I have been fine tuning my timing today.I was trying to get alittle ping that was present at about 2000 RPM in 4th gear which is about cruising speed.When I would step on the gas at this RPM I would get alittle pining from the motor.I have an MSD pro billit dist with a 6A box.I started with the black bushing 18* mech and 18* intitial with the vacuum @15* with the two blue springs which is all in at 2500 and I was getting pining at 2000 with this so I backed off the initial timing all the way to 12* initial to get the ping out.I know the motor should be set at a higher inital so I went back to the 18* and put in the next stiffer spring set up so that the advance would come in later which is the heavy silver spring and the light silver spring which had it all in at 3000 and I had to back the initial to about 14* to get the ping out.So I went to the next stiffer spring set up which is the heavy silver and the blue spring which is in at 3300 so with my initial set at 16* with the 15* from vacuum and 18* mech the ping is now gone through the whole rev range.

So my question is do I need more total timing or is 34* enough?? I could put the blue bushing in that will give me 21* mech for a total of 37* and with the springs that I have in it wont change the curve of advance just that the total wont come in until 3500.

sounds like you're on the right track. try the bushing see what it does.

IMO you want to back up a couple degrees from audible detonation though. sub-audible detonation exists and there's the inevitable tank of bad gas.

IMO you want to back up a couple degrees from audible detonation though. sub-audible detonation exists and there's the inevitable tank of bad gas.

Bingo, I'm thinking the exact same thing.

If you're not running 93 Octane (I'm assuming you are), you should be - of course, then you'll have to do this all again...

Yes Im running high octane gas.I just put the blue bushing in and will be going out for a ride.initial is set at 16* with the blue bushing at 21* for a total of 37*.The 16* is down 2* from ping at 18* intial but will try 15* to be safe.

You had it right the first time with the 18* base and 18* mechanical.The problem is the 15* of vacuum advance.
34* total isn't enough...set it for 36-38* total and back your vacuum advance off so it only puts out 10* and not 15*

How would the vacuum advance effect it at 2000 rpm??Is it pulling vacuum at 2000 rpm at light throttle??And how do I limit the vacuum advance to 10*.It is the elchin that comes all in at 8" and 15* advance as my motor has 10 1/2" at idle

How would the vacuum advance effect it at 2000 rpm??Is it pulling vacuum at 2000 rpm at light throttle??

It's pulling planty of vacuum at 2000

try running w/o the vacuum advance with 38* total and see if it still pings at 2000

Mr4speed I reread the ignition 101 thread and yes I see that it will be working at 2000RPM.I made a vacuum stop and have it down to giving me 11* instead of 15*.I can still adjust it to a lower vacuum if I want so I reset the initial to 18* and will start again with the two light blue springs and the black mech (18*) and start again.Just my luck though it started to rain so no test driving right now.It should clear up by WED and I will let you know how it goes.

Ok I have the vacuum advance only putting out 10* and I have 17* initial and 21 mech for a total advance of 38*.The car seems to idle better as in it sounds like it has a cam in it now.Before with the 15* vacuum advance at idle it sounded like just a big motor.Still have to test drive the car,and I also put back in the heavy silver spring and light silver spring to have it all come in at about 3200 RPM.I still have to test drive the car and I think it will be nice enough to do it tommorow.

Keep us posted. I need to go through the same exercise that you are going through with mine. I tried 18 initial and the black bushing but got pretty bad pinging out of it. I backed the initial off to 12-14 and the pinging went away but I haven't tried swapping the bushing yet for more total so I very interested in your results.

Rich, what's your CR? can you give a little rundown on your build?

Kevin, you too? basic build specs and CR?

Rich, what's your CR? can you give a little rundown on your build?

Not trying to high-jack but since you are Moderator I guess it's okay just this once.

355
holley aluminum heads, 68 cc, 2.02/1.60 valves
11.8 cc domed pistons, actual compression is around 11.3-11.4 to 1
1.5 roller rockers
lunati hydraulic cam .490/.490, 235/240@.050, 290/297 adv. dur., 112 lsa.
holley street dominator intake
holley 770 cfm vac. sec. carb.
msd distributor and 6A box
1 5/8" headers, 3" exhaust
turbo 350, 3000 stall
was 3.36 gears now 4.11 (no runs yet)
Stock bodied 69 malibu
BFG drag radials 275/60/15

That's about it. Let me know if you need any more info.

