Exhaust Detonation / Timing - Team Camaro Tech
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post #1 of 17 (permalink) Old Jan 16th, 17, 06:07 PM Thread Starter
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Exhaust Detonation / Timing

I have been having exhaust detonation when revving or backing off the thottle on my 67 327/210.....I tried to advance the timing down to the factory spec of 2btdc but it wants to stall when I get down to about 4....I have it set at about 10 now and it runs good but still detonates....Dwell is right at 30....both the timing and dwell were set with the vacuum advance unplugged and capped.

Any insight would be appreciated.
Thanks, Dan
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post #2 of 17 (permalink) Old Jan 16th, 17, 08:40 PM
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Re: Exhaust Detonation / Timing

Are you having detonation on acceleration or popping or backfiring on deceleration? Or both?

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post #3 of 17 (permalink) Old Jan 16th, 17, 09:51 PM Thread Starter
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Re: Exhaust Detonation / Timing

Quote:
Originally Posted by Luwi67 View Post
Are you having detonation on acceleration or popping or backfiring on deceleration? Or both?
I am Having popping and backfiring on deceleration
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post #4 of 17 (permalink) Old Jan 17th, 17, 05:33 AM
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Re: Exhaust Detonation / Timing

I would perform these 4 steps to start:

1. Read and understand JohnZs Timing 101 and/or Lars Grimsrud's Timing papers. 2-4 degrees initial timing is way too retarded.
2. Set your total timing to 34-36 degrees all in at 2500-3000 rpm. (This should put your initial somewhere around 14-16. If it doesn't your distributor advance curve may need work)
3. Make sure your vacuum advance only adds about 10-12 degrees at idle
4. Tune your carb because you likely have a lean condition

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post #5 of 17 (permalink) Old Jan 17th, 17, 12:49 PM Thread Starter
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Re: Exhaust Detonation / Timing

Quote:
Originally Posted by trland View Post
I would perform these 4 steps to start:

1. Read and understand JohnZs Timing 101 and/or Lars Grimsrud's Timing papers. 2-4 degrees initial timing is way too retarded.
2. Set your total timing to 34-36 degrees all in at 2500-3000 rpm. (This should put your initial somewhere around 14-16. If it doesn't your distributor advance curve may need work)
3. Make sure your vacuum advance only adds about 10-12 degrees at idle
4. Tune your carb because you likely have a lean condition
I read this in a couple different threads from JohnZ

"Total timing for a 327/210 is 34 degrees @ 4000 rpm (2* initial plus 32* in the distributor - "smog" curve)"
"I wouldn't bump it up much - the 327/210 distributor had 32* of centrifugal advance (to make up for the 2* static setting)."
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post #6 of 17 (permalink) Old Jan 17th, 17, 01:49 PM
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Re: Exhaust Detonation / Timing

If everything is stock, your initial timing should be 2 to 4 degrees advanced (depending on manual or automatic). Much more than that and you will detonate. I would concentrate on getting the engine to run well at idle with 2 to 4 degrees of advance and go from there. Look for a vacuum leak. Reset the idle mixture. Once you have that, begin to then attack the backfire. My problem proved to be a crack in the vacuum line going to my brake booster and I found it while working on getting the motor to idle correctly.

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post #7 of 17 (permalink) Old Jan 17th, 17, 03:16 PM
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Re: Exhaust Detonation / Timing

Quote:
Originally Posted by Rack Man View Post
I read this in a couple different threads from JohnZ

"Total timing for a 327/210 is 34 degrees @ 4000 rpm (2* initial plus 32* in the distributor - "smog" curve)"
"I wouldn't bump it up much - the 327/210 distributor had 32* of centrifugal advance (to make up for the 2* static setting)."
Obviously you'd want to limit the centrifugal advance to around 24* if you wanted to try 10* initial.
I'm sure it would idle better using the more modern settings that we know work better in the sbc.

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post #8 of 17 (permalink) Old Jan 17th, 17, 04:38 PM
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Re: Exhaust Detonation / Timing

Detonation is usually not on deceleration unless I am mistaken.
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post #9 of 17 (permalink) Old Jan 17th, 17, 05:01 PM
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Re: Exhaust Detonation / Timing

Quote:
Originally Posted by bigblockragtop View Post
Detonation is usually not on deceleration unless I am mistaken.
X2. There are so many factors involved on decel popping that it hard to know where to start. backfire is through intake/carb

#1 verify correct timing and working VA

#2 Idle mixture

#3 Exhaust Leaks which may actually be #1

#4 plug wires crossed

#5 Vacuum leak
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post #10 of 17 (permalink) Old Jan 17th, 17, 06:40 PM Thread Starter
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Re: Exhaust Detonation / Timing

I'm guessing my terminology is not correct in using the word detonation...my bad!....I saw those same sysmptoms on a couple Youtube videos and they called it that!

What I am getting is popping and small backfires when I left off gas after accelerating...I am unable to get the engine to idle at 2-4 degrees advance...I have also adjusted the fuel mixture screws and messed with the points. I started with setting the dwell at around 30...which seemed ideal.....then set the timing to the best I could, which right now is about 10 initial....

Now the mention of an exhaist leak may be real, as I just replaced the exhaust system with a bolt up kit from D&R.....maybe I need to go back a weld it all up instead of using the clamps...The vacuum leak could also be a real possibility as well, as most of the lines look very old...

Great info...thanks!
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post #11 of 17 (permalink) Old Jan 17th, 17, 07:16 PM
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Re: Exhaust Detonation / Timing

So have you always had this issue or did it just start?
If so what is the last thing you worked on before it started?
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post #12 of 17 (permalink) Old Jan 17th, 17, 07:21 PM
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Re: Exhaust Detonation / Timing

Get up close to your entire exhaust system and see if you can find any little carbon tracers at the connections, that'd be your leak.

X2 on the last thing you worked on before the decel popping.

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post #13 of 17 (permalink) Old Jan 17th, 17, 08:42 PM Thread Starter
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Re: Exhaust Detonation / Timing

This is a new ride for me... I bought it and drove it about a mile before I dismantled all of the engine accessories and cleaned and detailed the engine, gave it a tune-up and installed the new exhaust system... So I don't know what it was like before
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post #14 of 17 (permalink) Old Jan 18th, 17, 07:49 AM
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Re: Exhaust Detonation / Timing

My engine won't run at 2* - 4* initial, you'll need 10* - 12* initial I'd think as suggested and then 32* - 36* all in. The low initial timing was specified for emissions purposes with little regard for the best performance setting (IMHO).

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post #15 of 17 (permalink) Old Jan 18th, 17, 07:54 AM
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Re: Exhaust Detonation / Timing

Could be a spark issue as well. I would recommend dumping the points and going with an induction setup like MSD or Pertronix. Change out for a modern high output coil at the same time. The upgrade would be invisible and would eliminate your issues with dwell. Poor spark leads to unburnt fuel in the exhaust which ignites when load is quickly removed. Even if this does not solve your backfiring issues, it will make the car more reliable.

My comments about too much initial advance was related to that causing detonation on acceleration or "pinging". If you can run higher amounts of advance and the car still runs well and does not ping, then you are fine. More advance usually means better acceleration but the tradeoff can be detonation while under load.

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