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Old 03-23-2012, 09:19 AM
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Setting HEI timing? 350sbc

I have a stock newly rebuilt engine,350, with stock cam. 84 c-10 SWB , 350 trans. I need to set the engine timing and have probably read to much and confused myself,lol. I am at 16* initial with no vacuum advance right now. I want to get the initial , mechanical, vac ad. and total dialed correctly. I have a adjustable timing light, and timing tape. Do I just advance it till it knocks and back off a couple degrees and call it good? Thanks
Post any links if you got them please.

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Old 03-23-2012, 04:23 PM
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Ok, I got 34 degrees total all in at 2700 RPM with the vacum advance plugged. Is that it? I also have 16 degrees initial at 800 rpm with the vacum adv plugged. Stock cam
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Old 03-23-2012, 06:03 PM
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"Do I just advance it till it knocks and back off a couple degrees and call it good?" Basically, yes. 18 deg sounds like a little much, 12 to 14 sounds better for a performance engine......BUT.... It all depends on the combination, engine bits (Aluminum or iron heads etc.), gearing, car weight, fuel, vehicles purpose etc. Then you have a baseline on where the initial should be, dial in the mechanical advance to reach the total advance you want and set the advance curve of the mechanical advance that suits the vehicle combination and then, if it is a street vehicle, you adjust (reduce) the vacuum advance to avoid pinging. And you do it on a distributor machine. Ask around at the local cruise nights or speed shops and see where others are getting their distributors set up. But on a stock engine I'd just set the timing to factory specs or advance it until it pings and then back it off a bit, that would take into account your altitude and gas quality. Good luck.
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Old 03-23-2012, 07:58 PM
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How many degrees is the vacuum advance adding? I believe that a total advance number, mechanical + vacuum should be 50 - 52*. So your vacuum advance unit should supply 16 - 18*.
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Old 03-23-2012, 08:17 PM
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catfish,

follow my name and my posts yesterday, look for cobalt27's post and there is a link there to an article that will get you exactly where you need to be.... sorry havent figuered out all the in ans outs of how to nav this site or id put the linkhere.

Good Luck
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Old 03-23-2012, 08:48 PM
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Here's the link for ya'.
http://www.crankshaftcoalition.com/w...EI_distributor
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Old 03-24-2012, 09:42 AM
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Quote:
Originally Posted by ol'rodder
"Do I just advance it till it knocks and back off a couple degrees and call it good?" Basically, yes. 18 deg sounds like a little much, 12 to 14 sounds better for a performance engine......BUT.... It all depends on the combination, engine bits (Aluminum or iron heads etc.), gearing, car weight, fuel, vehicles purpose etc. Then you have a baseline on where the initial should be, dial in the mechanical advance to reach the total advance you want and set the advance curve of the mechanical advance that suits the vehicle combination and then, if it is a street vehicle, you adjust (reduce) the vacuum advance to avoid pinging. And you do it on a distributor machine. Ask around at the local cruise nights or speed shops and see where others are getting their distributors set up. But on a stock engine I'd just set the timing to factory specs or advance it until it pings and then back it off a bit, that would take into account your altitude and gas quality. Good luck.
Thanks for the input
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Old 03-24-2012, 09:48 AM
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Quote:
Originally Posted by glen242
How many degrees is the vacuum advance adding? I believe that a total advance number, mechanical + vacuum should be 50 - 52*. So your vacuum advance unit should supply 16 - 18*.
I agree , my vacuum adv. is adding 10 degrees.
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Old 03-24-2012, 09:49 AM
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thanks vicariouslynova and RWENUTS
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Old 03-25-2012, 09:16 AM
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Quote:
Originally Posted by Catfish11
Ok, I got 34 degrees total all in at 2700 RPM with the vacum advance plugged. Is that it? I also have 16 degrees initial at 800 rpm with the vacum adv plugged. Stock cam
Overall I would say that is pretty good setup right there for a stock cam 350. 16 and 34. This along with the fact your vacuum advance is adding only 10 deg adv tells me that the HEi has most likely had some work done on it either limiter plate or other means of mechanical stops on the mechanical adv and vac adv. Good stuff, give the motor what it likes.

10 deg vac adv is OK but with a stock cam and a light truck you could add another couple degrees vac advance to bring the maximum adv to around 48-50 all in while keeping the mech + initial @ 34. This can provide increased part throttle efficiencies.

I am coming to the conclusion that total timing (initial + mechanical) is more important that initial timing especially if running vacuum adv from manifold vac. It becomes a matter of question,,,are you timing your engine on the conservative side for a daily driver or timing it for max performance?

