I had been running with an advance of driver side 5 degrees, passenger side 3 degrees (I'm assuming this is 5 degrees both sides once the engine is warm).
I did this after removing the old supercharger. Now the new improved supercharger install is about to be completed.
Murf SuperShark Stage 3 (intercooled)
I'm hoping to hit around 9psi.

Should I set the timing back to 0 driver side 2 degrees retard passenger side or leave it the way it is?

The car has 88,000 miles and as far as I know original pistons, rings, head gasket, etc.
I loved the way it pulled running advanced and my goal isn't to run a bunch of quarter mile drag races, more like when I'm in a sporting mind set I'm cruising around keeping it spinning at 4000 to 4500 rpms and prepared to answer the roll on challenge if conditions allow (on a closed course with full emergency crew support of course!).

Oh, one last question, approximately what RWHP would I be making at 9psi in a 1988 S4 model with Stage 3 kit, X pipe, 5 speed LSD, Shark Tuned?

 

no

 

+1

I suspect you'll be hitting more than 9psi (depending on the pulley you run) The SCer will more than make up for any power issues that you may have been trying to compensate for by advancing the cams.

I would set it back to stock and crank up the boost! But that's me.

 

Thanks! I figured that was the case but I don't completely understand the effects and/or differences between cam timing and ignition timing adjusted with the SharkTuner...I didn't want to give up any mid range power if it isn't necessary.
Would there be any wisdom in retarding the cam timing a few degrees considering the boosted scenario?
And does anyone have a guess at the rear wheel horsepower I'll be making? I know Tim was at or over 500 but I don't recall which engine that was with or what other mods he had done.

 

With Ethanol, yes, but with regular high test gas, I think you need to retard the timing a bit.

 

For any given boost level / gas octane / compression ratio there is a sweet spot for ignition timing. Go too advanced and you will detonate or the brain will retard it (if it is able to), go too retarded (haha) and you will be leaving power on the table. With a fixed boost level, you want to find that specific spot. The only way to find it is to advance the timing with the gas you want to run and run the car on the hottest day with the A/C on full running the steepest hill at the torque peak with the engine as hot as it can ever get for as long as you can and record knocks. Then back of the timing and repeat until you get few to no knocks in that scenario and you found it.

Dan
'91 928GT S/C

 

He is asking about cam timing. Ignition timing is pre-set on the chips provided with the kit.

 

I was going to raise that point, but thought most people wanting to contribute would have picked up on that.

 

Sorry, my lack of knowledge on the subject is kind of muddying the waters.
I'll keep it simple.

What potential failure does boost+advanced cam timing pose, not advanced to the point of valves hitting pistons I know about that extreme, but is it just detonation or something else?

And for ignition timing is it just detonation or something else as well?

As it stands now I'll go back to 0 degrees cam timing, the SharkTuned files Tim sent will go into the PEM's in my EZK and LH and they will dictate the ignition timing and fueling, I have a Shark Tuner but most likely won't try to change those maps unless I see something going bad.

My goal isn't to wring every last bit of horsepower from the thing, I'd rather have 90% of it's potential and be safer. I just wasn't sure if I was giving up some low end grunt unnecessarily by setting the cam timing back to stock but I think Andrew kind of cleared up the obvious for me, with all the extra power the boost brings who cares about moving the curve a little bit unless you're tuning for a race track.

 

You're gonna have so much grunt all over the tach with a stage-3 murph system that you'd probably never notice any extra power from the cam advanced a few degrees. you'll probably be more worried about traction and slowing down in time for that corner coming up waaay to fast to ever fret over 10+/- hp, which remember is a trade off for upper rpm power anyway, a trade you sure won't need to make.
thats just my total novice non-s/c having view on the matter so take it w/ a grain of salt. sounds like a great project though have fun w/ it!

 

Oh young grasshopper you have much to learn

Ever see the cylinder wall of a 928 or 944 engine missing? I have.

Smokey Yunick once said (going from memory here) if you pile up every engine failure not caused by detonation on one pile, and all of the detonated engines on their own pile. The second one would be much larger.

Please do us a favor. Keep the engine stock & get the kit installed. After you have driven the car a bit and you say “This sum-bitch is too slow” we will then turn you over to Todd for the next level.

What spark plugs are you running? Should be running Bosch Copper #6 (or 5 depending on your driving style).

 

I like the takeoff feeling of the cam advanced, but I finally got to dyno back to back how the advance/retard works on a 32V (S³ w/X-pipe).

Going from +3° to -1° (hot), I gained around 20 rwhp and tq!

The HP peak moved from 5700ish to 6000ish (in my experience, roughly 1°:100rpm), so more might be gained retarding to -3° or -4°, which should still be under the 6400 limiter.




Honey Bunny...I need to get a 5-speed 928, too, to see how the low rpm torque is changed, it's difficult to dyno under 2500 with an auto...

 

BTW, let me tell you, it's a royal beyotch changing the cam timing on a dyno hot engine!

Ow, ow, ouch, ow, @#$%@#!

 

Especially when something slips and your finger is stuck between the cover and the head, on a hot engine…..right Tim?

 

Was it smokey that Todd was quoting when he said that a detonating cylinder's pressure is 10 times that of a normal combustion event. That means that a detonating engine that makes 500hp is Trying to make 5000 hp because of the detonation or pre-ignition (cylinder is moving up as the explosion is happening) Would we expect it to stay together long in stock form at 5000hp? No. So we must not let it detonate. Without detonation, I think the block can handle ALOT of power.

Well, I mean, I sure as hell hope so for my sake.