ptuomov

Me, too.

He may not get the ideal power level, but he will get the constrained optimal power level.

The '87 S4 was the first of these 928's with knock sensors. I think the factory engineers went to town to get some use out of them. While the S3 has equalish runner lengths, the S4 has runners clearly tuned for different resonances. It's as if they were fine with the car knocking every now for some of the cylinders and relied on the knock sensors to pull timing.

I think (but do not know) that the flappy operation doesn't only depend on rpm but it also depends on load. How did you deal with the load dimension when reversing the flappy directions?

I think that the factory added the load dimension for the following reason. When you are just cruising around, you don't want the torque to suddenly change with a jerk when the rpm just happens to go above certain threshold. So the flappy stays closed and no jerk. When the load is high however, the driver expects the car to pull and make noise for many reasons, the little jerk is not noticeable.

If the charge doesn't burn fully for any reason, isn't the wbo2 sensor going to register high oxygen demand? Maybe you could trace it back from there.

I got 1.85 liters per plenum. I think we may have been measuring a different thing.

With pump gas and hot and turbulent charge, we're not having any problems with the stock ignition system. Admittedly, that's an easy charge to ignite.

I think (but do not know) that the two main effects from the carbon build up are increased compression and the carbon sometimes heating up and acting as a "glow plug." Both would increase knock probability.

PorKen

I'm going to dial in some retard (probably -4°), and see what happens with the MAF log and/or knocks.
(I'm more motivated now that I don't have to remove the fan assembly SOB = PKrank)

Failing that, I'm going to finish the tank and fill up with Super.


There is a load threshold. (Both load and rpm also have hysteresis levels.)

I left the load stock. I lowered the initial rpm level to ~2500 (now ~2300) and swapped the open code with the closed.

worf928

I agree on both counts (that I do not know, but think that...)

However, just in case, the implication is that any "weirdness" with respect to a single cylinder might convolve with carbon build-up.

mark kibort

and i used this bell mouth, thinking it wouild really help the S4 , and it didnt.

the flappy is pretty useless for racing, as you never use the RPM that it is designed to help. (i.e. 4500rpm to redline) So, i removed the entire mechanisim after a lot of dyno testing of it working, not working, working intermitantly, etc. sure on the street, its kind of nice to have 30 more hp if you floor it at 3500rpm, but in a race, you would never needed it unless you got caught in the wrong gear.

we need an intake. i cant believe we dont have a version of the CF intake that is reliable and wont implode and grenade an engine.

ptuomov

When Hans gets that intake flange project completed, then there will be options. Anyone can put together their own intake manifold. Some will work well, some won't, and then others will copy the best designs. Let's hope Hans can get those flanges out quickly and at a reasonable price.

PorKen

The flappy, closed, creates torque from 2600-3600, peaking at 3200.

The flappy, open, makes about the same TQ at 3500 as it does closed.

PorKen

I hope this shows what 0° vs. -4° retard does to the S4 intake flow.
I had to go way, way back to find a RPM graph to match - it's slow going from 2000-6500 with the retard.
Might be able to pump up the ignition timing at the low end to pull up the slack, but I'm not sure it will be enough.

Anyhu, the tipping point appears to be at ~5350? Airflow is improved over 5850, but at the expense of the lower rpms.

These are the highest MAF readings for this S4 I've seen so far, at any air temp.
On the dyno, it probably means a plateau instead of a drop-off past 5800, not necessarily a higher HP peak.

BC

Meaning?

PorKen

Meaning it's doesn't seem to be good to retard, unless you drive like Kibort, keeping RPM above 4500.



I suppose you can look at the overlay graph above a little differently, whereby the airflow is the same, just at higher rpm (+124?).
Looking at it this way, low rpm airflow is the same as at zero, but moved up, and high rpm airflow is improved.
If this is the way to look at it, then high rpm flow might improve even more with yet more retard.


At the moment, the result is the same, though - it's still slow.

