Yeah I know that the setup listed in my signature is different, but I put my GM Stage 2 kit during the winter time, I install as well my stock CAI, stock mount etc...

I'm again on the GM Stage 2 kit and all what we have here is 91 octane gaz.

I did a pull against the famous stock with CAI yellow Cobalt SS/SC (I talked about that in an older tread, that is my friend's one) and what I observe is this:

From 40 mph in 2nd, I pull on him and no knock??? but as soon as we are both in 3rd gear, I dont get any farther and I see knock in my Interceptor gauge, most of the time between 2 to 5 degrees, and during a certain period of time. I get those knocks passed the middle RPM range so when we race, of course, after the 2nd gear we are passed 4000 RPM in 3rd gear and that is where I get some knock.

Could this be because of the 91 octane gaz we have here? I've seen that often in USA, people use 94 octane gaz and because the boost is higher on the stage 2, logically this asks a bit more octane.

Or my plugs? I have the stock one for the stage 2 kit, gapped at 0.36. For the OTTP kit, I use NGK V power 2 step colder, at 0.32.

Well, I don't see any other reasons why he suddenly keep up when we are both in 3rd gear. I'm getting knock and he certainly doesn't get any. He uses as well 91 octane gaz because this is the only choice here in Quebec but because he is stock, no stage kit, maybe 91 octane is enough for not having any knocks.

Also I have to say that of course, I shift at 7K RPM all the time. I don't shift at 6000 RPM from 2nd to 3rd... therefore, I don't think that shifting points is the problem. And I recall, weirdly, I never get knock most of the time in 2nd, that is in 3rd where this is more critical.

What do you think?

 

Its because you're using a 2.7" pulley (I'm assuming you're using the Stage 3 from OTTP since Stage 2 is 2.8" and the fact you're using a Dual Pass endplate). Those agressive stage setups do not like 91 very much. If you can find 93 or 94 somewhere, use that instead.

 

No no no... I said GM stage 2. I even really said that in the title. The 2.7" pulley you see, justly, is for my summer setup. Like I said also, during the winter, I put back my GM Stage 2 kit, that is, with the 3.06" pulley...

To make things clearer, here is my winter setup:

GM Stage 2 kit | stock CAI | CTI header | CTI 3" downpipe | OTTP 2.5" stainless steel catback | OTTP heat exchanger | GM dual pass endplate | Hatrickstu's cooling mod | stock mounts | AEM wideband-gauge | Aeroforce Interceptor gauge | stock boost gauge | ZZP Triple pod A-pillar

This is what I'm using right now. I put that in bold not for you but for other people who will watch the tread too!

 

Try puttin 1 step colder plugs in. I have to change my plugs every 5,000 miles or so because they get beat and I start getting knock, then I replace them and it is gone.

 

yes it's normal with gaz, you need to empty your tank and refill with GAS

 

^^ lol

 

91 ******* yanks. GM states that their stage kit requires 93.

 

Yeah.... GAS!!! You will see often of those misspellings, cuz I'm from Quebec and I'm french. You will laugh a good time sometimes

So I got a vote for 91 octane gaZ (not enough octane for GM' Stage 2 or above)

Oh and for the plugs... good idea. But I checked them today and I forgot that I installed NEW plugs before the winter, instead of keeping my stock ones!!! Those are the NGK BKR7E, 2 step colders, gapped at 0.36. Some black carbon deposit... but they are not bad, they look fine except for all that black carbon.

 

if 91 is all you can get then it sounds like you really need a water injection kit on there to be a knock suppressant

 

too low of octane

/thread

 

So if I recap, it sounds like:

Stock, 91 can be ok.

GM Stage 2, we need at least 94 for 0 knock. 91 can be ok but we can get some knock up top.

For a smaller pulley, 94 is needed, but meth injection is recommanded

And ... for the TVS guys, meth injection or E85 is NEEDED, or you don't pass over 300 whp.

 

Couple things to note.

From a tuning standpoint I and a lot of other tuners can tell you that a lot of gm stage 2 cars WILL knock on both 91 and 93 octane.

If you don't have 93 octane in your area there are a few things you can do to help the issue. Either get a tune, use methanol injection, or use octane booster every time you fill up. Obviously the best solution would be to get tuned + methanol injection and or just a tune.

