Importance of ignition advance in high boost applications?

[Rafs-T-Type]

The funny thing about this thread is that when considering the timing most havent even verified their actual timing . Imagine what is really happening when one thinks they are running 21* and they are really at 25*.

What's the best way to verify timing?

 

[forcefed86]

After much reading last night it seems that many of the E85 8 cyl guys put the car on the dyno and keep bumping up the timing until they don't see any more gains, then back it down a couple. The consensus seemed to be that the car will stop making power (or loose power) before detonation occurs. Again this info is for E85.

Exactly my point...

That is also how I have seen most tune. If we know boost makes power over timing... why not lower the timing and up the boost until the car stops making power? From what I've seen/read, most set a fixed amount of boost and adjust timing to it.

I would think more power could be had setting a fixed amount of timing... and adding boost until detonation. Once detonation is reached, lower the timing until the detonation clears. Once free of detonation add another pound of boost. Rinse-wash-repeat until no more power is being made.

The way I see it engines (mainly cylinder heads) have progressed to the point where they require less and less advance. Igniting a mixture 20-30 degrees before TDC wastes alot of energy. Assuming an engine was 100% efficient and the burn was instant, wouldn't you want to light off the ign at TDC? The faster the flame front/burn time the less advance you should need.

I can see how a high rpm hemi headed engine with a 3.3" bore running 4o-50lbs of boost at lean AFR's would require much less timing than the average boosted v8-v6. Yet it also seems common to lower timng at peak torque (lower rpm), and advance timing through the upper rpms? Why would this be on a boosted engine?

Now I'm not saying I'm right in anyway. I'm sure if that was the way to tune, it would be done. Just makes more sense to me.

 

[Rafs-T-Type]

Part of the problem of finding the boost threshold is that many say detonation is skipped and you go straight to pre-ignition aka good bye engine. But keep jacking it up and let me know how it goes

 

[forcefed86]

Couldn't the same be said for timing?

I was speaking of the people that already have done it with the smaller engines. There’s no guess work there, it’s been proven to work well many times over. I was hoping to find a TB member that pushed the envelope a little and compare that timing map to the smaller engines map. Doesn’t seem to be any pump gas shoot outs in the performance buick world. That’s usually where I’d see the “uber” low timing maps.

I did try to run more boost on my setup, but I ended up floating the valves at anything over 30lbs. (110# springs factory valvetrain) Also I was scolded a bit when my car went 10.06 with only a roll bar in it. If I could afford to legally push it anymore I would. Although, going by trap and weight I’m right around 600 hp. I think I’d find the breaking point of the oem block/ rotating assy before I found my boost limit. Surprised I haven’t broken anything with a pt68 at 9:1 and 30lbs honestly.

 

[Rafs-T-Type]

I think that with the right turbo and valvetrain you would just continue to make more power as you upped the boost, more so than upping the timing. But the increased cylinder pressure would lead to pre-ignition.

 

[bison]

What's the best way to verify timing?

First you verify the timing tab with a piston stop and degree wheel to find true tdc. True tdc is zero. Once that is done you can disable the timing advance so you are running off the modules timing with no advance from the ecu. Then you use a timing light to see where you are. If you have an aftermarket ecu you just adjust the crank offset angle so that its at 10* with the light on it. You could have your chip burner burn in the advance or retard if you're on the stock ecu. If you want to get fancy and your reluctor ring is way off you can press it off and re-clock it. I typically see 1-2* error on most cars because if the reluctor rings. A lot of bhj balancers were off 4* for no known reason.

 

[Reggie West]

I was speaking of the people that already have done it with the smaller engines. There’s no guess work there, it’s been proven to work well many times over. I was hoping to find a TB member that pushed the envelope a little and compare that timing map to the smaller engines map. Doesn’t seem to be any pump gas shoot outs in the performance buick world. That’s usually where I’d see the “uber” low timing maps.

You should ask AlkyV6 ( Don Wang ) about that. He may have some insight for you.

 

[forcefed86]

I've spoken with Don a few times. We both agree it's a necessary evil and to use as little as possible. Of course he says this and runs 30 degrees at 7800 rpm and 29 psi boost through a 91mm turbo! Methanol tuning is alot different, and his engine setup is unlike any other I'm aware of.

 

[kidglok]

perhaps in a smaller displacement engine due to the shorter stroke the mixture needs to ignite closer (or sometimes before) tdc to fully combust before the piston bottoms out?

