andy-gts

I am going to sell the raptor stage 2(with intercooler). I have been told the down side to the gts sc I did was the lobe seperation angle of the cams...gt cams much better, but if you are going the sc route I would be tempted to get custom cams from simard(gundrilled) with greg brown and simards reco's on grind....oh that would rock!!!!!

dprantl

I'm pretty certain that my car still has the original head gaskets from the factory. 234k miles now, last ~60k miles with the S/C on.

Dan
'91 928GT S/C 475hp/460lb.ft

Cosmo Kramer

OK I will agree to disagree! : While the S4 does have the knock detection system which is very beneficial for boost, the factory timing is set close to the edge so adding boost with stock timing will definitely have it knock. The EZK kicks in and takes out timing (more then required). This makes it a necessity to change the factory timing in mild boost applications on an S4. The S3 is timed very conservatively from the factory (around 6 deg less at top RPM then S4), so adding mild boost will keep you out of the knocks and if the owner is worried they can always connect the octane loop to take out an additional 3 deg.

From my personal experience, octane is the most important factor to keep the knocks away. With stock timing and octane loop connected, I was getting audible knocks above 8 psi on 91 octane. Switched to 94 and it all went away. Now I am at 6 - 7 psi with custom chips with -3 timing removed just to be safe. I don't have knock sensors and I want to air on the side of caution, but I am certain if I kept the high octane in the stock timing would be just fine.

hacker-pschorr

That's downright scary.

Tuning based on audible knock is worse than tuning based on knock counts.
The professional tuners I know disable knock sensors when tuning an engine (when possible, not all systems allow this).
You do not need knock sensors to find the knock threshold of an engine, and you sure as heck do not want to wait until you can hear it audibly.

Yes octane is a factor, it's also very hit and miss. Tune your car for Green Bay gas then go to Chicago and fill up with reformulated. Or go to a gas station with four month old fuel versus your regular station that is flushed / filled on a regular basis. This is what knock sensors are for, saving your engine when conditions fall outside of those used to tune it, or worst case something fails like an injector.

Yes the 85/86 EZF is a bit "de-tuned" from the factory, so is the S4 EZK.

Not only is giving people advice about running 8psi on full factory timing a bad idea, you are not even running an intercooler. So to make matters worse, your intake air temps are scientifically higher than what the stock timing map was created for. If any engine should be running less timing than stock it's an 85/86 non-intercooled car under boost.

Your one saving grace might be the intake air temp sensor that is probably always past the cut-off zone which lowers your timing 3 degrees (if my memory serves me) same as the low octane loop.
This is something else most might not be aware of. If the intake air temp sensor has already lowered the timing based on it's parameters, the low octane loop is cannot lower it anymore. It's one or the other.

Cosmo Kramer

^^^ agree 100% Hacker. Wasn't trying to say running factory timing and 8 psi is OK, just kind of explaining my experience and what I did to correct it. In a mild boost application (say 5 psi, like Carl's system) the stock timing and premium fuel should be completely safe. I actually know someone with a mildly boosted S3 actually running AA clone chips in his EZF with no issues! Yes audible knock was scary on my car and I fixed it right away. It is a tough game tuning without knock sensors, you want to be safe yet not leave power on the table. Being able to data log with knock counts is such a useful tool to have!

This is my current tune. I have progressively removed -1 to -3 timing above 4500 rpm at 0 vacuum and above, WOT EZF map delete, -1 to -3 removed from the intake air temp sensor from 110F - 135F, LH open loop at .5 PSI instead of on the WOT switch. BEGI FMU set at 40 psi baseline. AFR under boost is mid 12's at onset and mid 11's at 6-7 psi. On the dyno with the hood open and me standing right beside the engine no audible knocks at all on 94 octane (10% ethanol).

Back on point, because my system was kind of a DIY I had to mess around with it quite a bit to get it where it is now, especially being an S3 you have to be SO careful that you don't damage anything due to detonation. Buying a Murf with the tuning already done plus the expandability is a great option for when you have to keep feeding your addiction!

Jon B.

