This is from another thread about helping out with a distributor machine. I have a machine and have set up a lot of Pontiac's but no Chevrolets other than a few inline sixes. Here is the engine, 3200-lb 1963 C10 with a Balanced 1965 .030 over 327 about 325 hp with 10:1 CR, Aluminum Camel Hump Heads 2.02/1.64 valves & 64 CC, with 2 Valve Flat Top Pistons 1.675 compression height. Howards Cam MC110991-08DL 221/221 & 470/470 with Lobe Separation 108° & Comp Cams 981-16 Valve Springs, Sanderson Shorty Header's 2 1/2" exhaust with zoomies & 2 1/2" pipe to back of bumper. 3.73 gear's, 26" tires, Muncie SM330 Standard 3 speed 1st gear ratio 2.85, Edelbrock C3BX Intake Manifold & Holley Carb 780 cfm with vacuum secondaries What would you set total timing at, how much vacuum, and how fast of a curve? For the Pontiac's, dad and I like to have the mechanical all in by 2200 - 2400 rpm with around 24 degrees, then the initial can be set around 10 degrees depending on the engine. The vacuum advance is limited to 10 degrees with an adjustable slide plate in case it needs more or less. The trick is to get timing in quickly, but return to zero before idle speed for easy timing setting at a normal idle rpm.
You can go right to 14 degrees initial and 32-36ish total...today's gas changes the rules considerably. Here's my learing process... https://www.jalopyjournal.com/forum/threads/327-chevrolet-timing.1317135/
I agree an initial around 12 degrees is a good point to start with. Then drive and see how it does, if hard starting, it might need a little less. If it responds to more than 12, as long as not knocking it may be better. Most older style OHV V8's like SBC seem to like 32-36 total, as the chambers and port design are not as efficient as some later model stuff. You really need to just experiment a bit as to where the engine is happiest. Many stock distributor curves are a bit lazy and using lighter springs to bring centrifugal advance in sooner can be beneficial. Remember that the values discussed here are without the vacuum advance contribution. I like manifold vacuum for the distributor, as it gives more advance at light throttle, and pulls back when you have your foot in it. You can sometimes hear when cruising light throttle and then increasing throttle it may knock for brief time initially until the vacuum advance goes away.
Based on what I found with two of mine last year I think you're right about experimenting. I find mine ran/sounded better at idle on ported vacuum, manifold seemed laboured. I might test it again this year though. However, in all the research and testing I did, manifold vs. ported really only makes a difference at idle. Once the throttle is opened vacuum is the same above and below the throttle blades, so there's no difference once you're on the throttle (save a tiny moment for equalization). Manifold adds timing at idle theoretically giving smoother idle, runs cooler, and better on fuel. However some engines like one better, and it depends on the characteristics you like.
In my thinking & hands on Initial would be from start point True 14 ish - 18 ,maybe more , each engine different , then curve & total would be Determine by testing & experimenting , Notes . Weather conditions can change what engine likes 20 mints later , engine would like a different adjustment.
Thanks guys, it looks like the SBC is pretty much like the Pontiac's I'm used to except with a little more initial. Testing is the only way to know for sure. With a distributor machine, you can at least get the points, dwell, total mechanical, and vacuum limited. With all that information, the owners can adjust up or down and see how it acts.
@Joe H I commend you on providing all the info in your first post. That is what is needed to be able to answer the question properly and many people don't do that. Kudos! A distributor machine is the measuring tool. It allows easy access and repeatability. The vehicle is the final use. It's why the manual and spec sheet is very useful, but just like alignment specs, they are a guide, not absolute. I will also mention that the least amount of advance to get performance, the better. What I mean by that is if 12 and 14 both provide the same result, go with the 12. This allows for a bad load of fuel, barometer change, and isn't on the ragged edge.
When I send out distributors, they always get a paper with all the details. I start at 600 rpm and write down the timing degrees all the way up to 6000 rpm in 200 rpm steps. The owners can see just how much advance is at any given rpm. I write down how much vacuum is needed to start coming in and how many degrees it goes. They have all the information needed to properly tune with.
