How do i time my 400 SBC? - Chevy Nova Forum
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Old 16th-November-2008, 08:34 AM   #1
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How do i time my 400 SBC?

I finally put my engine back in my car and i need to time it with the timing light. What number of degrees am i looking for at idle? This is my first time timing an engine. I read somewhere that 14* at idle was close to factory specs. I have a SBC 400 with stock heads and internals and a edelbrock carb, intake manifold and a mild cam.

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Old 16th-November-2008, 02:32 PM   #2
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did you ,,

After you changed the cam , did you put an advance kit in the distributor ? If the new cam has more overlap its not going to run well timed to stock specs , now its got a personality all its own.
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Old 16th-November-2008, 03:18 PM   #3
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Nope just put everything back to the way it was. Whats this advance kit you talk about? I have a crane came with .450 lift. Any help would be appreciated.

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Old 16th-November-2008, 04:55 PM   #4
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advance kit

Your timing comes from 3 sources, initial set at idle with a timing light , vacume from the engine and centrifigal from the advance system in the distributor.

If you really want to nail down the timing on your car, this is what i'd do.
1st) i'd go get a advance curve kit that fits your distributor (moroso or mr gasket , or accel is where i'd look ) since the new cam will have different advance needs than the cam you removed.

2nd) I'd get a timing tape that fits the harmonic balancers diameter of your engine ( mr gasket has them ) , clean your balancer up very good then put it on

3rd ) decide if you want to keep the vacume advance feature in your distributor , fuel mileage might suffer without it , but it will be easier to set the distributor up without it. Your call. But i'd buy an adjustable vacume advance canister for your distributor if you want to make the oil cartel nervous and install it while your putting in the advance curve kit

4 ) re-install your self made hi-po distributor

Most advance curve kits come with a bushing to limit total centrifigal advance to 20 degrees. Check into this , this might be a good time to change distributors. IMO , i like the early chevy point distributor because you can convert it to electronics or use the points with an MSD box and I like the centrifigal advance system better. Accel makes a great kit for this distributor to convert to dual points that comes with a vacume advance lock out bracket and it has the bushing to lock the centrifigal advance to 20 degrees if i'm not mistaken , and also includes an advance kit as well. If you want to use points with the MSD , remove one set of points and the condensor and adjust the set of points just so they open and close and your done there. The MSD box will only send 5 volts to the points at a low current so a set of points will last a long time. I ran this set up for years and it was mis-fire free to 7200 where I wound my engine to. An MSD tech at a national event turned me on to this set up and it worked great for me. I have found that even this combo provides better starting than an electronic trigger from a HEI but thats me.
Might seem old fashioned but I like stuff that works.

With the car at idle , set it for 14 degrees at idle , with the vacume advance disconnected , watch the timing mark with the light and raise RPM at see where the timing tape is now telling you your timing is advancing to. Hopefully it should be close to 34 total with the advance kit installed.
This is a good time to decide if you want to continue to use the vacume advance. Since the new cam will defunct the stock settings, IMO , i'd connect it to manifold vacume instead of "ported " and set the new adjustable canister to add about 10 degrees timing checking what its doing with a timing light on the timing tape. Drive the car like this , do a full power run and listen for detonation. If you hear it , back the timing down 2 degrees and try again, back it down 2 more degrees until detonation goes away. If you want to go down a spring size on the centrifigal advance, listen again for detonation and adjust from there. A chassis dyno would be a great help but testing at a track is prolly the best place to set centrifigal advance.

If you decided to keep the vacume advance , do some driving up hills and listen for detonation using as smooth of throttle aplication as possible so you can ensure its the vacume advance thats doing anything with the timing at this point. You might slow the centrifigal advance down with a heavier spring and keep all the vacume advance as u can but you'd have to do some back to back testing to decide which way was working best. You might instal a vacume gage to tell how well your engine is staying at a steady speed without applying more throttle while increasing engine load going up inclines. This will give a more precise indication of what you just changed is doing. You could go back to the " ported " vacume source and see which way your engine likes best, but i bet it will like manifold vacume better

You could disconnect the vacume advance and see if it is helping your fuel mileage and lock it out if it isn't. This will give you certain numbers what your timing is doing but might be more intended if you step up in performance later on

I hope this helps you.

