[nolimitpkr]

I am in the process of installing a new msd streetfire. I bought the advance kit and as it stands I am going to install the light springs along with the weights from the kit(pn,msd-8428). This should give me 24* of mechanical advance at 30000 rpms, along with 12* initial my total should end up right around 36* @30000 rpms.

So the question is, will 12* of initial be enough? My cam specs are .474/.498 amount of lift, and the duration @.50 is 214/220. Motor is a 383 with dart pro 1 heads. I see most people like to run 14-16* degrees on their initial......

Thanks
Brian........

 

[Munro]

Thats a pretty small cam so you should be fine. My experience has been the bigger the cam the more initial you need. Make sure you have vacume advance too but it may need to be limited.

 

[nolimitpkr]

Yes I will be running the vacuum advance, if the total timing with the vaccum advance connected is under 50* will I be alright?

 

[Jerry Briggs]

I try to start at around 12-15 with a total of 36-38. Jb

 

[gnicholson]

Try hooking the vac. adv. to both ported and manifold when setting your idle.Manifold vac. should give you plenty of advance at idle with your 12 deg.Your comb. should like 45 - 50 deg. at part throttle high vacuum cruise conditions.If it pings during those conditions you will have to adjust the rate or slot length of your vac. adv.

 

[vrooom3440]

For ignition timing the real objective is to achieve maximum cylinder pressure around 20 ATDC at any speed and/or loading.

As mentioned, typically the amount of initial advance increases as cam duration and overlap increases. Bigger cams corrupt the mixture with burnt exhaust gasses more and generate lower cylinder pressures at idle, both of which slow down mixture burn thus needing more advance.

The "total" amount of mechanical advance stays the same at about 36-38* for typical Chevy engines. This parameter is most influenced by combustion chamber design. Which is why the new Vortec type heads require less advance.

At cruise another factor comes into play, which is that lean mixtures tend to burn slower than rich mixtures. Thus economy carb settings and lower cylinder pressures of cruise will need more advance. Like total this is pretty consistent across Chevy engines at 50-52*.

Now in this instance the cam duration is not that long, usually this becomes an issue when duration goes over 270* advertised. An initial of 12* may well work. A good way to make sure it works though is to configure a vacuum advance on manifold vacuum. This will give you some extra at idle when you need it.

 

[nolimitpkr]

For ignition timing the real objective is to achieve maximum cylinder pressure around 20 ATDC at any speed and/or loading.

As mentioned, typically the amount of initial advance increases as cam duration and overlap increases. Bigger cams corrupt the mixture with burnt exhaust gasses more and generate lower cylinder pressures at idle, both of which slow down mixture burn thus needing more advance.

The "total" amount of mechanical advance stays the same at about 36-38* for typical Chevy engines. This parameter is most influenced by combustion chamber design. Which is why the new Vortec type heads require less advance.

At cruise another factor comes into play, which is that lean mixtures tend to burn slower than rich mixtures. Thus economy carb settings and lower cylinder pressures of cruise will need more advance. Like total this is pretty consistent across Chevy engines at 50-52*.

Now in this instance the cam duration is not that long, usually this becomes an issue when duration goes over 270* advertised. An initial of 12* may well work. A good way to make sure it works though is to configure a vacuum advance on manifold vacuum. This will give you some extra at idle when you need it.

Great info thanks everyone...