95RON is pretty much piss water. I'd aim for 8.5 or so.

8.0 might be overkill, though for small turbos you won't lose too much spool or off boost torque.

YMMV, its a debatable topic.

I've had good luck with gaskets on the 2.7t (throttlebody placement movement notwithstanding) but no experience with 1.8t motors.

Do you mean it wont squish properly around the water jackets etc because it's too thick? I think I'm going to go for that set of BAM Pistons, I was just a bit worried because the 3rd one down looked a little shabby with a couple of light scratches here and there, I'm hoping they will clean up and be good to go. Worst case scenario I just buy a single 1 for a little extra. I'd much rather go 9.0:1 with a proper set of the BAM pistons rather than experiment with a thicker head gasket. I just figured here is a good place to ask before I buy anything, as I know this forum is full of BT builders that daily these cars and I value your opinions.

I'd also have the option to try the HG or an inbetween OEM and the 2.5mm thickness in the future if I wanted more like 8.5:1 etc

I actually run 10.3 on my converted engine still, but its nothing crazy like you are planning to do, only 0.5bar on t04e. on 95 sometimes 98 ron(european/russian gas). Still got aight timing , ofcourse lambda is decently rich. AEB head with VVT too. Daily for 2 years now.. but changes are coming.

Obviously if you could you'd wanna keep the highest CR you can but if you dont have access to good gas(with wallet ofcourse too) or toulene maybe, then yeah I'd forget and just go for boost/timing with lower CR. oh and get VVT if you dont have it already.

Once I'll start pushing higher levels I am contemplating on what do too, because I might wanna bore the engine to 82.5 because I have a set of pistons made for 20v with 82.5mm with high CR. But I have access to toulene too thats that. Future plans anyways we'll see.

Also I do not think you'd have any issues with squish with lowering plate, the 1.8T headbolts are pretty much gold until like big power territory, so they must have some decent clamping force. VR5T/VR6T run decompression plates without issues AFAIK.


Also a warning SPA shipping is a lot to europe afaik. I believe on ebay you can find thicker decompression HG's for 1.8T's when I checked few years back. Also BAM is a small port head.

My focus was on squish band
https://upload.wikimedia.org/wikipedia/commons/thumb/8/8f/Squish_band.svg/1200px-Squish_band.svg.png

But on 5V engine there is not much squish area, sii I think it wont effect too much on that.

BAM have same CR as any other 1.8T acording to ETKA, so piston crown schould be same? Or I am wrong

The big port head is simply better for your turbo, if you want one get from ADR(early version, will require 1 cam change atleast), AEB, AGU or AJL(AUQ is small port too yes). Prj said in the past that the big port head is a better design which definitely goes against the grain, tho havent seen concrete comparsion between small and big  I tend to agree, the runners look better into the combustion chamber., also the latest ever 20V head had the big port design too(i think even enlarged, havent measured) wasnt on a 1.8 though I think the velocity loss talk came from the fact that most people who put the big port heads havent added vvt lol, since all of them came without VVT, so the loss would be visible vs a small port head with vvt on the cars that have it enabled, or something along those lines I guess.


You are wrong yes, the BAM runs 8.9(~9) CR, the pistons have bigger combustion chamber diameter and lower depth too.

I chose a similar solution in my 2.7 AGB with K04 RS6 Hybrids. It has Mahle pistons with 9.0:1 compression(stock was 9.3), +0.5mm in diameter + 034 Motorsport headgaskets with 0.5 CR drop. Heads(2.8l big port) were already shaved 3 times, so i assume im somewhere around 8.6-8,7CR. I already put 40k km on this setup and it works great.
Moreover, BAM is small port, but it has VVT.