[RESOLVED] Just installed bc272's and now it's knocking

[8urv8]

Just as the title says. I installed the 272's the other day and went out tonight to do some tuning. The log is a 1st, 2nd and 3rd gear pull. I cannot do just a 3rd gear pull because as soon as I put the gas to the floor at 2,000 rpm's in 3rd gear to do the pull, it start's to knock. This is what really bug's me. I can start off in 1st gear like I'm taking off from a light and run through the gear's and it only knock's at the end of 2nd gear and a little at the begining of 3rd. If I'm just cruising and downshift to third and get on the gas, it knock's right away. I've got to check my base timing with a timing light since I took the cas off when I installed the cam's but I marked around it with paint so I could get it back in the right position. I'm also gonna pull the car apart on saturday to ensure the timing marks are all lined up. When I did the cam install, I took the timing belt off and just retimed it. I triple checked all the timing marks before I put everything back together so I'm pretty confident that they are all lned up. This is really bugging me guys. Any and all input is greatly appreciated.

 

[turboglenn]

Is that a 2-3-4 pull or 1-2-3 gear? In fourth when heat soak and internal heat should be causing the most detonation. It looks like it really started the knock when you switched gears the first time. were the wheels spinning after the first shift or anything? It's just odd that you got your best numbers in the higher gears, that would leave me to believe it's not because of a tuning issue, but rather something making noise that the sensor is picking up some times ( in that 2nd gear you logged)

Check that CAS first. I marked mine with a punch right at the gasket surface for the valve cover so i was able to re-align it almost perfectly, but when i checked base timing i was AT 2* BTDC, and because of my particular setup i should be at 10* BTDC...so i was way off 8* anyway, and was loosing a ton of power.

I seem to have a knock that i can't get rid of that I'm starting to think has something to do with my cams after reading about cams causing knock or false knock (I'm not sure). I'm at 20 psi 17* timing through the whole boost range and one cylinder is pulling as much as 7 degrees ( i have aftermarket knock control that only pulls timing on the knocking cylinders.. but I'm starting to think it the cam's making noise in one area of the motor. I'm doing more tuning and testing as it may be that the amount of meth I'm running is just on the border of being too little volume for a mix of almost pure meth and it may be causing more heat and knock while it's being injected.

 

[8urv8]

I'm a complete jackass!!!! My base timing was way off. I thought since I marked the cas, when I put it back it would be right in time......Well that was not the case. Thanks for your input^^^^^^^^^. Later guys.

 

[Black_Bullet]

I'm a complete jackass!!!! My base timing was way off. I thought since I marked the cas, when I put it back it would be right in time......Well that was not the case. Thanks for your input^^^^^^^^^. Later guys.

So the knocking went away.
When i first installed my 272s i was getting 7-8 counts every pull were as pre cams on the same exact tune it wouldnt ever get more than 2 counts which is negligable.

Anyways when your doing logs, its best not to run thru the gears, you can pick up fake knock when shifting, especially when your bouncing off the rev limiter or using NLTS.

Just start at about 3k and floor it in 3rd or ( if you have enough road and is safe enough ) even 4th gear and bring the rpms up to about 7k, or roughly 400-500 rpms higher than whatever your known peak shift point is.
( So for me on my 16g that would be 7k.)..

I like to do 4th gear logs because you are more likely to knock the higher up in gears you go, so i figure if i can get no knock in a full 4th gear pull then theres less chance that 1st, 2nd, or 3rd will knock on me.

Occasionally i go thru the gears when logging, but found that to be inconsistent.
With those cams you are likely to have to pull some timing back between 4-5k the most when you are aiming for even higher boost...
Goodluck.

 

[turboglenn]

I'm glad you got it figured out! Sometimes it's the dumbest things that we humans overlook that cause the most irritation in life (not just in cars)

Black Bullit raised some very good points, but i'd like to add one thing. Tune as he said in the highest gear you can for no knock. BUT...Now when you're roasting tires and bouncing around in 2nd gear, wheel hopping and fighting for traciton and THEN you see that knock, it's most likely coming from a noise being transferred from something else rather than real knock a.k.a. pre-ignition or detonation. So you shouldn't even worry about that type of situation and seeing some aggressive "false knock". But if you're pull is smooth and you see knock it's most likely real

I love to tune in the highest gear avialable to me, as the most TRUE knock will come under the highest loads, as long as it's not being induced by something else making a noise that's similar (like piston slap at high rpm low throttle situations or during shifts) I can do 4th gear pull at 25psi with no knock. But i can drop to 14psi and nail it through 1st and 2nd, then when my front end is dancing and bouncing all over the road i can see a fast 4-7 degrees get pulled by my J&S knock sensor and it's a lot better at distinguishing real knock from false knock. but still will interperet other noises as knock none the less. But it gives my timing back fast, a lot faster than a mitsu ECU.. i get 1-2* back every 20 motor revolutions that it hears less or no noise. Plus i can tune it, and it only pulls the knocking cylinders on an individual basis, so the rest can continue making as much power as possible! (sorry i love the J&S safeguard..can't brag enough about it)

 

[Black_Bullet]

I'm glad you got it figured out! Sometimes it's the dumbest things that we humans overlook that cause the most irritation in life (not just in cars)

Black Bullit raised some very good points, but i'd like to add one thing. Tune as he said in the highest gear you can for no knock. BUT...Now when you're roasting tires and bouncing around in 2nd gear, wheel hopping and fighting for traciton and THEN you see that knock, it's most likely coming from a noise being transferred from something else rather than real knock a.k.a. pre-ignition or detonation. So you shouldn't even worry about that type of situation and seeing some aggressive "false knock". But if you're pull is smooth and you see knock it's most likely real

I love to tune in the highest gear avialable to me, as the most TRUE knock will come under the highest loads, as long as it's not being induced by something else making a noise that's similar (like piston slap at high rpm low throttle situations or during shifts) I can do 4th gear pull at 25psi with no knock. But i can drop to 14psi and nail it through 1st and 2nd, then when my front end is dancing and bouncing all over the road i can see a fast 4-7 degrees get pulled by my J&S knock sensor and it's a lot better at distinguishing real knock from false knock. but still will interperet other noises as knock none the less. But it gives my timing back fast, a lot faster than a mitsu ECU.. i get 1-2* back every 20 motor revolutions that it hears less or no noise. Plus i can tune it, and it only pulls the knocking cylinders on an individual basis, so the rest can continue making as much power as possible! (sorry i love the J&S safeguard..can't brag enough about it)

Yea thats pretty cool...