 

[we4Mateo]

First you verify the timing tab with a piston stop and degree wheel to find true tdc. True tdc is zero. Once that is done you can disable the timing advance so you are running off the modules timing with no advance from the ecu. Then you use a timing light to see where you are. If you have an aftermarket ecu you just adjust the crank offset angle so that its at 10* with the light on it. You could have your chip burner burn in the advance or retard if you're on the stock ecu. If you want to get fancy and your reluctor ring is way off you can press it off and re-clock it. I typically see 1-2* error on most cars because if the reluctor rings. A lot of bhj balancers were off 4* for no known reason.

When I put on my BHJ balancer, I had to go to 19/17 timing settings in the chip to run 20-25psi without knock on alky so I know there was a difference between that balancer and stock as I always ran 21/19 before that on the same chip. I just adjust accordingly. I'll take boost over timing though. 18psi and low timing in the winter when the alky's off and it still rips pretty hard.

 

[murphster]

It seems like the you can make pretty good power on the pump gas and alky cars with some low timing. On race gas it seems like a lot more timing is needed. I wonder if this due to the fact that a lot of people use C16 which is supposedly very slow burning as compared to pump gas. I've gone down to 17-18 degrees timing and run some of my fastest times as compared to 21-22 degrees timing on pump gas/alky. As I turn it up more to get closer to the 140mph range it will be interesting to see how the boost vs timing dynamic turns out.

 

[bison]

It seems like the you can make pretty good power on the pump gas and alky cars with some low timing. On race gas it seems like a lot more timing is needed. I wonder if this due to the fact that a lot of people use C16 which is supposedly very slow burning as compared to pump gas. I've gone down to 17-18 degrees timing and run some of my fastest times as compared to 21-22 degrees timing on pump gas/alky. As I turn it up more to get closer to the 140mph range it will be interesting to see how the boost vs timing dynamic turns out.

Stay conservative on that timing and keep throwing boost and a lot of fuel at it till you get the mph. If you are injecting alky keep the targets in the low 10's

 

[bison]

When I put on my BHJ balancer, I had to go to 19/17 timing settings in the chip to run 20-25psi without knock on alky so I know there was a difference between that balancer and stock as I always ran 21/19 before that on the same chip. I just adjust accordingly. I'll take boost over timing though. 18psi and low timing in the winter when the alky's off and it still rips pretty hard.

Throw a light on it and see how much its off. I remember a few years ago a well respected vendor or two had a couple ringers that would run like a mofo to the eighth and that was about the end of it once they made enough power to go 135+. The ring was off by about 4*. Yup they were running 26-27* advance when they thought they were at 22-23*.

 

[johnnyttype]

its not a race car by any means but my other car is a cobalt ss.. LNF engine, 2.oL Turbo. Running on 93 octane its common to see people running 22-24psi and 12-15degrees timing up top, but it also has VVT. Equates to 300-330fwhp and mid 300's torque. My cobalt is currently 22psi and 12.5 degrees timing

Just adding this for comparison, seemed relevant. i can post timing maps if anyone is interested

 

[we4Mateo]

its not a race car by any means but my other car is a cobalt ss.. LNF engine, 2.oL Turbo. Running on 93 octane its common to see people running 22-24psi and 12-15degrees timing up top, but it also has VVT. Equates to 300-330fwhp and mid 300's torque. My cobalt is currently 22psi and 12.5 degrees timing

Just adding this for comparison, seemed relevant. i can post timing maps if anyone is interested

I think it's apples and oranges comparing DOHC small bore 4cyls to pushrob 2valve engines with an oversquare bore, I do love those Cobalts though . The rpm's are different, the cylinder fill is different, everything is different. Timing numbers are just that, numbers. The charge needs to be lit a certain amount of time before TDC so that maximum thrust will be forced upon the piston without it happening so soon that it tries to stop the piston on its way up, pre-ignition. Whatever that number before TDC, or advance is, is different for every motor and fuel combination, but the end result is the same, namely, a good burn after TDC. Everyone gets hung up on the number. Like Bison stated, I need to put a timing light on my car to see where it's at; I'll be checking my advance with my new TR6 ignition module, but until then, I set the chip for whatever number makes it run the fastest without knock. The number in the chip is really irrelevant compared to mph at the track which translates to winning races on the street.

 

[mgmshar]

...a very good question. As somebody who studied internal combustion engines a lot in college many years ago (yes, I'm one of "those guys"), I'll try to give the answer to the original question. I'll try to keep this from becoming too much of a scientific paper.

There are primarily two reasons why the guys who run small engines with 4-valve heads generally run lower timing than we do...

1. Their spark plug is located in the center of the cylinder. All other factors being equal, it will take less time for the flame to travel across the cylinder when the spark plug is in the center of the cylinder (the case for most small four-valve engines) than when the spark plug is located on one side of the cylinder (like our Buick engines). The flame front only has to travel half as far after the spark plug ignites it.

