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View Full Version : Brass T w/Knock Sensor & Drain


VTJC
11-18-2004, 01:54 PM
Has anybody installed a brass T between the block of an TBI EFI 350 and the knock sensor? I am hoping to be able to install a drain on that side. Thanks in advance for you input. Jamie

paulphillipson
11-18-2004, 02:14 PM
I had one on mine. No problem

prostar205
11-18-2004, 04:01 PM
I bought the drain kit from SKIDIM and was told NOT to install anything in the location of the knock sensor. To drain that side of the block, I simply removed the knock sensor. Fairly easy task.

Diesel
11-18-2004, 05:39 PM
Has anybody installed a brass T between the block of an TBI EFI 350 and the knock sensor? I am hoping to be able to install a drain on that side. Thanks in advance for you input. Jamie

Why?? :confused:

JimN
11-18-2004, 05:42 PM
I wouldn't put a fitting between the block and the knock sensor. The brass isn't the same density and can decrease the amplitude of the signal that the sensor is tuned to pick up. In a hot, dry region, that can be a problem if the knock is persistant. Besides, it's not that hard to get to the KS, anyway.

VTJC
11-18-2004, 11:02 PM
I got the same info from Skidim. They said they know some people are using a T. I just donít understand how the knock sensor functions. In the fall it would be nice to just flip the valve open and head out after ski sessions. Jamie

JimN
11-19-2004, 12:04 AM
The knock sensor basically acts as a microphone, to send the sounds caused by spark knock to the ECM. The ECM is programmed to look for certain frequencies and amplitudes while the motor is running. If it hears knock, the ECM tells the ignition control module to retard the timing by 5 degrees at a time, till the knock is gone or it's at the minimum advance allowed by the program. Brass is a different hardness from cast iron, therefore, it has a different resonant frequency and the ECM won't see the signal it needs to work properly. Soft materials generally have a lower resonant frequency than hard ones. The effect it similar to removing midrange and treble on a graphic equalizer. If the main function of human hearing is for speech, removing midrange and treble causes speech to be unintelligable because of the frequencies where human ears are most sensitive. The ECM doesn't care about frequencies outside of those caused by knock and if the knock falls below the threshold set in the program, the ECM can't try to save the motor from damage.

As I said before, it's not that hard to remove the sensor. Maybe 2 turns with a 7/8" socket on a ratchet. It also doesn't need to be tightened very much. Hand tight, then add 3/4 of a turn.