Technical Ignition advance on E85

[V8bait]

Results look solid. Good research and nice work!

 

[AD-ENG]

@jyamona - Took me longer than expected to respond due to some inconsistencies I was seeing that I wanted to test further. I'll have to start off by eating some crow as my previous test at idle was inaccurate due to how heavily the DME uses ignition timing to stabilize idle speed. I let the car idle for a while and watched my scope in rolling mode and the inconsistencies were plain to see. The previous finding is also made moot by the MSD81 documentation suggesting the CPS gets pulled to reference voltage (5V) when a tooth is present in front of the hall effect sensor however that doesn't appear to be true. Instead it is pulled to ground when a tooth is present which is common for automotive gear speed sensors. I noticed this after capturing the waveform so I had to invert the signal later causing the blue channel 2 trace (IGN #1) to be inverted so please ignore that.

I started off by wanting to verify that reluctor tooth #10 is indeed TDC for cylinder #1 so I performed the following test:

* Scope in roll mode
* Coils unplugged & #1 spark plug removed
* Rod in cylinder #1 spark plug sitting on top of the piston
* Key on to provide reference voltage to the CPS
* Turned engine over by hand until I found the missing reference teeth and counted teeth from the reference until cylinder #1 stopped rising.

This test confirmed tooth #10 is TDC for cylinder #1.

Next I hooked the scope back up and flashed the car with a tune that locked timing at 1000-3000RPM @ 6.0 degrees and 3000-4000RPM @ 12.0 degrees. I also disabled multispark although I saw a very long almost double discharge at 4000RPM but it didn't cause a problem with the results.

First test @ 1500 RPM:
View attachment 14555

Timing was reporting a constant 6.0 degrees, scope captures were very consistent. With the capture inverted correctly you can see the discharge was on the falling edge of tooth #9. If we follow along with the math again then we know 1 tooth = 6 degrees of rotation so our spark is indeed being delivered at 6 degrees before TDC.

Next test @ 4000 RPM:
View attachment 14556

Timing was reporting a constant 12.0 degrees, scope captures were also very consistent. With the capture inverted correctly you can see the discharge was on the falling edge of tooth #8, two teeth before TDC or 12.0 degrees.

From my testing, the MSD8x is delivering the exact ignition timing it is reporting. I now believe Syvec is either triggering on the incorrect tooth or they are looking for reference voltage in the presence of a gear tooth instead of a ground which would put their delivered timing about 3 degrees more retarded.

I'm out of time tonight to edit my original post tonight but I will update it tomorrow morning for consistency.

Did you confirm timing with a timing light after you identified the trigger tooth offset?

What are you probing for your coil blue trace?

 

[bahn]

Did you confirm timing with a timing light after you identified the trigger tooth offset?

What are you probing for your coil blue trace?

Hey thanks for the question @AD-ENG :
I have not tested again with a timing light as the process is identical, find TDC on cyl #1 and mark something to use as a reference (crank hub or in this case a electronically with a reluctor gear tooth). The blue trace is an attenuated back probe of the white coil wire (primary coil), since it's electromagnetically coupled to the secondary coil the discharge timing is identical. Keep in mind the blue trace is inverted in my capture so flip it vertically to see it as captured. Let me know if you have any other questions or suggestions on how the test was performed.

 

[AD-ENG]

Hey thanks for the question @AD-ENG :
I have not tested again with a timing light as the process is identical, find TDC on cyl #1 and mark something to use as a reference (crank hub or in this case a electronically with a reluctor gear tooth). The blue trace is an attenuated back probe of the white coil wire (primary coil), since it's electromagnetically coupled to the secondary coil the discharge timing is identical. Keep in mind the blue trace is inverted in my capture so flip it vertically to see it as captured. Let me know if you have any other questions or suggestions on how the test was performed.

The main reason I ask is in the video you use a wire to find tdc and call it good once it stops. That's no true tdc necessary. Because of piston dwell, finding true tdc is taking the crank angles the piston is up and dividing by 2. With that said, I believe that it will be a fully tooth, just becuae of how the math works out. However, it's worth checking.

The reason I asked about the trace is because it can be use to get a pretty accurate picture of coil dwell and discharge time. Then use those numbers to see if your data is feasible.

 

[bahn]

The main reason I ask is in the video you use a wire to find tdc and call it good once it stops. That's no true tdc necessary. Because of piston dwell, finding true tdc is taking the crank angles the piston is up and dividing by 2. With that said, I believe that it will be a fully tooth, just becuae of how the math works out. However, it's worth checking.

The reason I asked about the trace is because it can be use to get a pretty accurate picture of coil dwell and discharge time. Then use those numbers to see if your data is feasible.

@AD-ENG while I did eyeball the piston movement stopping I did the test about 5 times before recording the video. Piston movement stops at around the rising edge of tooth #10 and resumes movement back down around the rising edge of tooth #11 and I split that difference to find TDC (falling of tooth #10). That seemed about right for the dwell time calculations I ran using a stroke of 89.6mm and a rod length of 145mm which I came up with 6 degrees of dwell. Each tooth on the reluctor represents 6 degrees of crank rotation so #10 - #11 rising edge = 6 degrees so somewhere around the falling edge of #10 and the dead space between is where true TDC is. That matches up with the MSD8X documentation I have perfectly as well. Getting a dial indicator to be accurate without the head off seems difficult, maybe you could get a bushing with the same thread pitch as the spark plugs and a rod that fits very tightly to the hole in the bushing. Do you have any other ideas? Thanks for the response and questions btw, I appreciate it.

