Interesting info on B3702 Injection timing

Interesting thread, thanks to all involved. I am on LS1B COS2 (01290002), so only have B3702 (and B3703) to play with. Conversation seems to have centred on later OSs with B120x (for understandable reasons), but is anyone able to confirm the LS1B tables are indeed in reference pulses (mS vs. milliseconds) as Gelf postulated back on page 9? This seems to tally up with the HPT people, and the 5.55 number that keeps cropping up. It also seems a better (more apt) unit than milliseconds.

For the stock LS1 (2004 Monaro) cam I have:
IVO IVC EVO EVC
377.5 574.5 140.5 347.5

And my cam:
361 583 129 355

So I assume if I want to set injector end to IVO, I want to advance 16.5 degrees, so subtract 0.183 from B3702. If anyone could sanity-check it would be a great help :)

I think it's correct, subtracting 0.183 advanced EOI 17 degrees in my spread sheet calculator, I'll post it later

After reading all of this again, especially the logic of the quoted section on the previous page, are we advancing the Injector timing or retarding it from 490-220 in the E67? I have a much larger cam now in a 427. It only opens 3* earlier than my previous cam but now has 21* of overlap instead of the 10* I was dealing with. I can see where with a large overlap period hitting the valve after it opens some could be beneficial. I am having a very hard time leaning out my VVE table far enough to compensate for my -LTFT's which to me says I am running rich not lean. Now I just confused myself. Crap. I am going to have to put it in Open Loop and start messing with just injector timing to see what I get for AFR's. Then I guess go back and adjust everything again to get it back to stoich.

Here is what I ended up doing and it worked great for my build. I used injector base pulse width at idle vs. my cams seat to seat timing to find my new EOIT. I took out my degree wheel and input the .050" and .002" numbers for my stock cam and my current cam. This was a serious eye opener. The stock cam has -16* of over lap at .050" but 0* at .002". Then I input my cam. It has 21* at .050" and IIRC 73* at .002" This made me realize that I was advancing it no where near far enough to actually get the injector to fire prior to the intake valve opening. The small adjustments I was doing was still firing into an open intake valve since I was using .050" numbers to get my injector advance calculations. Next, I checked my IPW at idle which was 1.85ish ms at 900rpm. That data was invaluable to me. I used it to calculate how long it took my injector to fire in crank degrees which is 10*. I had no way to check how long the stock injector takes to fire. But I can only guess that it was around 20* or so since the stock EOIT is 5*ATDC. So I advanced my EOIT 43*. This put my EOIT right at where my intake valve starts to actually open. My idle and low rpm driving improved substantially. The car doesn't buck above 1,200rpm now. I am also averaging 18mpg and getting around 25mph at 60-70mph on the highway. Mind you this is in my 3.73 geared 07' 4,100lb CTS-V with a LS3 427 with ported LS2 heads, 21* overlap cam, ported stock intake and stock cat back. I am also running 52lb injectors. I will say that I have done a bunch of VVE tuning and my MAF is lined up properly. I don't see much over +/- 2 LTFT's. I still have some work to do in the fueling department and I haven't touched dynamics yet since I don't have a good grasp on it yet.

Mike, wish I could have met you a couple weeks ago when I was down in Atlanta. I stopped by and finally me Ron after eight years of dealings and checked out the shop. I was hoping we would be able to talk some tuning face to face but you were on vacation. Maybe next time.

PRAY,

My name is Christian, I just happen to work with Mike... :) but i'll send him your regards... And yes... he was on vacation and pretty much NO communication... I think he forgot his name during that week...

Okay, thanks. Sorry about that, I was confused by the end of your post.

These spreadsheets...is the injector really firing this early at lower temps? am i reading this right?

That's the data from the PCM

SPY2520
They do this to "Preheat" the fuel on a cold engine. This allows the fuel to evaporate on the back of the valve because it is the warmest thing in the airstream at those temps!!
You also have to remember the amount of fuel that is being commanded at those levels, just look at your Open Loop Fuel and cranking fuel tables.
It's still an engine and if you aren't evaporating the fuel, it has to be done with a larger amount of the mixture.
It also aids in Catalyst light off, low timing, high amounts of fuel, and you make the first thing to be warm!

