smon

ive searched and read many different articles on timing. i just finally figured most of it out and set the timing today. i have a couple questions. here is where i should be.

18 initial timing (vac disconnected)
36 all in by 2500 rpm (vac disconnected)

right now i have the initial at 17 (to avoid detonation) at about 950 rpm. engine wont go much lower than that. i have
and my problem is at the total "all in" stage. im usin a stock 75 hei with a rebuild kit and im using the gold springs.
i set my light at 36 but the line on the balancer is flattening out before it reaches "0" when i run it over 2500-3000 rpm. is my total coming in too early?(centrifigul advance coming in at idle-which is raising my initial timing?

i have a pretty aggresive cam...what is the limit on initial while tryng to keep detonation from happening? i have hookers iwth max flows so im afraid it might detonate and im not going to be able to hear it.

Thanks in advance
Sean

SH-60B

A stronger spring on one side or a pair of them will keep mechanical from coming in until you rev past "idle", I guess your idle is so high because of that cam. IDK how much advance to run with your combo. Read the plugs for signs of detonation.

69427

Max timing varies with the setup and air/coolant temperatures, so there's no absolute number. Given that you have an aggressive cam, you're going to need a bunch of advance at idle to compensate for the low cylinder pressure and the residual exhaust gas in the cylinders, as both will slow down the burn rate. Just give it enough to where the idle quality is satisfactory, and where you also don't have cranking or dieseling issues afterward. Double check the advance reading to make sure you don't inadvertently have some wild advance setup.
There's a couple ways of detecting detonation. A quiet system would obviously let you listen for knock, or installing a modified mid 80's ESC system (with an LED readout) will give you a visual indication when knock occurs. I did the latter, as I spent a lot of time at the track with the turbo uncorked, and the exhaust noise masked the knock noise. I always knew when the engine knocked by the indication of a bright flash of the LED I had mounted on the internal rear view mirror. I'd get out of the throttle when that happened, and then made some timing changes (burn a new chip in my case) in the pits between sessions.

Scott Marzahl

Just curious, what is aggressive to you? Try one stock spring and one gold spring, that may get you closer to the ball park.

smon

How hard/expensive of a job is this?

Not sure what to look for here, this stuff is all new to me.


ill try a stiffer spring on one side this weekend and see how that does. I have to keep the idle prety high in Park so when it drops down into D it doesnt die. This may be solved when i change the springs they letting the advance come in too early during my initial timing.

Thanks for the help,
Sean

SH-60B

http://www.dansmc.com/Spark_Plugs/Sp...s_catalog.html This is one of the better charts I've seen.

69427

It's pretty easy if you are comfortable with some basic electronics, or have a buddy who dabbles in some simple transistor and resistor or op-amp circuitry.
The knock sensor and ESC unit off of a mid 80's 350 (I can get you the part numbers to look for if you want) works well. The ESC unit will switch/toggle one of its outputs every time there's a knock occurance. By adding a couple transistors, resistors, capacitor, and a large LED, you can make a little buffer/pulse stretcher circuit to blink the LED every knock episode. I attached the LED to my rear view mirror. Very easy to see while I'm driving the car. If you're serious about doing this I can get you a few more details on how to build the pulse stretcher.

smon

69427...thanks for the help. i am interested in this setup but i am a beginner with electronics, i can find someone here to lend a hand in this though. Where would the sensor go? will i have to drill and tap a hole for it, thats one thing i wouldnt be too comfortable with if shavings could get into the engine/ i dont really want to dissasemble my new engine.

thanks for all the help,
Sean

stingr69

Sean,
If I am reading you right, the issue is with the centrifugal advance. 36 degrees is the total of all the available centrifugal advance plus your "preferred" 18 degrees of initial advance. You say you want 18 degrees available in your centrigugal advance but that is not what you have available in your distributor.

This curve you describe is not possible unless you have exactly 18 degrees "available" in the centrifugal advance mechanisim. Your distributor has some other amount + or - of centrifugal advance available so the total curve is not what you desire.

You can change the rate of centrifugal advance with different springs to make it come all in early or come all in later in the RPM range but it will allways have the same amount of degrees available regardless of the springs you put in there. You must alter the mechanisim to change the number of degrees available in the centrifugal advance.

Try this - Plug the vacuum advance and set your dial back light to 36 degrees. Rev the engine high enough to get to the top of the centrifugal advance curve where the timing will advance no further and adjust the timing so the "0" marks line up. This will set your timing so that you will actualy have 36 degrees as the sum total of all the available centrifugal advance plus whatever the initial will be. Hook the vacuum advance back up, adjust your idle speed and give it a test run. This is as close as you can get to your desired curve without modifying your distributors available centrifugal advance mechanisim.

You can check the initial and modify the centrifugal advance mechanisim if you want the initial higher or lower than where it ended up now.

Bottom line - the mechanisim decides how much is available and it will also decide your initial timing for you. Total 36 minus available = initial. You can change the initial by rotating the distributor but the total will change along with it and that is not what you want. Keep the total arond 36 and modify the mechanisim if the initial is not where you want it.