What power are people getting out of Tim's Stage 1 system? Also, what is the cost to upgrade from that to the Stage 3?

Cosmo Kramer

I believe for an S4, 380 - 400 rwhp for the stage 1. Not sure on the upgrade cost for the stage 3.

Jon B.

I would think it would be pretty similar on an S3 though. Didn't Shane's car do something like 495rwhp on a Stage 3? That's up there with the Stage 3 S4's i've seen.

My car is a 5-speed S3 so that's why i'm curious.

AO

+928

I also believe it's a bad idea to tell people they're fine with the stock tune on a boosted car.

I believe Z told me that a knock event produces 100 times the forces in the combustion chamber! Keep knocking and you'll have a head gasket replacement party before you know it... or worse!

Yes, there are some band-aid approaches you can use to help limit knock in an S3, but they are really no substitute for having a properly tuned fuel & ignition map.

Cosmo Kramer

My S3 auto at 6 psi put down 370hp/344tq to the wheels, with a manual I would expect a bit more due to less parasitic loss in the driveline. Mine isn't a Murf system, however I believe Shane's car when it was a Murf Stage 1 put down exact same numbers.

Cosmo Kramer

I believe my setup is the same as Murf's Stage 1, stock 24 lbs injectors, 8-1 FMU and EZF chip with timing removed. Carl's at 928MS is the same too, only no EZF chip because his 85-86 kit only runs 4-5 psi. 85-86's are a bit of the bastard child for tuning, requiring a Sharktuner that costs over 2K. If Voila can make the replacement tunable LH for our cars that would be the cats ***!

Don't get me wrong, knock is BAD I know that. I have crossed that line and came back, luckily with no issues. I was just trying to make the point that an S4 with it's more advanced timing would constantly be adjusting the timing back 9 degrees via knock sensors where the S3 with its more conservative timing would be already below the knock threshold at a low boost level.

I wonder if the is an easy to install temporary knock counter we could install on our cars for tuning?

hacker-pschorr

As I said above, this "version" of the Murf kit is being phased out in favor of 42lb injectors and a custom LH chip.

AO

Again, you're wrong...

With the S4, you can adjust how much timing is taken out if it detects a knock event. I believe the maximum retard is 3° per event on that cylinder only, but you can dial it back to ~1° (it's been a while). If subsequent events occur, it will retard it further up to a maximum of 9°.

Then, based on a user-defined time period, timing is advanced in incremental stages per revolution.

In my case where I'm running a fairly aggressive tune, I think I have it take 1.3° of timing out per knock event and have it reintroduce timing within 1 second. I've never seen 9° of timing taken out. Usually it's 2.6° (2 knock events) occasionally it'll hit 4° (3 knock events) on the same cylinder. On my last full pull on the dyno, I think I had a total of 14 knock events - sadly on cyl #2 or #6. if memory serves.

Before getting the SharkTuner, I tried to use the Innovate data logger to record knock, but unfortunately it samples at 12samples/sec = too slow for knock count.

I thought PorKen came up with a knock light. Not sure it's accuracy, but it might be the best tool given the circumstances.

dprantl

Why would stock timing be ok for a 928 running 5psi? How would you know without a knock sensing system? Just because you can't hear audible knock, doesn't mean it's not there (audible knock, as was said earlier is like the death toll).

This kinda reminds me of the timing belt paranoia thread, some people go for 180k miles on 2 belt changes, but is it worth risking an engine rebuild? I don't think so, especially when a knock system and proper tuning is not that expensive to begin with.

Dan
'91 928GT S/C 475hp/460lb.ft

Shane

It did 475 on the dynojet in Green Bay on the initial tune with heavy backpressure on the exhaust and was loosing fuel pressure at the rails. When I got her home I pulled the rear muffler and stuck her on a different dyno here in WA. Dyno sheet said 450, and the operator said for dynojet comparo add 10% = 495rwhp.

However before I could add an 044 fuel pump and a S4 regulator to bump the pressure up and retune, I got stupid with boost and launched in 3rd and WOT! Damn

With your 5speed and a Murf Stage III you will see 500+ easy...