total timing too high?

[My427stang]

Good chamber, tight quench, high compression, rich mixture, all lower the requirement for total timing (while allowing it to be more tolerant of a quick curve)

Open chamber, loose quench, low compression, lean mixture, all raise the amount of total timing (although many of those things make it unhappy to get what it wants)

I haven't done any BBM stuff, but sure see the guys who do make power closer to 32, I wouldn't sweat it.  Then you can have it come in quick as Brent said for part throttle snap on the street.

All makes perfect sense

[plovett]

This is most definitely a tangent, BUT one thing I (almost) never see mentioned with regard to timing, is octane and compression ratio. I think octane and the resultant time of ignition affect the timing requirement, especially in combination with compression ratio.

I don't have a tome of empirical evidence to back it up.  I can remember one event which drove this home to me.  I had a low compression 428 (9.3:1) with a decent sized cam in it 242/246, on the dyno.  We used race gas just to be safe since it was a brand new build.  I don't remember the exact octane, but it was race gas.  It was certainly over 104 octane.

So........this engine kept making more power as we increased the total timing.  We got up to 45 degrees total and it was still making more power.  I got a little freaked out at 45 degrees total and stopped adding timing, despite the improving power figures.  It just seemed weird.  TDC and the balancer had been checked afterwards to verify the numbers.  I'm using all the same pertinent parts including the distributor on my current 428 build and it likes a "normal" 37-38 degrees for an Edelbrock chamber. 

I don't think the rate of combustion is significantly affected by octane and compression, but I do the think the time of ignition is affected.

Like I said, it's just a tangent for 99% of applications. 

JMO,

paulie

edit: Hmm.  I say that and then it doesn't make sense.  Certainly most people would think that the "time" of ignition is rigidly controlled by when the spark is ignited.  I'm not so sure that I'm right now that I think about it a bit more.  I'm not sure that I'm wrong, either though.  It may be much more complicated than we think.  The combustion process is probably not linear in terms of it's speed.  I know this all sounds esoteric, but I don't think it is.

[Falcon67]

Best way is MPH or timed pulls from some MPH to some MPH.  I can tell you that with the AFD heads in the dragster, a drift from 28 degrees to 34 kills a little over 4 MPH.  Thats at 11.8:1 with leaded 110 racing fuel. 

[Tobbemek]

Its really easy to google "gas octane test" and find old poprod ore hotrod magazine tests when you still could get 100 octane gas. and see what octane  does to advance timing needed.  NASCAR engine 101 on you tube is very informative on the subject also. 
Higher octane gas like 100+ in a engine with 9:1 something static comp is a waste of power/time consuming combustion
higher octane burns slower, to gain near the same power with 104 octan as with say 98 0ctane for an engine like dis you have to advance the timing like to maby45¤ advance.

Every Engine has its on ideal crank angel maximum combustion pressure / degree depended on  stroke / rod ratio etc. that's the spot we are looking fore to hit.
As mentioned here before me, a richer fuel/ai mixture ( more / closer to each other fuel particles will burn faster and vice vers with a leaner mix,
and to that dynamic combustion pressure difference/ throttle openings rpm/ overlap hot gases situations 
Assuming  (You don't win races assuming) all is god with ignition system and plugs intake carb and so on. (Will try to get dis understandably )
AT WOT and just WOT the engine wants less advance at peak torque  ( cylinder max packed with fuelmix faster burn ) than peak power and should have a slop on approx 1¤ advance/1000 rpm or so depended up on engine type up to peak rpm ( less VE ) fore max power.
In Dyno test you almost never read more than " it made max power at that advance " then it coms in to play the vehicle it self
light,heavy   auto/ manual  gearing converter gforces on intake tract and carb ( go in to youtube BLP N&S test jmarkaudio) something and look watt happens to fuel in carb bowl up on dragrace launches and figure if that's altering  you jetting / E bleed calibration compared to dyno pulls )

Bill Jenkins was the first ( I belief ) to have a high  gear retard  in his 327 S/S chevy II manuel trans. The trick was to have a 42-44  advance ( as i recall ) launching the car  to make it rev faster and then retard to 38( ore watt ever it was) in higher gears when the engine was loaded and working hard fore best power. Combustion it self takes the same amount of time provided the same fuel air mix and so on , piston speed goes up in square by rpm ( i think it was, my old beat up brain cant remember as much as i want to ) Any way the important ting to remember is like Blykins seas
GO FORE LEAST ADVANCE TIMING TO MAX POWER not max advance to max  power  A light car low gear high stall conv. can take a faster advance curve than the opposite combo. Then we have the cruising advance situation all ready mention several times last week come in to play
Phuu 

[Drew Pojedinec]

edit: Hmm.  I say that and then it doesn't make sense.  Certainly most people would think that the "time" of ignition is rigidly controlled by when the spark is ignited.  I'm not so sure that I'm right now that I think about it a bit more.  I'm not sure that I'm wrong, either though.  It may be much more complicated than we think.  The combustion process is probably not linear in terms of it's speed.  I know this all sounds esoteric, but I don't think it is.

