NefMoto

I just want some opinions really. I have a stock setup with a pretty aggressive tune in terms of boost. I wondered at what point higher boost actually stops you adding timing so is limiting your power.

High boost with stock IC = Higher IAT and tendency for knock retardation
Moderate boost = lower IAT so timing can be advanced instead to gain the same power?

I have really limited roads locally to run multiple logs without upsetting the law so I'm curious if anyone has some empirical testing around this?

For crappy gas (91 oct here in CA), boost-- + timing++ by a longshot.

Then again, maybe a better benchmark would be to find the *worst* "reasonable" timing, and aim for that? say minimum 5 degrees at torque peak, 15 deg at redline?

Opinions?

Certainly, after some point, adding boost gets you less HP than the HP you lose from retard.

It is not that clear cut and might depends on other factors like how your car responds to timing and knock, cooling of the charge, meth or no moth etc...

The fact is that you should always aim at most charge in the efficiency band where you don't slow your exhaust gas just to get couple of PSIs more but all you get is hotter air at the expense of improperly vented cylinders.

what I found is that FATS running 20 psi with max timing I can get was 0.1 -0.2s behind running max PSI (22.5-23PSI) and max timing I could afford.

So yes, boost is the king unless your timing REALLY sucks. With 22psi at 7k I still time ~18-20degrees with meth so I guess that's the perfect combo.

Certainly for K04s, I think people are running a bit far off the edge of the compressor map's ideal efficiency area...

Just a plug for ECUxPlot, which plots PR vs flow :) which you can compare against your compressor map.

In my experience, there is a point where turning up the boost makes more torque but no more power.  My rule of thumb is if you're adding boost, gaining torque, but not making more power, it's probably a good idea to turn the boost back down.

Err. HP is tq * rpm

How can you make more tq but not more hp? :)

And don't say peak tq. When tuning, you should be tuning at all operating points.

Thanks people.

This is, I think where my interest should focus. I've a stock 1.8t with K03-52 which I suspect is having it's neck wrung to get headline BHP which is way outside the useful band and right off the edge of the compressor map.

So, would a good approach be to tailor boost to keep the compressor within it's optimum envelope, then optimize timing? I realise this might be somewhat iterative.

Cheers!

Any engine needs a minimum Advance timing to produce power and rev at high RPM.
This minimum timing it depends on the piston size basicly and then it is being limited by the CR or dynamic compression!

So boost the engine until you keep at least this "border adv timing". Then you can fuel extras or water-meth to give some degrees more timing.
But in some engines it is better to work a little bit higher than this boarder timing so you need to cut the boost

I definitely am saying peak torque.  I guess I should have explained myself better by including turbo sizing....

It's possible to increment the boost on K03 and K04 cars past a point where you increase peak torque, but have no increase in peak power, because the turbos can't keep up in the upper rev range...  Julex kind of touched on that.

Some people argue this is "fastest" - and that sudden rush of torque due to the obscene boost spike helps...  Yeah, okay, I will never argue that more torque under the curve is bad... however...

Usually this scenario lands you way off the efficiency island and is hard on the turbo(s).  And if you have poor quality fuel, I don't necessarily think it's a good idea to initially overboost in the rev range the engine is most likely to ping in either.  However, if you consider the turbo a consumable item, by all means, turn up the boost.

While there are lots of pros/cons to various turbo sizing schemes, if you want to make gonzo power with these cars, you have to make it with high RPM and lots of boost.  That requires a much bigger turbo as you know. 

As hammersword mentioned there's actually minimum advance required to spin the engine high, and essentially high boost high RPM engines just pour the timing back in over 6k.  Much less propensity for detonation in the high rev range based on ignition advance - it is more sensitive to lambda at this point.  You'll actually blow the spark out if you don't have enough timing advance.

A friend of mine has a 1.8 that is a great example of this - He hit a wall at 775whp @ 8700rpm and 37 PSI where it was just blowing out the spark when he added boost... once he started adding a degree or two of timing with the boost, the flame stayed lit and he hit 820whp @ 8700rpm - 41 PSI.  It seems counter-intuitive, but there is a point where more boost requires more timing. :)

This seems to reflect my own experience. I guess I need to spend some more time logging to keep my next turbo in a more desirable effficiency range. After I've replaced the one that's dying that is.