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356-930 356-930 is offline
Acceleration Junkie
Join Date: Aug 2007
Location: Laguna Beach, CA
Posts: 263
Originally Posted by fredmeister View Post
This is exactly what I stated in my post, except I see 22 degrees of advance without vacuum connected because it runs right up to the 29 degree timing mark, I guess this is still within tolerance of 20 degrees which you said was normal.
But what bothers me is the fact that with 18 degrees allowable in the mechanical advance, this puts me at 47 degrees BTDC at 4000rpm with my current set up.
Now if I hook up the boost retard line and get back 8 degrees that leaves 39 degrees total under boost conditions. This still is about 12 degrees too far if you target 27 degrees BTDC at 0.8-1.0 bar boost which from previous posts on the forum I see as safe limit. Is 27 degrees too conservative or can I run more safely? What is a real safe timing limit above 27 degrees I hope.
In order to get here I need to run 5 degree ATDC timing at idle.....and from my experience the driveability of the car at low rpm is absolutely horrible at this setting. I have even run around 0-1 degree BTDC before and this is the reason I am now at 7 degrees BTDC.......
I cannot see how the factory set the car to run at 5 degrees ATDC and got the car to move out of its own way at low speeds.
Last season when I was running the 0.8 bar spring at these same timing settings it ran well and I never heard pinging. I just wonder if it was still happening just not audible enuff for me to pick up on it, or if something has changed in my distributor over the past few months.
Need to try teeing the vacuum line into the boost retard fitting on the dizzy can and at least getting that amount of retard back....thanks for the tips.
Agree, 5 deg ATDC yields no power.
Yes, 27 deg is conservative. 29 is reasonable but you are apparently well above that.
Try setting timing at 4000 by advancing until engine stumbles/mis-fires, back it off till smooth again. You won't hurt the engine as it's not under load. Even if timing gets high, no damage. See where timing settles at idle. If still 7 deg BTDC then that's where the engine is happy.
Do hook up the boost retard. If you're not running all the control valves, just plumb the vac and boost pots is parallel. Works for me.
It's possible the crank pulley is mis marked but not probable.
If you were running same timing at .8bar and didn't burn a piston, chances are you were not detonating. With 1bar, I'm with you, be concerned. Also agree that with all the noise these engines make under boost, hearing ping is impossible.
Bosch makes a knock sensor but I don't know how it works. Probably a piezo-electric accelerometer. Might be something to play with.
J & S Electronics makes a knock sensor system that might work (I believe it uses a Bosch ping sensor) but the single coil system will be out of production for another 2-months. It reportedly has a boost retard capability as well as adjustable rev limit. Don't have any experience with the product but it's specifications look promising.
If you can't wait for the J & S unit or if the advance you have used in the past is needed to wake up the low end and detonation at 1bar is a real possibility, go to the MSD ignition with boost retard module. You can pull out 15 deg total with that system.
Let us know how you resolve the problem.
Old 04-11-2008, 10:07 AM
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