Setting initial timing on 350 with no vacuum

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10-22-2007, 01:18 PM
richmondb

Setting initial timing on 350 with no vacuum

Okay guys. I need some help setting my timing up on my Chevelle. First let me tell you about the engine. I have a 350 bored .30 over with a Comp Cams XE268, World Products SR 68cc heads, and a Mallory unilite distributor. I just bought my first timing light and am trying to get this newly rebuilt engine running smooth.
There are 3 different curves I can choose from depending on where my vacuum advance is hooked up: the carb, the intake manifold, and plugged. Here are my curves under the 3 conditions:

Plugged:
800: 10 degrees
1000: 11 degrees
1600: 22 degrees
2000: 28 degrees
2600: 31.5 degrees
3000+: 36 degrees

Hooked up to the manifold:
800: 34 degrees
1000: 35 degrees
1600: 47 degrees
2000: 52 degrees
2600: 56.5 degrees
3000+: 60.5 degrees

Hooked up to the carb:
800: 10 degrees
1000: 11 degrees
1600: 43 degrees
2000: 50 degrees
2600: 56 degrees
3000: 58.5 degrees
3600+: 60 degrees

My question is which one do I use, and what should I adjust the distributor to? As you can see I don't have much vacuum from the carb at low RPM.

Any help would be greatly appreciated.
10-22-2007, 01:34 PM
TyphoonZR

First off, you want to set your timing with the vacuum disconnected. Then depending on the amount of timing advance in the distributor, you go from there, but in any even, you do not want more than 38 degrees total timing at 3000 = rpm. This could mean that at idle it is 16 degrees. You want to be carefull not to have more than 38 degrees at full throttle.

I always hook up my vacuum at the manifold. In this way at light throttle I have plenty of advance for throttle responce and smooth idle but at full throttle I have no vacuum advance, just mechanical and in this way I am ensured no predetination.

Hopefully that helps, we'll see what light some others can shed on this topic.
10-22-2007, 01:36 PM
nitrowarrior

Have you actually fired it with a timing light hooked up? Numbers seem out of line for your setup.
10-22-2007, 02:52 PM
richmondb

Yes I fired it up with the timing light hooked up. That's the way the timing light instructions had me do it.
10-22-2007, 03:19 PM
richmondb

I capped off the vacuum lines and adjusted the initial to 18 degrees at 650 RPM with 45 degrees all in at around 3000 RPM.
10-22-2007, 03:29 PM
jerry clayton

Make sure you use 87 octane
10-22-2007, 04:04 PM
richmondb

My compression is around 9.5:1 so I use premium and it doesn't ping. Can I use too high of an octane?
10-22-2007, 04:06 PM
richmondb

Should I leave it capped off?
10-22-2007, 04:30 PM
richmondb

At 10 degrees I don't get as much punch at take off as I do with 18 degrees. I was reading one of the old forums where it said I should have 16 to 18 initial.
10-22-2007, 04:51 PM
pat mccarthy

the vacuum should not be bad? low is 2or4 going to a lighter spring will help with the punch i would not run 16 on the crank try 10 to start you want all of it in at 3000 or less .with out vacuum pull hook up and adjust the pull were you want it
10-22-2007, 05:24 PM
35Mastr

I dont want to hijack the thread.But have some ? myself.I have been reading along here and am a little confused on this timing issue.I am also running a sbc 350 stock motor with and edelbrock 650 carb and a ready to run MSD dist.No box.If I set the timing to 16 with the advanced on the dist disconnected.Then connect it after thats done. I had 36 at idle@650RPM.Is this correct.
10-22-2007, 05:27 PM
krazziee

like the man said ........ no more than 38 degrees total advance above 3000 RPM all the way up to full throttle , it should give total advance by 3000 RPM, the rest would be in the dist. with the weights and springs to get it to crank easy and have the advance curve that you want , that is my understanding of it and that is what I do. It seems to work well for me.
10-22-2007, 05:37 PM
richmondb

So according to that, I should dial it back to 10 degrees at idle and plug the vacuum advance and not even use it so I have 36 total all in at 3000?
10-22-2007, 06:56 PM
TyphoonZR

Richmondb,
1. start your engine,
2. disconnect the vacuum,
3. set the timing at 38 degress at 3000 rpm
4. bring the engine to an idle and see what the timing is
5. connect the vacuum.
10-22-2007, 07:05 PM
skids72

I won't say 38* max is a hard fast rule, but 45 total mech (i.e. not vac) is really high for your application. I have run up to 42* on pump premium at 10.2:1 compression but I'm at high altitude and can get away with it.

I think for your application 36* total, probably around 12* on the crank is a very good starting point and you can tweak from there.

-Chris
10-22-2007, 07:14 PM
pat mccarthy

just pull back just before the pistons melt in to the oil pan:3dSMILE: if you have 10 on the crank and 26 in the dist then its 36. or 12 on the crank and 24 is 36 good place to start go to lighter springs to get it all in at 3000 or lower 2500. this works for me and have set up many this way this works i would not run 40 on it should not need that much . if you have a MSD they are very easy to do .what do you have ?you can pull 50 but will help around town but you do not need it under aload:eek:
10-22-2007, 07:34 PM
HemiTCoupe

Is the answer here?

http://www.chevelles.com/forums/show...ghlight=timing

Pat
10-22-2007, 07:55 PM
pat mccarthy

Quote:

Originally Posted by DennyW

That does look familiar, doesn't it ?? :LOL:

why yes it do:LOL: hey denny nice head lights:D :D
10-23-2007, 06:10 AM
Eliot Ness

Quote:

Originally Posted by HemiTCoupe

Is the answer here?

http://www.chevelles.com/forums/show...ghlight=timing

Pat

Could I break in and ask a quick question? I get the impression from that linked thread above that a mechanical advance distributor is not recommended for the street, do you guys agree with that? I have an Accel 51000 series electronic (mechanical) distributor and I'm wondering if I'd be better off with a vacuum advance?

Also with a mechanical distributor should the numbers (i.e. advanced be the same) as on a vacuum advance (with the vacuum plugged)?

Thanks
10-23-2007, 11:42 AM
richmondb

Just trying to get all the help I can :) I am going to go with the consensus and crank down the initial back to around 12 so that I have a total of around 36. In the past I have found that the guys on the Chevelle forum know Chevelles but you guys know more about engines.
10-23-2007, 02:14 PM
skids72

Quote:

Originally Posted by Eliot Ness

Could I break in and ask a quick question? I get the impression from that linked thread above that a mechanical advance distributor is not recommended for the street, do you guys agree with that? I have an Accel 51000 series electronic (mechanical) distributor and I'm wondering if I'd be better off with a vacuum advance?

Also with a mechanical distributor should the numbers (i.e. advanced be the same) as on a vacuum advance (with the vacuum plugged)?

Thanks

I think that is the case... you're mechanical curve should remain the same, the vac advance just puts more in when you have a light load. This helps fuel efficiency tremendously, also helps to run cooler. I run a mech only distributor and my road mileage is horrible (6-7mpg if I'm lucky). I might swap back to a vac advance and just disconnect the vac on race day... I'm slow to do it because I spent good money on the distributor I have now. The right answer for me is to get a trailer **)

-Chris
10-23-2007, 02:29 PM
jerry clayton

I seem to remember that the vacume on a ford was adjustable with a allen wrench thru the inside of the nipple on the dist vacume diaphram---but remember I'm getting old--what were we talking about?

Jerry