How to determine timing on a new non-stock engine

[fairlaniac]

I got to thinking lately about ignition timing. I recently built my 427 (484 cu/in) engine. I was given a timing number and RPM buy the person who did my heads and spec'd the cam. I thought I'd like to find out how the proper timing is determined. I watched a quick YouTube video yesterday and they indicated that you initially find your total timing at the RPM when timing is all in. Adjust the distributor to that and when the engine returns to idle, your initial will be determined. So I was given 37 degrees all in by 3000 RPM. I'll do that later today. But how is 37 degrees determined? I'd be curious how initial and total timing are determined on a non-stock build. Also how does a MSD Pro Billet distributor affect that? I currently have the 18 degree bushing installed. How do I know if at 37 total that is the correct bushing? Any good reads or share your experiences. For good reason this question will not be asked on Facebook :-)

Thanks!

[blykins]

Total timing is determined by the compression ratio, cylinder head design, along with the application, what fuel, etc.  Quite a few variables.

Also, to add, you set the total timing the way you described, but don’t just leave the initial timing where it lies.  Initial timing plays a big role in how an engine operates at idle and off idle, until total timing comes in.

If the initial timing isn’t correct, then it will need to be adjusted by recurving the distributor.

[6667fan]

Doug, that 18 degree is an okay place to start. You will have the rest via centrifugal. There are probably bushings that will take that distributor to 21 degrees but you don’t want to have too much advance for initial or you might get into hard starting scenario. ( if that happens with the 18 there might be a 15 in the kit).
Also, even though the heads/cam were spec’ed for 37 the motor could end up liking anywhere from 32 to 40. You get to have fun finding that out later. Happy tuning!

JB

[GerryP]

You can tune only by what the engine wants.  You can tune for maximum performance or for broadest octane tolerance.  If the engine pinged or detonated at 37 total, would you leave it there because of some arbitrary reference?  I understand the 37 degrees is around what the consensus is for many combustion chambers like for total, but with the variety of combustion chambers and combustion efficiency, you will see that number for total from 25 to 45 or so degrees.  There is just no way you can use that number as a tuning target.  It might end up there, but only because the engine runs well there.

Everyone arrives at a different tune up based upon a collection of what they read, what they know from experience, and what tune up best conforms to their driving behavior.

Getting the total right and letting the initial fall where it may can work, but if it doesn't, you have to be able to tune it so something that does work.

The MSD distributor won't make any difference in your tune up.  It just makes it easier to tune since you don't have to fully disassemble the distributor to change the centrifugal advance rate or amount.

You don't need a video telling you what numbers you should shoot for.  That's pure nonsense.  You need videos or web sites telling you what all the ignition timing elements mean and how each affects the other and what the affects are on how the engine operates.

[fairlaniac]

You can tune only by what the engine wants.  You can tune for maximum performance or for broadest octane tolerance.  If the engine pinged or detonated at 37 total, would you leave it there because of some arbitrary reference?  I understand the 37 degrees is around what the consensus is for many combustion chambers like for total, but with the variety of combustion chambers and combustion efficiency, you will see that number for total from 25 to 45 or so degrees.  There is just no way you can use that number as a tuning target.  It might end up there, but only because the engine runs well there.

Everyone arrives at a different tune up based upon a collection of what they read, what they know from experience, and what tune up best conforms to their driving behavior.

Getting the total right and letting the initial fall where it may can work, but if it doesn't, you have to be able to tune it so something that does work.

The MSD distributor won't make any difference in your tune up.  It just makes it easier to tune since you don't have to fully disassemble the distributor to change the centrifugal advance rate or amount.

You don't need a video telling you what numbers you should shoot for.  That's pure nonsense.  You need videos or web sites telling you what all the ignition timing elements mean and how each affects the other and what the affects are on how the engine operates.

I've never played at this level of tuning. So how do I go about tuning the engine and establishing timing settings? So the engine fires up, where do I go from there?

Thanks!