Only ever touched one Pontiac, about 1974 my neighbor had a 350 Firebird that wasn't running right, he thought it needed a tuneup, come to find out it was a bent pushrod, I replaced it and it ran fine. As you say about Pontiacs, I'm a Chevy guy, never did much more than set timing by the OEM specs and the seat of my pants as verification. I am curious how you originally arrived at the numbers for Pontiacs, was it gained from your dads experience, were they set based on OEM specs? This post on the Nova site I visit is similar to your situation. "I have an L30 in my 67 but the engine in question is in my 63. It is a 1965 327 block. Bored .060 over. Automatic transmission. It is on its 3rd life for me now. Third car it has been in since I originally got it way back when. That's a story in itself. I have not checked TDC but it is next on my list. After last rebuild it had a Winters intake, Holley 650 DP, reproduction L79 cam, double hump heads 2.02 & 1.60 valves, stock distributor with Pertronix ignition. Broken in on a Dyno. Initial timing 16 and total of 38. No vacuum advance. Right at 300 hp. Ran great once it was in the car but was hard to start when it was hot. Put 1" phenolic spacer under the carb and seemed to help. Drove it like that for probably 3 years with no problems other than the starting quirk. Then one day it just started overheating and it has been down hill battle and many $$$ later and I'm still not happy. Initial timing is currently 8 deg and 24 mechanical advance for total of 32. I now have vacuum advance and with everything I think it is 46 or 48 deg. Set initial timing at 800 rpm's. In gear it idles right at 600 rpms. Complete new pertronix distributor and Holley Brawler carb now." From Here: https://www.stevesnovasite.com/threads/initial-timing.679157/
Just going off of the current numbers, and nothing else, I can see why he's not happy. The pertronix distributor isn't helping a damn thing either! IMO 24 degrees is too much mechanical advance. 18-20 is more than enough, all in by about 2000-2200rpm. Then bump up the initial to give around 36 degrees total, give or take a couple. Hook the vacuum advance back up... 1000 rpm idle shouldn't be a problem with the right converter, and he should be off to the races... so to speak. Never understood why some people think that a performance engine should idle at 600-800 rpm's...
@DDDenny @RodStRace @Kerrynzl & others Maybe over thinking , splitting hairs When We or I think about a Distributor do you think about all the timing in parts , points or Electric style . from gear , to shaft , to plate ,to point cam , to rotor ,to line up pin for cap, Cap brand to brand , rotor plate, The rotor itself , to rotor tip , polls on cap , ect , even more . If I am thinking correct on V8 there is only 45 deg between each poll, So at 45 deg's of initial is where the rotor full of current /energy to find the Easiest ground that causing spark ****ter between the 2 polls ? Or if 45 degs between the 2 polls , Lets say pole A to pole B is 100 degs or Distance is 100 , Is the 45 degs between pole A & B B being 45 degs of initial to fire pole B. seems being up around 50 deg of initial Like some say are running @ cruise That much seems maybe fire to cylinder @ wants or voltage drop because rotor between 2 poles on cap , but I know rotation of rotor is moving towards next pole in cap. Just seem to me the more initial timing used the more "precise timing" from the Points cam,/ relector wheel & above required .. (Distributor use) Am I over thinking , this something only Serious Elite Performance engines engineers look at like F-1 ? Also talking about timing with all the parts in distributor how it works , In last 15 ish years there are adjustable Rotor ****ons for correct index to line up tip of rotor more square / precise with pole in cap. Like using crank trigger Zeroing out Rotor to pole. Bigger cap more stable / forgiving then Small cap ,, Because in a bigger circle & further apart " the poles for each cylinders " I would like to have Access to a machine do experimenting . Just for reference of all the part's that are machined and timed
Dad and I raced our Pontiac's for 15 years, he kept at it a little longer than I did. We were budget racers, when we did buy parts they had to be right so a lot of testing was involved. Our local strip was close to home, so every chance we had were making p***es. Dad has over 2200 p***es logged and I had close to 1500 before quitting. It was nothing to make 7 or 8 p***es a night testing something. Dads wagon was very repeatable, no tire spin, so even the littlest changes would show up. I did the home made intakes, head porting, and header work first, then dad would refine them for his car. If the weather was good, both of us could go for weeks with out changing our dial-in for bracket racing.
