Importance of Ignition Advance on a Boosted Engine

[forcefed86]

Orignially started this topic debating the use of extremly low timing and high boost VS the typical lower boost levels and moderate to high timing timing.

To me, lots of boost an low timing is a good way to burn out exhaust valves and cause detonation on long pulls due to the exhaust valve turning into a glow plug.  Just my opinion...  I think of boost as a variable determined by proper tuning of fuel and ignition.  An engine likes the right timing and fueling.  Adding boost and having to compromise those ends up being bad in my eyes.  If you want more boost than what the fuel and ignition can handle, either change the engine or the fuel.  That's just my opinion...and I'm open to hearing other arguments from those who have tuned a ton of cars.

I’ve never seen any evidence of exh. valve damage. At what point does valve damage occur? Can it even been monitored with EGT temps?  I’ve personally never seen my EGT’s go much over 1500*F on E85. When I ran my smaller turbo 36+lbs I actually ran 0* at peak torque, and then ramped up 18* by redline. Again, EGT’S were never outrageous.   Have you personally burnt valves this way in the past? I’ve seen my share of burnt valves, but none were from a low timing high boost engine. 

A few years ago I got to witness David Buschur dyno tune his pump gas evo record car (2 litre 4cyl). To demonstrate how little timing affected his tune Dave ran 6* peak timing and made over 600hp @ 39psi. Now I’m not suggesting anyone runs 6* of timing. But in every application when I upped the boost, ran optimal AFRS (12.0 or leaner), and used timing instead of rich mixtures to slow the burn I’ve gotten a much better time slip. It seems to me the old school methods of rich AFR's were being used to slow the burn. Then the addition of high timing is used to speed the burn back up. Why not run the engine at the peak power AFR and use the ign to slow the burn? Obviously at some point there will be diminishing returns. From what I've seen people are afraid of boost and tend to steer towards high timing. Where I'm the exact opposite.   

Somewhat similar to a diesel. The more compression you have, the easier it is to light off early and cause preignition or detonation. So by pulling the timing back closer to TDC you are able to run more compression/boost...to a point of course.   

[Darth Viper]

We had a Viper come in with exhaust valves burnt to hell, but no signs of detonation damage etc.  It was tuned with high boost and compression, but very little ignition timing.  Now the fact that you run E85 probably gives you a lot more leeway in needing to worry about EGTs/detonation.  I also agree that running rich isn't a cure for much of anything (And I mean pig rich...not 11.5:1).  However, I also caution that from a flame propagation perspective, igniting at the proper point in the revolution gives you the best conditions for ignition.  The mixture is at it's peak state of turbulence and has the shortest distance to propagate burning.  Granted, no ignition timing with infinitely fast burn speed is ideal, but impossible.  Adding timing does make it harder for the piston to rise as it comes near TDC, so that's why reducing the ignition timing doesn't hurt as bad as you'd think.  It's another reason for the extra power LS motors make over built smallblocks with many other factors the same...they require less timing.

I guess I look at it as an OEM typically does (or at least do now).  You can make more power on a given setup by running more boost and less timing, or running more fuel to cool the chamber, but it's all taking the engine away from it's optimum operation.  This is a good way to do it when you're starting with a stock motor or other budget option.  However, If I building something from scratch, I calculate to an operating point I anticipate reaching (infinity HP usually).  I have made calculators I use to size turbos (hot side and cold side), piping sizes, and have some others to help me with cam/compression ratio selection.  These tools are similar to what Garrett and Borg Warner have recently released, but allow me more customization.  The nice thing about E85 is that it's so damned tolerant of everything that you can pretty much get the best of all worlds.  Run a big cam, high compression, high boost, and optimized tuning.  It's magic juice. 

Lastly, running extra boost usually makes your exhaust backpressure ratio go up, diminishing the volumetric efficiency vs. ideal.  Effectively, you are making your engine/turbo pump more air at a given power level when your tune isn't ideal.  So by running a ton of boost and less timing, you are compromising this.  As I said, I think you can make more power this way, but it's sorta taking your engine away from its happy place to do so in my opinion.  I also would say that your turbo's headroom has a big effect on this.  If running more boost still has your turbo in an efficient place, I'd imagine the negative effects of high boost/low timing would not be nearly as detrimental as if you're pushing a stock turbo to the edge to get that extra boost.  I'd like to hear Tracy's take on all of this. 

