOCK DOES!! LOL

KR or "Knock Retard" itself is merely the value representing the displacement between the ignition timing values of the High Octane and the Low Octane tables within a particular load cell/site + the amount of any "active" (trimmed) retard. The fact that you SEE KNOCK RETARD should mean that KNOCK is no longer present, providing the values in the Low Table and active retard are sufficient to eliminate it.

To the OP, w/ Stage tune I would recommend using an octane booster for regular driving, then order a 45-drum of 103 Unleaded such as VP Street Blaze for race nights.

Meth injection is another option, but you would want a custom tune for that

HTH
Wop

 

Ok, so if a scan gauge reads some kr, it's pulling timing to reduce the knock back to 0?, So, do the values kr indicate match how much knock is actually being produced? I think I'm starting to figure it out. I think I'll run stage 2 along with a scan gauge and see how much knock it actually produces. With such cold air up here, Im hoping a few cooling mods can reduce it. No one has explained yet, but what role does elevation take on knock. Read it in another thread that it somehow affects it. Im guessing the density of the air plays some sort of factor?

 

the values of knock, as far as i know, are an indication of how much timing needed to be pulled to ensure that your knock sensor stops reading knock. (I dont know if its directly proportional to actual * of timing, i dont think it is)
at that point it then starts feeding the timing back in, as long as it no longer detects any knock.
which is why youll see KR go like this


0..0..0..0..5..5..4..3..2..1..0..0..0

 

Yeah. KR won't hurt your engine, but it is an indication that you could do something to reduce the amount of KR needed to reach 0 knock such as run 93 octane. Although, you could still see some KR with 93 as the computer will also try to advance the timing further for better economy and performance and then having to taper back down to an optimal level.

 

If knock learn was active on our stock PCMs, this wouldn't be a problem, but everything I can monitor tells me its not. No idea why GM would disable it on a factory boosted engine.