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I pushed ignition targets and began to encounter knock, perhaps with changing atmospherics warmer/cooler weather conditions playing a role in why I wasn’t seeing knock earlier. I’ve adjusted the EZK rpm points to try and work around peak torque, no dyno yet but I’d guess at three distinct peaks around 2, 4, and 5K rpm.
Marti, I began to see knock in two distinct conditions: higher ignition loads 67% and up right through the range from about 3k up so ive scaled back my targets and adjusted the rpm points to try and still push timing where it can be taken. It seems with warmer weather and higher ambient temperatures knock has made an appearance. But I can tell you that the engine did like more advance for a short time in the cooler air. I need to invest time and improve the ducting to the radiator from the front nose clip - this might see the engine able to take more advance. But in the mean time im happy enough scaling it back a little and avoiding damage.
I am also seeing some knock at lower rpm points in transitions ie when rev matching while downshifting, so again im just data logging every drive at this point and adjusting the maps as I go, ill post an updated screen shot after more testing.
Have you been able to feel so far what peak torque rpm was?
Is there a clear rpm point past which the engine suddenly accelerates harder?
The S62 ITB + runner set up you seem to be running may not give the cams the chance to shine as much as they could, as from the pictures it looks like the inlet tract between each bellmouth and the inlet valve may not be any shorter than on the stock S4 intake. It's all guessing though and more input like a (even just calculated) torque curve, even at this stage of relatively early tuning, would be useful to get a feel of how the engine already accelerates on full load.
I would not worry too much about knock counts when changing the gears down, as the engine is under no load from the transmission when the clutch is disengaged and what the ECU then picks as "knock" counts could probably be just harmless clutch noise.
Interesting that it is sensitive to air temperature, I will need to watch out for that.
I am currently getting no knocks with advance in excess of the map you posted earlier in the thread and I am wondering how far I can push it and where to expect knocks so this helps.
I guess i will will keep pushing until knock start happening and report back.
General comment around performance is that it has given the car a noticeable bump in power on top of the mechanical changes already so I will be surprised if I can find even more power in the midrange
I pushed ignition targets and began to encounter knock, perhaps with changing atmospherics warmer/cooler weather conditions playing a role in why I wasn’t seeing knock earlier. I’ve adjusted the EZK rpm points to try and work around peak torque, no dyno yet but I’d guess at three distinct peaks around 2, 4, and 5K rpm.
Amazingly enough, having owned and used my own dyno for over 30 years, the vast majority of dynos are almost worthless for tuning fuel and timing. "Normal" dynos will generally have a few fans to keep the engine temperature "under control", but they do not move enough air to simulate what happens in the real world. The exception are dynos that can move extremely high volumes (and speeds) of air past the vehicle, but these are very rare and generally combined with a wind tunnel.
Keep tuning the way you are....except drive the car, ignore the laptop, and collect the data, which you can view later.
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
just a suggestion, since it is a pure race car consider using race fuel. Knock kills 928's stupid fast and the increase in fuel cost is minor compared to a new engine! E85 is even better if its readily available to you, but does require new fuel pump and injectors
My current ignition mapping showing the difference to a GT map which is already advanced over an S4 map
At which rpm points does the flappy open and close?
Generally speaking, is the flappy only actuated in function of engine speed or also in function of engine load through some hysteresis loop?
At which rpm points does the flappy open and close?
Generally speaking, is the flappy only actuated in function of engine speed or also in function of engine load through some hysteresis loop?
The flappy is opened by the LH Ecuador based on engine revs only. It is adjustable with a Shark Tuner. Opens around 3.5k revs as standard
Does it not close past a certain engine speed though?
I found some conflicting information in the archives about that. It would make sense to me that it would close above 5500+ rpm as the runners on the S4 intake are in my opinion too long to make the engine benefit from any charge effect up top.
The SharkTuner interface suggests that a closing point can be set up.
Does it not close past a certain engine speed though?
I found some conflicting information in the archives about that. It would make sense to me that it would close above 5500+ rpm as the runners on the S4 intake are in my opinion too long to make the engine benefit from any charge effect up top.
The SharkTuner interface suggests that a closing point can be set up.
You are correct that it closes again after 5k, forgot to mention that. The closing revs can also be adjusted via the ST. I have done very little work on adjustment of these yet as fuelling and timing comes first.
Ive softened the advance under 2k rpm so that the car moves off from idle/part throttle more smoothly, ive also softened the ramp from 0% load through to 33% higher up so that its easier to feather the throttle in corners. The low load high rpm numbers are just numbers - seems like a lot of work to try and map these points on the road at this time.
Marti, I was starting to get spooked when it seemed like I was able to keep adding advance with no knock, its been really useful starting this thread. I ended up with a solid 28 degree advance from about 3900 rpm up - and the engine loved it I didn't want to give it up! I must have been right on the edge of knock and then warmer air has tipped the balance - whether that's through the engine running warmer or the intake charge going up a degree or two or both. Definitely when heat soaked in town I get more of the knocks when shifting/pressing the clutch - and another reason ive pulled timing lower down.
Thom, peak torque is somewhere between 4-5K. Runner length I cant say much about except this setup is most definitely an improvement over stock. Thanks for the feedback about the ECU seeing clutch engagement as knock - ive still pulled timing just in case tho.
Greg, thanks for the encouragement. Ive found that adjusting the rpm points in the map has definitely allowed me to feed more advance and id recommend anyone else without the flappy to worry about would find the same. I am curious tho to see eventually what it looks like on a dyno and this might allow me to fine tune more accurately. I recently received in the mail one of your oil filler baffles, at the moment ive got a blanking plate installed but im going to open the crank breathing more - even tho im drysumped. it lifts a lot of oil at higher rpm which might also be affecting how much advance it can take. The current map runs pretty sweetly tho both from seat of the pants and also no knock at load.
Ice, its still completely street legal and at the minute my daily driver to and from work! Im sticking with the commercially available pump gas- for now.
I would say that the stock S62 runners you are running at the moment are too long for top end power, if this is what you are after.
It's not hard for me to imagine that shorter runners of equal length will give better top end breathing than the bizarre stock intake with its unequal length runners.
The firing order shows that the 4 "short" (or same side) runners (5/4/8/1) are being fed alternatively to the 4 "long" (or opposite side) runners (3/7/2/6).
This means the charge effect is not optimised to work best either at low/mid range (with 8 equal length "long" runners) or at high rpm (with 8 equal length "short" runners), and that's without even mentioning load losses due to bends. If the flappy, when open, is supposed to improve charge effect at low load, it's no going to help at all at upper rpm because the runners remain too long, and probably the reason why it is programmed to close at 5k rpm on a stock engine.
Sorry if this is not the right thread to discuss it, but what do experienced 928ers think about it?
10-13-2018, 07:43 PM
I didn't want to give it up! I must have been right on the edge of knock and then warmer air has tipped the balance - whether that's through the engine running warmer or the intake charge going up a degree or two or both. Definitely when heat soaked in town I get more of the knocks when shifting/pressing the clutch - and another reason ive pulled timing lower down.