Timing: Is a dyno or track the only way to know if total timing is set correct?

[XH29N0G]

I am looking for an answer to the question in the subject heading.

My understanding of timing is primitive, but I will explain what I think I know and let those who know more correct me.

       Initial timing is set by finding the timing where the idle is best (best vacuum and fastest idle speed). 
       The timing curve is set to bring in the total timing as quickly as possible without causing detonation.
       The total timing is set at something like 34-38 (higher for low compression cars). 

The specs on my engine that I believe are relevant are 10.1:1 compression and a cam with duration at 0.5 of 236/246 centerline of 105 and LSA of 112.  I have a MSD pro billet distributor with a 6AL.  I am happy to provide other information if necessary.

My total advance was set at 31 with an initial of 14.  If I went higher, I had knock.  I recently changed the advance curve to a less aggressive curve and found it idles best at 18 and this puts it at 35 total.  So far I have not heard knocking, but will test tomorrow.

If there is a way to check whether the 35 is better than some other value, I would like to know. 

[cdr]

the track is the best way, a dyno will get it very close.

[XH29N0G]

That is what I suspected.  I have never been to the track  but I am interested in trying it sometime.  So there is no real way other than those two to really decide what is the best total advance.

[cdr]

seat of the pants, ie the butt dyno.  just take to a chassis dyno tuner that has a good reputation

[XH29N0G]

seat of the pants, ie the butt dyno.

Thanks. 

I should admit that my butt dyno is not that good and my sense of time warps when the pedal is down.

[BSB67]

That is what I suspected.  I have never been to the track   but I am interested in trying it sometime.  So there is no real way other than those two to really decide what is the best total advance.

I don't recall.  How do you know that it is 10:1 CR?

Track is a lot better for determining timing.  If you choose a chassis dyno, be sure that you use average hp that is reflective of the shift recovery rpm to establish the range.

Despite popular belief, I have found that 40° to 42° with iron heads and decent compression ratio on my heavy car, tight converter, tall gear stuff ets the best.  Actually there were several of us that had similar results.  You won't read that in a magazine.  However there are a lot of factors and I do believe that atmospheric condition matter as well.


PS, my butt dyno is worthless.  I suspect that most are.  I cannot tell when I add an honest 20 hp to my car.  Most people confuse tire spinning (usually from a from a roll) with more power.

[XH29N0G]

Thank you.  For the information and experience.  It looks like the ideal setting is something that depends a lot on the specific set up and experimentation/calibration is the way to go.

The compression estimate is off the build sheet from muscle motors from 2012.  It has eddy RPM heads (nominally 84 cc - 60929) with nothing done that I know of other than inspect/clean up the valves and install different springs/retainers, a 3.9 stroke, 6.7 rods, flat topped, forged diamond pistons (4.285" -  the pn# is not listed but I scribbled in a number of 51910), a deck height of -0.004 and (1009) gaskets (I think this is 0.039 Fel-Pro).  You would have a better sense of whether this adds up.  By I seem to remember my quick calculations indicated it was pretty close. The gears are short (4.30).  It has a 5 speed (5th = 0.64) TKO 600 and I use 255 60/15 ET Street radials so it won't spin as much.  The set up does what I want and has held up so far, so I am happy with it.

I think I need to visit the track and learn, but I have no experience there and my guess is that my shifting and driving might be bigger variables than the ignition timing (at least to start).  

From the responses and what I read, I am guessing I should be fine with 35/36 for now (instead of 31/32) and by watching out for any ping.  I believe I can hear it pretty clearly when it happens since I have a fairly quiet exhaust system.  If there is anything I need to look out for in the mean time (sounds, behavior, etc....) that would tell me I am missing something that could really damage my engine please let me know.
   

[c00nhunterjoe]

I too am in the 40+ total timing and mid 20s initial. Unless you know how to speed shift and launch your car consistantly with a stick, i doubt the track will do you much good. Your ets and 60' will be all over the place. The only good thing you will have going for you is comparing mph BUT without a weather station, you wont know if the air changed or your adjustments affected the car.

[BSB67]

I too am in the 40+ total timing and mid 20s initial. Unless you know how to speed shift and launch your car consistantly with a stick, i doubt the track will do you much good. Your ets and 60' will be all over the place. The only good thing you will have going for you is comparing mph BUT without a weather station, you wont know if the air changed or your adjustments affected the car.