So i have read through this entire post a couple times now and I am still lost on how the spread sheet actually works. Can someone please help me clear this up?


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So here is the way it is calculated...

EOIT is X lo res periods (B3702) after the boundary (which is typically 6.5).
So...... 6.5 x 65 = 422.5 BTDC
Injector fires 5.5 (stock at normal coolant) after the boundary it means 6.5-5.5 = 1 x 65 Lo Res Periods = 65 BTDC.

Hope this helps.

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Originally Posted by Highlander

So here is the way it is calculated...

EOIT is X lo res periods (B3702) after the boundary (which is typically 6.5).
So...... 6.5 x 65 = 422.5 BTDC
Injector fires 5.5 (stock at normal coolant) after the boundary it means 6.5-5.5 = 1 x 65 Lo Res Periods = 65 BTDC.

Hope this helps.

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do I read that as "(6.5ms - 5.5ms)*65deg/ms = 65 deg BTDC" ...? I'm not sure where the 65 comes from (and is it deg/ms...?)...?

I never said its ms.

Its lo res periods. One period = 65 degrees crank. Its a calibratable value.

Ah, lo res periods, not ms, I see, thanks.

Has there been a consensus on which direction to go with big overlap cams (20*+)? On one hand it looks like the goal is still to put EOT just before IVO. On the other hand there it does seem like a good idea to hold off until closer to EVC.

After listening to a pod cast interviewing Greg Banish, basically whatever slope (cold to warm) the factory is using, for cammed cars you continue with the slope. By this i mean the following, for LS1, the slope increases from cold to warm, therefore 'add' numbers. For E38, the slope decreases from cold to warm, so therefore 'subtract' numbers. For mild cams i start with adding 0.5ms to LS1 and subtracting 20* from E38, it's worked well so far for idle and low speed/rpm driveability.

Thanks for the info.

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Originally Posted by Gelf VXR

I think it's correct, subtracting 0.183 advanced EOI 17 degrees in my spread sheet calculator, I'll post it later

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I want to understand how to use this spread sheet.

Attachment 22591

Attached is my cam card.

How do I convert to what ever units I need to convert to?

I've been digging back into this lately and notice a discrepancy between the spreadsheet posted in this thread vs others on hptuners. IDK what's right and either way a calculator is only going to get you so close. There's different theories on whether or not it's better to advance the end of injection or delay the end of injection with big cam swaps... I think generally delaying is more well liked based on what I've come across.

Either way, your best bet is to probably do a little trial and error and see what your car likes. I am going to fully warm up the car to keep that variable constant, and then try increasing or decreasing B3702 value in 0.2 increments, datalog idle conditions and see how they look. I'm going to run closed loop, LTFT disabled and look for the setting that gives me lowest fuel trims, i.e. least amount of fuel required to maintain standard 14.7:1 idle. This should translate into what's most efficient for my new injectors, cam timing etc.

I just changed injectors and figured it was good time to dive into this before re-tuning the whole fuel map now. I'm using Deka 80 lb/hr injectors and a B3702 value of 5.35 at operating temp and with reasonable VE table values my fuel trims were +25-30 percent, so something seems off and I want to see the effect that injection timing has before just adding to the VE table. My values were changed to put injection earlier, but now I run a totally different style of injector so the theory of spraying fuel onto a hot valve to evaporate may not work out as well. If I want to delay my injection until after EVC (@ 0.050"), I need a value of ~5.6 or ~6.3 depending on which calculator I want to trust.

If someone has a better technique let me know!

Update, I did what I posted above and tried values of 5.55, 5.8, 6.0 and 6.2. Average idle pulsewidth varied by less than 0.005 ms and fuel trims varies less than 0.5%..... made absolutely zero difference.

