Bypassing knock sensor? And.......reducing e/t's.
Burning Brakes
Joined: Sep 2001
Posts: 1,013
Likes: 9
Originally Posted by Sinister87
lowering the crown nuts on your spring, to help with weight transfer(this gave me 3/th's at the track)
Thread Starter
Racer
Joined: May 2004
Posts: 392
Likes: 0
From: VA
Yes, lower the crown nuts on the bolts,this gives the rear leaf spring more suspension travel, helping weight transfer. This advice was given to me several years ago (1997) by Ron Bilyeu, owner of Pro Auto Tech, out of FT. Myers FL, Anyways he was one of the pioneers with getting L98's fast, one of the first to go 11's. He use to test TPIS's stuff and ran down in the low 11's with a 355 L98 last I heard, of course that was back in 1997 I believe. He has been featured in CORVETTE FEVER MAGAZINE, along with being in the back of TPIS's catalog. He also has his own catalog along with an 11 sec recipe book he sells. No I'm not advertising.
Anyway's long story short, this mod along with drag radials gave me a solid 3/th's at the track. My 60ft was reduced from a 2.021 to an 1.883 and the et went from a 13.026@108.81 to an 12.74@108.64. Yes the tires helped but with these two mods, one being free, I gained 3/th's back in 1997. Hope this clear's it up.
Anyway's long story short, this mod along with drag radials gave me a solid 3/th's at the track. My 60ft was reduced from a 2.021 to an 1.883 and the et went from a 13.026@108.81 to an 12.74@108.64. Yes the tires helped but with these two mods, one being free, I gained 3/th's back in 1997. Hope this clear's it up.
Thread Starter
Racer
Joined: May 2004
Posts: 392
Likes: 0
From: VA
Been thinking again, another trick from back in the day before you had all these aftermarket shock choices, was to get some worn out high mileage shocks from an earlier year vette 85 or 86 and put these on your car. They acted like a drag shock and helped with weight transfer, this was strictly for dragging the car though. 
Pro
Joined: Mar 2005
Posts: 746
Likes: 0
From: Rochester PA
I'll ask again. Would open headers cause the knock sensor to send a signal to the computer? Also, would opening the headers cause the tune to be drastically different, saying it was tuned with the exhaust running through the pipes and mufflers? TIA.
Rich K
Rich K
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Originally Posted by JOHN89
You can put a toggle switch on the ground wire for the knock sensor module. This is the only way to bypass the knock sensor without throwing a code or SES light. It is located on the passenger side under the hood near the passengers door. This will allow full ignition advance so be careful! I installed it on my 89 because I suspected false knock due to my headers. I was correct and yes I did pick up over 1/10 in the 1/4 mi. I still have the switch installed but I don't use it much.
John
John
On my 86, I wired in a resistor to simulate the reading and fool the computer by giving it the reading it was looking for. That totally bypassed the knock sensor and didn't cause a code to set.
Jake
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Originally Posted by thirdtimevetteowner
I'll ask again. Would open headers cause the knock sensor to send a signal to the computer? Also, would opening the headers cause the tune to be drastically different, saying it was tuned with the exhaust running through the pipes and mufflers? TIA.
Rich K
Rich K
The operative word here is "drastically". Yes, the tune will change. When running with open headers, the A/F ratio will lean out due to increased exhaust scavenging.
Without testing, how much it'll change is anyone's guess. There are several variables that have to be factored in. Header tube lengths, bends, and diameter; collector length, diameter, camshaft duration and overlap, etc.
Now, whether this will help or hurt depends on the tune.
If the tune is on the lean edge, going leaner while running open headers can definitely hurt the engine if the A/F ratio goes too lean for too long.
If the tune was on the safe (richer) edge, the leaning should increase power.
All depends.
Just my thoughts.
Jake
Safety Car
Joined: Sep 2003
Posts: 3,599
Likes: 24
From: Orange County NY
St. Jude Donor '10-'11-'12-'13
Originally Posted by JAKE
On my 86, I wired in a resistor to simulate the reading and fool the computer by giving it the reading it was looking for. That totally bypassed the knock sensor and didn't cause a code to set.
Jake
Jake
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Burning Brakes
Joined: Nov 2003
Posts: 914
Likes: 1
From: Redding Ca
There is an excellent article on this very question in the most recent issue of GM Hi Tech Performance. The article name is Detonation! Essentially whenever the knock sensor detects a "knock" (I think usually not heard by our ears) for whatever reason, it retards the timing. They agree that a switch to bypass the knock sensor can (not "will") pick up some ET (if there is retarding going on for whatever reason). A simple solution if it is caused by pre igition is to run 100 octane. And if that does not work, there is something more serious than timing and octane causing the problem
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Originally Posted by byebyeL98
Jake - What Ohm resistor did you use? 100K?
