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Old 01-19-2013, 06:40 PM
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Whats the best way to detect knock and retard timing with gm hei

I want to use gm hei without an msd box. Its street car and had bad luck with msd on the street.

I want to use gm hei and have an knock detector that can show a warning light and also pull the timing back even if it pulls it way back. One degree or even half steps would be best but not really worried about mantianing power as much as dealing with a single crap tank of gas without smoking the motor.

Lots of traffic and bad gas stations with crappy old tanks and owners that will do anything to save a buck. Actually seen the citgo truck filling the tanks in an exxon. I now its all the same gas from the same plant but still too many corners being cut to trust it. Getting 87 from all three pumps is not unherd of.

I have seen several warning light systems for off the shelf knock detectors. But looking for something a little more professinal and not away from the original hei. Since it works fine for most chevy builds. It would also be nice if the system was brainless so i could put it on engines that are not for me personally. Keep brainless people from killing a motor with a bad choice in city gas stations.

This is for a high compression natural asperated chevy 350.

Any helps would be greatly appreciated.

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Old 01-19-2013, 07:12 PM
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You want a knock sensor design I think.

This one does work , but how well...
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Old 01-19-2013, 07:49 PM
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Well forgot the mention this is for carbed engine. With aluminum manifold and gear drive just to make things more of a pita. I have seen these articles and know how to build something that can pickup the signal and light and led but really trying to find out how i can use it to retard the timing without and ecm even if its a cheap and dirty few degrees its better than nothing.

Would also love to find something plug and play. And cost effective. I refuse to pay more than the cost of a set of pistons to save the pistons.

If something like this does not exist i may make something up. But i am thinking someone has to make a detect and retard box for gm hei with carb. If not i am sure that is something worth making at least for me. I dont want to be told something is wrong fix it and tell me its being fixed. By the time the light comes on and lets me know to let off the gas it might be too late. For n2o or blower detonation can go wrong very quickly.
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Old 01-19-2013, 07:49 PM
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MSD did make a stand alone Boost timing master box that does not require a MSD 6 spark box.

It, has a internal inductive discharge type ignition amplifier. (probabily much like the MSD 5 box.)

Connects directly to a GM HEI.

They are out of production but you can still get them.

Timing is reduced relative the boost pressure applied and the setting of the dial.

MSD #5462 ( Some are labled Vortech)

The is another MSD box that works on as GM HEI too. Dial for driver adjusted timing retard.
hooks up to a HEI too. MSD #8682 may be out of production too.


A 5 PIN style HEI module can be used for fixed timing retard. The fifth pin gives aprox -10 deg retard with activated
(either by grounding it or applying 12V+ to it. not sure which)

None will detect for you..

the OEM s spend big bucks in getting a knock detector dialed in to each specific engine design so it detects knock and not normal engine sounds. Each one is different. Crane makes their mechanical street roller cams designed specificly to run quite enough so as to not effect the knock detectors.
The gear drive is going to be a step back.

Last edited by F-BIRD'88; 01-19-2013 at 07:58 PM.
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Old 01-19-2013, 08:11 PM
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Quote:
Originally Posted by F-BIRD'88 View Post
MSD did make a stand alone Boost timing master box that does not require a MSD 6 spark box.

It, has a internal inductive discharge type ignition amplifier. (probabily much like the MSD 5 box.)

Connects directly to a GM HEI.

They are out of production but you can still get them.

Timing is reduced relative the boost pressure applied and the setting of the dial.

MSD #5462 ( Some are labled Vortech)

The is another MSD box that works on as GM HEI too. Dial for drive adjusted timing retard.
hooks up to a HEI too. MSD #8682 may be out of production too.


A 5 PIN style HEI module can be used for fixed timing retard. The fifth pin gives aprox -10 deg retard with activated
(either by grounding it or applying 12V+ to it. not sure which)
Thats good info. Is the 5 pin a common hei, good performance moduals out there? 10 degrees is not going to be good for performance but good for detonation. If it falls on its face then you know it started knocking. And thats fine i would much rather keep it safe then to make power while its out of tune.

I could probably rewire the knob style msd box. I have seen them before. And could make a circut to adjust the timng based on the amount of knock. But may be a lot of work to get dead on.

Running a big cam and high compression so any way to save the engine while tuning without having to install an egt on each cylinder. Great for tuning but not cheap enough to run in all my cars.
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Old 01-19-2013, 08:14 PM
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More 5 pin info. Copy paste.

