You will make more torque throughout the rev range with 8.5:1 than with 9.25:1. What you say holds true at around the 7.0:1 mark, as you go lower. Not at 9+.
Load of complete rubbish. You will never reach the same figures unless you use a fuel on which the engine never knocks. Which you are not doing.

Well, why don't you go 20:1 compression ratio then? It doesn't work like that, plain and simple, because fuel has something called an "octane rating".

A 1.8T 20V with 8.0:1 will outspool, outpower and outtorque the same engine with anything higher on pump gas, any time you go near WOT. Whether on boost or off boost.
A 8.0:1 engine will make 70-80 more horsepower and up to 100nm more torque compared to your 9.2 engine with that turbo. And it will be more responsive in the entire rev range. Furthermore, because you are able to utilize fuel more efficiently at WOT (10+ degrees more spark advance without encountering knock), you will have lower EGT's and less waste heat.
The only thing that will suffer is fuel economy on light load cruise, that's it.

As a background - there is a "break-even" compression ratio for every engine with every fuel, where you start noticeably losing torque down low and the engine becomes an "on-off" switch. But for this to occur you must be able to run non-knock limited MBT any time you are off boost.
This does not happen even at 8.0:1 CR on the 1.8T 20V with pump gas. Anyone who has *any* experience tuning these engines on a steady state dyno can confirm this.

It seems a pretty popular myth with the 1.8T crowd...
I had a couple clients with 1.8T's who were saying exactly the same thing as the OP, and had bought high compression ratio pistons. Oddly enough I have never had any issues with 2.7TT and audi I5 people, they seem to understand compression ratio a lot better and don't try to buy stupid high CR pistons.
I always ask first what fuel people are going to run, because if they are running E85 then the higher CR can be beneficial, as E85 has very good knock resistance.

But people getting high CR on coke bottle sized engines, which they are going to try to boost to 30 psi on pump gas is just a badly made decision.

I very much agree with you. Just because people repeat the same mistake over and over again, it does not make it right.

So I'll ask a question since compression ratio has come up. (Sorry to the op for being ot). On a turbo charged car (I can't imagine that size makes that much of a difference 1.8 vs 2.7?), what compression ratio do you advocate? I see you mention 8.5, and then go on to say 8.0. This question is for a daily, not a track car, running 93 or E85. Thanks, and apologies again, I just find this topic fascinating, especially since it seems most 1.8t forums have a lot of misinformation.

P.S.- Happy Holidays

The OP is looking to reduce by .25 of a cR from standard anyway on an increased capacity build. I have seen many BT builds running all kinds of management on this CR with no issues at all. We have decent fuel over here in the UK. As i understand it, the standard fuel in the US is effectively below what our "normal" fuel is. This seems to be where the confusion comes from. I am perfectly happy with my 1985cc stroker on an 058 block with CR 9.25-1. No problems with knock on my CR of 9.25-1 and it's tuned with ME7.5 with standard sensitivity of knock sensing ATM. I have more to come when I build my head.

What cr do you suggest? I assume the same as ddillenger for a street car.

No, it's not that simple. Put it on a dyno, and you will know.
But from my experience if you go WOT on a GT35R at 3000 RPM on a dyno, where absolutely nothing happens boost wise then at the resulting load site then your MBT is still knock limited even at 8.0:1.

What turbo are you planning to run? There is no "magic number"...
It depends quite a bit on a plethora of factors, such as fuel, the engine in question and so on.
Greatly simplified (would need some corrections to be 100% correct) - dropping compression ratio will result in more power and torque everywhere, where you were knock limited before, and less power and torque everywhere, where you weren't.
To prevent the car from being sluggish down low, you have to stop dropping CR when you are no longer knock limited off boost, and that's pretty much it.
The only time your car will feel sluggish with lowered CR is if you are flooring it, there is no boost yet, and you are not knock limited anymore. But to reach that, you have to go rather low on pump gas.

No, it's not. RON and AKI are directly comparable with a conversion factor applied.
So next thing you want to tell me that laws of physics do not apply in the UK? Or that your 1.8 lump is somehow special because it is in UK?

Just out of curiosity, how many engines have you mapped on a dyno?
How many of those engines made more than 300hp/liter?

How about you counter any of the physical facts stated instead of just vaguely going on about "that works and that doesn't" ?

correct on the fuel, thanks for that.

It's not special, It's a built engine running 9.25CR without problems and without it self destructing

What physical facts, all i have seen here is you stating it won't work, when others here have plainly seen different.

I have personally tuned none, I have however been present when many engines have been tuned, including low and high CR engines. Viewing the logs and interpreting the information I have not seen what you speak of in real life.

Explain to me how a larger capacity engine with higher CR will possibly have poorer spool and off boost performance?

The engine will surely breath easier and make power easier off boost, then the increased air flow through the engine will surely drive the turbine to spool the turbo faster?

Explain?