Ignition timing & vac reading

Mr. O

New Member
Apr 20, 2020
3
1
3
74
upstate NY
Looking for advice on initial timing number. Newly rebuilt 400 sbc. Bottom end is stock. Aftermarket heads: iron, 72 cc, 210 cfm intake flow. Hydraulic flat tappet cam: 443 lift, 214 duration, 110 separation. Aluminum dual plane intake: 165 cc runner. Carb: 600 cfm dp. Stock hei distributor: 20 deg. built in. Running with a manual 4 speed transmission. What should I set idle timing at? Have messed with 10 to 18 deg. btdc. Cannot get a vac rdg above 14-15". What is an acceptable vac rdg & where should my be initial timing? Any thoughts?
 
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Vilanus

Daily Driver
Jun 2, 2019
22
1
3
Canada
Hi, first 15" of vacuum is great! Basically you Will want as Much vac as you can get from tour initial timing. Factory is 8deg on a sbc. But depending on your setup initial timing could be anywhere from 10 to 20. So you need to set intial timing where the vaccum reading is highest.
 
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Mr. O

New Member
Thread starter
Apr 20, 2020
3
1
3
74
upstate NY
Hi, first 15" of vacuum is great! Basically you Will want as Much vac as you can get from tour initial timing. Factory is 8deg on a sbc. But depending on your setup initial timing could be anywhere from 10 to 20. So you need to set intial timing where the vaccum reading is highest.
Good to hear 20" of vac isn't necessary. Thanks for your info. I'll try adjusting dist. for best vac rdg. It is at 12 now that gives the 14". We'll see.
 

Killerdave8813

Dragway Regular
Jan 16, 2008
904
2
18
Cincinnati,Ohio
I've got a 350 with around 9 to 1 compression, Dart 180 Aluminum heads, Edelbrock Performer EPS, 600 Holley, HEI and a Comp solid cam with (I don't remember the exact numbers) somewhere in the 280 degree duration and .512 lift range with 1.5 to 1 roller rockers, I run 12 degrees initial and 36 total timing with the vacuum advance hooked up for constant vacuum so the timing drops when you initially step on the throttle, I have a dedicated vacuum gauge in the car and it idles at 15-16 " cruises at 20-21" and on deceleration I've seen as much as 26", I run it in front of a 4- speed transmission, it's got a really cool choppy idle, great throttle response will spin 6500 rpm in a heartbeat and runs on 87 octane fuel, what's not to Love, every part plays into a combination, I got lucky but I also didn't go too radical with anything as I was shooting for a good tractable street engine which it is and then some, tune your idle air screws to the best vacuum you can get, as much timing as you can without ignition rattle and keep in mind SBC's don't like much over 36 degrees and go for it!! Hope this helps, Later
 

Mr. O

New Member
Thread starter
Apr 20, 2020
3
1
3
74
upstate NY
I've got a 350 with around 9 to 1 compression, Dart 180 Aluminum heads, Edelbrock Performer EPS, 600 Holley, HEI and a Comp solid cam with (I don't remember the exact numbers) somewhere in the 280 degree duration and .512 lift range with 1.5 to 1 roller rockers, I run 12 degrees initial and 36 total timing with the vacuum advance hooked up for constant vacuum so the timing drops when you initially step on the throttle, I have a dedicated vacuum gauge in the car and it idles at 15-16 " cruises at 20-21" and on deceleration I've seen as much as 26", I run it in front of a 4- speed transmission, it's got a really cool choppy idle, great throttle response will spin 6500 rpm in a heartbeat and runs on 87 octane fuel, what's not to Love, every part plays into a combination, I got lucky but I also didn't go too radical with anything as I was shooting for a good tractable street engine which it is and then some, tune your idle air screws to the best vacuum you can get, as much timing as you can without ignition rattle and keep in mind SBC's don't like much over 36 degrees and go for it!! Hope this helps, Later
Appreciate the feedback. Even though your engine is a stronger set up than mine the 15 " is okay. I continually heard 20" was expected for sbc. I'm gonna mess with the idle mixture as you suggest. Thanks.
 

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