M54b30 Turbo build questions (planning phase)

[zoomer40]

Hello Gents,

I am in the process of building an M52TU/M54 turbo engine and there are some question marks that I am yet to figure out so some input from the gurus here would be greatly appreciated.

The engine will be installed in a pre-facelift e30 coupe. Its my fun car and also I go to 5-6-7 trackdays per year so it will see some action on the track.
My target is somewhere on arround 500ish whp (probably more like 450ish) while having as smooth torque curve as possible.
My plan is to initially build the engine as NA, so that I can break it in with the stock ECU and probably drive it NA for the next season while collecting data and money to turbo it.

So far I am planning the build to be the following. Some of the parts I already have others I decided to use due to legal requirements in my country or financial reasons.

M52b25TU block (as far as I know its the same as the M54 still has iron sleeves and according to paperwork it is 170hp which will make it considerably easier to legalize it in my country and will help me pay considerably lower taxes and insuarance)
M54B30 rotating assembly
standard cranshaft
forged 135mm rods (I have those from my previous turbo build)
standard m54b30 pistons (I was contemplating on getting forged ones but they are beyond my budget and also since planning to drive the car NA for a while I dont want to lower the compression ratio)
I've sent the head for port and polish (should be ready mid December)
and I already have Schrick camshafts that are 250 degrees with 10mm lift
UUC Underdrive pulleys
Raceware head studs.

Here come 2 very important questions:

I really dont want to spend the 1000$ (when imported in my country it will reach 1000$) on ATI super damper. I am planning to buy brand new Corteco harmonic balancer and not planning to rev past 7k rpm (since I am going to use stock valve springs and retainers).
My question is how crucial is it to get the ATI Super Damper or I can get away with the Croteco damper.

Another thing is piston ring gaps: when aiming for high power there is more heat in the cylinder and the piston rings expand more, so having in mind the power goals should I just gap the rings as they are specified by the manual or gap them slightly more (I would like to avoid blowby) and if yes, should I increase the gap only for the compression rings or for the oil one as well.

Turbo setup:
I already have 3" exhaust and Mitsubishi Evo 6 intercooler, so I am planning to reuse those. (the IC fits perfectly in the E30 without showing outside).
My main question here is the choice of turbo.
What I am looking for is a turbo that should be able to spool up to roughly 1 bar at 4-4.5k rpm and still push enough ponies so that the car is fast.
So far I have 2 possible candidates: Garrett GTW3684R and Borg Warner s360SX-e. Precision turbos are quite hard to source in Europe so they are not much of an option.
Apart from the turbo, I would love to be able to have the turbo with bottom mount (probably impossible with the BW due to size). Most likely I will have the manifold custom made to fit the car.

I already have ECU Masters EMU that will control the engine once the turbo kit is installed.

Any advise and proposal is welcome.

[Vexatus]

Re rings gap, here's a lot explanation and a formula to calculate for your engine like mid of the page:
http://blog.wiseco.com/everything-yo...about-ring-gap

What is the issue with legalizing engine in Bulgaria? Do you need to re-legalize your car as it's a SWAP?

[zoomer40]

Thats nice article however I think their formula is not specific enough (also there is contradiction they say that the 2nd compression ring gap should be bigger but in their formula its smaller for turbo engines).
Regarding the legalization issue - here you cant just swap your engine with different, it needs to be checked that it is good to be driven on the road, and it is impossible to legalize a turbo conversion of any kind (this is why I would like to fit the turbo with bottom mount if possible so that it is not that obvious when you pop the hood).