IME with a 5 pin IGN module

Obtain a EMR Ingition module from a early 80's GM car, I have seen them in 260 Olds powered cars, and I have read about them in Olds 350's in 1980 also. As per Jim Hand, use a GM module, not a garden variety parts store replacement.
This module is a direct replacement for the 4 pin std 990 module, only it has an additional termal marked "R". This terminal when grounded, reduces ignition timing by 10 degrees. High compression engines have problems with starting when the initial ignition is too high. But with this "mod" the module will allow you to start the car with ease (and less abuse to the starter) with the flip of a switch. GM used this with a vacuum switch to at certain times it would pull timing back 10 degrees, or run normally. But this was done with a fixed timing distributor.
You can install this, then increase your initial timing by 5-10 degrees, use the EMR Pin "R" to retard timing at start, and then return to higher timing for cruise. This will now require modifications to the overall mechanical timing curve. As now it is advanced what you cranked up initial base timing, now needs to be removed from the mechanical timing curve. Once removed you will have a much tighter timing spread and have a overall much faster curve and more repsonsive engine. The area under the curve is fuller and will have overall higher combustion efficiency.


.
Example:
.
Base timing:-->10 degrees
Mech Adv:--->24 degrees
Total Adv:--->34 degrees
.
Modified with EMR
.
Base timing:-->20 degrees
Mech Adv:--->14 degrees
Total Adv:--->34 degrees
.
Now WOT power is unchanged, and part throttle power is up by upwards of 0-10 degrees (in the above example) so your overall timing curve is faster and you are doing most of your driving with higher base timing, improving fuel economy and throttle responsiveness. Higher compression engines will need to be adding possibly less than the full 10 degrees, but low compression cars will welcome the full 10 degrees. I have found most lower compression cars enjoy as much base timing as possible while limiting the overall total timing, but still increasing it.

A knock sensor has peizo charateristics convert the knock volts to optical led, then to photo sensor switch to ground for the R pin. or something.

Last edited by spinn; 01-19-2013 at 08:25 PM.
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Old 01-19-2013, 08:52 PM
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Thought i had it licked for a minute but the 5 pin modual is only offered as a normal after market item not a performance part. Stock style is all done by 5500 rpm.

Not sure the 5 pin solution will work stock modual in the four pin design is no good. But maybe the 5 pin is better. Most of the performance stuff is 4 pin with some 7 and 8 pin moduals as well. But did not even see a 5 pin for sale from summit.
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Old 01-19-2013, 08:59 PM
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The only HEI module you ever want to use is a Genuine GM/AC Delco part.
it gives you all the spark power you need for 7000rpm and tons of horsepower when the gap on the sparkplugs is .035"
and the engine is grounded with a ground wire to the body and chassis.

Last edited by F-BIRD'88; 01-19-2013 at 09:07 PM.
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Old 01-20-2013, 10:44 AM
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There are 3 different 5 pin ig modules for GM s .
The Electronic spark Timing EST (EMR)
The Electronic Spark Control, and the third you dont want is
Electronic spark selection ESS. That was used on 82-83 ish caddy and required a modified square wave signal from the ECM on the 5th pin. Maybe also on a canadian until 86.
Not that its a bad module, if its a GM as when hooked up and ran as a 4 pin module it will perform the same as a GM 4 pin (990)
The delco number for the 5 pin module that uses a ground on the 5th pin to retard the timing is Delco # D-1941
GM number 10482282

Still a lot of other questions regarding the other module (ESC) as to what source the 5th pin uses. 5 volt+ ? 12 volt + ?
The ESS module would only be a good replacement for a 4 pin, unless you can integrate it into a megasquirt setup or a MSD somehow. There may be more info on it . I would be interested in reading it.
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Last edited by LATECH; 01-20-2013 at 10:53 AM.
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Old 01-21-2013, 02:05 PM
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I decided to Build a circuit loosly based on this design. It weak and needs a lot of tweaking to be adjustable for different engines.

DIY Knock light (radio shack parts) - Miata Turbo Forum - Turbo Kitten is watching you test compression.

Fyi the link above wont work as is if you want to make your own i will try to post something when i get this complete.

I am going to try the dodge sensor and the 5 pin hei modules. Should be able to trip the mod and pull timing back 10 degrees at once and hold it for some time in order to alert the driver the tune is not working properly.

Adding a button in for hot start as well.
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Old 01-21-2013, 02:10 PM
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I did look into the msd and other ignitions but didnt find anyone that had good support for knock detection and correction.

I did see a few real nice stand alone systems but well over 500 bucks. Also seen a nice detector but was over 250 for a light.

Do any of the aftermarket ignition use the knock sensor like the oems do. Where the timing is whay out until it knocks so its always using as much timing as it will take without hurting the motor??
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