Jim bailey - 928 International

there are a handful 85-86 32 valve cars with the S-4 intakes running around . The hotter 85-86 cams used might really like the forced air . My primary concern would be about the vacuum adjusted ignition timing .

BrianG

Around what air pump is this kit constructed?

Tim Murphy

Are you thinking that the boost pressure feeding into the brain would not be good? Maybe you could just install a check valve to protect it from boost pressure and still let it see the vacuum. I would have to study it some more before I could say that is the answer though.

Tim Murphy

Vortech V2 S-trim, polished. (Take $150 off the kit if you want satin)

Jim bailey - 928 International

Tony , Tim no need to worry about freezing ..... Joe Dyer's GTS with the "FAST/ Eric Monk et all " blower has been spending some quality time with Mr Thomas !

Joe Dyer

Jim,

Only for a larger oil cooler, then missing injector clips caused small fire. Vacuum lines and new harness in the engine bay must be done.

ViribusUnits

Tim, do you know if your knock sensor retard the timeing as the boost comes on?

I'm willing to bet that they do. However, unless you get someone to watch the timeing while your doing a dyno run, I'm betting it's diffuclt to check.

My understanding of the vacuum advance is that when the brain see's the vacuum, it advances the timeing, so that you get better fuel milage. As the vacuum is reduced, the timeing is retarded.

Will the brains sensor deal with boost? If it does, thats cool. Will the brains map retard the timeing as boost comes on? How much you wanna bet on that?

I can't imagion that the S4's who's timeing curve is ment to match with a N/A engine will be the same as a blown engine. In otherwords, I'm betting the knock sensor are doing they're job.

If you install a check vavle so the brain doesn't know there's boost, or the brain can't conpensate for the boost, then you'll have too much advance, and thus detonation, no?

Tim Murphy

Someone needs to teach me how to split up the post so I can insert answers between the lines.

Anyway, The knock sensors only retard the timing when knock is present, they have no idea that the boost is present. When the knock sensors detect knock and retard the timing it is very significant.

The s4 and later cars do not have the vacuum connection at the brain. With the cars that do, my guess is that the brain would only advance up to the point there was no more vacuum and stop there. I don't know what the effect the boost will have on the brain and that is why I suggested the use of a check valve in an earlier post.

BarryW

The pressure sensor in the ignition brain advances timing in the partial throttle range (vacuum) for lower fuel consumption and retards timing during full throttle (low vacuum) because of knocking danger.(Page 59 of Porsche Service Manual WKD P21) With positive pressure, the timing would always be retarded but I don't know if it would be enough to prevent detonation.

Fastest928

Hmm, I think that we might see a few white cars.....and NA one making about 570 rwhp, and one or two in the 550-650 rwhp range running 6-7 psi boost.....mabye both white???

And the best part, maybe we will drive them to the event! Ohh, darn, did I gets someones undies in a bunch with that statement...sorry.....



Marc
DEVEK

sweanders

This sounds VERY interesting!

I'll sit around here on the other side of the Atlantic to see how it goes for you guys.. Hopefully the dollar will go down a bit more so that the number of exported SC-kits can go up..

Kevin in Atlanta

For those 85-86 owners interested in s/c, I have an S4 Intake with throttle body for sale for $250 plus shipping.

As an aside, I own the other '93 GTS that was S/C'd. It, too, had missing injector clips. Not any more.

ViribusUnits

Does the S4's ignition brain an input from the MAF to let it know the amount of air?

I understand the knock sensors only opperate at WOT, because thats really the only time it's needed. However, to get good fuel economey at part throtal, something has to advance the timeing, so...

What sets the base timeing? Rpm only? With knock sensors to retard it for WOT and near WOT opperations?

Z

Not really sure why you'd think that. At this point there may be as many as five (more?) boosted cars coming from Wisconsin that would all be driven to the event.

Z

The signal from the MAF goes directly to the fuel injection computer.

The knock sensors will also operate at part throttle, not just full throttle. At full throttle, the S4 timing is about 10 degrees BTDC, and then it switches to about 30 degrees BTDC at around the same RPM point that the intake resonance flap opens.

We've never seen any timing retard from the knock sensors in any of the dyno testing that's been done. As a matter of fact, back when Tim was making 8psi of boost, with no intercooler, and fuel injectors that were too small, we actually advanced the timing while on the dyno and didn't see any timing retard occurring. That was with premium pump gasoline.