In the Wiki on (oem) HEI systems there is a mention of a five wire HEI that connects to a knock sensor.

Has anybody here successfully incorporated one of these into an early motor?

I think it would be ideal for me as my 425 was put together with the stock 10.5:1
pistons and I will need to run it on the edge of detonation..

David

 

i was looking into this for ernie... that has been put on hold.


bill

 

I guess the question would be whether the knock sensor would have a direct connection to the distributor or not.

If it is a direct connection and it takes 10 deg out when it senses knock that seems like a pretty usable idea.

Maybe it could also be activated by a dash switch, if you get stuck having to buy some 87 octane somewhere.

Looks like it might have been a short run distributor; 88-89 only?

From the looks of it I'm surprised there is not great demand for these..

 

Reviewing the below, I think it is a request to REPLY here. First had to
register. Better to send email.

There were a lot of HEI module design variations. After the original 4 pin.
there was a 78-79 Cadillac EFI module, that allowed a step in advance for
cruising or retard for starting, under control of an ESS module. The 77-78
Toronado had an early electronic spark advance control module attached
to the HEI module and engine sensors. Apparently using temp compensation,
these allowed the 403 to meet emissions while delivering the same relative
performance as a 350 engine. Non Toro 403 HEIs had an advance curve
not nearly as great as a 350 HEI; replacing this with a 350 HEI will definitely
perk up the engine and probably improve mileage.

80s HEIs went to full electronic spark advance control, eliminating any
mechanical or vacuum moving parts. These again required more HEI module
wires connecting to the engine computer. There was a default mode allowing
a fixed advance "limp home" for the CCC modulated carb 5L engines built for
a decade.

To answer the question, a knock sensor first requires a "noise filter" to
separate knocks from other noise, then an input to the engine computer
(setting timing) or spark retard unit. These then in turn adjust the spark
trigger timing into the HEI module, which is nowhere near this intelligent.

Some module info on this site;
http://www.megamanual.com/ms2/GM_7pinHEI.htm

Usually knock isn't present at the majority of cylinders. Perhaps an
ideal knock spark retard unit works by only retarding the offending cylinder(s) as needed, leaving the rest at full power. J & S
Electronics makes the SAFEGUARD.

Bruce Roe
++++++++++++++++++++++++++++++++++++++++++++++++++ ++++++++
Hi Bruce,
Here is a topic I started over on CO,
https://classicoldsmobile.com/forums...-question.html
When I did a little more searching the olds wiki had some quotes from you
but there was no mention of how these 5 wire HEI distributors function.

Do you know if the 5th wire either thru a shunt to ground or a +12 provides
a constant 10 degree retard of the timing or is it more complex, some form
of computer control? Thanks as always David Bond