Thanks, Rich

Thx Rich. Are you using it for a street car at all?

Rich,with 11.3 to 11.4 to 1 compression I would not run vacuum advance IMHO and experience. How much cylinder pressure do you have?

Kevin,keep us posted..hope the ride is good with no ping.

Tom,

Yes I drive it on the street. 93 octane. I drive it mostly around town, not much interstate stuff.

Chris,

I don't run vacuum advance. I have no idea what the cylinder pressure is. It had a fresh rebuild about a year and a half ago. Mileage is still pretty low.

Rich

396 .030 over (402)
closed chamber oval port heads with stock valve size about 9.8-10-1 CR
1.7 aluminum roller rockers
dual springs
comp cams 233 dur 555 lift flat tappet hyd
air gap intake with 770 SA carb
MSD probillet dis with 6A box
headers 2 2/1 exhaust
Tremec 5speed
3:73 12bolt posi

Street car might go to the track just to see what it will run but not sure.Dont want to brake anything.

Hey 69BU dont worry about a thread jack I dont mind at all.Im in the learning stages also and want all the info I can get.:thumbsup:

Kevin, do you know what pistons you have? Are they the stock type with the small domes?

How about just putting heavier springs in the distributor to slow the curve down?

MSD's comes with the heaviest springs from the factory, comes in at like 4500 rpms. I ran mine like that for years, then put light spings to get it in all by 3000. I even had it come in as early as 1800 rpms. I never felt a difference in performance.

Tom they are 844-L2240NF30 which I think are stock type pistons with a small dome.I see with 100cc heads it gives you about 8:1 compession ratio.My heads are 3904390 and are supposed to have a 96cc chamber.I did some looking around and my how to rebuild the BBchevy says they are 96cc but I did some looking on google and found up to 98cc so now iam not sure.Im sure I have lower compression than first thought.I bought the car with the motor in it that was just rebuilt but didnt get the info on CR.But I have tore it apart to make it my own.

Also the weather cleared up and I went for a drive.The initial was set at 17* with 10* vacuum advance with 21 mech.NO PING.Bumped the initial up to 20* NO PING.Im going to leave it there cause its running good.Im going to put the 18* bushing back in for mech for a total of 38*.It seems to be working.

ALSO HAVE TO GIVE PROPS TO MR4SPEED FOR THE VACUUM ADVANCE SUGGESTION.It seems to be working:thumbsup:

How about just putting heavier springs in the distributor to slow the curve down?

MSD's comes with the heaviest springs from the factory, comes in at like 4500 rpms. I ran mine like that for years, then put light spings to get it in all by 3000. I even had it come in as early as 1800 rpms. I never felt a difference in performance.

I tried evey combo of springs and nothing got rid of the ping so Im sure it was the vacuum advance having to much advance.I will try different springs now to see what it does if anything.Right now it has the stiff silver and soft silver in it to come all in at about 3300 but I will be changing out the bushing back to the black one to give me 18* mech and it will all be in at 3000.I think if it runs good there I will just leave it alone and quite driving myself nuts with it.

Also the weather cleared up and I went for a drive.The initial was set at 17* with 10* vacuum advance with 21 mech.NO PING.Bumped the initial up to 20* NO PING.Im going to leave it there cause its running good.Im going to put the 18* bushing back in for mech for a total of 38*.It seems to be working.

ALSO HAVE TO GIVE PROPS TO MR4SPEED FOR THE VACUUM ADVANCE SUGGESTION.It seems to be working:thumbsup:

Kevin,glad I can help!! :)

Kevin,glad I can help!! :)

Ok here is an update.Took the car on a 200mile each way trip to a car show here in Washington.The car ran fine until I hit some hills where in 5th gear at 2000 rpm got some bad ping so I stoped and backed off on the timing to 17* initial and put the biggest springs in the dist. That did better but still at times I get a little ping on a hill but it all depends on how much throttle I give it.I think I will back off alittle more on the initial.