[cjshaker]

If it's your initial run-in, I wouldn't worry about total. Just set your base timing (about 16* to start off) so that the engine fires quickly and you don't have to crank on it, which is really really bad for initial run-in.

After that, you can chase total timing. At 37* recommended, I assume you have iron heads? Sorry, I don't recall the engine build off hand. But if iron heads, that's a pretty safe total to start off with. Iron heads can go up to 40-42 total if you're chasing maximum power, depending on the things that Brent said. Once you start chasing total timing, you have to be diligent about checking your plugs to see if you're going too far. If you see any dark metallic speckling on the ceramics, back it off, or move to a higher octane fuel, because that's a sign of detonation.

My 427 started to show signs of speckling at 40-41*, on the dyno, but that was with 93 octane and bone stock Medium Riser heads. It also made it's best power at 41*, so I mix race gas 50/50 so that I can get away with that on the street. If I don't have mixed gas, I back it off to 38* to stay safe. I have my intake and distributor marked in 2* increments, so that I can do a quick "adjustment" on the fly if I have to. It isn't precise, but in a pinch, it gets me by till I either get better fuel or can put a light on it.

Once you find out what your car likes for total timing, then you can go back and start fiddling with the distributor to get your initial where the car likes it. And like Gerry said, that's easier with the MSD, but you still can't always get it "perfect" and may have to settle for an initial that "works" with your total. Most people will just end up setting the total and the initial ends up wherever, but that can lead to hard start issues, so it's best to take your time and try and get it right.

But like I initially said, if it's an initial run-in, forget about total for now. Just set it where the engine will start and run easily.

[GerryP]

If it's your initial run-in, I wouldn't worry about total. Just set your base timing (about 16* to start off) so that the engine fires quickly and you don't have to crank on it, which is really really bad for initial run-in.

...
But like I initially said, if it's an initial run-in, forget about total for now. Just set it where the engine will start and run easily.

Here's the best advice that will get your engine up and running without worrying about overheating from retarded timing, Doug.  I would add that if you have vacuum advance, disconnect it during the initial run in.  A healthy initial, throw in some centrifugal, and you add the full vacuum advance from the low throttle setting from initial run in and you can easily be over-advanced.  You'll know this by an engine that seems to have a misfire and is popping out of the exhaust.  You take out the vacuum advance and you pretty much eliminate that problem.

[fairlaniac]

This is not initial fire up. Engine has about 3 hours run time, almost an hour of that on the road, 5-10 minutes at a time. I started off using a tuned 750 DP from my old 390. That way I wasn't fighting carb issues on initial start up. Started off with 14 initial and the 21 bushing in my Pro Billet distributor. Then when I had some time on the engine and a couple oil changes I then set the 18 bushing in the distributor and initial at 20. So I'm around 38 right now to begin on figuring out how to "fine" tune it as best I can. I also want to install my 850DP meant for the engine and tune it in. This is not a racecar. The only drag strip passes I see are at the FERR once a year.

I have aluminum Edelbrock heads, Craft Stage II w/Blair Patrick touched up the finished product @. 72cc. I have Racetec  23 cc dish pistons. .675/.656 lift mech. roller cam. 10.5:1 CR.

Thanks,

[cjshaker]

From everything I've seen and read here, 37* sounds high for those heads, but I don't have tuning experience with modern aluminum FE heads. It seems they typically come in around 34-35* max, but I'd defer to the guys that have lots of experience with them, like the 3 B's on here.

[GerryP]

Pull a plug.  Look at the ground strap.  Strong light and some magnification will help, but you should see a heat line on the ground strap.  If timing is in the zone, the line will be right around the middle distance on the strap.  This has nothing to do with the plug's heat range.  It's just looking at timing.  There are other indicators, but the heat line is a good place to start.  If the line is toward the tip of the ground strap, the engine could use more timing.  Opposite for too much timing.  You might try to google on how to read plugs to better understand this.  And, no, it's pointless for you to try to read other plug features.  You need a very strong otoscope and some experience in understanding what a fuel line looks like and where it should be for a given plug heat range, tune up, and combustion efficiency.  If you're not tuning for maximum power, you just need an engine that starts and behaves good for how you use it.