The first thing I do these days when it comes to setting up an distributor is to power time the motor. (assuming TDC is verified) Determine a total timing setting you want usually 32-36 deg adv. (block the wheels) Disconnect and plug off the vacuum adv. rev the motor in park to 4500 RPM and turn the distributor to get your desired total (block the wheels) did I say that twice? Let the motor idle and setup the carb base idle rpm and mixture screws with a vacuum gage. Ensuring that no mechanical advance is coming in at idle, check the initial timing. If you are anywhere between 12-18 then it is your lucky day(depending on the cam and other aspect's of the engine/car). If your are below 10 deg then pull the distributor and figure a way to limit the mechanical advance. Once and only once you have the total figured out including the mechanical limit and curve via spring tension can you start to add or meddle with vacuum advance. This usually involves a limiter plate to keep the total amount of vac adv from exceeding 14. In this case I would say your basically good to go unless you feel like working on something.

Running the vac adv on ported vs manifold vacuum advance is a matter of what works, if you run manifold vacuum at idle you are going to need to do some carb tweaking once you plug it in. This manifold vac adv can be a benefit with bigger cams and gererally speaking helps to improve off idle transitions and throttle responce, not to mention reducing garage tears from unburnt fuel.
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Old 05-10-2012, 08:09 PM
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Another hei post

I just replaced my HEI with a new one so I am retuning it for the truck. I have a 84 C-10 short bed, with a bone stock rebuilt engine. I am getting 19.5 hg with the vac adv connected.
I was going thru the timing sequence earlier and dont know if things are going to move since its new but It seemed difficult to get anything exact. I let the engine cool for a few hours and rechecked quickly with the engine warmed up. Heres what i got.

36* total in by 3500rpm with the vac adv plugged
18* initial at 700rpm with the vac adv plugged.
26* @ 700rpm with the vac adv connected.


The truck starts well cold or hot and runs nice, I just dont know why my numbers are off.

With 36* total vac adv disconnected and 18* initial vac adv disconnected, do I have 18* in my centrifugal adv weights?
36*-18*=18*

Also if I have 18* initial with the vac adv disconnected and then connect the vac adv and get 26* , does that mean I have 8* degrees adv from the adv can?
26*-18*=8*
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Old 05-10-2012, 09:11 PM
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Quote:
Originally Posted by Catfish11
Another hei post

I just replaced my HEI with a new one so I am retuning it for the truck. I have a 84 C-10 short bed, with a bone stock rebuilt engine. I am getting 19.5 hg with the vac adv connected.
I was going thru the timing sequence earlier and dont know if things are going to move since its new but It seemed difficult to get anything exact. I let the engine cool for a few hours and rechecked quickly with the engine warmed up. Heres what i got.

36* total in by 3500rpm with the vac adv plugged
18* initial at 700rpm with the vac adv plugged.
26* @ 700rpm with the vac adv connected.


The truck starts well cold or hot and runs nice, I just dont know why my numbers are off.

With 36* total vac adv disconnected and 18* initial vac adv disconnected, do I have 18* in my centrifugal adv weights?
36*-18*=18*

Also if I have 18* initial with the vac adv disconnected and then connect the vac adv and get 26* , does that mean I have 8* degrees adv from the adv can?
26*-18*=8*
Yes your math is accurate and I would say you are good to go, especially if as you say the thing runs good. What is the make model of this new HEI? sems as if it is nearly a plug n play unless you set the mech and vac advance limits yourself?
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Old 05-10-2012, 10:36 PM
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Quote:
Originally Posted by Custom10
Yes your math is accurate and I would say you are good to go, especially if as you say the thing runs good. What is the make model of this new HEI? sems as if it is nearly a plug n play unless you set the mech and vac advance limits yourself?
I am still checking into it but i am using the 375,41 gm weights that are supposed to give 21 degrees of timing adv. for some reason I am only getting 18 degrees. I pulled some original GM weights from the junk yard and check there specs and decided to use them instead of the ones that came on the pro form dist , even though they are identical in shape and weigh the same. I am going to try some more springs (changed them too, they are from my old dist.)tomorrow maybe the ones I am using now are not fully retracting all the timing at idle. I did modify my vac. can to give 10 degrees and am only getting 8 degrees there, again i pulled the part that came on the new dist and used my old vac can.
The dist I am using is the ProForm hei NOT pro comp. After a while searching and reading pretty much all of ignition mans posts on the web it what I decided to go with. I believe they make one or two of the name brand dist. same dist just rebaged, and they also are licensed to make and sell some HEI for gm. The weights that come in them are identical to the 375 and 41 weights that come in the ZZ4 dist. I installed my own parts but the pro form dist came with the parts that are needed I guess I was just being anal about it since the pro form parts matched exactly what I replaced them with. In other words I should of just left it alone
http://www.jegs.com/i/Proform/778/66...oductId=746781

Last edited by Catfish11; 05-10-2012 at 10:51 PM.
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Old 05-11-2012, 07:04 PM
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Got the issue fix, user error. Like I said I should of left the dist. alone.
I put the springs that came with the dist back in and now I got 16 at idle no vac and 36 total, what i was looking for. The spring I had installed were to strong.
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