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Discussion Starter · #1 ·
Assuming we are talking about a 16vT, and if it were my car then a 16vT with LH2.2 and stock everything. If increasing boost pressure via apc what psi level would I expect knock? Then leaving that thought aside. If I raise the rise-rate, when would I get knock?

This is why I ask:

I've changed the base boost to 6.5psi, modified the distributor advance/retard capsule, installed a 3 bar fpr, k&n cone on the amm and upgraded with the apc. Now I'm having fun with the pots. If I give WOT then I will get engine knock at around 10.5-11psi at say 3000-3500 rpms. If I turn down the rise rate I can't get anything over 10psi (it'll do the stupid apc thing where is sits at 10 then taper down from there).

Further Questions:

Could my wastegate actuator be weakened(I basically had to wind up the arm ALL THE WAY to get 6.5psi for the base boost)?
Am I setting the rise-rate too high; moreover, should I not expect anything higher than 11 psi out of the apc?

Soon the temperatures will receed from 100 degrees and I will be able to play with my saab again.

I think that my 20 year old turbocharging system may need to be completely replaced along with an engine overhaul, but this costs me money which I currently do not have(real estate is god damn expensive in phoenix now a days).
 

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A major consideration is your ignition timing. You will knock like crazy if it's too far before TDC. I find 18 BTDC at idle and the vac capsule modified to provide around a 8 degree advance on full boost works best.

You can get much more pressure "out of the APC" than what you are running. The t3 could do over 20psi easily, but knock will essentially always keep it below that.

It seems you are more likely to get knock if you crank the rise rate pot up, it will back off quicker it seems.

6.5psi is a pretty high base boost, you'd be nearing the end of he travel on a well-used wastegate, but it's no big deal, it's only a spring and diaphagm inside there.

good luck,

-Rob
 

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i can mentain 1.4 bar of boost with no knock at all , but i have the mods to support the high boost levels otherwise the engine would probably pop :D
 

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Yes Alan dont forget you run super high Octane fuel like 97 Ron.

Turbo cars love and need high octane fuels, this is what the APC is about, even with lower Octane fuels it gives you safe boost with protection.

You can say knock happens at such and such a PSI, like Alan said if you have adjusted everything and uprated the IC exhaust and APC then you have less chance of knock.
 

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Discussion Starter · #5 ·
Yeah I know that with big mods, big things can happen, but 11 psi is stock from what I know. From what I am experiencing I think that my timing may still not be quite right on (the timing marks are incredibly hard to read off the flywheel but it sounds and feels like it's timed properly) or the rise-rate is too high and my weakened wastegate can't support large psi anymore.
 

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I can see 1.1/1.2bar in my T8 without any knock at all :cheesy: :cheesy:


Paul

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Sleeper baby, no show & all GO.............................
 

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Knock depends on the octane rating of your fuel, timing, ignition retard during boost, intake temp. spark plugs and the amount of fuel your fuel system can support.

Fortunatley Saab did their research when they designed their engines and have pretty much come from the factory ready to support lots of boost.

Make sure you have a good distributor, plug wires/leads, spark plugs and I'd stick with the stock 16° of timing and plenty of fuel if you're boosting over 15psi.
 

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i would have to say that the last three weeks i have had the same troble as you i found out that i had a bad APC box. so you may want to change the apc box or try one that is a known working box. but the funny thing is my car seems to be able to boost with low octane and stay right around 14psi with the apc box i have in with no knock at all it has my friends woundering.

stephen denton
c900 notch back
 
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