PorKen

Part of the reason it needs to be opened earlier is the movement of the flappy plate spoils the last bit of the peak.

I have reversed the flappy operation so that the flappy is normally open, only closing for the first peak (2500-3500).
You can see in the red graph above that the flappy movement squiggle has moved to 2500.
As a result, I have closed it a little earlier to blend closed TQ into the open graph more smoothly.

On the S3, both the lid inlets and the tubes are smaller.
There is a jump in MAF voltage over the entire range with the airbox lid removed.
(This is another reason stock S3s dyno lower.)

No such easy fix on the S4, however (for stock-ish airflow).
MAF voltages are the same with the lid and tubes in place as with an open top.

SeanR

That was what we expected and we were pleasantly surprised when both GTS's (GT Cams/X-pipe), and both S4's (stock except X-pipes) showed 8hp and 11tq improvements. All dyno pulls were back to back and the same day.

Mike Simard

Do you ever contemplate the ignition and it's spark strength? For some reason I have a hunch that there's room for big improvement there.
The engine is a nice 4v central plug design after all, shouldn't knocks be rare?

It would be nice to strap on something like a top fuel magneto system for a few minutes to rule ignition out!

69gaugeman

The Bosch coil as used on the 928 is one of the most powerful ones out there. If the caps,rotor and wires are good, you will be hard placed to be able to fire the mixture any better.

PorKen

Folks with COP or CNP get monster torque out of the S4 with aftermarket brains.

There are (only) two programmable outputs from the EZ-K, Check Engine and a knock flag.

I'm no electronics guy but for simple wasted spark circuit, I think all you need is one output, calculated using the hall sensor, along with the existing left and right coil outputs?



With the stock spark plug gap.

AFAIK, you need something stronger to fire across a much larger gap to get more power.

Mike Simard

That's what I was thinking, I have some robust COPs that fire sequentially and don't live with detonation, it surprised me and caused me to re-think the importance of ignition in general.

Lizard928

I have still seen some mild detonation on a stock 5L when pushed with standalone systems, both with coil packs as well as COP ign.
Though I am planning on doing further testing on this.

One of the things that I feel is that the S4 heads, the port is slightly too large leading to a slow port velocity. This coupled with how close the injectors are to the valves results in much more lean/rich pockets which makes it more prone to detonation.

I'm currently working on ruling that out on my own car.

ptuomov

Half the S4 runners are 20cm long and the other half are 30cm long. Yet they all have the same fuel and spark map. This begs the question why wouldn't it knock?

GregBBRD

One of the variables on the S-4 engine is the amount of carbon that has collected on top of the pistons. It is pretty easy to change the static compression ratio by a couple of points, by just having a thick layer of carbon.

I just finished up working on a Sharktuned GTS that had a very significant layer of carbon (as a matter of fact, it burned a valve from excessive combustion chamber heat.) We cleaned the heads and the pistons of all carbon and were able to add another 8 degrees of timing when we were done.

My theory is that until you get rid of the oil going into the intake system (which makes lots of carbon and reduced the effective octane of the fuel) and also get rid of the carbon deposits on the pistons (very difficult to do, with the engine together) you are going to have a tough time adding timing into these engines.

BC

I mad a side cover for the S4 intake that can be made to fit a D plenum on both sides and have a frontwards TB set, or a Y into one TB. It may be a good compromise with the info given about the horns and the obviously issues with the plate blocking them.

Bigfoot928

I have been telling people for years that the GTS will not make the power it is supposed to until the oil drain back holes in the pistons are drilled and the oil ingestion issues are resolved. Oil fouls the fuel, especially the octane rating and just by removing the oil from the fuel issue more ign advance can be added and hence more power from the same fuel minus the oil.

I had my intake measured once and the tag I still have is 9708 CC just for the top half of the intake minus the lower throttle body...... Hopefully that will add some info to the mix and help out...

Bigfoot928

This is EXACTLY why a stock engine could increase the HP and torque just by adding an aftermarket ecu that can trim or tab the A/f mixture for each cylinder....

Bigfoot928

If your fuel map is good for each cylinder it will be good enough.. but they built the ignition to handle the over fueling and under fueling to compensate for the intake differences.... if you can remap the fuel the factory ignition system can generate some incredible power...

worf928

This is a great thread. I have little to add as my fluid dynamics knowledge has been molding unused for 20 years. (Other than that we need to remember that air is compressible and that a pure focus on steady-state observations will likely hide important complexities.)

However, on this topic I will jump-on and agree totally with Doc Brown:

A couple of years ago I had a 32k-mile GTS with cylinder #3 constantly misfiring - to the point where one could say that it simply wasn't firing - and the Hammer showing knocking on overrun.

Long story short, when I pulled the head there was 2 - 4 mm of carbon buildup on the pistons. So much that the bowel in the piston was hard to make out. Getting rid of the carbon completely transformed this stock GTS. It was a totally different animal when it wasn't choked to death. (It's now running around (on sunny Sunday's only) with a ProVent to help prevent oil ingestion.)

The buildup on all pistons was reasonably uniform, but only #3 exhibited severe misfiring. Note that injectors were freshly cleaned and balanced, MAF was a fresh rebuild, new plugs, caps, yada, yada, yada.

So, bottom line, carbon buildup on the pistons can cause issues. The more carbon on the pistons the more it seems to exacerbate imbalances in combustion cylinder-to-cylinder on a stock motor.

victor25

Here is my current combination of injectors and locations. It made a huge improvement in power and tune-ability of my car. Zero knocks, easier tuning, and much more timing advance.

I would still love to know the flow values of the individual intake runners if anyone has it