 

[MoreBoost]

From Reaper0995:
Just for talking sake, here are some head flow numbers from various engines. Obviously more to the discussion than just the DI space in the head, but an interesting start point. These are values I found on fast google searches, they may be higher/lower but in any case they all crush the N54! These are for the intake ports in CFM, most values are taken around .500 lift, but not al (LS series might be higher).

N54 stock: 165 cfm
N54 ported: 225 cfm
hayabusa motorcycle: 223 cfm
GTR stock: 276 cfm
GTR ported: 330 cfm
B18 stock: 260 cfm
B18 ported: 288 cfm
LS3 stock: 300 cfm
2JZ stock: 225 cfm
2JZ ported: 280 cfm
Evo 8 ported: 277 cfm

Filippo

Off topic

The numbers above make me sad.

Would porting an n54 head without valve or cam changes make much difference?

 

[Milan]

It's not about flow it's about velocity. There is a reason the price of head porting varies so much. Anyone quoting CFM only and didn't give you a dyno or trap speed increase probably didn't gain anything. In the LS world this is pretty well documented, the difference between Tony Mamo heads and some off the shelf porting is huge. Lots of times those generic head porters don't get any gains (or even lose power). Also, the way CFM is measured is hardly standardized so throwing up all those numbers is pointless IMO.

 

[MoreBoost]

It's not about flow it's about velocity. There is a reason the price of head porting varies so much. Anyone quoting CFM only and didn't give you a dyno or trap speed increase probably didn't gain anything. In the LS world this is pretty well documented, the difference between Tony Mamo heads and some off the shelf porting is huge. Lots of times those generic head porters don't get any gains (or even lose power). Also, the way CFM is measured is hardly standardized so throwing up all those numbers is pointless IMO.

Well it's going to be about both isn't it. An engine is an air pump. If I can get more air through it in less time then I have more power. I can fill the cylinder quicker. I could choke down the ports to raise velocity but the volume of flow may suffer too much. A restriction can be detrimental depending on the flow dynamics. There's clearly a happy balance.

It'd be great to see some results with ported heads.

I'm very interested in this thread because like others I want to understand why our cars run so little timing advance.

 

[Optigrab]

@AD-ENG while I did eyeball the piston movement stopping I did the test about 5 times before recording the video. Piston movement stops at around the rising edge of tooth #10 and resumes movement back down around the rising edge of tooth #11 and I split that difference to find TDC (falling of tooth #10). That seemed about right for the dwell time calculations I ran using a stroke of 89.6mm and a rod length of 145mm which I came up with 6 degrees of dwell. Each tooth on the reluctor represents 6 degrees of crank rotation so #10 - #11 rising edge = 6 degrees so somewhere around the falling edge of #10 and the dead space between is where true TDC is. That matches up with the MSD8X documentation I have perfectly as well. Getting a dial indicator to be accurate without the head off seems difficult, maybe you could get a bushing with the same thread pitch as the spark plugs and a rod that fits very tightly to the hole in the bushing. Do you have any other ideas? Thanks for the response and questions btw, I appreciate it.

Hey great work! Is this the documentation you are talkin aboot?

 

[Hydra Performance]

It's not about flow it's about velocity. There is a reason the price of head porting varies so much. Anyone quoting CFM only and didn't give you a dyno or trap speed increase probably didn't gain anything. In the LS world this is pretty well documented, the difference between Tony Mamo heads and some off the shelf porting is huge. Lots of times those generic head porters don't get any gains (or even lose power). Also, the way CFM is measured is hardly standardized so throwing up all those numbers is pointless IMO.

What you commonly hear being referred to as "velocity" in domestic V8 circles, is really cfm/valve area or cfm/port area, and is basically another way of expressing flow coefficient for a given flow depression. The N54 head casting on the other hand, is quite limited in what can be done as far as valve/port sizing goes. So really ends up being about opening up and smoothing the choke on the inlet side, cleaning up the short side radius, and other detail work. I don't recall seeing a modern cylinder head design as (deliberately) restrictive as the N54/N55 in recent memory. My only conjecture is they were designed this way to help maximize torque between 1750-5000rpm...

Well it's going to be about both isn't it. An engine is an air pump. If I can get more air through it in less time then I have more power. I can fill the cylinder quicker. I could choke down the ports to raise velocity but the volume of flow may suffer too much. A restriction can be detrimental depending on the flow dynamics.

That is precisely what BMW have done

I'm very interested in this thread because like others I want to understand why our cars run so little timing advance.

smallish 84mm bore, undersquare design with compact low-angle combustion chamber, 10.3CR, spray-guided DI, very high mean port velocities, and <7000rpm operation (for most) probably have something to do with it

 

[fmorelli]

This gets my vote for Spoolstreet Thread of the Year.

Filippo

 

[boostE92d]

Good read for sure.