[Darth Viper]

OK, this is really pretty simple, so let's just put the facts out there:

Mixture burn rate is mainly dependent on fuel type and octane, and cylinder pressure.  Simple as that.  Increasing octane gives you a slower more controlled burn, and increasing cylinder pressure (more dynamic compression, more boost, etc) speeds it up.  There are other factors like chamber design, etc. that can have a smaller effect, but in the interest of simplicity, let's just go with the big ones.  Ignition advance is nothing more than the tool used make the big boom/peak pressure/complete burn/whatever happen at the right point of crankshaft rotation.  Most things you read on average/conventional Otto Cycle reciprocating piston engines will tell you that this point occurs 15-20 degrees ATDC.

Every dynamic load and speed state of a given engine will have an ignition timing point that yields maximum brake torque.  Also very simple.  Advancing the ignition past this point will create pressure spikes, negative torque, and detonation, and retarding it from this point will cause loss of efficiency and excessive exhaust temperatures.  Too retarded is mechanically safer than too advanced, but neither is optimal.  Running an engine with excessively retarded timing is, well, retarded.  There just isn't any reason to do it given modern accurate electronic engine controls, especially those with knock control capabilities. 

Retarding timing excessively just to use a higher boost pressure than you normally could for a given dynamic state is counterproductive.  No good tuner does this.  A book could be written on the how and why, but just think about the things I wrote above and give them careful logical consideration.

[Darth Viper]

I think it is important that I clarify my above statements to acknowledge/emphasize the faster burn rate, and therefore lesser need for timing advance as boost climbs.  This is yet another reason why pulling lots of timing doesn't hurt as bad as one would expect compared to an NA engine.  But still, it's not optimum as the master said above. 

[forcefed86]

We had a Viper come in with exhaust valves burnt to hell, but no signs of detonation damage etc.  It was tuned with high boost and compression, but very little ignition timing.  Now the fact that you run E85 probably gives you a lot more leeway in needing to worry about EGTs/detonation.  I also agree that running rich isn't a cure for much of anything (And I mean pig rich...not 11.5:1).  However, I also caution that from a flame propagation perspective, igniting at the proper point in the revolution gives you the best conditions for ignition.  The mixture is at it's peak state of turbulence and has the shortest distance to propagate burning.  Granted, no ignition timing with infinitely fast burn speed is ideal, but impossible.  Adding timing does make it harder for the piston to rise as it comes near TDC, so that's why reducing the ignition timing doesn't hurt as bad as you'd think.  It's another reason for the extra power LS motors make over built smallblocks with many other factors the same...they require less timing.

I guess I look at it as an OEM typically does (or at least do now).  You can make more power on a given setup by running more boost and less timing, or running more fuel to cool the chamber, but it's all taking the engine away from it's optimum operation.  This is a good way to do it when you're starting with a stock motor or other budget option.  However, If I building something from scratch, I calculate to an operating point I anticipate reaching (infinity HP usually).  I have made calculators I use to size turbos (hot side and cold side), piping sizes, and have some others to help me with cam/compression ratio selection.  These tools are similar to what Garrett and Borg Warner have recently released, but allow me more customization.  The nice thing about E85 is that it's so damned tolerant of everything that you can pretty much get the best of all worlds.  Run a big cam, high compression, high boost, and optimized tuning.  It's magic juice. 

Lastly, running extra boost usually makes your exhaust backpressure ratio go up, diminishing the volumetric efficiency vs. ideal.  Effectively, you are making your engine/turbo pump more air at a given power level when your tune isn't ideal.  So by running a ton of boost and less timing, you are compromising this.  As I said, I think you can make more power this way, but it's sorta taking your engine away from its happy place to do so in my opinion.  I also would say that your turbo's headroom has a big effect on this.  If running more boost still has your turbo in an efficient place, I'd imagine the negative effects of high boost/low timing would not be nearly as detrimental as if you're pushing a stock turbo to the edge to get that extra boost.  I'd like to hear Tracy's take on all of this.

It seems to me more boost and less timing is key to making a stocker perform. (esp when fuel limited) In no way am I saying it’s the best setup for peak power with an endless budget and nice parts.   

This discussion was geared towards adding a turbo to a budget OEM engine. Then trying to extract the most power out of one without blowing it up. IE putting the least stress on the internal parts. I’ve personally seen a “stockish” long block junkyard 5.3 run 8.6x’s 167.9mph at our local track at 24psi through a TC78 turbo. Although it did have aftermarket cam/springs/head studs/MLS HG’s. Still that’s over 900hp.  Although he doesn’t wish to comment on the current timing, when the car was first out on the track he was running as low as 10*. Must be doing something right/different to make 900 hp on a factory setup! 

