Desensitizing Hellcat Knock Sensors

[16GoManGoHC2]

I have a compressor to so. I just don't have the tool to test. I see harbor freight has one for $70 but I'm not sure how much I would trust that. I have to have a friend with one.
Edit friend down the road has one

Your going to need a compressor a bit bigger then those little pancake ones like the 99$ Harbor Freight one, I tried mine because I didn’t want to fire up the big one but the little one would not keep up and give a stable inlet pressure long enough to get a good and accurate reading, especially if your having more then 2-3% leak down. Stock Hellcat engines are built tight, mine when it was happy had only 1/2% leak down per cylinder, 100 in 99.5 out. It is one of the things that kill them when pushed beyond factory HP levels especially if you rattle them knocking, stock ring gap is around .014-.020 and when you rattle them the rings unseat and you now blow by super hot combustion gases which heat the rings up even more and they butt and get even tighter in the cylinders and get even hotter expand and pop the weakest part of the piston out which is around the valve reliefs and the ring face delaminates and losses seal and runaway train from there. See the slight blips of Kr in the midrange? It would not go away after the -14 degrees of Kr that resulted from not using octane booster one tank for tuning purposes, only happened once, I felt it and heard it and got out of it but the damage happens in a second at 4-5000 rpm’s.

 

[Speedy!]

People like to ding me for trying to sound like a pro tuner, so take what I say as being from a NON PROFESSIONAL LOL. I'm just some guy on the internet that plays with this stuff trying to learn more about the platform after all With that out of the way, I enjoy these types of technical discussions.

When I had the new RE engine put in, I started with a base tune and set all the knock sensor values to stock settings including the Knock Window. Testing for STKR I would see 4-6 deg if STKR at 4,000 RPM on a commanded timing of 6 deg. This was running 109 octane, so I knew it was likely impossible to be real knock. The STKR was because the knock sensors would hit right around 2V at 4,000RPM. I started with the knock window and it helped but at 4,000 I still needed to tweak the thresholds a bit. Once I had 4,000RPM pretty well sorted (I may see .5 deg stkr occasionally which tells me the sensors are still listening) I looked for other areas and right around 2,000 did the same thing, just not as severe. Fueling was confirmed and triple confirmed as good at .82 - .83 lambda which is what I wanted for gasoline so I knew it wasn't some lean condition causing it. I even went as fat as .78 lambda just to see if it mattered, and it did not. I have dozens of logs as I dialed in the thresholds over about 3 weeks of testing.

When my original engine failed, I suddenly got 14 deg of STKR and the car fell on it's face. Luckily this happened at the drag strip in a controlled (mostly) environment. After that 14 deg STKR happened, it did it every time after that in the same spot of the run (right after shift to 5th) until the engine popped which happened 3 runs later. On the run it broke, it happened at the shift to 2nd instead of 5th so something was getting worse each time.

Originally we thought the exhaust was hitting or something as the engine sounded just fine, but in the end I suspect a rod bent, a piston skirt cracked, or both. Logs never showed any knock before this happened, but I did find some plugs with the electrodes melted and I think one had plugs with cracked porcelain which some folks believe was indicating knock. I'm not sure if that could have happened during the failure though since the tune was actually very conservative. When the engine failed all the temps shot through the roof and when an engine pulls a bunch of timing things heat up very quickly.

The only other time I had something like that happen, I was making a final pull testing E85 and right at the 4-5 shift got 14 deg of STKR. I seriously thought I'd hurt the motor. Got home and started checking things and found the bell housing inspection plate bolt had backed out 1/2" and the plate was clanging on the bell housing. Put some blue loctite on the bolt, tightened down, and went and made 3 more tests, no more STKR (thank God).

OH and P.S. - When my car was bone stock I have logs of it on 93 getting 4-5 deg of STKR at the track. I dumped in 5 gallons of RM109 and knock dropped to .5 to 1 deg. That's why I never recommend anyone race these cars on 93 octane gas much less 91. In later model years the timing maps have been reduced quite a bit on the Hellcat vs my 2016 model, but still better safe than sorry. It's entirely possible that knock bone stock helped end my original motor.

 

[jonx96]

People like to ding me for trying to sound like a pro tuner, so take what I say as being from a NON PROFESSIONAL LOL. I'm just some guy on the internet that plays with this stuff trying to learn more about the platform after all With that out of the way, I enjoy these types of technical discussions.

