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KR.... Educate me please

BrandonHall10

BrandonHall10

Solving problems
Why is it...

From a 40 roll, when I stab the throttle, it drops a gear and I can see the KR spike to 10+ degrees. I let off after a second, but not more than two.
BUT...
From a stop, or even if I'm already moving, if I roll the throttle to 100%, I can run all the way up to the shift with less than one full degree.

Current mods:
E85, 1;9RR's, Headers, 3.1" pulley. The only thing engine/fuel related I changed in the tune was scaling the injectors for E85.

Can someone explain why aggressive throttle entry would cause so much KR, but slow(er) entry would cause almost none? Just looking for knowledge.

Thanks.
 


Look into a thing called burst knock, it's something our computer can't really do.

It's something on the V8 computers.


It's a huge transition from a steady state to a wide open situation, tons of air has just entered the cylinders and lots of times the fuel mixture is not going to be spot on. It's not going to be correct right away and you can see knock appear. Thats just another reason.
 
^^X2. I've heard a lot about this recently as I just asked a mechanic I trust basically the same question. He threw the burst knock knowledge at me too. Sounds about right for where i see the little knock i see.

But the possible burst(s) that i see are only about 1-2 * then it goes away. 10+* even just a burst is worry some. What's your recovery rate on your knock in your tune? Is it stock? If so seeing that much knock must really set your performance back.
 
E85 and a spike to 10* of knock? I don't understand how that's possible...
sub'd for curiosity... : )
 
Mine did this in the early stages of my E85 change over. Im sure that could be a coincidence but when mine does it, it spikes to ~5* and comes down to ~1* or so for the rest of the pull. From a roll, I cant make it knock. Mine only does it when its above 80* ambient though otherwise its a rare so Ive never really trouble shot it.
 


Fivefingerdeathpunch said:
Look into a thing called burst knock, it's something our computer can't really do.
Click to expand...

Interesting reading there. Sounds like the LS guys have had good success tuning it out without any adverse effects.

chrsmi1 said:
10+* even just a burst is worry some. What's your recovery rate on your knock in your tune? Is it stock? If so seeing that much knock must really set your performance back.
Click to expand...

Me too! Not sure what the recovery rate is. Tune is essentially stock, as far as that stuff is concerned.


So am I to assume the KR spike I see is "computer generated," and therefore not actual harmful detonation?
 
^ What he said. It's real, and troublesome. but knowing how it's caused you should be able to avoid it and not damage your engine.

I know it's gonna be hard, It was for me, But roll into it, don't just slam it to the ground and it should be good.

Not sure if reducing timing somewhere in your table could reduce it. Better tuners than me would have to jump in on that one. But you can increase your KR recovery rate from the stock .86 (i think) to 2 or 3 per second.
This at least will make sure it doesn't take you 8 or more seconds to recover when you see that knock.
 
Not that I am a pro by any means but I changed my WOT AFR enable TB% from stock to like ~10% lower.... Again I still see it here and there but it helped.
 


GTPpower said:
No it's actual detonation.
Click to expand...

Well, that certainly changes things.

chrsmi1 said:
^ What he said. It's real, and troublesome. but knowing how it's caused you should be able to avoid it and not damage your engine.

I know it's gonna be hard, It was for me, But roll into it, don't just slam it to the ground and it should be good.
Click to expand...

Exactly. Considering my trans is still bone stock, I probably shouldn't be stabbing the throttle anyway.

gtpsleeper said:
Not that I am a pro by any means but I changed my WOT AFR enable TB% from stock to like ~10% lower.... Again I still see it here and there but it helped.
Click to expand...

I'm still kind of learning/playing with the tuning stuff. I will keep this in mind as I start to dial things in.

blueguy said:
Stranger danger.
Click to expand...

There are so many creepers on here. :)
 
I also get something similar to this. But it happens when I downshift on the highway. If I floor it and as the car downshifts I will see a spike of KR ~2 or less. I have stock pulley with 1.9 rockers and a 3 inch downpipe. I thought this would go away with the new downpipe but I still get the spike. Not sure if this is true knock or just the sensor picking up something when the transmission downshifts.
 
BrandonHall10 said:
Why is it...

From a 40 roll, when I stab the throttle, it drops a gear and I can see the KR spike to 10+ degrees. I let off after a second, but not more than two.
BUT...
From a stop, or even if I'm already moving, if I roll the throttle to 100%, I can run all the way up to the shift with less than one full degree.

Current mods:
E85, 1;9RR's, Headers, 3.1" pulley. The only thing engine/fuel related I changed in the tune was scaling the injectors for E85.

Can someone explain why aggressive throttle entry would cause so much KR, but slow(er) entry would cause almost none? Just looking for knowledge.

Thanks.
Click to expand...