I did find the part number for an ESC module that Gordon Killebrew recommends - 16038331 (Wells cross reference RSC108) that he says reduces sensitivity to false knock.
I took his advice and bought the new ESC module and, at the same time, removed the resistor.
I'm going into the garage now to check to see if I still have the package the resistor came in. I installed it a couple of years ago, so I don't know if I still have the package.
If I recall correctly, I got the specific info on which resistor to use from the ThirdGen.org site. If you log-in and do a search you may come across it.
I'll let you know what the garage search turns up.
Jake
Burning Brakes
Joined: Mar 1999
Posts: 858
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From: Fl,USA
Don't use a resistor. Put a toggle switch on the ground wire (pin D) to the knock sensor module. Ground disconnected gives no knock retard (switch off). Ground connected (switch on) normal knock retard operation. This is the way to go. It will help determine if you have false knock.
Burning Brakes
Joined: Mar 1999
Posts: 858
Likes: 5
From: Fl,USA
Originally Posted by thirdtimevetteowner
I'll ask again. Would open headers cause the knock sensor to send a signal to the computer? Also, would opening the headers cause the tune to be drastically different, saying it was tuned with the exhaust running through the pipes and mufflers? TIA.
Rich K
Rich K
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Back from the garage.
Nope, didn't find the package but I did find two of the resisitors that had been in it. The resistors I bought came in a package of five and I still have two left (at least that's all I found in my search).
They are light blue in color. There is a wide dark blue stripe, then a thin red stripe then two wide red stripes. There are no numbers that I can make out.
Maybe someone who's familiar with these suckas can decode it for you.
Sorry I couldn't help more.
Jake
Nope, didn't find the package but I did find two of the resisitors that had been in it. The resistors I bought came in a package of five and I still have two left (at least that's all I found in my search).
They are light blue in color. There is a wide dark blue stripe, then a thin red stripe then two wide red stripes. There are no numbers that I can make out.
Maybe someone who's familiar with these suckas can decode it for you.
Sorry I couldn't help more.
Jake
Melting Slicks
Joined: Jun 2004
Posts: 3,032
Likes: 4
Early C4 ecm's do not check for the knock sensor- therefore no code is thrown- as CFI-EFI implied (and I personally experienced). Although this may only apply to L83 and early L98 ecm's.
Last edited by mikey whipreck; Apr 12, 2006 at 06:44 PM.
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Originally Posted by mikey whipreck
Early C4 ecm's do not check for the knock sensor- therefore no code is thrown- as CFI-EFI implied (and I personally experienced). Although this may only apply to L83 and early L98 ecm's.
For the 86, code 43 sets and indicates the ESC circuit failed the start-up functional check. When the engine is first started the system performs a functional check by advancing the spark timing. The SES dash light will illuminate and remain on until the ignition is turned off or until a knock signal is detected.
Although I don't believe the original poster stated this, but I believe he has an 87. Correct me if I'm wrong on that.
Jake
Pro
Joined: Apr 2005
Posts: 590
Likes: 0
From: Boynton Beach, FL
Several years ago I spent a lot of time researching and trying to trick the GM knock sensors.
1) The resistor trick will not work.
a) I've tested it.
b) The KS circuit has a band pass filter that looks at the frequency
of the signal, not the amplitude. Resistors effect amplitude, not
frequency.
2) You cannot hear the knock that destroys an engine. Ask me how I
know. It was an $8000 mistake I won't make again.
3) The knock sensor IS sensitive to other than just engine knock noise.
I had no end of grief because I was getting knock retard when I
shifted due to my dual mass flywheel. I was able to see it on my
Diacom.
4) Unless you REALLY KNOW what your doing, don't mess with the KS.
Larry
1) The resistor trick will not work.
a) I've tested it.
b) The KS circuit has a band pass filter that looks at the frequency
of the signal, not the amplitude. Resistors effect amplitude, not
frequency.
2) You cannot hear the knock that destroys an engine. Ask me how I
know. It was an $8000 mistake I won't make again.
3) The knock sensor IS sensitive to other than just engine knock noise.
I had no end of grief because I was getting knock retard when I
shifted due to my dual mass flywheel. I was able to see it on my
Diacom.
4) Unless you REALLY KNOW what your doing, don't mess with the KS.
Larry