All very good points.  A weather station is pretty inexpensive, and the down track data can be used to work around the 60 ft data.  But you still need to be consistent from run to run on all of the shifts.

[XH29N0G]

Thanks. 

I had a chance to do a little more testing today and by trail and error am mapping out RPM/Advance settings where it knocks and does not knock.  It looks like I will get a slight (very faint) ping at 3000 if I am at 36 total but not 34.  at 3500 it looks like 36 total is OK.  I think I will map a little more, choose advance springs that come in early but are in a safe range.

   

[cdr]

are you running vac advance ?

[John_Kunkel]

I always wanted to try incorporating a knock sensor as a warning device i.e. advance it until it rattles and back it off a few degrees.

[XH29N0G]

A quick answer. I only have mechanical advance.  

Regarding the knock sensor - That is an interesting idea to install one as a warning device. I have a hard enough time trying to identify pings by ear, and having something that could pick them up directly would be a good thing.  I don't know if I have the patience right now to do this though.

And a few findings.  The idle wants to be something like 18 advanced. The total advance for the light spring sets (fastest advance) cause it to knock under load in higher gears.  Configurations that work

Fastest springs        13 at idle       29/30 total at 2000     idle suffers and there is run on (dieseling).  
Medium springs       15 at idle       32 total at 2500     still runs on a little.

My next test will be to set the idle at 17 for idle and then try the heaviest springs which should give somewhere around 34/35 at 3500 RPM.  Dieseling stopped at this idle advance - maybe throttle blades closed down more (?).
 
What confuses me is that I read that the goal is to have the timing come in as early as possible.  It comes in later with the heavier springs, but I can then use more total advance.  I am using the black bushing which gives the advance mechanism the least amount of change and over the smallest RPM range.  Is there any common wisdom on this issue?  

My current plan is to find the combinations that work, and then to go back to them for a direct comparison at a later date.  
 

[cdr]

what is the AF ratio when it starts to rattle ?

[XH29N0G]

what is the AF ratio when it starts to rattle ?

I will need to check that.  Inn some cases I know it is good/lean 14 to mid 15.  In others I believe it is solid 13 (maybe 12).  I need to check because the tests have been in 4th and my A/F testing has been in 2nd/3rd.  3rd is no rattle and 12.5 to 12.9/13.0 at WOT.  It is a slight detonation.  I had one case where it was the classic type (like I used to hear in the late 1970's).  I may get a chance to check today, but I have some things to do first at work.

[BSB67]

What spark plug are you using?  You should not be using anything hotter than a -7 NGK plug.  This, and/or a 160° thermostat could make all of this go away.

If you are really wanting to get all of the variables right and maximize power, it really is time for you to go to the track.  If the 18°/35° all in at 3000 or 3500 does not rattle under WOT in first gear, leave it there.  As long as the advance is all in at 3500, you're fine.  If it pings just a little on the street, just drive around it (i.e. prevent it by driving technique)

Your cylinder pressure is probably on the edge....which is perfect!  I hate giving up any compression ratio (i.e. horse power). 

My guess is that you will make the car a bunch faster buy learning to drive it, and tuning what you have.  You could spend three more years playing with it the way you are now, and never finding the right combination.

[c00nhunterjoe]

Have you also verified fuel pressure is consistant as you are running through the gears? Perhaps a compression test will help give us some more information as brian suggested.

[XH29N0G]

Update.  Found another setting without ping or knock - idle set at just under 16 degrees (I think the total should be somewhere 32/33 but have not verified), the black bushing and the heavy springs (all in by 3500). 

Now responses to your questions. 

BSB67: I am running NKG BCPR6ES-11 so it is hotter than an NKG 7.  The engine was originally set up with NKG 7 but the plugs were getting sooty from idling.  I think I have the carburetor set up better now and after your comment are considering going back to the NKG 7 just to see what they look like.

I am almost certain my thermostat is hotter than 160 (I think 180 degree).  Next time I run it I'll check the temperature of the coolant to verify.   The engine seems to run better when it is hotter.  It has forged pistons and is fairly loose when cold.  I get the impression the engine gets really quiet and runs best after I have gotten it to heat up by running it up through the gears.  You know more about this than I do, but this is my sense.  Right now I am inclined to leave the thermostat as it is.

