Cam timing, and critique my tune

[oldskool]

What are people changing in the cam tables? Are there gains in economy and/or power to be had?

I've gone through my first generation of a "boost bump" tune, and I'm quite happy with the results. I only modified air load above 2500 rpm because of the article I read here about SIDI engine modes and how we cannot add more fuel below that value. So i have a smooth ramp up from stock boost to about 20PSI at 3000rpm and drops off to about 18-19 at redline. I also slightly richened up the 90 and 100% load tables. It's very smooth, and im really only getting tip-in knock retard that can be seen on a stock tune. Also, there's a little more room to grow if need be. My max MAF output was 32 lbs/min, so it's at least competitive with other tunes out there

Has anyone been able to completely eliminate knock retard on this system, or is it just a product of how the system works? I've read here that if you're not getting a little knock retard, then you not making as much power as you should be. Seems like faulty logic to me, but i'll ask anyway. I occasionaly get 1 degree KR or so under WOT, but I've seen as much as 3 degrees on throttle transitions, which is kinda scary.

Thanks for reading!

[PSYKOSTEVO]

When I tune I don't have tip-in knock retard. So yeah, you can write a knockless tune.

As for the cam phasing tables I typically only change them at 100% and 200% airload limits, and above 2,500 rpm. A little advance helps on the warm tables.

3* is not really scary. If you start having misfire issues (common problem on the LNF) then look to change your plugs. Cylinder #3 is prone to this.

[oldskool]

I don't have misfire issues for now, i'm happy with how smooth it is. I was mostly worried about the observed KR.

I'm really a novice when it comes to cam timing, all i really know is that the amount of overlap affects where in the RPM range power is made, so changing the overlap vs rpm can broaden the powerband.

What would be the effect if the LNF didn't have VVT - for example if all cam tables were set to 0*? Just a hypothetical...

[black06g85]

hmm, I did an 09, no misfires, no KR, 22 psi spike falls to 18 at redline, running 15-17 degrees of timing under boost, did a little messing with the cams timing too, nothing too drastic though

[cobaltssoverbooster]

3* advance on both cams or just one?
i see the adjustments are up high does moving the cams fix timing issues up high or just increase turbo efficiency up top?

[SSpdDmon]

I tried to do a little cam timing research and found some text concerning N/A tuning for what I believe was Hondas. If I understood correctly, their rule of thumb when tuning cam timing is to advance the intake cam in small 1 or 2 degree increments (4~5 degrees rule of thumb setting for most of their stuff) and retard the exhaust cam slightly (1~2 degrees rule of thumb). This in effect creates some overlap, which helps to make power on the top end. I tried to illustrate what happens when you change the valve events quickly in Paint below. The green represents the intake charge, the red is the exhaust charge and the blue is where those valve events would overlap if you were to alter the time they are open as mentioned above. Since we are working with fixed numbers (i.e. the duration of time the valves stay open doesn't change), changing cam timing simply is fine tuning the point in time when the opening/closing of the valves is optimum. This really needs to be done on a dyno so results can be measured.

As for our cars, it's hard to say that we'll need the full Honda rules of thumb. I say this mainly because we're forced induction and those rules of thumb are N/A. Too much overlap may eventually affect boost levels or worse, cause engine damage. That's why a dyno is a must.

Looking at the warm intake and exhaust cam tables, you can see the engineers set the cams fairly far apart for the lower RPMs (most likely to make sure the power under the curve was there to build boost faster) before bringing them closer together up top. This corresponds to basic cam theory as listed in the following article:

An unfortunate result of excessive overlap is reduced torque and soft throttle response at low engine speeds (e.g., below 3,000 rpm). So why build in all this overlap? The answer can be found when you look into the time that is compressed at high engine speed. At idle, there is plenty of time for the exhaust gas to move back up the intake tract and dilute the incoming charge. The intake air charge is also moving at a very slow speed. But buzz the engine to 6,000 rpm and there is precious little time for the exhaust gas to do anything except exit past the exhaust valve. Add the inertia of high-speed air entering the cylinder when the intake valve opens, and overlap is very useful for initiating that column of air into the cylinder.

So, essentially what I would do on a dyno with the cam tables is as follows:
1st - make a baseline pass or two keeping an eye on temps (all pulls should be with similar temps)
2nd - make some slight advancements (1~2 degrees) above 3K on the intake cam timing (done by bringing numbers closer to 0) & and allow the car to cool slightly if necessary.
3rd - make another pass or two to compare to the base line
4th - if more power is present, repeat steps 2 & 3 once more.
5th - retard the exhaust cam 1~2 degrees (done by bringing numbers closer to 0) above 3K and make another pass or two.
6th - observe the various results and keep the changes that made more power.

Based on these assumptions, I would interpret Steve's advice as "just advance the intake cam (warm) table 1~2 degrees over 2500rpm for the last column or two" which would be done by bringing the nubmers closer to 0. (right Steve?)

**BE WARNED** I have very little knowledge on this subject and have made these statements based on my interpretation of the way our cars & tunes work. Until someone with accurate knowledge on the subject can confirm or deny my assumptions, I'd highly recommend not taking any of this information as fact.

[cobaltssoverbooster]

ya can someone clarify going which direction in the chart advance and retards both cams.

ex. intake cam-increase number = cam retard

[oldskool]

ya can someone clarify going which direction in the chart advance and retards both cams.

ex. intake cam-increase number = cam retard

I think a positive value is advance and a negative value is retard in degrees. Zero would be no advance or retard.

I'd like if a professional would correct me if I'm wrong though. I thought we had plus or minus 25 degrees of cam timing adjustment, but some of the base warm tables have values as high as 40 in them.