SBC Timing/total timing NEED HELP

From MSD website

TIMING FUNCTIONS​

Before continuing with the installation, here are a few definitions you should be aware of:​

Initial Timing: ​

This is the base timing (also referred to as idle timing) of the engine before
centrifugal advance begins.​

Centrifugal Advance: ​

The centrifugal advance mechanism is made up of weights, springs,
advance cam, and an advance stop bushing. The amount and rate of advance that your
distributor is capable of is determined by the centrifugal timing. If you ever wish to lock out
the centrifugal advance, refer to the centrifugal advance section.​

Total Timing: ​

This is the total of the initial timing plus the centrifugal advance added together.​

Example: 10° Initial + 25° centrifugal = 35° Total Timing

 

So right now my total timing is 18 degrees

How do i get another 10 or so

 

You need to add some centrifugal advance to your distributor. What kind of distributor are you running? If it's stock you need to figure out why you only have around 10 degrees centrifugal advance in it. Could be gummed up or rusted.

I usually try for around 12 degrees initial advance and 24 degrees advance in the centrifugal advance for 36 degrees total. But that's just me.
Larry T

 

Stock HEI

About a year ago I put a curve kit in it. Didnt really know much then (still dont know alot now but learning) I think the aftermarket weights are in there, and some close to stock springs?

So what about the vacumn can? If we get the 36 total timing how much timing does vac can add?

 

So total timing+initial+mechanical


I thought total=initial+mechanical+vacumn adv

I think I know someone with a sun distributor machine, are they yellow? I dunno if it works or not but maybe i'll pay him a visit and ask about it, hes a old high school shop teacher

 

NEW TIMING (TWEAKED A LITTLE SINCE LAST REPORT)

Ok...just went out and retimed.

At idle 750 rpms or so 29* (no vac adv)

At roughly 3000 rpms I get 39* (still no vac advance)

 

bump to the top

 

Something isn't sounding right.

My guesses would have been, with vac adv disconnected...

initial ~10 BTC
Centrifugal ~25 more

Example: 10° Initial + 25° centrifugal = 35° Total Timing. Vac Adv comes into play based on engine load, so playing with it while parked really isn't important. Just look at the two described about for now.

Your Centrifigal seems low (I.e. too heavy of springs) aren't getting you more centrifigal adv. I would be playing with the weights.

http://www.msdignition.com/instructions/Products/Distributors/8428.pdf?terms=8428

 

Sounds to me like there were some installation problems with the "Advance Kit". A good rule of thumb for a motor like yours would be to start something like this.
12-14 degrees initial advance
32-36 degrees total advance, all in at about 3,000 RPM
All reading done with vacuum blocked off.
Hook vacuum to ported vac source.

I really think that distributor needs to be curved by someone that knows what they are doing, as what you are reporting is all screwed up.

Don
PerTronix Ignitions

 

I believe it does have some heavy springs

So I MAY have access to an old sun distributor machine. Could this be of help? Im calling the guy now...

 

Let's end this , go buy you a new hei, do not modify it. Coat the gear with some moly lube. Install. With no vacuum set the timing at 36-38 degrees btc. Hook up vacuum line and drive.

 

Yep, check the distributor, put 24" centrifigul advance in it. Drop it back in the engine, set the initial timing at 12 degrees, hook up the vacuum advance and you should be In like Flinn.
But I think that's already been suggested.
Larry T

 

Going out to swap some lighter springs.

Should I be using GM weights, or aftermarket curve kit weights?

 

Take it to the guy with the equipment to check it, but I usually use the OEM weights, limit the total by brazing up the slot in the advance plate (a bushing might get you there) and use a spring kit to set the advance rate.
Larry T

 

I got a # to a guy with a distributor machine. Going to call him shortly..

Im going to attempt to do what larry t just told me. please bear with me guys im a new hotrodder LOL im still learning im 19.

Kustomz-buying a new distributor is a great idea but i really have more time than $ right now for a decent dizzy.

 

I dont feel comfortable welding my distributor honestly. I do own a mig welder with gas. Is there anything I could make (bolt on modification) I could do intsead?

I have an adjustable advance timing light. 2 different 'recurve' kits. Do I need an adj van can or any other parts I should order?

Thanks guys please help walk me thru this..