[JamesonRacing]

I have the street Pro-ports on my 465 with flat top pistons.  This engine runs very well with 34 total timing at 3k rpm.  I typically have started with the distributor bushing that will give me the most base timing and the softest springs.  If you find that the engine kicks back when starting, then you need to take out some base timing so the engine can start without drama.  If you determine that the engine is pinging when accelerating at lower revs with a load, then you probably need stronger springs in the distributor to delay the rate that timing is added.  I'm sure others tune ignition differently, but that's my method.

On my race 496 with older Ed head and pistons with small domes, the engine seems to like 36-38 degrees locked out with, using the start retard in the MSD-7AL3 when cranking.

[66FAIRLANE]

Heres something I do to find out how much is in the distributor without having to start the engine. Of course this does not tell me when & how things start to happen but it least it gives me a starting point & lets me know when I bump up initial that I am not going silly on the other end.
I have a protractor screwed to an old rotor. I then fab a little pointer much like a degree wheel for a cam. Just slip the rotor/protractor on & physically move it. Observe your movement then double it & add your initial. This will at least tell you where your total is limited to. ie. if the rotor has 10 degrees movement then there is 20 in the dizzy. If you set initial at 18 it will be capable of & only have 38 total. Assuming your advance is not in play at idle. How, when & if it gets there is up to your springs & tuning ability.

[plovett]

Mostly trial and error to "determine" the best timing.  Even the pros didn't use a formula to determine optimal timing.  It is more a matter of experience.  They can look at compression ratio, cam timing, combustion chamber shape, fuel octane, the vehicle weight and gearing, etc., etc.  But the dyno or the stopwatch is not an educated guess.

I found best power with 36-37 degrees with a 10.5:1 428 with Edelbrock heads and a 240/246 solid cam, on 91 octane.

Your 18 degree bushing is good as it will allow you to run 18-19 degrees initial timing and get the 36-37 total.  Then just use the springs the MSD chart says to use for the curve.   Depending on the weight and gearing of your vehicle you might want the total in by 2500, no later than 3000.  The "high" initial timing will make your idle and low rpm response much more snappy.

Your combination may be different, but the above will get you close based on my experience.

JMO,

paulie

[Barry_R]

We usually start off with around 36 total on Edelbrock headed engines and tune from there.  Your's might have an improved chamber shape and respond to a couple degrees less.  Off the shelf Edelbrocks sometimes want a little more - you have to watch plugs, time slips, and learn to listen to the engine.  Updated head designs often run with much less total timing and we have had to make our own advance bushings for those.  My earlier Blue Thunder heads in a 505 wanted only 28 degrees in a +/- 750HP combination.  I have moved away from running the lightest advance springs - they seem to let the timing chatter/wobble/bounce at low speeds.  I have better part throttle behavior from letting the setup work against the springs a bit - as long as it hits peak advance before the launch RPM it won't really have much impact on ET slips anyways and it helps below that.

[GerryP]

You know, Barry, your timing strategy is contrary to Internet consensus truth.  Internet truth is all advance has to be by 3k rpm or earlier.

I'll tell you my timing strategy as long as you promise not to rat me out.  I run a very stingy advance curve that looks a lot like the Ford factory map.  It rises quickly with about 8 degrees added at around 2.5k RPM.  It stays relatively flat and begins to rise again around 4k RPM.  The remaining 10 degrees is in by around 5.2k RPM.  I use a light spring to bring in the early advance and a heavy spring to delay the high speed timing.  I run 18 initial and 6 vacuum on manifold vacuum.  So, my total is 36 degrees.  It took a lot of work to get this timing map to run that way.  I'm doing everything wrong, I know.  They'll probably revoke my posting rights if they ever find out.