Last edited by levisnteeshirt; 16th-November-2008 at 06:00 PM.
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Old 16th-November-2008, 05:26 PM   #5
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Thanks for all the great info. Ill order it and give it a shot.
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Old 16th-November-2008, 10:17 PM   #6
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So..... did you get your timing spec yet?
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Old 16th-November-2008, 11:04 PM   #7
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Right now its at 16* at TDC at idle. Cant do much else as i cant move the car because my drive shaft is out and waiting for some new U-joints to come in.
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Old 16th-November-2008, 11:19 PM   #8
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You can still figure out your total timing.
Your cam specs should give you a basic idea of what your initial timing should be.
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Old 17th-November-2008, 04:31 PM   #9
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I looked at my cam specs sheet and it says the following-

CAM TIMING-
Intake
opens- 7*BTDC
Closes-31*ABDC
Max lift-102*ATDC
Duration 218*


Exhaust -
opens-39*BBDC
closes- (1*)
max lift- 110* BTDC
duration-218*

So i have the timing but how do i go about setting it. My harmonic balancer has numbers as well as my timing cover tab. Sorry for the newb questions as this is my first time.
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Old 17th-November-2008, 04:39 PM   #10
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You guys are confusing cam timing with ignition timing. Though they interplay a little they're totally different animals.

Ignition timing has everything to do with spark events compared to piston location in the stroke.

The cam timing relates more to valve events during the strokes.

Yes a different cam will change ignition timing characteristics, but trying to decide how much initial timing a motor will handle from a cam card is impossible.
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Old 17th-November-2008, 04:49 PM   #11
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So my IGNITION timing should stay be the same before i put in the different cam correct?
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Old 17th-November-2008, 07:03 PM   #12
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16 is probably fine if that's it's was before your cam change. If you want to see just how much initial it can take overall there is a way. With the motor not running move the dizzy counterclockwise advancing the initial a few degrees at a time. Try to crank it, do this until you hear the starter do that rhythmic groaning against the motor's compression. You've hear it before rrrrrr.......rrrrr......rrrrr......rrrrrr....vrooo om. Back off a few degrees until it cranks smoothly again and that's a pretty good place to start with initial.

People that have that rhythmic groaning when trying to start their cars are using too much initial timing or have locked out so much advance they have to start with a ton of initial timing to get full advance of 32-36 centrifugal. Not really the way to tune your motor IMHO.

Most of the time they'll just tell you "it's just THAT race"
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Old 17th-November-2008, 09:45 PM   #13
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read this too ,,

read this thread from a different site , it has some good info as well about setting up your own distributor advance. Back years ago there used to be a " distributor machine " that would help adjust all of this in , but i haven't saw one in years

http://www.thirdgen.org/hei
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Old 18th-November-2008, 01:44 PM   #14
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What I was trying to say was
Most cam manufactures will recommend a base timing spec depending on how much duration at .050" lift
There was a great timing article somewhere on the web by Barry Grant explaining this.
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Old 18th-November-2008, 07:21 PM   #15
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BLake,

Don't let them scare you off, all you need is a wrench to losen you dizzy and the timing light to do a decent job. The 400 will time just like a 350 or 283 your cam is going to make any measurable difference if any at all.

Lets not re-invent the f-n wheel here.

Go to the BEST OF TECH thread its located at the top of drivetrain & performance, open the thread about basic vacum advance timming that Johnny wrote and follow it.

If you don't have a vacum can on the side of your dizzy with a black tube going to the carb then its mechancical and its a bit different, let us know if thats the case and we may have to give you a bit more info.
this should be the link to the thread
http://www.stevesnovasite.com/forums...ad.php?t=11689
Chuck
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Johnny is a very helpfull guy (nphnp)
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