I bought 2 re curve kits, the last one I bought advertised a limit bushing, but didnt come with one...(summit racing)

http://www.summitracing.com/parts/SUM-G5212/

 

I think the Mr Gasket recurve kits have the bushing in them.
You can actually get a pretty good idea of how much advance is in the distributor with a protractor or small degree wheel.

 

http://www.summitracing.com/parts/MRG-6011/?rtype=10

Thats the mr gasket kit, or did you mean just springs/bushings/weights?

 

Two of the white bushings (hats) are for the advance weights. I THINK the others are to press on the pin that fits through the slot on the advance plate and limits the advance.
Like I say, I usually just braze them up and buy a spring kit.
Larry T

 

Right now WOT I have 36* with no vac adv idle is 14* with no vac adv
This is achieved with mr gasket weights and 1 big 1 medium spring.

Been using manifold vacumn for my vacumn source?

Realized my center bushing I THINK was upside down I have a pix of my phone i'll post later gonna do a test run shortly..

 

To many things to consider, fuel ,carb settings ,cam specs, combustion chamber specifics (cc's), piston configuration, dome height, flat top, RPMRange, intake runner volume, valve sizes, etc., etc. This is not a general one size fits all answer.......

 

Id like to get in the ballpark or in the ballfield parking lot. I was pinging/no power etc etc etc

thanks guys

 

A limiting bushing can be made from a piece of red "nylon" air line tubing - left over from an accessory air bag suspension conversion. Cut to the length you need, add a drop of Locktite and press onto the limiting pin.
Getting the advance curve correct means the difference between a so-so running engine and a very energetic running engine.
Stay with the learning curve - it takes a few years to discover all the subtle nuances of the combustion process of which ignition timing is paramount.

 

Will this madness ever end?

 

What madness

Ok,total timing is 36* (still unsure what rpm it comes in at).

vacumn advance is hooked to ported vacumn. It doesnt ping up hill, starts great cold and hot so far.

So far this is the best its ever ran.

 

I'd say 36 total and 14 initial with the vac adavnce disconnected should be pretty close. Usually manifold vac source for vac advance is best.

 

I'll change to manifold vacumn, right now it feesls like i just got another 50 hp lol

I checked initial, I wanna say it was like in the upper 20's????!?!? I dunno but it runs GREAT!!

I'll have more info (when the max timing is at in the rpms etc tomorow or something) thanks ALOT guys!!!

 

Ported or manifold vacuum....it depends. Check this out.

http://www.club-corvette.dk/forums/ccdtechnic/pdf_technic/Vac_Adv_Spec.pdf

 

Now thats some good info there, Chief.

 

Good lord....

lol!!

One simple rule in engine tuning, especially for beginners tuning by seat of pants and ear: "adjust one thing at a time then test."

One thing at a time, or you don't know what made it "better or worse" you will only be guessing and chasing your tail.

SBC rule of thumb start at 12* initial with no vac at idle. Start with stock weights and springs, leave that stuff alone until you know you need your mechanical advance to come in faster or slower.

I find 12* to 16* initial works for most street SBC for initial. I'm also of the manifold vac school. I like to see the vac portion of the advance fade under load to help prevent pinging since I like to ride a finer line to max with the mechanical.

Boundaries for initial adv are pretty much determined by how well it starts warm and or pinging under low rpm load.

Stick with the stock mechanical adv travel distance and the weights too, lighten up the springs if you feel you need more advance with your low to mid rpm acceleration. Stock springs will usually suit you fine, heavier springs... unlikely needed for you because your initial would have to bee too high to start decent to require it.

Tell ya what, here's a real goofy sounding tip that will help you find a nice initial timing point with manifold vac adv hooked up.

Start at 12* initial at idle with no vac adv hooked up. now hook up your vac adv and walk back to the tailpipes and listen for about 15-20 seconds. Listen for an erratic single flutter tone from one of the pipes. keep advancing a very small amount at a time and checking exhaust tone until you hear that erratic single flutter tone.

Play with it and you will see what I'm taking about. From my own personal experience with tuning streetable SBC running manifold vac adv, they seem happy right at the point where that hyper little flutter just starts to present itself in the exhaust tone.

Otherwise throw stock weights and springs in the dist, set initial at 14*, run manifold vac & drive it.

If you feel that manifold vac pushes your initial into too hyper of an idle you can always slap on an adjustable vac advance and limit the distance the diaphragm travels to tame it down.