aight, so I don't think that I have a boost leak. Lemme first say that I did NOT yet perform a BL test, but I did some logging and I've found that while while I am about 5inHg short on vaccuum at idle and short 5psi boost at WOT, I have the same airflow as before the cam change. These pix should show that:

Before cam change:


After cam change:


If the MAF HZ are any accurate indication of airflow, what I'm seeing is reduced peak boost (went from 25ish down to 20ish) but consistant airflow. I have not touched the MBC.

I ran the car on -4/-1 yesterday and it made no difference on boost/vaccuum/knock differences... I am still getting rediculous knock in the 2500-3400 area when just cruising, it actually clears up at WOT. Weird. Could it just be the lifters setting the knock sensor off? Should I really go more aggressive? Like -4/+2? (BTW: I noticed a significant loss in midrange punch w/ the -4/-1)

 

I don't think going to -4/+2 is going to help anything. Yes, the -4/-1 setting reduces midrange punch.

As for diagnosing your knock trouble, it's difficult to do that remotely. It appears as though something is amiss, although it could be a number of things. I'm not sure of exactly what I'm seeing in the graphs, but I see some very lean AFRs.

 

The above graphs show that before and after the new intake cam I have the same airflow... even though my boost spike is 5psi less. I run a leaner AFR up top to compensate for taper and the fact that 5th gear gets way too rich b/c it runs in the same load cells as 4th.

So you think that midrange, closed loop knock is not a result of the new cam? Just to make it clear, because I dont know if I've communicated it well yet, but I'm running the GSC 272 intake cam, and a Buddy Club 272 exhaust cam (which I've read is the same spec as HKS). So I want the midrage that -3/-3 gives on HKS 272s so to match LSA for my setup I calculated that I need -2/-3 to match the 110 LSA.

Do you have any thoughts on the boost issue? No matter which end of the spectrum I'm at (+2/0 or -4/-1) I am consistantly making the same airflow as before, but less Intake Manifold Pressure. Do you think that this is due to the advertised duration of the intake cam is 280, and is so opening earlier but with less lift?

lol this boost and knock thing are driving me crazy!

 

I wouldn't assume that to be accurate for one minute, and I have seen no specs for those cams.

 

What would be the setting on the Comp Cams to be like the HKS -3/-3 setting?

 

Comp Cams are ground on 104/112 LCs, so to get the equivalent of -3/-3 in HKS speak, one would need to dial them to -6/-4.

 

oh i see, i understand now...and you said that you personally perfer the -3/-3 setting for better mid-range and is more streetable rather than -4/-1 wich would be better for drag racing?

 

Correct.

 

lol, alright. Found a boost leak. I feel like an idiot. Back to 15ish inHg and 25ish psi. These leaks are getting harder and harder to find.... I still have weird midrange knock when I'm cruising ~35%TPS Ted, in your oppinoin would the more aggressive cams (assuming they are the specs that I've said) want more timing perhaps? I go as low as 9 degrees in the 2750RPM area and it still knocks... I dont think it wants less considering that the stock map called for something like 28-35 degrees. I breifly tried raising the timing, but I've since fixed the leak and set the gears to -1/-2 (and I'm leaving them there!!! lol)... and it wasn't really conclusive anyways. I understand all the LSA stuff now and can now easily do the calculations in my head, but could you take a moment to explain whether timing requirements might change at crusing and why? Thanks bro.

 

I told you so . . .

Preignition, if that is really what you're seeing, is the result of heat and pressure. Certain cam settings increase cylinder pressure in certain rpm ranges, which tends to lower the detonation threshold in those same ranges. In your case, experiencing knock at part throttle with such low ignition advance would usually be due to (a) a lean fuel mixture, or (b), a lean fuel mixture as a result of a leak (that allows air in, which leans the fuel mixture).

It is difficult to diagnose this any further from where I'm sitting, but unless there is something seriously wrong somewhere, it boils down to this one way or another.

 

alright. I've got the leak/lean concept down. AFR is normal cruising 14.7ish with STFT near 0 all the time, so no leak that I know of w/o a specific BL test.

I suppose that is the answer I needed though, I'm assuming by your answer that at least MY cam combo shouldn't require any rediculous timing changes (+10 or -10 etc.). I suppose I will continue looking at all the normal suspects now. ---perhaps time to look into those knock tables...---

 

+2,+2 is it really better any dyno charts.
I might have to try it out