  I’m aware you lose power from excessively low timing. Also aware additional back pressure will effect total performance. But these losses do not come close to countering the added HP from the additional manifold pressure. The whole point of my post was to discuss at what point you will stop seeing beneficial gains by lowering timing and increasing boost. Not argue if this is the proper way to tune a car.  The small engine communitys have recently started pushing this to the limits and I was just amazed at the boost/timing these guy are running (all on e85).
 
For example...
There are currently several DSM (2.0 4cyl) guys running 60mm holset hx40 turbos into the 37-43psi range and making close to 700Awhp.(e85) None of them run over 18* of timing up top (usually around 16 or less). The few that I have spoken two persoanlly run 0-8* at peak torque.

I just thought it was odd we never see low timing and much over 15-20psi in the larger engine community, but it’s very common to see high timing and low boost (25-29* or more).

         
On a side note...
I had read that the addition fuel past peak power AFR’s to “cool” the chamber is common myth? Further read that the only thing adding more fuel does is slow the burn, which accomplishes the same as retarding the timing? (from innovative's website) This made sense in my application and most of the tuning crowd I communicate with using e85. On the other hand I too had always believed one of the reasons alcohol fuels worked so well was because of the volume of “cool” fuel injected. Assuming the above is correct it’s the slower burn of the alcohol that makes it such a better fuel for boost.

[forcefed86]

My 3.8 for example... At 25* of total timing and 23psi ran great. Anymore timing or boost and I would see a slight amount of knock on the logs. 

You can have too much timing lead (enough to kill off some power) without knock, and that's exactly where you were.  Those numbers, on pump gas with a 3.8, are excessive.  This isn't something you can do by the seat of your pants - you have to have the thing on a dyno.

Now take that serious tooner crap to the other thread.  This thread is strictly for the funnies.

This was on e85. Sorry I didn't clarify. I consider that pump gas here in KS. I tune my cars with log data, MPH, and plug reading at the track. Dynos are rich boy toys... 

[Speedfab]

I don't know what your static compression was, but no way should you have had that thing over 20 degrees with that kind of boost.  I've tuned a number of turbo 231s from near stock to twin turbo race motors, pump 93 to C16 to M1 methanol, and just looking back through some of that stuff I never had that much timing in any of them at that pressure level.

[scuter83]

In regards to the small engine vs. large engine differences, I think you have to take into account bore size for timing/flame propagation.  For the small engine community, the flame doesn't have to travel as far from the center of the bore to the bore walls, as the bore is smaller.  Also, if you pushed a large engine to the boost levels of the small engine guys, the timing would be more retarded as well.  Those small engine guys have to run that much boost to get the really high power to increase their displacement so to speak.  A 2L running say 45lbs of boost is really running around like a 8L.  (Every 15lbs is ~2L more air through the motor).  Put that into perspective of a large engine (say 6L running 15ish psi, which would be about a 12L).  Then the 4cyl guys get to rev it out to get their power and larger engines get the torque.

To put it to extremes, look at a diesel engine.  Those things run around at 24psi or so.  So a 6.6L Duramax is moving air like a 18L almost.  That is where their crazy torque comes from.

[forcefed86]

I don't know what your static compression was, but no way should you have had that thing over 20 degrees with that kind of boost.  I've tuned a number of turbo 231s from near stock to twin turbo race motors, pump 93 to C16 to M1 methanol, and just looking back through some of that stuff I never had that much timing in any of them at that pressure level.

That must have been a long time ago? The starting point of basic meth/pump gas chips now is 21* of timing. 28lbs+ on 23* timing or more is common place with 91 octane and meth inj these days. E85 guys seem to get away with more.

I just gave it what it wanted. This was back when E85 first came and everyone was instructing me to run more timing. It was a factory compression unopened engine. (8:1) I just locked in the boost I wanted to run and tuned timing by MPH/plugs. I stopped adding timng when the mph stopped climbing or I saw knock. Thats where ended up. At that time I haden't really thought of more boost because people told me I'd blow the engine.  My current times 10.0x slips (roughly 600hp by weight) are made with 9:1 comp, 30psi (larger turbo) and 17*. small 218/218 cam, Factoy heads/valvetrain/yadda yadda...

