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Old 12-21-2008, 06:53 PM
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Help Setting Initial Timing on Chevy V8

I've got my motor back together with some new valvetrain parts. I have the initial timing (no centrifugal and no vacuum advance) set around 16 deg BTDC @ about 700 RPM. I think there are several theories and methods of setting the initial timing. I don't know them. I've just heard that 14-18 deg BTDC is a good base point, and that you want all advance to be in by about 3000 RPM, and no more than about 38-40 deg total advance.

Having said that: Back to the initial question: What is the best way to set initial timing? Do I work backwards, and set the "total advance" instead or initial, or do I set the initial timing only - and then make sure the total is not more than 38-40?

I've got a 468 Chevy with a solid roller cam (performance), ported iron heads, 10:1 compression, headers, dual plane intake, MSD dist with vacuum canister and centrifugal advance bushings and springs (adjustable) with the "blue" bushing installed (21 deg cent advance), 850 CFM carb, etc.

I also have a good digital timing light that allows me to do advance features.

where do I begin?

Lee

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Old 12-21-2008, 07:06 PM
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How big is the cam? Big cams like more timing.

Last edited by Jsup; 12-21-2008 at 07:12 PM.
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Old 12-21-2008, 07:12 PM
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Total timing you want minus total advance your distributor has= Your base timing. Just verify what your total advance really is. I always set my base timing and work from there.
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Old 12-21-2008, 08:24 PM
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Quote:
Originally Posted by Jsup
How big is the cam? Big cams like more timing.
It's a comp cams 11-771-8 Extreme Energy (on billet core -9)

280/286 duration, (242/248 deg duration @ .050" lift)

.646 .653 valve lift intake/exhaust. 110 LSA
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Old 12-21-2008, 08:29 PM
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That's a pretty big cam. Similar to my specs. I can't get an idle under 10* base. I'm set at 12* base if that helps you at all. Then it's all about the weights.

I'm not totally done with the tune, and I'm not doing the tuning, just shadowing the guy who is. I can't tell you the total timing at this point we changed it so many times.
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Old 12-21-2008, 08:44 PM
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Quote:
Originally Posted by Jsup
That's a pretty big cam. Similar to my specs. I can't get an idle under 10* base. I'm set at 12* base if that helps you at all. Then it's all about the weights.

I'm not totally done with the tune, and I'm not doing the tuning, just shadowing the guy who is. I can't tell you the total timing at this point we changed it so many times.
Mine idle's pretty good with the initial set at about 18 deg BTDC. No problem there.

The frustrating part for me is, I can probably get it to start, idle, and run good at different initial timing settings (14, 16, 18 deg BTDC). I don't know where it runs best though. Very frustrating. My motor is probably 550 HP. I don't know. So if you loose or gain 10-20 HP by messing with the timing, it's kind of hard to tell by just driving it. A dyno would be best but I don't have access to one.

How do the pros do it? Do they use a dyno and see where it runs best at? I mean if I have to pay a shop $100 to dyno it and find the "magic timing" setting, maybe I'll do it. Any suggestions?

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Old 12-21-2008, 08:49 PM
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Quote:
Originally Posted by leejoy
Mine idle's pretty good with the initial set at about 18 deg BTDC. No problem there.

The frustrating part for me is, I can probably get it to start, idle, and run good at different initial timing settings (14, 16, 18 deg BTDC). I don't know where it runs best though. Very frustrating. My motor is probably 550 HP. I don't know. So if you loose or gain 10-20 HP by messing with the timing, it's kind of hard to tell by just driving it. A dyno would be best but I don't have access to one.

How do the pros do it? Do they use a dyno and see where it runs best at? I mean if I have to pay a shop $100 to dyno it and find the "magic timing" setting, maybe I'll do it. Any suggestions?

Well, I have a guy who I think is one of the best in the business doing my tune. FOR MY CAR, A 1990 CORVETTE few people know this care like he does. Greg Carroll of Carroll Supercharging.

His method, and he's a bit old school.....get the tune right, once the tune is right (remember I'm running fuel injection) keep moving the timing up till it pings, then back off a couple degrees. Basically, trial and error. Then check the AFR to ensure it's not running too lean.

I'm sure people are going to yell and scream it's not scientific enough...but makes sense. THEN adjust the spark plug temp until you get to the coldest ones you can put in, and you're done. I'm sure you'll get different schools of thought on that too.

Hope any of this helps. There's nothing you can't do on the street for timing that you need a dyno for. A dyno is just more convenient.

