Ridiculous Initial Timing
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Joined: Nov 2020
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From: Vacaville, CA
Ridiculous Initial Timing
Hey all!
Anyone know why my BBC struggles at any initial timing below 25, and sounds best at around 40°?! Initial for big blocks should be well under 20 iirc. All wires are going to the right spot, this blows my mind! I’m scared to go near total timing like this!
1050 Holley Dominator
272 @.050 Lunati Cam
365cc Dragon Slayer Heads
I really don’t think the build matters but just extra info to isolate the problem. Thanks!
Anyone know why my BBC struggles at any initial timing below 25, and sounds best at around 40°?! Initial for big blocks should be well under 20 iirc. All wires are going to the right spot, this blows my mind! I’m scared to go near total timing like this!
1050 Holley Dominator
272 @.050 Lunati Cam
365cc Dragon Slayer Heads
I really don’t think the build matters but just extra info to isolate the problem. Thanks!
Thread Starter
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Joined: Nov 2020
Posts: 55
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From: Vacaville, CA
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From: Youngstown Ohio
For your engine you need to have the dizzy custom curved. Total timing 35-40° by around 3000 rpm, with initial at around 20-25°. This would mean about 14-16° mechanical built into the distributor. A 270° @.050 cam will not idle low.
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From: Vacaville, CA
Custom advance dizzy eh? Something for me to look more into! Thanks for the input. Ill try turning the idle up a bit too, it sits at around 600 now. A cam that big should be around 1000, no?
Tech Contributor
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From: At my Bar drinking and wrenching in Lafayette Colorado
That cam needs initial timing in the high 20's and an extremely short centrifugal curve of about 8 to 10 degrees. You're not going to be able to use vacuum advance on an engine with that cam, so you have to make up for the timing loss at idle with pure initial timing. 600 rpm idle is crazy - it should be up around 1000-1100.
Lars
Le Mans Master
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From: Hermosa
If you can get it to idle @ 600 RPM then it's pretty happy with your initial timing. No reason to idle it up.
Is my vette stock?? HAHA
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did you verify top dead center? maybe your distributor slipped
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From: Cool Northern Michigan
People that lock their dizzy are 80% strip and 20% street.
You better have a good battery & starter. In these situations, an IGN Off switch is installed. The engine is cranked fast, then you hit the IGN to fire it up.
That will prevent kick-back, busted starters.
Are you willing to install that for daily driving?
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i disagree. you are idling at 600 cuz you have too much initial. get your 38 to 40 full advance and see what initial is and live with it with idle cranked up. OP said he didn't want to go near full advance with that initial. then he can never drive over 2500 or so rpm, cuz it goes to full advance whether you are looking at a timing light or not.
Burning Brakes
Joined: Apr 2020
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From: Western NY
If you have a MSD pro billet dist there is a company called four seconds flat - I think and they sell 2 custom bushings for that dist - a 14* and 10*. I use the 10* with 22*-24* initial on my 496. They ain’t cheap - around $40 I think but they work. It probably would not be a big deal to make a set .
Pat
Pat
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From: Vacaville, CA
I love this site, so many enthusiasts that know so much about every issue! I’ll certainly look into those bushing limiters. As for the low idle, sounds like the best thing to do is take some timing out and raise the idle up a bit. Thank you all!
-Sam
-Sam
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I'm assuming you an MSD distributor? They typically come with several bushings. The black one is the largest and will allow you to crank in appropriate initial and then make up the rest as centrifugal and it will have several springs to choose from to determine the rate of advance.
JIM
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I would like to see 22 to 26 initial at 850-950rpm idle. Then total all in by 2800-3200rpm 34 to 38. Then vacuum advance 44-50* btdc for highway cruise.
The spread depends on compression and fuel quality. Using 93 octane at 9:1 you will be closer to the upper numbers. 11:1 compression it will be less timing, the lower numbers. If using alcohol fuels as methanol or ethanol then the higher timing numbers. If the engine is high compression then starting could be an issue so like somebody said, get it spinning first then hit the ignition. Or some kind of starting retard box I guess. Probably would start well with 8 to 12* of timing if very high compression.
The idle A/F ratio has a large influence on idle quality. If you idle 13's it will smooth out and can use less timing. But if you run a crisp 15:1 idle a/f ratio which is what I recommend to control carbon buildup and keep plugs clean, it will take more timing and idle rougher. Rough idle is nothing to worry about but if it annoys you then... its better to drop the cam than drop the a/f ratio and timing.