2. Most four valve engines introduce a lot of air and fuel tumbling into the air that is flowing into the cylinder. That air is still tumbling around even after the piston comes back up towards TDC and the spark plug fires. The more vigorously the air is tumbling (and/or swirling) at the point of ignition, the better mixed the air and fuel will be, the more rapid the combustion will be, and the air and fuel will burn more quickly. You can do some research on the internet to learn more about "tumble" and "swirl" in engines. Generally speaking, newer engines are designed to introduce more tumble and swirl into the air charge as it enters the cylinder than older engines like ours. More tumble and swirl = more rapid combustion = less spark timing needed to get best torque. Ever wonder why newer, naturally aspirated engines make more torque and power per cubic inch than older engines? More attention to tumble and swirl are part of the reason why.

One other possible factor is simply that they are getting more cylinder filling than we are - they run more boost, and their engines breathe better than ours. So, on each intake stroke, they are cramming more air and fuel into the cylinder than we are. All other factors being equal, the more dense the air mixture is in the cylinder, the more rapid the combustion, and the less timing you need to reach best torque. Ever wonder why you need a lot less timing at WOT than you do at part throttle? The increase in the speed of combustion as the amount of air filling the cylinder increases is the primary reason.

We did some studies back in the day, and we found something very interesting about gasoline engines. An engine will make the best torque (i.e. produce the most "oomph" on the piston) when the peak cylinder pressure occurs at about 17 degrees after top dead center. This was proven over a wide range of gasoline engines, and it's a testament to the fact that the geometry of most gasoline engines (bore to stroke ratios, bore to rod length ratios, etc.) are actually pretty similar. Whatever spark timing results in combustion that produces peak cylinder pressure at about 17 degrees after TDC will result in best torque, assuming you can run that spark timing without knock. Strange, but true. Note: I'm typing 17 degrees from memory, because I don't have my old college books handy, but I'm pretty sure I remember that number correctly.

Hopefully this helps answer the original question.

 

[charlief1]

Thanks Mike. I've been following this since it was posted and have a question. With the stock RWD head on an engine or a StageII head which will require the least amount of timing to produce power?

 

[mgmshar]

Thanks Mike. I've been following this since it was posted and have a question. With the stock RWD head on an engine or a StageII head which will require the least amount of timing to produce power?

This is a bit of a trap question, because it's not cut-and-dried. If we make some assumptions (you'll have to decide if these assumptions are really true), then maybe we can develop and answer. Let's assume we have two engines, and both engines have the following in common:

1. Same short block design (same pistons, same stroke, etc.)
2. Same compression ratio (higher compression ratios usually require less spark advance, because the air/fuel is more dense with higher CR).
3. Same cam lift, duration, timing, and lobe separation.
4. Same induction system (turbo, intercooler, intake manifold, etc.)
5. Same exhaust system (headers, turbo, downpipe, mufflers, etc.)
6. Same fuel-air ratio target (i.e. the chip calibration is essentially the same)
7. Both heads produce the same amount of tumble and/or swirl to the air charge as it's going into the cylinder (this is a big one - I don't know enough about Stage 2 heads to know for sure if this is a good assumption).
8. Both heads are made from the same material (if the Stage-2 heads are aluminum, more heat will get sucked out of the combustion chamber during compression and combustion, which might affect the results a bit).
9. Both engines are being fueled with something that will allow timing to be set wherever you want without knock being a problem. This is another big assumption, because in boosted engines, conditions causing spark knock often occur at more retarded timing than what would produce best torque. So, we're talking about relatively low boost and really good fuel like C16.

If we make all of the above assumptions (which is a lot!), then I would say the Stage 2 heads will require LESS spark advance than the stock heads at the exact same boost pressure. Why? Well, the Stage 2 heads should flow more air into the cylinder (assuming they have bigger ports and valves) than the stock heads at the same boost pressure. Therefore, the air-fuel mixture will be more dense during compression, and the burn rate will be higher during combustion.

Of course, very rarely do we find a case where all of the above assumptions are true. Usually a set of Stage 2 heads is going to be teamed with a different cam, different turbo, different compression ratio, enough boost to cause knock before reaching best torque timing, etc. than a set of stock heads. So, unless you a building two identical engines except for heads, you just have to find out where the best timing is yourself.

Is that enough of a non-answer for you?

 

[charlief1]

Thanks again Mike. What I'm actually looking at is a hybred engine of sorts here. A stock RWD block with Series II heads and a fabricated intake. Since the Stage II and Series II heads are simular that should give me some ideas of what to expect if I ever get it done.

 

[Mike T]

I've become very interested in this topic. Curious if some opinions have changed over the last four years when this was originally discussed?