I hope this helps.

-Mark.

69427

The sensor simply screws into the coolant drain hole (I forget which side. I'd have to look at the car again.) above the oil pan gasket. The sensor is then wired up to the stand-alone ESC module. It's easier if you can also salvage some of the module wiring harness off of a donor car.

Older Than Dirt

I have easy access to junkyard parts. Could you give me the part numbers, details, and wiring schematic for this. I would surely appreciate it. If you wish e-mail it to me. Thanks....

smon

thanks for all the help guys,

i was able to get the timing about at 36 total and then i was able to get my idle down lower. Now that my idle is down my initial is more consistent ( centrifigul was coming in at idle), but it is still a little higher than i want, especially with my vacuum canister. im ordering a new one with less advance.
I understand now that is not exact 18* centrifigul. It makes more sense now.
How is this done? if someone could show me a picture of the part that would be great since im no distributor expert.

Thanks,
Sean

BarryK

most HEI's came with a 20º mechanical advance. that means if you set total timing to 36º your initial timing should fall at 16º.

If you need to change the amount of mechanical advance the distributor puts out there are two basic ways to do it, change out the advance limit stop bushing and/or change the length of the advance slot in the Autocam.

The way the mechanical advance works is that as it spins faster and faster with RPM the weights (controlled by the springs) swing out and the advance pin, with a stop bushing on it, slides inside the slot of the Autocam. The length of travel available in that slot controls how much or how little advance the distributor will give.
Reducing the amount of travel reduces the amount of advance and increasing the amount of travel increases the amount of advance.

You can get from a local speed shop or online vendors a kit of Advance Limiting Stop Bushings. Increasing the size (O.D.) of the stop bushing will reduce the amount of travel therefore reduce the amount of mechanical advance. For example, if your distributor now has 20º advance it could reduce it to 16º advance with the right bushing.
By putting on a stop bushing with a smaller O.D. you increase the travel and therefore increase the amount of advance. For example increasing mechanical advance from 20º to 22º or 24º.
If you need to change the mechanical advance by just a couple of degrees a different stop bushing will probably do the job for you.

the other way to change the amount of mechanical advance is to change the actual length of the slot in the Autocam by making it longer by filing it and increasing the length of space the pin can travel or by welding it closed a bit to decrease the amount of travel and reduce the amount of mechanical advance.
Unless you know what you are doing I would not try this method yourself although someone that has experience, good welding techniques and a good Sun Distributor machine to check everything and set it up properly can repair an old distributor fine this way.
The distributor in my '65 had previously had the advance slot length increased and to get it back to the correct level of mechanical advance it had to be shortened by welding than filing it to the exact length for the amount of travel and advance we were looking for.

If you want to play around with and change your mechanical advance I'd recommend getting the kit of stop bushings and try different ones until you get the amount of mechanical advance you need.

Older Than Dirt

Although this is for a MSD distributor, it will visually help you understand how these parts work.

http://www.msdignition.com/pdf/8361_85551_frm23794.pdf

69427

I'll dig out my folder of information about this and post the information in a little bit. To be continued.....

69427

Okay, I found my parts list. You'll need to find/use a 5.2 kHz knock sensor. This is found on a lot of 4.3L V6 cars and 5.7L V8 cars and trucks. This sensor has a white plastic connector on it (do not use the ones with the black connector), indicating it has the correct internal impedance (100 kOhms or higher). The metal cover surrounding the connector also has a bluish anodized color. You don't want any other color cover. The blue color indicates 5.2 kHz.
There are three ESC modules that work on a range of small block engines for this particular test. The part numbers are 16038331 (Code CXX), 16052401 (HKR), and 16128261 (ANUC).

Just got a pet emergency to deal with. I will continue this post later this evening.

Okay, I'm back. I'll need to take the dog to the vet in the morning to get it checked out. Some redness/swelling on its foot.

The factory service manual shows the ESC module pinout. For testing purposes you can make a simple harness to allow you to hook things up without affecting the car harness. Pin C of the module will toggle (switch from about the normal 8 volt level to a low, nearly zero volt, level) when knock is heard by the sensor. The pulsewidth of this low level will reflect the intensity of the knock (the ECM is fast enough to measure this pulsewidth, but our eyes aren't). The more intense the knock, the longer the pulse will stay low. But for our testing, we just need to have an add-on circuit to be triggered by pin C of the ESC module. This add-on circuit does two things. It turns on a large LED so that you are notified when knock occurs, and it also lengthens the LED pulse so that it is easier to monitor. The add-on circuit can be built with an op-amp/comparator or a transistor/resistor combination, along with a small capacitor to allow an RC time constant. Electronics hobbyists can build this circuit rather easily. I'm too lazy to describe every aspect of this circuit, but I can answer some questions if they come up.

smon

69427 thanks, ill go hunt for those parts then find someone who can help with the wiring and circuits. If i have any questions ill let you know.

Small price for the protection of my engine.

Hope your dogs OK

Thanks again,
Sean