Interesting info on B3702 Injection timing

[picnic_george]

I'll get a grasp around the mathematical equation eventually. I'm just trying to understand that raising the value delays the injection cycle and people have(generally) seen smoother idle and less fuel smell with overlapping cams. Due to not sucking unburned fuel out of the exhaust, even though GM designed it to spray on a closed intake valve to help atomization(which it will no longer do). I'm still doing a lot of reading and some of the numbers seem awkward to me, but I'm pretty good with numbers so I'll get it lolol

Thanks

[Gelf VXR]

Unless your IJC is maxed out, start to end of injection happens while that inlet is closed, and some time before it opens to allow for vaporization, with a high overlap cam I would try advance far enough so vapor rather than raw fuel can be drawn into the exhaust.

It's theoretically possible to have the injection event after EVC, it doesn't for much duration before IVC, and only when at running temperature, not a very efficient burn

[picnic_george]

What's IJC?

From what I've been reading it seems like people have been having luck delaying the injector some(til the tail end of the EVC events and not paying too much attention to the IVO events). Too early you suck fuel out the exhaust valve, too late and you can't use the exhaust to help draw the fuel in. Granted that happening eliminates the fuel hitting the closed intake valve. I guess I should have joined the discussion a few years ago lolol

Thanks

[joecar]

IJC ---> I think Gelf meant IDC (as in INJ DC).

[Gelf VXR]

What's IJC?

From what I've been reading it seems like people have been having luck delaying the injector some(til the tail end of the EVC events and not paying too much attention to the IVO events). Too early you suck fuel out the exhaust valve, too late and you can't use the exhaust to help draw the fuel in. Granted that happening eliminates the fuel hitting the closed intake valve. I guess I should have joined the discussion a few years ago lolol

Thanks

My bad i meant IDC, thanks Joe.

You have to remember the calibration is for the end of injection EOI, SOI is calculated in advance from EOI depending on pulse width, so SOI happen after EVC, you need to retard EOI well into the induction stroke. If your running closed loop idle, a poor homogenous charge surely will play havoc with O2 sensors, keep adding fuel if O2 reads lean because the unused O2 in the combustion.

I don't have a high overlap cam so I have not tried for myself so I could be wrong

[PRAY]

I made a sheet that explains all the math because I had to spell it all out the long way before I understood it. What it boils down to is you need to add to the injector timing table how ever many degrees the IVO of your new cam is over/before your stock cam and play with it from there. So, stock cam opens at 16* ATDC and new cam opens at 8* BTDC then you add 24 to your injector timing table. I also noticed in my particular tune that there was no advance in Timing vs. RPM. All the other cars I found had some. So I copied and pasted to see what would happen. It seems to be working.

[joecar]

I made a sheet that explains all the math because I had to spell it all out the long way before I understood it. What it boils down to is you need to add to the injector timing table how ever many degrees the IVO of your new cam is over/before your stock cam and play with it from there. So, stock cam opens at 16* ATDC and new cam opens at 8* BTDC then you add 24 to your injector timing table. I also noticed in my particular tune that there was no advance in Timing vs. RPM. All the other cars I found had some. So I copied and pasted to see what would happen. It seems to be working.

Can you post your sheet (or an image of it), please...

[PRAY]

I suck at posting pics and what not on the net. Can I email it to you? It is all of the notes I have made and the math that goes with it for this subject on a word document.

[PRAY]

Hey Joe,

Did you get my email?

[joecar]

I'll check my email...