Heh.... this is diesel engineering 101 in regards to fuel burn.
Yes, in gasoline engines people don't think much of it due to burn rate, but in large industrial diesels this is a well known principle.  Always consider your fuel and it's characteristics.  There is timing (we know this one), injection lag (how long it takes for the full fuel load to be delivered with the injector stroke), ignition lag (how long it takes for the fuel to begin igniting, and how long it takes to fully burn), atomization vs penetration, all are important considerations, etc.  The larger fuel particles penetrate further into the chamber, while the finer ones burn rapidly, often so rapidly that unused oxygen is still available.....  (the redneck pickup truck crowd blowing black smokes comes to mind).
These are all factors that are very important in a diesel, especially when you are dealing with a bore and stroke larger than ten inches.
Gasoline engines are no different in that different grades of fuel burn faster or slower.  To throw in another curve ball with a gasoline engine you have rich and lean burn characteristics that very greatly with everything else being exactly the same.

With my specialty (2stroke diesels) this is even more critical as you have considerably less time to burn the fuel properly before the engine is pumping fresh air into the cylinder.

[fryedaddy]

i failed to mention that i run half 110 leaded and half 90 no ethanol and im around 11 to 1 compression,could that be why i thought i needed more timing

[blykins]

Technically, you would need less with higher compression and an efficient chamber.

I would run a little colder plug too. 

[fryedaddy]

thank you everyone.it think im about to get this straightened out.i put the black bushing in ,lite springs.that let me set my initial to 16 which let me back my idle screw on my carb off alot. win win  thanks

[bn69stang]

Hey Fryedaddy , i am running the black bushing , and 14 initial with my BBM s , it s on a 428 .. Bud

[fryedaddy]

Hey Fryedaddy , i am running the black bushing , and 14 initial with my BBM s , it s on a 428 .. Bud

thank you,all i wanted to know was those settings.im going to keep it in the 32-34 range from now on.i have it on 34 right now and its running like a scalded cat,im happy

[Tobbemek]

Good to hear wish i could tag along for a ride with you. 

[plovett]

So here's what I'm wondering.  Does an engine run best on the lowest octane fuel that is sufficient for its needs?  Maybe less total timing needed?   I'm not saying that's a good thing to do in practice, as you want some cushion for different driving conditions.  Still, as a theoretical question?

paulie

[Tobbemek]

As a theoretical question! Yes if one look at it octane only wise. Different fuel labels can have different additives that of cause com in tho play also Earlier start of ignition point, fight against piston upwards motion  fore a longer time, and in general lower octane burns faster / needs less advance = more power  I keep telling you good folks GO IN TO "NASCAR ENGINE 101 ON YOU TUBE and give it 40 minutes  very informative on the combustion subject and Why they have " splited" different  timing points to all the cylinders.

[Barry_R]

I do not have enough time to get too deep into this discussion - but need to point out a couple things. 

Fuel burn rate and octane are two different characteristics of race (or street) gasoline.  Octane is the resistance to self ignition and does not tie directly into the rate of burn once that ignition occurs.  They are obviously inter-related as all chemistries are- but race gas does not burn slower than pump gas as any sort of rule. 

Think about it for a moment.  Both fuels are designed and optimized for a particular need.  A street engine will need to run its best at idle and lower RPM.  A high performance application will need to run its best at very high RPM.  At high RPM you have much less time available to use for each combustion event.  In order to get the combustion event completed and get the most power from the engine you will want the race gas to burn faster...and it does....

[plovett]

As a theoretical question! Yes if one look at it octane only wise. Different fuel labels can have different additives that of cause com in tho play also Earlier start of ignition point, fight against piston upwards motion  fore a longer time, and in general lower octane burns faster / needs less advance = more power  I keep telling you good folks GO IN TO "NASCAR ENGINE 101 ON YOU TUBE and give it 40 minutes  very informative on the combustion subject and Why they have " splited" different  timing points to all the cylinders.

I think this is the video you are referring to? 

https://www.youtube.com/watch?v=rBZCnG1HwDM

It's pretty informative.  Thanks for that.

I notice when talking about combustion speed, the measure is usually pressure vs. time.  I think it would be interesting to see mass vs. time.  That is, the mass reacted vs time.  I'm not exactly sure where I'm going with that.  It just seems like it would be helpful to understand the combustion process.  Measuring pressure is an indirect means, and influenced by other variables, I think.

JMO,

paulie