In regards to the small engine vs. large engine differences, I think you have to take into account bore size for timing/flame propagation.  For the small engine community, the flame doesn't have to travel as far from the center of the bore to the bore walls, as the bore is smaller.  Also, if you pushed a large engine to the boost levels of the small engine guys, the timing would be more retarded as well.  Those small engine guys have to run that much boost to get the really high power to increase their displacement so to speak.  A 2L running say 45lbs of boost is really running around like a 8L.  (Every 15lbs is ~2L more air through the motor).  Put that into perspective of a large engine (say 6L running 15ish psi, which would be about a 12L).  Then the 4cyl guys get to rev it out to get their power and larger engines get the torque.

To put it to extremes, look at a diesel engine.  Those things run around at 24psi or so.  So a 6.6L Duramax is moving air like a 18L almost.  That is where their crazy torque comes from.

Good point, haden't thought of that... 

[ttv8rx7]

so on a side not would i be safe to say that i wanted to run about 15-18 psi on my 68 327 with plugs 2 steps colder and 18* total timing and be safe @ 8.5:1 comp and 93 pump gas?

[skinnies]

We've ran as low as 3 degrees on big boost without a problem, use the low timing in bottom of 1st for traction on the street. You have to have good spark/coils to do this though or it'll break up.  Back when I had the first iron 5.3 in my rx7 we did a test at 11lbs, 10 degrees vs 20 degrees vs 26 degrees....10 vs 20 made about 50rwhp difference, 20 vs 26 made less than 10rwhp difference.  I can say we've seen 50rwhp gain at over 1100rwhp going up a few degrees of timing in the high 20's and almost 30lbs of boost. Each combo will be different, I personally like the higher boost and lower timing as it hits the tires easier(we do a lot of street racing).  The timing curve will play a big role also, we've learned a lot on these stock motors and plan to push them even harder this year, shooting for over 1000rwhp on a jy 5.3 with some twins in a friends car.

[forcefed86]

so on a side not would i be safe to say that i wanted to run about 15-18 psi on my 68 327 with plugs 2 steps colder and 18* total timing and be safe @ 8.5:1 comp and 93 pump gas?

Hard to say. Start out with low boost and work your way up watching plugs. Maybe invest in a knock sensor.

We've ran as low as 3 degrees on big boost without a problem, use the low timing in bottom of 1st for traction on the street. You have to have good spark/coils to do this though or it'll break up.  Back when I had the first iron 5.3 in my rx7 we did a test at 11lbs, 10 degrees vs 20 degrees vs 26 degrees....10 vs 20 made about 50rwhp difference, 20 vs 26 made less than 10rwhp difference.  I can say we've seen 50rwhp gain at over 1100rwhp going up a few degrees of timing in the high 20's and almost 30lbs of boost. Each combo will be different, I personally like the higher boost and lower timing as it hits the tires easier(we do a lot of street racing).  The timing curve will play a big role also, we've learned a lot on these stock motors and plan to push them even harder this year, shooting for over 1000rwhp on a jy 5.3 with some twins in a friends car.

Thanks for chiming in. In the process of getting my new 1st gen together. It will be a boosted LS similar to your setup. Plan to see how far I can push it. If it pops I’ll throw another cheap OEM long block back in. Still torn on the EFI VS Carb and Twin VS single. May not make it this season, running behind.   

[SpendOne]

When I had my dsm I always tuned it for the most timing advance as possible. This was on a stock bottom end. Th car was on 32 psi and e85 with a peak total timing of 19-20 degrees. Never showed a count of know amd afr's were at 11.0-11.5. Motor made 578hp/458ft lbs on a mustang dyno. The motor had 180k on it.

[forcefed86]

Just to bring some more light on my point of view. This graph is the factory timing table of the a Mitsubishi Evo8. This timing map is successfully being run in many 500+hp applications. One, a close friend of mine running a hx40 holset at 30psi on pump fuel (93 octane). This is with an 8.5:1 compression bored and stroked 2.3 litre 4g63 engine.

As you can see the timing in the boosted regions is unheard of in the v8 turbo community.Yet this is what the mitsubishi engineers have settled on for a factory timing map.

[mwatson185]

Im not really seeing which of these numbers are unheard of until you get to an RPM above the range of most LS based engines.  6k RPM 2.0 bar and 13 deg of timing sounds about right to me (for 8.5-9.0 CR).  At 9k rpm you will be at a much higher ign advance (18 deg @ 2.0 bar in this case), but nothing seems out of the ordinary.

Every combination is different, but based on compression ratio, load, rpm, and tuning for a static safe AFR, there will be an optimum amount of timing that is both safe and creates power.  That being said, too much advance is obviously dangerous, too little is leaving power on the table, and way too little can increase combustion chamber temperatures to a dangerous point as well. 

-Marques