Firepinch - You can hit over 300whp on the TVS without meth/e85. It's not simple, but it's all in the tune, it can be done without to much stress.

 

Big thanks for your reply Zach06CobaltSC! This tells me somewhat what I thought about my situation, that I have to raise up the octane.

You and other tuners certainly touched some STOCK cobalt ss/sc? Did they have the same knock problem in both 91 and 93 octane? I bet that this is less of an issue when the car is in its stock form... (less boost)

 

Boost is nothing but a restriction of airflow, however it does deal with knock at times also. The main problem with the gm stage 2 tunes is the increase in timing, not the drop of pulley size. I have seen cars run VERY small pulleys with stock timing and have not knocked. Pulleys generally speaking won't cause knock, it's the timing that does.

 

Heat generated from the smaller pulleys will cause knock...

 

Bika - Absolutely, I was breaking it down to a very general basis though. Also depending on how the tune is setup when iat2's hit a certain point timing will be pulled so knock doesn't occur, but yes you are absolutely correct

 

We only have 91 here and before I went meth then E85 I was running a 2.8 on 60's with only a H/E as a cooling mod and it took to 19* all day long. But our 91 may be better than your guys' im not sure

 

19* is not that much for a 2.8".

I set all of my tunes to pull timing at 140 iat2.

 

I know 19* isnt that much on a 2.8 but stage 2 is less than that (barring multipliers) and he is seeing knock on the same gas and a larger pulley. We will blame it on the gas though

 

Thanxs for the replies guys!!

Yeah I'm gonna try some octane booster in order to see what this will do. Anyway, when I will put back my summer setup (so the OTTP kit with the 2.7" pulley), I plan to buy a meth kit.

But I was just concerned for now, because I'm now on the GM Stage 2 kit and those knocks really bothered me. I was not sure to know why I could see those knocks...

And yes, I have heard that our 91 octane gaZ in our province can be often shitty...

 

Old thread I know!! But I just saw that I have knock again with my 2.7" pulley. I'm now with the setup you see in my signature.

The knock get up to 3 degrees during a pull, after 5500 RPM in third gear and then disappear!

I've been datalogued by Trifecta 2 years ago and he said that I had like 1 degree of knock during a pull and it was no big deal. But now I see like 3.

And sometimes, I have only 1 degree. So it's weird!

But I'm quoting your response Bika because I wanted to know if you can see the reducing of timing as KR when it's about IAT2. What I mean is that when you set the PCM to reduce knock after 140F of IAT2, do you see it as KR in the Interceptor gauge?

 

Holy old thread batman! lol

140* does not = knock. It's just a point where I feel is too warm to run optimal timing. It doesnt "reduce KR" but it pulls timing progressively past that point to avoid knock. I never saw any KR due to heat. I also pull boost at similar IAT2 temps. I do this for if the h/e pump quits which sends temps ^


That being said, check your cooler pump. make sure the fluid is circulating.
What is your AFR when you are getting this knock? What are the IAT2 temps?

I recommend getting a dyno / street tune by someone who knows their way around these cars. Canned tunes can be way off.

 

This thread was about when I had my GM Stage 2 setup but now I have the setup in my signature.

But I still have some knock... sometimes. Most of the time NEVER in 2nd gear but when I get some this is often in 3rd gear.

About 1-2 degrees, during a second... my AFR is around 11.9 at that time.

My AFR goes down to 12 until 5500 rpm then goes down to 11.8 at 6000 then 11.6-11.7 at 7000.

 

meh. could be a little richer in the mid range. w0t afr seems ok. nothing that screams "DANGER, Will Robinson!" lol.
I forgot to ask, how many deg of timing are you running?

 

haha cool that's reassuring! Me too I find the tune a bit lean in the midrange... Vince from Trifecta told me that the tune was aggressive in the mid range when he saw my datalog! I bet that the car has more torque than average if I go dyno it! It definitely feels very snappy when you depress the gas pedal at 3000 rpm!

If I'm not mistaken, my timing is only 17.5 degrees at wot. But I think I've seen 18. I will have to check out tonight to see how much I get. But this is definitively around that area!

I swear I could have a meth kit! Bumping that timing to 25 degrees and seing very cool IAT2s. By the way, the phenolic spacer from ZZP will arrive to my door in the following days! It is shipped now! I will tell everybody how much good it is for intake manifold temperatures!