The spread depends on compression and fuel quality. Using 93 octane at 9:1 you will be closer to the upper numbers. 11:1 compression it will be less timing, the lower numbers. If using alcohol fuels as methanol or ethanol then the higher timing numbers. If the engine is high compression then starting could be an issue so like somebody said, get it spinning first then hit the ignition. Or some kind of starting retard box I guess. Probably would start well with 8 to 12* of timing if very high compression.
The idle A/F ratio has a large influence on idle quality. If you idle 13's it will smooth out and can use less timing. But if you run a crisp 15:1 idle a/f ratio which is what I recommend to control carbon buildup and keep plugs clean, it will take more timing and idle rougher. Rough idle is nothing to worry about but if it annoys you then... its better to drop the cam than drop the a/f ratio and timing.
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what do you do with this car that needs a cam like this? displacement? CR? because 427Hotrod (post 13 above) has a big block runs high 8's and i don't think he runs a cam this radical. i joined offshoreonly back when i thought i was young enough to crawl around on top of a big block jammed under a boat back seat. and in engine discussions i remember a guy saying that was too much cam for such a small engine. i was thinking "it's a 454! WTF?" then i found out those guys were running 540's at the smallest. i think you overbuilt this 489 and will be a lot happier with a shorter duration cam and some thicker head gaskets to drop CR a bit.
Last edited by derekderek; Jun 4, 2022 at 07:55 AM.
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Im far far from being an expert. I bought a 68 NOM BB and I have no idea of the comprssion ratio, cam specs, or even displacement. Bubba (s) was deep into all areas of the car. Distributor had no vacuum advance and I had to index it to get one to fit. Pointless conversion had a protruding screw that was interfering with the mechanical advance. After some trial and error I got the timing to 38 at 2800 and the initial fell out to 23. Had to limit the vacuum advance. Won't idle below 900. No pinging and runs great. I guess my point is if the engine performs well then the timing numbers are whatever the numbers are.
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From: Vacaville, CA
what do you do with this car that needs a cam like this? displacement? CR? because 427Hotrod (post 13 above) has a big block runs high 8's and i don't think he runs a cam this radical. i joined offshoreonly back when i thought i was young enough to crawl around on top of a big block jammed under a boat back seat. and in engine discussions i remember a guy saying that was too much cam for such a small engine. i was thinking "it's a 454! WTF?" then i found out those guys were running 540's at the smallest. i think you overbuilt this 489 and will be a lot happier with a shorter duration cam and some thicker head gaskets to drop CR a bit.
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I built this 489 for a weekend monster/strip. I have a solid valvetrain/bottom end to see 7000+ rpm. I wanted as much hp as possible past 5,500. I went with an Edelbrock single plane intake, monstrous heads and fat cam to support this high RPM. This IS a pump gas car, so compression is 10.4:1, which i know isn’t best for bigger cams.
JIM
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From: Memphis TN
Hey all!
Anyone know why my BBC struggles at any initial timing below 25, and sounds best at around 40°?! Initial for big blocks should be well under 20 iirc. All wires are going to the right spot, this blows my mind! I’m scared to go near total timing like this!
1050 Holley Dominator
272 @.050 Lunati Cam
365cc Dragon Slayer Heads
I really don’t think the build matters but just extra info to isolate the problem. Thanks!
Anyone know why my BBC struggles at any initial timing below 25, and sounds best at around 40°?! Initial for big blocks should be well under 20 iirc. All wires are going to the right spot, this blows my mind! I’m scared to go near total timing like this!
1050 Holley Dominator
272 @.050 Lunati Cam
365cc Dragon Slayer Heads
I really don’t think the build matters but just extra info to isolate the problem. Thanks!
a motor like that should have timing locked ,32-36 total degrees full time (i ran mine at 36)
no advance no curves ..... You will prob need a good mini starter and an MSD timing retard on start up
depending on cranking compression ..Idle will be at around 900-1000 in park and not much change in gear
Also if you have a 4500 carb they usually do not come with power valves,you may want to add a 4.5 to the front bowl
and change the primary jets so you dont foul the plugs and ride like a pig...
I ran a 454 Roller motor on the street for years,1050,700 lift etc etc..Shakes the ground !
Last edited by excelerater; Jun 5, 2022 at 07:30 AM.