@19Eddy30 I believe that's commonly referred to as rotor phasing. Yes, it was a concern during the emissions era and still is. I believe that was a big influence in the larger diameter GM and Ford caps. Example https://do***ents.holley.com/techlibrary_rotor_phasing.pdf Obviously, the crank to cam interface is more of a concern with valve timing, but as you mention there is the gear interface and other relationships in the dist.
Also need to remember that although the dist cap poles are at 45 degrees apart, the timing is set at crank degrees, which is equivalent to half of the dist cap spacing. I.E. the 45 degrees between dist cap poles is equal to 90 degrees of crankshaft rotation. So having for example 44 degrees of total advance from centrifugal and vacuum, is really only 22 degrees on the cap.
I like this approach. With so many variables in the build you need to be prepared to experiment and take notes. The only thing I might add to the equation is using a vacuum gauge when experimenting and when test driving afterwards. As a rule, you're looking for the highest steady manifold vacuum readings under various driving conditions as well as at idle. Find the specs for your vacuum advance and power valves or metering rod piston springs, and the vacuum gauge will tell you when these items are operating, or not.
@38Chevy454 After I posted to ask Question Don on me Two different timing events piston to terminal on cap.. Now asking or pointing out The point cam / Relator wheel that collapse so coil fires , in relationship To rotor tip to cap terminal post . If you move housing you move cap Avance or retard it changes the point cam / relator wheel , its either on Start of cam lift to peak or back side Points or pick up .. think like cam & lifter with deg wheel. With a Distributor , I do not see how you can get multiple good Voltage spark from Idle ,cruse , Wot with a Non Lock distributor.. A lock Distributor of good precision quality you will have points cam / R-Wheel all timed to gather with a adjustable phase rotor for lets say 60,000 V , & cap terminals if are Precision . Same with crank trigger & Most Mag's are locked , you lock it @ what ever Timing BTDC .. This would be the highest voltage delivery to spark plug wire . Im thinking might be a Daaaa this why MSD , dual points to keep spark energy of coil on distributor with Avance to over lap the misalignment of Point Cam to point / R-wheel with pick up Inrelation to cap & rotor . Threw Idle , cruse, Wot
@19Eddy30 Timing of spark from coil thru cap/rotor/cap to plugs only needs to be such that it doesn't 'jump' to another terminal. A wider rotor tip will help with timing changes, but also hurt at extreme changes when it's out of phase. Even if the cap/rotor gap increases at big offsets, it's less voltage to jump there than at the plug (under compression/burn pressure). It will simply increase the needed voltage to jump all the gaps. Provided the coil can output the needed voltage, it will still work. I saw plenty of HEIs with no maintenance having .080"+ gap spark plugs. Those were really hard on the ignition parts, but would still run without misfires at idle (p*** smog). I didn't test them at WOT (customer cars, didn't want them hot to service).
Theory can be whacked at times, the last time I put the 440 in the photo to the left on the dyno it made the most hp and tq with 38 degrees total timing but the car has always been faster with 41 degrees total degrees of timing. We were testing intake manifolds so we had a pull at 130* and more around 140-150* without much variation from timing.
@oldiron 440 Peak HP or through the curve? I always figure it's milliseconds at top RPM HP peak, on the road or track. The operating range and where it drops on a shift is more important. Dynos are just like dist. machines and vacuum gauges, measuring tools. The proof is how it works in use.
I agree, the only change I’ve made to how I run it is I don’t run this engine to 7000 rpm anymore only 6600, the peak is around 6450 and I have more interest in longevity than performance. I should say that it’s in front of a 4500 rpm stall converter so it’s only operating from getting whacked at the line to 4500 through 6600 rpm. It’s a fun 11 second ride with the front wheels of the ground sometimes two feet or more. It does get street miles but the converter and 4.86 gears make timeing curves unnecessary except for a 5* retard at startup.
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