When I had the new RE engine put in, I started with a base tune and set all the knock sensor values to stock settings including the Knock Window. Testing for STKR I would see 4-6 deg if STKR at 4,000 RPM on a commanded timing of 6 deg. This was running 109 octane, so I knew it was likely impossible to be real knock. The STKR was because the knock sensors would hit right around 2V at 4,000RPM. I started with the knock window and it helped but at 4,000 I still needed to tweak the thresholds a bit. Once I had 4,000RPM pretty well sorted (I may see .5 deg stkr occasionally which tells me the sensors are still listening) I looked for other areas and right around 2,000 did the same thing, just not as severe. Fueling was confirmed and triple confirmed as good at .82 - .83 lambda which is what I wanted for gasoline so I knew it wasn't some lean condition causing it. I even went as fat as .78 lambda just to see if it mattered, and it did not. I have dozens of logs as I dialed in the thresholds over about 3 weeks of testing.

When my original engine failed, I suddenly got 14 deg of STKR and the car fell on it's face. Luckily this happened at the drag strip in a controlled (mostly) environment. After that 14 deg STKR happened, it did it every time after that in the same spot of the run (right after shift to 5th) until the engine popped which happened 3 runs later. On the run it broke, it happened at the shift to 2nd instead of 5th so something was getting worse each time.

Originally we thought the exhaust was hitting or something as the engine sounded just fine, but in the end I suspect a rod bent, a piston skirt cracked, or both. Logs never showed any knock before this happened, but I did find some plugs with the electrodes melted and I think one had plugs with cracked porcelain which some folks believe was indicating knock. I'm not sure if that could have happened during the failure though since the tune was actually very conservative. When the engine failed all the temps shot through the roof and when an engine pulls a bunch of timing things heat up very quickly.

The only other time I had something like that happen, I was making a final pull testing E85 and right at the 4-5 shift got 14 deg of STKR. I seriously thought I'd hurt the motor. Got home and started checking things and found the bell housing inspection plate bolt had backed out 1/2" and the plate was clanging on the bell housing. Put some blue loctite on the bolt, tightened down, and went and made 3 more tests, no more STKR (thank God).

Well I always joke with friends we are youtube certified mechanics Since you are the one making the video I'm not sure what level of certification that is but it's pretty good.

@16GoManGoHC2 I have a lot better compressor than a harbor freight 90 dollar one. I think Mine was in the 300 to 500 dollar range from menards My neighbor has a really big compressor if mine isn't enough but I'm sure it is. I'll do a smoke check again. I'll chase on the Busa with a go pro on my helmet. Darn for not having a dyno so I have to be creative

 

[Speedy!]

If doing the smoke check on the highway, you're just going to see a very quick "whiff" from one or both tail pipes. It may not be obvious until you closely review the video. Easier to see on the dyno, but I've watched cars at the drag strip and I can see it pretty obvious especially when the sun is shining on the back of the car.

 

[Mean Cat]

Are most desensitizing knock sensors on these cars? I see a fair amount of STKR on take off with a 2.85 and e85 using stock timing down low. Ramping it in up top I get no STKR. I feel I should be able to add 5 to 7 deg down low without getting any STKR.
I'm thinking I'm going desensitize a little to a little bit in the ranges I am seeing the KR.

I think most tuners DO desensitize knock sensors with pulley change & cat deletes or headers. A lot of the STKR is false knock. Just don't want to go too far.
I think mine are set at 20% desensitized.

 

[fumanchu182]

Thank you all for this thread. Dealing with this now. Tonight is a track night, I’m putting in a 104/116 blend (screw my cats). Lets see how she does.

 

[16GoManGoHC2]

Thank you all for this thread. Dealing with this now. Tonight is a track night, I’m putting in a 104/116 blend (screw my cats). Lets see how she does.

Give her hell!! I think tonight’s going to have the air to net you your 9 second pass!! 🤞🙏

 

[jonx96]

Thank you all for this thread. Dealing with this now. Tonight is a track night, I’m putting in a 104/116 blend (screw my cats). Lets see how she does.

Full Send!

 

[Speedy!]

Good luck the Q16 should make things obvious. Use the entire can and get as low as possible on 93. Less than a quarter tank.

 

[Hickster]

Like I deem myself, and others do, I am a street mechanical engineer. I, myself, and I have been de senc itized since my divorce. 1993.