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Originally Posted by aaronc7

I've been digging back into this lately and notice a discrepancy between the spreadsheet posted in this thread vs others on hptuners. IDK what's right and either way a calculator is only going to get you so close.

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Yes, but when you want to experiment with different values... it helps to know if you're even in the ballpark.

What are your cam specs?

226/230 113 +2. IIRC, IVO 357* and EVC 359*. I did use the calcs to get in the ballpark, there is just a discrepancy in the one posted here vs most others on hptuners. Either way I saw virtually no difference in fueling by retarding injection timing by up to ~60* which I find surprising, but it's what the data says.

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Originally Posted by aaronc7

226/230 113 +2. IIRC, IVO 357* and EVC 359*. I did use the calcs to get in the ballpark, there is just a discrepancy in the one posted here vs most others on hptuners. Either way I saw virtually no difference in fueling by retarding injection timing by up to ~60* which I find surprising, but it's what the data says.

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Yeah, but think about where that ~60* is.

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Originally Posted by aaronc7

Update, I did what I posted above and tried values of 5.55, 5.8, 6.0 and 6.2.

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5.55 is 60*BTDC
6.2 is TDC

Hmmm.... your comparing spraying on a closed valve to spraying on a closed valve. I wonder why it didn't make any difference?

The correct way to calculate EOIT was figured out experimentally by Bluecat about 8yrs ago.

https://forum.hptuners.com/showthrea...OI-fuel-timing

Enjoy!

The calculator actually said I should go to about a ~6.3 value, I guess perhaps I should actually try that as it would be slightly after TDC. I have read that thread and understand the formula. Even in this thread there seems to be some disagreement on the formula and 'reference period', but the bluecat thread was the most conclusive thing I've come acrosss

edit: A value of 6.3 should start the inj pulse at 360* and end at 368". I'll try values of 6.3, 6.4 and 6.5 and see if it makes any difference

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Originally Posted by aaronc7

Even in this thread there seems to be some disagreement on the formula and 'reference period', but the bluecat thread was the most conclusive thing I've come acrosss

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Bluecat proved experimentally how injection timing is calculated. I don't understand why some people on this forum have other ideas, but Bluecat's formula is correct... and contrary to what some people on this forum think, a reference pulse is actually 90 degrees. You can use the same principle to calculate Gen4 EOIT. The main differences being that Gen4's use crank degrees and they calculate backwards from the boundary where Gen3's calculate forward from the boundary... and yes, the stock timing is the same for both.

Thanks for your comments and thoughts, I'll follow up my little experiment. With these new injectors, I am needing pretty high idle VE values, so I have been digging into injector data to include this timing stuff, before proceeding further.

Well, I did the same test for 5.55, 6.2, 6.3 and 6.4. I dialed in my VE table so trims were spot on with the 5.55 settings. I had identical results again across the board for all injector timing values. Average fuel trims varies about a couple tenths of a percent and IBPW by .005 or so on average. Perhaps my cam is just mild enough and does not have have enough overlap to see benefit in this.

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Originally Posted by aaronc7

Perhaps my cam is just mild enough and does not have have enough overlap to see benefit in this.

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That's exactly right.

I can see that you like to experiment and find things out for yourself, rather than just accepting what some random idiot tells you on the internet... which is why I helped you down the path to what might seem like a dead end, but at least now you know how to calculate EOIT and you've proven to yourself that spraying later doesn't have any benefit with your cam.

The real benefit is for pure race cams... and the benefit shows up as a reduction in ET over the 1/4 mile.

You are right that I don't like to just accept whatever I read online as fact...actually so much misinformation that just gets parroted and before long everyone is an expert and it's a 'fact'. What's interesting is over on hptuners forums you see plenty of guys who have a cam with similar specs to mine and claim this made a big difference, etc. Maybe faulty test measures, I made sure IAT/coolant/oil temp were as consistent as possible.

Either way, I'm glad to have worked thru this and press on with the tune.

reminder to self: brush up on eoit calc.

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Originally Posted by joecar

reminder to self: brush up on eoit calc.

