axr6

I just installed my AEM UEGO wideband A/F gauge. Also got a new PFC with maps from Rick's Rotary Performance.

Took car out for the firsts tune/feel session. Fuel ratios seem to be close. At P11 I am down to 12.7, at P16=11.8 but, then, P17 is up to 12.5. Seem like I'm running out of fuel a bit at P17.

What worries me, however is the very high knock readings from the PFC. I started off with a real-time read of about 12 then accelerated in 3rd gear getting to about 6-8 psi boost. The knock value jumped immediately to 123 before lifting. After lifting the knock value peaked at 203.

I seem to have a pretty conservative ignition map, when compared against some posted on these forums. I am wondering if the knock value is so high because of my straight pipe cat back exhaust. I do have a DP and a stock cat converter.

Has anyone recorded any knock values with this kind of loud, open exhaust? I would not be surprised if that sound would reflect back into the engine.

ImranRX-7

I believe your knock values are REALLY high. During a recent canyon run, at .89 kg/cm^2 and 7600rpm I had a knock reading of 63.

rynberg

The knock sensor is just a microphone. It could be loose or damaged. There could be other noises it is picking up as well.

Are you stock other than a downpipe and cat-back?

KaoticFdR1

so what is the best way to monitor knock?

axr6

I also have an M2 intake and an M2 Med IC.

I have to go back out and see the pattern of the noise. My wife was monitoring the PFC knock graph and she said that it just jumped from about low 10s to 123 with no transition. That would suggest some kind of noise other than knocking. I need to see if there is a large jump in the graph, followed by an equally quick decline (I hope) while still accelerating. She seemed to remember that it was a spike but, was not sure.

The straight 3" pipe seem to flow a lot at high RPM. I had proven that with comparison tests years ago. That is probably the reason that my AF read actually went back up to over 12 in P17. Rick probably developed that fuel map for some kind of regular exhaust.

axr6

First, the high knock values.

I went for a drive today and paid close attention to the graph on the PFC. The high knock value is an instantaneous spike when the turbo spools up, lasting momentarily only.. After that the knock value drops back to low levels and stays there. Still, the highest knock values come when I lift off the acceleration after a high rpm boosted run. Probably due to the straight pipe exhaust.

Second, the Air/Fuel values with my exhaust.

As I stated in the top post, I was running pretty rich up until WOT, lines P16 and P17 on the PFC. Those last two load lines leaned out to about 12.5 AFR. Today, I kept going higher and higher on the Commander's Inj Map to lower the AFR for those two WOT lines. I almost had to max out the Commander's Inj. Map range to finally come back down to about 11.3 - 11.7 AFR.

Conclusion:

I got this "conservative/rich" fuel map when I purchased my PFC from Rick's Rotary Performance. Yet, with the straigh CB pipe it was not rich enough. That pipe flows a hell of a lot more at high RPMs than most high performance mufflers. I proved that in a series of high speed tests way back in '94 on my first FD.

Also, that explains why I lost my engine in this FD just recently. When I got this car it had an M2 Stage 3 ECU with M2 Med. IC and Intake but, stock exhaust. I was not familiar with the M2 ECU but was assured that it ran pig rich in the high RPM range. So, first thing I did was to replace the stock CB with a straight 3" pipe. On the way home from the muffler shop, during the third acceleration attempt, the apex seals left the engine...

Guess, the M2 is running quite a bit leaner than the stock ECU. Back in '94 I ran staight CB, DP, MP, IC, Intake on the stock ECU with the only changes being the redrilling of the pills and using Supertrapp plates to keep some backpressure to prevent the boost from going to 17.5. It worked fine with the stock ECU not only for street driving but, for two years of road racing.

moconnor

iTrader: (14)

I presume 17.5 is a typo? I can't imagine your car would have lasted very long beyond 10 psi with that configuration.

I just ignore the knock reading on my PFC - the number does not seem to be even remotely related to the predetonation likelihood. I suspect the processing algorithms in the PFC are not capable of filtering out the noise in the signal (which is the reason that the PFC does not use this value to alter timing in any way).

books

iTrader: (8)

In order to determine how restrictive my RacingBeat dual tip is, I datalogged consecutive runs. The first runs were with the catback disconnected at the midpipe, the second set of runs was completed with the catback attached. I am running a single turbo with 1300cc injectors.

Without the catback connected the following data was recorded:

Boost 101
Peak knock 64
AFRs appox 10.8
Injector duty cycles 74%

With the cat connected
Boost 101
Peak knock 69
AFRs approx. 11.1
Injector duty cycles 70%

axr6

With the stock ECU and MP, DP, Straight CB pipe, intake, the boost spiked to 17.5 and gave me fuel cutoff.

In the final configuration, pills drilled, as raced with the above mods, the initial boost spike was to 14 and quickly settled at a stable 11 lbs boost. Depending on track temperatures I had to either use 15 or 18 Supertrapp plates to prevent fuel cutoff. With this setup the car was bulletproof, proven by two full years of full-season track racing and bonzai street driving. As a matter of fact, as of today, the car still has the same engine in it with a little over 30 K miles. I know, because I tried to buy it back but, the new owner would not sell...

axr6

I used to run acceleration tests from 60 - 150 MPH to test my changes. Needless to say, other than running your car on a dyno for each change, that is the best way to tell if you lost or gained HP. I would repeat the test 4 times for each change, two runs in each direction to average out wind, road elevation etc.

The greatest single gain came from the straight cat back pipe. Look at the comparison:

Stock catback 60 - 150 MPH = 33.4 seconds.
Straight pipe 60 - 150 MPH = 27.15 seconds.

That is a 23 percent gain in acceleration times!

Going to a Dual K&N cold air intake AND Pettit SMIC gave me an additional 3.92 second off to 150.

Installing a downpipe gave me an other 2.07 second gain to 150.

Replacing the cat converter and installing the free flow Borla muffler (had to replace the straight pipe in the back to reduce sound levels for Laguna Seca) did practically nothing. The gain from the midpipe, combined with the twin tip Borla's restrictions pretty much cancelled out any further gains. That is why I keep my stock cat and used a straight pipe for street.

I eventually did replace the cat with an MP not beacuse of any power gains but for less weight on the track.

books

iTrader: (8)

The primary purpose of that data was to indicate my knock did not increase without the cat attached. On a side note, since some use duty cycles to calculate power, those numbers show an increase of about 4% duty cycle without the cat attached.


Usually I run 3rd gear wot to tune my AFRs almost always in the same direction and on the same road.

Normally it is 3 consecutive wot, adjust fuel, then turn around and do it over again.

My experience with the switch from a high flow cat to a midpipe only netted 10rwhp. This was at the same dyno about a month apart at the same boost level. I believe others have seen higher results.