Injector timing theory with ITB

[LS_Coyote]

Hello all,

I have an LS7 with an individual throttle body intake and a medium sized cam (235/251 113+4). This has 17* overlap at 0.050". The car runs quite well, idles great, has very very minor surging at low load/RPM with a lightweight flywheel. However, at idle the car stinks. I feel that for this medium sized cam it stinks quite a bit too much. I've played around with the boundary table of the injector timing to try to solve the issue, but it doesn't quite make sense to regular thinking. From factory the boundary table is set to 520*. Combined with the ECT and RPM normal tables this puts me at ~400* when the engine is warm at idle. I've added and subtracted up to +-20 degrees to my boundary table, which put me in a range of ~380 - 420* with different tunes. Normally, the unburnt fuel scent goes with larger EOIT number --> 420*. However, it seems that with 380* EOIT the car smells less.

Now the question is, whether this is common on ITB intakes, since the reversions at closed throttle cannot really affect another cylinder. Is it better in this case to rather hit the closed valve with the fuel spray? BTW, injectors are downstream of the throttle blades at the end of the runners, in the same location as with the OEM intake manifold. It would be great if someone has experience with a similar setup.

Thanks!

[07GTS]

could be best to keep boundary at all 520 then lower the ect normal stock 110 lower it until your trims show richest showing more fuel is making it into the cylinders, just watch out for any reversion that may take place in the single tube try move it advance or delayed to use a inward pulse to help get the fuel in, then zero out the rpm normal and see how it goes

[LS_Coyote]

Ok thanks, I'll play with that in the next few days. I was also thinking of extending my range from 300 - 450* to really start seeing a difference. 300* should be about closed valve injection (CVI) and 450* open valve injection (OVI) with my cam.

[07GTS]

dont worry too much about it adding up compared to your cam specs as there is a little more going on then we see, according to may cam specs the stock settings should be fine but still took a further 20-30 deg shift to actually make a difference in fuel, your trims will show u whats going on

[LS_Coyote]

So I have taken the EOIT up to 470* up to 896 RPM and linearly advance it to 300* up to 4096 RPM. It makes a huge difference everywhere. The 300* is ~20* more advanced than OEM at that RPM. Crossing point between OEM and this (retard to advance) is at ~3000 RPM. My wideband shows richer pretty much everywhere now, while I've only had the chance to rev up to 5000 RPM so far. Yes, the advanced injection above 3000 RPM actually reduces richens the mixture and decreases some misfires I seemed to have heard before. Remember, that my camshaft opens the intake valve ~20* earliere at 0.050" than the OEM cam does.

At idle, I find 470* to be quite a bit retarded and I am somewhat concerned about cylinder fuel wash, so I may go back down to 450*. However, the driveability difference between 470* and 430* is huge. There is no more buckling anywhere with this setup. The car drives just like with the OEM cam, even though it has a lightweight flywheel.

I have read a few journal publications in the mean time on the topic. "The Effects of Port Fuel Injection Timing and Targeting on Fuel Preparation Relative to a Pre-Vaporized System" gives a good indication what goes on with CVI and OVI injection timing at idle. I assume there is no large cam overlap in that publication, which shows that AFR stability is better with OVI at the cost of higher emissions. With cam overlap, the emissions might actually also decrease with OVI. They also test an ITB system in that publication, however the injector is ahead of the throttle in that case, unlike with my Harrop Hurricane intake manifold.

I think what goes on with an ITB is a bit more different than a single throttle manifold. My setup is more comparable to manifold with intake port flow control or tumble flaps ahead of the injector. Ford calls this IMRC. You could compare my throttle blades to tumble flaps with respect to their effect on the flow. To this topic I have found the following paper: "Effects of Injection Timings and Intake Port Flow Control on the In-Cylinder Wetted Fuel Footprints during PFI Engine Startup Process". This states that tumble flaps create large turbulence and increase the swirl of the flow within the intake ports by up to ~300%. This highly increases the air fuel mixing and reduces cylinder fuel wash at OVI.

My cam ICL is ~110*, or 470* in crank angle. The piston is at its maximum velocity at 450* crank angle. This means that I will have my maximum suction/port velocity right in that window somewhere. With my ITB throttle in the runner, the flow velocity, turbulence and swirl generation about the nearly closed throttle blade will increase with suction. This could mean that I receive the best air/fuel mixing when my complete injection cycle occurs between 450-470*, or EOIT ~470*.

I highly welcome any different thoughts to this theory if anybody has experience with these type of intake manifolds.