I also posted this in the What did you do to your car thread, but I would suspect the injectors not opening up quickly enough... Reading from your sig I doubt 42# injectors are enough for a 3.1 pulley e85 build. You're probably at 90+% duty cycle at WOT
 
could also be something hitting against the subframe when you slam the gas and it be false knock the knock sensors pick up and once the car is moving the pcm kr recovery continues to count down to zero. the other thing someone mentioned is the converter not unlocking soon enough and the extra load is on there when in boost. i can bet yours is unlocking above 35% throttle. see if you can lower it to either 30% or like mine, around the 25% mark (i start getting into boost at 30% throttle)
 
hensleya1 said:
Reading from your sig I doubt 42# injectors are enough for a 3.1 pulley e85 build. You're probably at 90+% duty cycle at WOT
Click to expand...

Looking through my last scan, I see 69% duty cycle at WOT. I wouldn't think that's a problem.

fst said:
could also be something hitting against the subframe when you slam the gas and it be false...
Click to expand...

Nope. Wide open all around. I even have enough room between the rear O2 and the tunnel to get my fingers between them. I'm fairly certain my motor isn't moving that much. Solid motor and trans mounts, flipped dogbone bushings and poly dogbone inserts. She's solid.

fst said:
the other thing someone mentioned is the converter not unlocking soon enough and the extra load is on there when in boost. i can bet yours is unlocking above 35% throttle. see if you can lower it to either 30% or like mine, around the 25% mark (i start getting into boost at 30% throttle)
Click to expand...

This seems more plausible. The high knock I was seeing was on stock trans settings. I've been playing with them in the tune. I need to make another log. Not buying that's my biggest issue though...

From all the reading I've done about this, "burst knock" seems the most likely. For me the solution is simple: Just roll into the throttle. No more knock. I'm talking less than a half a degree from 0 to WOT, through the shifts... Besides, stabbing the throttle just results in a bunch of wheel spin anyways. :th_laugh-lol2:
 


At different times I suspected the headers hitting the sway bar or something similar.... but the trans dipstick is well away from the headers and there's a lot of clearance between the headers and swaybar. I have new mounts all around and poly's up top, the motor barely moves at all.

The torque converter I also suspected (and it does act squirrely sometimes) But it happens whether the torque converter is unlocked or not... If I'm at 15 MPH in 2nd gear and goose the gas, I get a big spike of knock too. Only thing that bought me some relief was lowering the PE threshold by about 20% across the board which allows me to roll into it... once PE is commanding an 11.2 and it's been there for a half second or so, I can mash the gas the rest of the way and there's no knock all the way through 2nd and 3rd.
 
Is part of that false knock? I'm totally stock now (besides poly motor mounts) and just cruising today on the interstate at 70-75 mph I will get knock readings of 2-3 when I'm going up a small incline still in 4th gear. My vacuum gets close to -1 or 0, so to me it seems like the engine is lugging and won't shift to 3rd. Is that what is causing that knock? Brandon, you might want to get some solid motor mounts to stop you engine from moving around so much. I could see you driving at 40mph, flooring it and going into 2nd WOT, could cause a lot of engine movement.
 
Cymaro said:
Is part of that false knock? I'm totally stock now (besides poly motor mounts) and just cruising today on the interstate at 70-75 mph I will get knock readings of 2-3 when I'm going up a small incline still in 4th gear. My vacuum gets close to -1 or 0, so to me it seems like the engine is lugging and won't shift to 3rd. Is that what is causing that knock? Brandon, you might want to get some solid motor mounts to stop you engine from moving around so much. I could see you driving at 40mph, flooring it and going into 2nd WOT, could cause a lot of engine movement.
Click to expand...

Your KR is likely real. If you get into the throttle a little more, you'll actually build some boost before the car will downshift, especially if you don't have the performance shift option/it's turned off. It's the engine being loaded up. Lugging is not a bad way to put it. You aren't likely to be in PE, so 14.7:1 while having even a small amount of boost is not good.

That all said, a degree or two of KR on a stock car usually isn't the end of the world... these cars almost all have knock from the factory.
 
Cymaro said:
Is part of that false knock? I'm totally stock now (besides poly motor mounts) and just cruising today on the interstate at 70-75 mph I will get knock readings of 2-3 when I'm going up a small incline still in 4th gear. My vacuum gets close to -1 or 0, so to me it seems like the engine is lugging and won't shift to 3rd. Is that what is causing that knock? Brandon, you might want to get some solid motor mounts to stop you engine from moving around so much. I could see you driving at 40mph, flooring it and going into 2nd WOT, could cause a lot of engine movement.
Click to expand...


these cars knock bone stock. i had 8* kr when i was stock. and yup high kr kills the timing advance, and the car falls on its face hard.

it needs to be tuned. case closed. move on nothing more to see here.


till some mods get tossed on.
 
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