Z06CE

I have a MSD billet distributor.
I'm using the lightest springs
I have 18 deg intial timing and 36 deg total all in about 2300 to 2500 rpm.
I think I have the blue or purple bushing installed.
The vacuum advance when connected is at 36 deg. At idle...
Is that correct?

7T1vette

No.

Z06CE

can you elaborate? 😆

Z06CE

Got the vacuum advance hooked up to the QJ as shown in pics.

C3USA#1

What’s the cam specs & manufacture?
Most all of today’s cams will need exactly what you’ve tuned.

7T1vette

Not at idle....

67:72

That's not much of a spread (18°) between 18° at idle and full 36°. My weights add 24° of advance between idle (12°) and 2800rpm (36°). You also have a high advance vacuum canister that adds 18° (my stock can is also high and adds 20°).

How is your idle speed and idle quality?
How does it drive across multiple speeds?
Any predetonation pinging (I wouldn't think so at just 36° total)?

Z06CE

Howards Roller Cam
.555 lift intake and exhaust
110 deg lobe separation
106 deg intake C/L
218.6 deg duration intake
226.6 deg duration exhaust

Z06CE

Idle speed is at 750 but spikes 50 rpm or so
​​​​​It drives ok but it feels like it should have more power for a 427
No predetonation.
I'm coming to the realization that the timing pointer is not at 0 deg TDC... not accurate. Set the intial timing at 29 deg and the idle is a lot better. Took it for a ride and no detonation.! Has more power.

derekderek

setting timing at 29 degrees. with or without vacuum advance? you suspect your TDC point. you can't be running that beast timed by ear.

Z06CE

I'm using a digital advance timing light. Vacuum advance is plugged off.. Set the advance 29 degrees. That's where the timing marks are lined up. No detonation.
I agree I need to verify actual top dead center.
BTW. The harmonic balancer is new.

Rescue Rogers

yes ot is correct for your question. 18* is your initial the 36* total is your initial plus your mechanical. When you plug in your vacuum can at idle you are seeing initial plus the vacuum advance which sounds like another 18*. You may have to limit it so your total doesnt exceed 50*

Rescue Rogers

Now onto having 18* initial is high. If you havent verified tdc at 0 you should, then re asses your settings

C3USA#1

not with modern cam.
at slow cruise with vacuum advance connected there could be 50+ timing. This falls back when throttle plates are opened and vacuum falls away. 18 initial and 36 in by 2800 is a great starting point however it’s a mute point since top dead center can’t be verified.

resdoggie

Using the lightest springs may be introducing some mechanical advance at idle. Have you checked with your timing light that there is no advance at idle speeds? Mech'l advance shouldn't begin until a few hundred or more rpms above idle.

CanadaGrant

On my 69 427/390 I run a Comp 270 hydraulic roller cam. I run 18 degrees initial advance with 18 degrees mechanical on the original 69 distributor. The trick is to limit the vacuum advance to about 12 degrees or so or you will get pinging/detonation when you step on the throttle. Aftermarket distributors and advance cans usually have way too much vacuum advance so you either have to limit it or run a different advance can. I run the original 69 MS360 advance can on mine as it produces 12 degrees of vacuum advance but vacuum advance limiters are available. I think Lars makes them if you get in touch with him.

Jebbysan

You need to verify and mark TDC #1 on the balancer. Your 18/36 setting is a good baseline. Take one silver spring off and run a silver and blue spring. The two light silver spring setup is too aggressive. The vacuum can is adjustable.......18 degrees vacuum adavnce is too much. Shoot for 30 degrees initial with the can plugged in to full manifold vacuum at idle......this means the can pulls 12.

Jebby

derekderek

i read this and said setting by ear is a bad thing. you said you are using a digital light not setting by ear. you set it to 29 deg initial. add the 18 mech you get and your full advance is 49 degrees. that is piston roasting territory. add vacuum advance and you are in the 60's until you know and trust that tdc mark, you are setting it by ear. if you drive it, which you should not, do not use full throttle. that is where all the bad stuff happens to pistons.

Z06CE

I found out why my timing readings are not accurate.
I have a Innova 3568 Digital Timing Light which may not be compatible with the Mallory Hyfire 6A and the MSD 8572 distributor. Is this true?
Which timing light could I use?

resdoggie

I have an Innova light also. It works perfect above 3000 rpm where multi spark discharge ends and only a single spark. Idle to 3000 rpm can be challenging on my timing gun at times.