I think you are right that the next step is the track and learning how to drive it. 

C00nhunter,  I have not done a compression test, and should to know more about the build.  Frankly, I am bit hesitant because it gets awfully hot by the headers after it is warmed up.  I will probably not check it right away, but ultimately, I will.  I have not put a gauge on the fuel pressure.  It has a mechanical pump and at least when it was on the dyno it was able to keep up.  I realize the dyno is out of the car and in the car with the fuel lines is very different.  That will also get on my to do list.
 

[c00nhunterjoe]

If it made full pulls on the dyno, then the pump is PROBABLY keeping up. You need the cooler plugs
That may be 90% of your problem as previously stated. You said you changed the carb due to a dirty idle? What did you change?

[cdr]

well from your post it has been on the dyno, they should have told you what the total timing should be. the rest is get the AFR correct & then like BSB67 said learn to drive around the pinging .

[1974dodgecharger]

Its not too bad get it up to 180 operating temp and wear some gloves of some sort and get those plugs out and test compression.

I guess Ill ask, 'Is it really pinging?'  how can you tell?

I ask because its pretty loud when my car runs and I hardly hear anything except the rumble, lol 

don't think I would ever hear any pinging or anything except one time I didn't plug in a spark plug and had it running on 7 cylinders  then it sounded like a ping to me.

[XH29N0G]

 :laugh:Thank you all.  I think I have enough things to try to keep me busy for the foreseeable future.  Here are some quick responses:  

C00nhunter: The carburetor was just me playing around.  I swapped out a perfectly good QF 830 SS for a QF Q-850 AN.  The 850 has smaller venturies in the secondary larger boosters so may flow less, but no choke tower.  Both worked well and I have no proof that one worked better.  I have been able to dial in the A/F of the 850 better and it is very responsive, but I also have been learning in the process.  I plan to try the 830 again to see if it was a real difference.  I will look into the cooler plugs to see if that makes a difference.  The issue was carbon build up on the plugs before, but I also had a lot of idling going on and was running a richer idle.

CDR:  It was broken in and run a few pulls on the dyno, but I did not get the timing information from them.  I sent one email asking about timing information and did not get a response.  I had responses about most other things though.  I did not follow up after the no response.  I assume they set the timing for what worked best.  They used the lightest springs and all advance came in before 2000 RPM. What I have found is that I can advance the setting at idle (which significantly improves the idle quality) if I use heavier springs to offset the timing at 32, 33, 34 coming in so soon that it knocks.  I will try different plugs some time in the not too distant future - but probably not in the next few weeks.   I think the AFR is pretty close to dialed in.  I have done numerous tests and then recalibrated the A/F meter and checked with no change.  

1974dodgecharger.  Thanks for the encouragement.   I will do the compression test, probably not right away, but maybe when I prepare to swap the plugs.  I have a fairly quiet exhaust system straight through mufflers and bullet mufflers as resonators so I can hear the engine pretty well.  I am sure the heavy pinging is pinging.  It sounds just like my dads 1978 4 cylinder chevy mallibu station wangon with 3 on the floor used to sound.  I am also pretty sure about the lighter pinging.  I can make both come in and go away by playing with the timing.

I'll also need to drive down to the track to find out what I need to do to run my car there.  I expect issues need to be addressed to pass inspection and also to fit with their basic rules.

[XH29N0G]

HI everyone,   Just an update.  Still not made it to the track, but I did two things that seem to have helped with detonation and allowed me to reset the total advance above 30-32 degrees.  (1) I switched back to a cooler plug NGK-7.  I still do not know if these will foul again, but I will check.  (2) I swapped in a different bushing into my MSD distributor (one I purchased from 4 seconds flat that gives it 10 degrees of advance instead of 18).  Now the idle is set at 24 and total is back at 34.  With the 24 initial advance, the carburetor idle screw can be backed off and the highest vacuum comes in at an A/F at almost 14 rather than the high 12's.  I will see if that helps with fouling.    Thanks for the feedback last year and I will let you know when I get to the track.