BTW, if you're getting away with 18, that's an awful lot.

Last edited by Jsup; 12-21-2008 at 09:00 PM.
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Old 12-21-2008, 10:08 PM
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You'll make the best power with 38deg timing on most all BBC's.
Exceptions are BBC's with huge piston domes that disrupts combustion speed or race gas that slows fuel burn combustion speed.
Shortening/limiting the amount of mechanical advance travel in the distributor will allow more initial at idle without overadvance at high rpm.
For your motor I suggest 18 to 22deg at idle and 38 total.

How do you tell how much timing is required to make best power?
You can put the car on a dyno or take it to a dragstrip and make time trials.
You want to watch the trap MPH. More 1/4 mile MPH = more power.
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Old 07-10-2013, 08:06 PM
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Initial Timing

Is anyone going to answer the original question,,,What is the best way to set initial timing??
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Old 07-10-2013, 08:17 PM
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That cam will require 20+ degrees initial at the crank.....plus centrifugal up to the limit of 38......
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Old 07-10-2013, 08:18 PM
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timing

Quote:
Originally Posted by Joer5000 View Post
Is anyone going to answer the original question,,,What is the best way to set initial timing??
dont make fbird mad,,, he will get you there,
I ran my 454 with 36 total and 18 initial.That gave me my best ET. Thats a good place for you to start.The initial timing will depend on "your" engine,not BBs generally.
If your engine likes 22 better then use that and shorten your advance curve so the total is around 36.
That engine would make a lot more HP with a single plane,my Camaro picked up 4/10s going to a victor jr oval port.
you did not finish giving your specs or support equipment yet?
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Old 07-10-2013, 10:17 PM
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Timing

Not wanting to high jack this post but my question was to set initial timing, do I disconnect the vacuum advance hose from distributor, plug the the hose then set the initial timing by turnings the distributor counter close wise to get about 18-20* of timing then lock it down. Then use the bushings inside the distributor to limit the total timing??
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Old 07-11-2013, 05:58 AM
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Never attempt to set the initial timing advance with the vacuum advance cannister connected. Disconnect the vacuum advance and plug the source of the vacuum. Adjust the carburator to the lowest possible idle setting and then turn (advance) the distributor to 11 - 14 degrees initial timing as shown on the crank with the timing light. The low idle will prevent the centrifugal advance mechanism from advancing the timing until you can set the initial timing advance. That is sometimes difficult to do because a long duration cmashaft sometime requires the idle speed to be past the RPM in which the centrifugal advance mechanism starts advancing the timing. The idle speed where the centrifugal advance starts depends on the design of the disributor. A GM distributor has an centrifugal advance mechanism that starts advancing anywhere from 700 RPM whenb equipped with a production camshaft to 1100 RPM when equipped with a high performance camshaft. I don't know of any SB or BB Chevy engines that had a camshat that used a centrifugal advance mechanism that started at more than 1100 RPM, even the 427 Chevy L88 engine advance mechanism started advancing the timing at 1100 RPM.

After setting the initial timing, reconnect the vacuum advance cannister, if your distributor has one. When you reconnect the vacuum advance, the idle speed will jump about 300 RPM. Readjust the idle to the lowest possible RPM, and that depends on the camshaft. The more valve duration the camshaft has, the higher the idle is gona be. A long duration camshaft is just like have a big vacuum leak.

Last edited by MouseFink; 07-11-2013 at 06:05 AM.
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Old 07-11-2013, 09:42 AM
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Quote:
Originally Posted by Joer5000 View Post
Not wanting to high jack this post but my question was to set initial timing, do I disconnect the vacuum advance hose from distributor, plug the the hose then set the initial timing by turnings the distributor counter close wise to get about 18-20* of timing then lock it down. Then use the bushings inside the distributor to limit the total timing??
Put a bushing in the distributor to limit the mechanical advance to 18*. Set the base timing at 20* at the slowest idle you can get with the vac disconnected. Make sure your weights and springs give you max advance by about 3k rpm. Connect the vac to manifold port and be done.
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Old 07-11-2013, 12:34 PM
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Quote:
Originally Posted by Joer5000 View Post
Is anyone going to answer the original question,,,What is the best way to set initial timing??
Well, check it out, the post you're referring to is 4 years old.

"Not wanting to high jack this post but...."

But you did, you should have started your own thread instead.

Your question is about as basic as it can get, try some self help, do a search on this board and you'll get more direction in basic motor timing than you can imagine.
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