Hello,
I have a 1972 sbc L48 that I will be adding vortec heads, intake, headers, and cam to. I have spent some time altering the stock setup for the performance ignition curve, but I have a tough time hearing knock. I set the distributor to have the max advance Lars recommended, about 52-54*, but I never really heard/recognized any knock during this process.

When I add the vortec heads and all the rest of the goodies, this will change the compression ratio along with other aspects affecting timing, and complicate the proper timing settings further.

I was wondering if anyone installed a light that would come on when knock is detected through the same knock sensor that was installed in the 1982 models. These models had a computer in them that the sensor would connect to, but obviously I don't have that.

(More back story below if you care to read)
When I bought the car the distributor was shot, and the tach gear was stripped, so I "upgraded" to an aftermarket HEI. This helped the car A TON after it was installed, even set at a way retarded setting.
Being after market, of course the weights and springs are set up for much more mechanical advance than stock, as well as the vacuum can, which makes things a bit tougher when I later tried to match Lars performance specs. I currently roughly have 12* initial, 36* all in at 3200 rpm, with about 18* vacuum advance hooked to manifold (using timing tape, so its a bit rough). The HEI has an adjustable vacuum can, but it seems like 18* is the minimum with the can that it came with (who needs the 26* max vacuum advance!?).
I looked around online for a replacement can, but very little detail is included with these and I'm worried I would replace with the can with one of the same specs. They all look the same, but it looks like it may be the accel one which can reduce advance by turning the allen key, not just how fast it comes in (any part number recommendations?).

When I look at the advance in my driveway with the vacuum can hooked up, it doesn't appear the vacuum can is starting to retard even at 3200 rpm, so I saw about 54* with the light. (Is this normal? ) I'm worried the can is giving full advance too long, and I'm thinking I essentially have to floor it to have it start retarding vacuum advance. (Woohoo! good engine vacuum around 19-20). I thought I was good with this timing set up until I was coming home on the freeway recently, and I thought maybe I heard knock. Again, I'm not sure because I'm a bit inexperienced with this, and I'm not sure I've recognized knock before on any vehicle. I watched a couple youtube videos, and it seems pretty subtle, especially while on the freeway with the old weather striping letting air in.
I've heard of some people making a vacuum advance stop by putting some JB weld on the vacuum advance channel to only allow a set number of degrees. This seems pretty bubba, and wouldnt affect the rate the advance comes in, but I may just do it.
I bought a mr gasket kit to alter the HEI mechanical curve, but haven't added anything yet, mainly because I'm a bit unsure how to properly reduce mechanical advance. The kit looks like it is made for upgrading stock distributors, so the weights still look similar, like they are set up for additional advance. i know I could replace with a stiffer springs, but that would just move the total mechanical timing higher in the rpm range, not reduce it, correct? I know this is safer, and could accomplish much the same, but I'd like to get it as close to Lars specs as possible, 18* initial with 36* all in at 2800-3000rpm and 16* vacuum advance.


(sorry for the long post)

 

You'll need some sort of interface (ECM or some stand alone circuit) that can interpret the signal from the knock sensor and turn that information into something useful.

 

I totally get that, but the stock ECM does a lot of things with that information, retard the distributor, etc. that I don't really need.

There has to be a more simple way to just wire up a light, correct?

 

Unless someone has built and sells such an interface, you'd have to design a circuit yourself.

I agree that it would be a handy way just to see if you have any knock happening-
I just haven't seen such a tool advertised.

I Stand Corrected:
Someone does make one but it's pricey!
http://www.nzefi.com/product/knockli...ation-warning/

Saw this on Summit's site but still requires a GM ESC module to work:
https://www.summitracing.com/parts/c...SABEgIA4vD_BwE

 

I have a custom built stand-alone system I use frequently. It uses the standard GM knock sensor (5.2 kHz) from the mid-80s and the ESC module (HKR broadcast code) from the '84 Corvette and other similar engines from that period. The output from the ESC module feeds a circuit that extends the "retard request" signal (that would normally go to the ECM) and drives/switches a retina-burning LED so that I can monitor knock in real time, and the bright LED is easy to notice, even while otherwise busy on the track.

 

I bet if you marketed that, you'd be able to make a few bucks from folks like us.

 

It would be nice if we could just use the ignition side of efi for spark control and knock retard.

 

I noticed you commented on this fellow's issue back in the day, which also has some wiring diagrams:

https://www.corvetteforum.com/forums...sc-module.html

I'm assuming you connected the ESC spark retard line to your light/switch?

What kind of switch or relay did you use?

Could you use the knock sensor for 1982 corvette, wire it to ESC from same year, then wire the spark retard line to your light/switch/relay?

 

looks like J 485 would be to ecu at 5v ?

 

at 5v, I'm sure I could find a light that could work wired directly to it, although I would maybe want it to stay on for a second or so after an even.