B6 and BP are the same architecture. Both have the same strengths and weaknesses. BP has far superior head flow so the gains over the B6 are more than just the 15% difference in displacement. The older BP05 head beats the B6 head in flow vs displacement. The later BP4W and BP6D head more still.

The advice has been given here many times, and it is correct: The single best modification to your B6 is replacing it with a BP.

Even factoring in having to rebuild a used BP, it's better to run an OEM rebuild BP4W than a modified B6. 200whp easy on a bone stock BP05. 250whp towards the top of what most experienced tuners would recommend for a BP4W or BP6D. At the very least do better engine bearings, heavier valve springs and forged rods. Keep the revs below about 7300, street use only and you can get away with everything else being stock. If it is going to be a track car and driven by and advance driver, that long block is just the tip of the iceberg in terms of prep and expense.

Making 250whp in a BP is cheap and easy. I think many here could do it for under $800 if challenged. Making it stone reliable under extended hard use is neither cheap nor easy. Figure $10k minimum to do it right once drivetrain mods, cooling, brakes, etc are all factored in.

^That synopsis is worth many thousands of dollars and the OP just got it for free. I hope he doesn't squander it.

:likecat:

I did a rods only 1.6 turbo build and it is OK. Just ok. Not wow holy shit this is awesome but it gave the car some much needed power. Buy the 1.8 and turbo that. I bought a 99 parts car for just that reason. I wanted more power than I had but your money spent will be worth more in a 1.8. I'm going to do a build on the 99 engine I have to hopefully make around 300 wheel horsepower. Plus the torque in the lower RPMs will help. The 1.6 is pretty gutless and a turbo barely makes it worth while.

The consensus - and not merely on this particular forum - favors the 1.8. This has also been my approach. I bought a 1991, because it was nominally "rust free"... but the engine was ailing. The cunning plan was to find a 1.8, swap it in, and then pursue various avenues of additional fortitude. Unfortunately, prospects of finding a 1.8 have thus far been muted. These engines are in high demand, especially the 99-00 (last years before VVT). The upshot is that one might end up massaging the 1.6, not because that approach is somehow preferable, but because alternatives are logistically sparse.

And yes, for what it's worth, I am very much in the market for 1.8.

thank you everyone for the education. I ended up purchasing a 99 drivetrain assembly. engine, 6 speed trans, and 3.9 torsen diff with axles and driveshaft. I have the motor disassembled and working on taking it to the machine shop. end game is 250 to 300 whp. once the machine gets the motor back to me I will be able to determine which way I want to build this thing. I know I can hit 250 with stock internals, but if I want to hit that 300 whp ill have to build the bottom end.

https://www.miataturbo.net/miata-par...ontent-100447/

buy his kit. Its a good deal and proven