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396 timing

7K views 27 replies 9 participants last post by  DT 
#1 ·
Finally getting around to timing my engine. What are you guys using for timing on your 396 ? Just curious. I started out 12 initial, 34 total.
 
#3 ·
Back then we could get away with timing by ear, that was when gas was good quality and better octane. Detonation will destroy an engine. Big blocks like timing, you can get away with 36-38 total but will have to listen for detonation and check plugs for metal specks. What is the compression ratio? Cast heads or aluminum?
 
#10 ·
Drat! I was hoping to help out. Oh well. But wait! Here's how the factory said to do it on mine.;)
 
#12 ·
You realize you will catch some grief for no vacuum advance... I run mine locked at 36 and pull timing back under boost(my ignition turns back timing when starting). A proper vac advance really is best but without one you will need to run as much initial as you can and max out at 36. If you can run a really small amount of mechanical advance that would be best. You can run it locked like me but having a start retard will be your starters friend. Or an ignition kill switch, let it spin without spark and then let go of the kill.
 
#15 ·
Yes I know regarding the vacuum advance. My DUI has 22* in by 3,000. I think I will set my initial at 14* then. I'm currently at 12 initial 34 total.

Thx
 
#16 ·
If u have 12 deg and total 34....
drop a VA in so its all in at idle....gives an idle of intial +whats in the VA.. usually between 7 and 10 degs... then also pull the advantage of better cruise mileage, and easy start with the lower initial.
 
#18 ·
Run the initial at 16* and with the 22* mechanical, will give you 38 total. I have a M. roller camshaft with 256/266 duration. I set the initial at 20* and the mechanical at 18* for a total of 38* on a 496 ci. I have a GM high torque mini starter that has been on the car since 1997. I haven't had any problems starter drag. If you have any problem with your starter decrease the initial by 2* at a time until it stops. But you have to keep a total around 38*. Burn some tires off!
 
#20 ·
I suggest to go along with what Doug says with the higher total... But keep the initial +cent+ VA total degrees under 42 unless have a knock sensor....last thing u want is in audible knock under cruise...
To find u best total (intial+cent).. power under WoT...start high around the 36/ 38 make 3 timed runs over a given distance.... preferably up a hill...
then drop the total back 2 degrees until u get a sudden increase in time... then up 2 degs
 
#22 · (Edited)
Most people with performance cams running vacuum advance will limit the can to 10 degrees total advance. You can buy a small limiter bracket that will let you adjust the total vacuum advance.

The total should be around 48 to 52 degrees.

So if you have what Doug recommended : 16 initial + 22 mech + 10 vac advance = 48 degrees at cruise and idle.

With this setting your engine will run cooler and give the best gas mileage.

From "Timing and Vacuum Advance 101" : http://www.camaros.org/pdf/timing101.pdf

At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).
 
#24 ·
Donny, You can try different initial timing settings up to 16* to see what it runs best at. Also if you have the eye watering fuel smell at idle increase the initial timing. Right now you are 12+22+8-10=42-44. I would try 16+22+8-10=46-48. In the older days in the Chilton manuals you would see initial 10*-12*+25+10-12=47-49. I have read where some have had a total + V.A.=50-52 but I think that's too much. All conditions have to be just right and I don't want to take the chance on ruining my engine. Try different settings to see if the eye watering gas smell goes away some. Also find a steep hill and ease down steady on the gas pedal and listen for any pinging while in drive. Is your engine a 396/325hp or 396/375hp?
 
#25 ·
Ping/ detonation starts why before anything can be heard......
We have some big money and time invested in our engines and cars.. I fail to in this century, now high end technoly like AFR , knock sensors and data loggers are so cheap.. so many remain back in the last century.
The old school tune by ear of the 50s, was very quickly replaced with a timing light when they became cheap....and later CO/ HC meters in the 80s...thu a few still stayed old school blaming so engine deaths on part failures rather part failures on poor tune specs.

Data loggers and sensors have been affordable home workshop tools for near on a couple decades now...
know what your engine is doing
not
" is that a knock???... I hear behind he sound proofing of the cabin, and noise of exhaust out the rear?"
 
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