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Old 10-14-2009, 09:43 PM
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SBC 355 Timing Question

I have finally installed the 355 sbc in my 74 Nova. It's a mild rebuild 9:1 compression, 882 heads, comp cam dual pattern 427/ 454 lift, edelbrock performer intake w/ edelbrock 600 cfm carb. HEI, jegs ceramic coated headers with 2.5" dual exhaust. What would be a good point to start at with base timing? Where should I start with total timing? It will be a street cruiser, just want the most go without effecting reliability.
Secondly I set the timing at 12 deg advance. I noticed the timing mark bounced between 10 and 12 degrees at idle. What could cause that? I used the original hei that came with the motor. I did install new cap and rotor, new wires, new plugs.
Thanks, Richard

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Old 10-15-2009, 06:34 PM
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Where do you have the vacuum advance hose hooked up to? 12 * is a good base but the timing mark shouldn't be jumping around like that. Do you have the vacuum hose pulled and pluged while your checking the timing? If you do I would suspect the dist. is worn.
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Old 10-16-2009, 10:33 AM
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Vac advance is hooked up to the edelbrock carb front drivers side port. Yes, removed vac line from dist and pluged with a small bolt before setting timing. If I get a new distributor is the summit just as good as the accel Hei? The price is better and they seem to have the same specs.
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Old 10-16-2009, 11:56 AM
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unhook your Vac- advance to set the timing. Run your total advance at between 32 and 36 degs . All in at 2500 RPM.
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Old 10-16-2009, 12:25 PM
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I'm not familiar with either. I've always used AC delco or mallory. sorry!
I'm sure you'll get feedback on that question though. Wait till everyone get's home from work for that answer.
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Old 10-16-2009, 01:51 PM
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Quote:
Originally Posted by Fasazu
I have finally installed the 355 sbc in my 74 Nova. It's a mild rebuild 9:1 compression, 882 heads, comp cam dual pattern 427/ 454 lift, edelbrock performer intake w/ edelbrock 600 cfm carb. HEI, jegs ceramic coated headers with 2.5" dual exhaust. What would be a good point to start at with base timing? Where should I start with total timing? It will be a street cruiser, just want the most go without effecting reliability.
Secondly I set the timing at 12 deg advance. I noticed the timing mark bounced between 10 and 12 degrees at idle. What could cause that? I used the original hei that came with the motor. I did install new cap and rotor, new wires, new plugs.
Thanks, Richard
First check it with the vacuum advance disconnected and the port closed to eliminate that as a potential cause. The next more difficult to isolate is the mechanical, which typically at idle shouldn't be engaging but here we make an assumption that this is true, but since this unit is not restrained vibrations, soft springs, excessive idle speed, etc, could be causing it to shake around and affect the base setting.

Worn bearings or drive gear of the distributor can affect the steady timing. The bearings, even with an HEI, can let the shaft orbit which will change the timing relationship of the reluctor on the shaft to the sensor on the distributor's housing. An excessive thrust clearance between the shaft and housing can allow the drive gear to move up and down in its engagement with the cam's gear, this will, also, change the timing of the distributor shaft.

Then consider the cam drive itself, two gears connected with a chain. There is plenty of opportunity for this to shake about, especially when being excited by the fairly slow idle speed which allows the crankshaft to slightly speed up and slow down as power strokes are applied and die away.

So there are a lot of possibilities that will cause the base timing to wander about a little bit. I really don't think a degree or two is enough to worry about. But it does demonstrate why racers go to crank trigger ignitions where possible.

Bogie
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Old 10-16-2009, 08:50 PM
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Thanks for the advise. I'll start trying to narrow it down in the morning. Hopefully this Wa rain will let up enough to get some time under the hood.
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Old 10-16-2009, 08:59 PM
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Hey, check out this site. www.kmjent.com they've got a 65,000v HEI w/adj. vacuum control for 49 bucks! wow, amost to good to be true.
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