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EOIT = 90 * (boundary + B3702) - 784

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Originally Posted by aaronc7

EOIT = 90 * (boundary + B3702) - 784

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That's referenced from TDC at top of compression (spark plug would have just fired), right...?

I'm out of town so I can't easily look in a tune file or in my notes...

where boundary does come from (I'm not going to like the answer)...?

( I'm going to reread this thread and the HPT thread )

Quote:

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Originally Posted by joecar

That's referenced from TDC at top of compression (spark plug would have just fired), right...?

I'm out of town so I can't easily look in a tune file or in my notes...

where boundary does come from (I'm not going to like the answer)...?

( I'm going to reread this thread and the HPT thread )

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I simplified the equation, but if you 'write it out' I think it makes more sense. At least it did for me in trying to figure out what the math meant.

EOIT = -784 + 90 * boundary + 90 * B3702

360* would be end of exhaust stroke / start of intake stroke in the valve overlap area.

From what I understand boundary is just a known reference/starting point, separate from the 'injection timing' table. The table is not visible by default on EFI and there isn't a CAX posted on here, but it's out there, apparently. It's in the HPT tables, but obviously you can see that any change to boundary will directly affect the timing, just as B3702 would. I don't think you really need to alter boundary unless you're trying to change the timing significantly.

-784 was just observed to the starting reference point for the calculations (previously linked bluecat thread). So you just start there and work your way back from there based on those 2 values. I don't claim to be an expert or anything on this, just a guy who recently dug into it.

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Originally Posted by joecar

That's referenced from TDC at top of compression (spark plug would have just fired), right...?

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Quote:

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Originally Posted by aaronc7

360* would be end of exhaust stroke / start of intake stroke in the valve overlap area.

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Ah, ok, I see.

Quote:

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Originally Posted by aaronc7

...

From what I understand boundary is just a known reference/starting point, separate from the 'injection timing' table. The table is not visible by default on EFI and there isn't a CAX posted on here, but it's out there, apparently. It's in the HPT tables, but obviously you can see that any change to boundary will directly affect the timing, just as B3702 would. I don't think you really need to alter boundary unless you're trying to change the timing significantly.

...

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Ok, that's the part I was not going to like...

ok, I guess we can play with table B3702 and not need to edit boundary.

Quote:

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Originally Posted by aaronc7

I simplified the equation, but if you 'write it out' I think it makes more sense. At least it did for me in trying to figure out what the math meant.

EOIT = -784 + 90 * boundary + 90 * B3702

360* would be end of exhaust stroke / start of intake stroke in the valve overlap area.

...

-784 was just observed to the starting reference point for the calculations (previously linked bluecat thread). So you just start there and work your way back from there based on those 2 values. I don't claim to be an expert or anything on this, just a guy who recently dug into it.

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Sometimes what is needed is a different perspective, then things make sense again... thanks :cheers:

( I just started a new job, so I'm flat out learning all the new systems and code... the faster I go the further behind I get... lol )

I'm rereading the HPT and EFILive threads on EOIT.

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Originally Posted by joecar

I'm rereading the HPT and EFILive threads on EOIT.

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Why does it even matter when your car is in pieces? :beer:

I'm tuning (playing with) another car (at night, after work), cam has some overlap, I want to see how EOIT change affects anything... someone said VE changes, but I don't see how it can.

Yeah... my car is in pieces, I'm slowly making progress... will post some pics soon as get suspension all back together (bushings (1LE), lowering springs (500 lb/in vs 360 lb/in), swaybars, swaybar mounts)... also new fuel pump (while rear axle is droped), new exhaust, new shorty CARB compliant headers...)

hmmm, I'm looking at the FAST 102 LSXR (has CARB EO) but this needs messing around with new fuel rails and new 100 mm TB.

What are the cam specs? It doesn't change VE in the actual sense of the meaning of VE, but best setting should yield lowest VE value/lowest injector pw. More 'efficient' / no wasted fuel I guess. If it's super aggressive cam and EOIT does indeed make a difference, then I would anticipate the low load/rpm VE table would need re-adjusted.