I could not advance the ignition timing. It knocks.
I'm going to fill it with super, and see if I can do any better. Then try back at zero.

Lizard928

Hey Ken, I told you that the S3 could make more power! hahah

BC

E85

PorKen

Sorry to pollute this thread with cam info...but it does affect the operation of the intake?

The S4 cam set is a tight 106° LSA with a short duration for no overlap.
The closeness of the intake and exhaust events will pack more air in, but only in a narrow range.
A tight LSA is prone to knock and requires lower compression and/or higher octane.
My thinking is the goal for the S4 was flappy derived monster TQ, not max HP.


After more runs with better weather (initial log was in the rain), retard does seem to favor the S4 cam.

Yesterday's runs compare well with those made in much colder air.
Low rpm airflow is the same, just higher in rpm. High rpm flow is enhanced.
The idle is smoother and it looks like AFR is less random between 5600-6200. (Yay!)
Roughly speaking, -4° looks like it improved airflow by 2%.


Before I tune the fuel precisely for -4°, I'm going to try -6°.
-6° will make the intake valve closing point the same as a GT.

Note on fueling: as the rpm range goes up vs. airflow, the entire map has needed to be 'richened up'.
It's not that it actually needs more fuel, it's just the rpm/maf calculation is changed.


I will log separate runs with the flappy open vs. closed to see if the flappy range needs to be moved.

hans14914

What a coincidence. Went back and revised the drawing and sent it out for bid for with a couple other foundries today. I fixed the thin spot, increased the thickness of the flange, and a couple other small tweaks. In fixing the thin spot, I did have to reduce the injector body bore to 16.5mm from 18mm, so this will require the modern ~15mm composite-body injectors. I still speculate that the 44lb Holden injectors with the 20degree split spray will be a huge upgrade on our cars. They are very linear, so think they should even be useable in a stock application with the lower pressure regulator.

Thanks
Hans

victor25

Hans... As we talked about earlier in the year, I am really looking forward to getting a set of these!! As I am sure many people are. Also I was wondering if it may be easier to make them in 2 cylinder sets instead of 4. Could all 4 then be the same verses swapping the 2 sides? I want keep the 2 cylinders that fire side by side in order seperated

Let me know if you want me to 3D print a set of plastic ones for you.

ptuomov

The camshaft does indeed impact the operation of the intake. I am guessing (purely guessing) that its impact is smaller for intake valve open tuning and bigger for intake valve closed tuning. But that's just a guess.

If there were more 928's out there, if the 928 owners would be willing to spend more money on their cars, and if the 928 owners would be able to spend more money on their cars, then the 928 would be the 911... Just kidding, but not that much. ...Ending digression, what I meant to say is that if the 928 performance market would be larger and if there would be more independent testing, then someone could make a quad pattern cam for the S4/GT. The idea in the quad pattern cam would be that its target market would be people who have to retain the stock S4 manifold and the stock S4 computers (although not the calibration), for example the poor owners residing in the bankrupt insane asylum of California.

I believe that one could make a good quad pattern cam with separate intake and exhaust profiles for the inside vs. outside cylinders. The long intake runners of the center cylinders are generally tuned for slightly lower rpms than the short runners of the outside cylinders. One could pair them with cam patterns that would feed the inside cylinders better at high rpms and the outside cylinders better at lower rpms. The result would, in theory, be a camshaft intake combination that would result in more equal air flow across all cylinders at all rpms.

It's an interesting optimization problem. You want to maximize the use-weighted average power over some rpm range subject to the smog constraint. The fueling is constrained to be the same across cylinders, and the intake runners lengths are two constants, one for inside and one for outside cylinders. My instinct says that the solution is to have later intake close for the long runner cylinders, such that at low rpms there's a bit more reversion for those cylinders and at high rpms there is a little bit more time to fill the cylinder with the longer runner.

So when are these flanges goign to be ready?