gosh ahhh I going to like explaining this one
:
1.6 B6T - Came in the 86-89 BFMR(4WD) or BFMP(FWD) 323/Familia. the 86-87 B660 first model came with 145HP with low impedence injectors, a smaller IHI VJ6 (7psi stock) turbo, a larger intake manifold, and a weaker fifth gear in the box. The 88-89 B677 facelift model came with 270cc high impedence injectors, a smaller intake manifold, larger IHI-VJ13(9psi stock) turbo, more efficient exhaust manifold giving out 165HP. Only the GT-Ae rally model came with a bigger IHI-VJ17 and the Infinity model came LSD.
Now both engines internally are the same, but what's nice about the B6T is the stiffened block, oil cooled 7.6 pistons, water cooled oil cooler and most importantly BEEFY connecting rods. This engine will pull a BF 323/ Ford laser nicely, but put it in a heavier BJ or BH and it will suffer. Oh another point to consider, its hard to upgrade, you cannot run any sort of fuel management on the stock airflow because it reads 5V to 0V not the other way around. If you want to seriously modify this engine I suggest an aftermarket ECU if you can find it or go full management like a Microtech LT8.
1.8 BPT, came in the BP26 90-94 BG GTX runs 185HP, comes with a bigger IHI-VJ20 turbo (9psi) and only comes 4WD. if you want it to work FWD you have to mate it to various 323 gearboxes any B series will work, as well as BJ ZL-ZM. It also comes with oil cooled pistons, a water cooled oil cooler, but with an additional aluminium sump. The difference is the GTX model BPT has weak NA connecting rods which will break after 300HP. the injectors are 310cc high. It will pull a BH or BJ easily and also is an easier fit. The BPT responds to upgrades like Apexi SAFC, Greddy E-manage. I have the wiring somewhere here...hmm...
Now the ultimate is to get your hands on the 210HP BPD GT-R spec engine, but its gold. This engine comes with a massive IHI-VJ23 turbo sadly running 7psi stock you have to "wake it up" LOL it comes with a better 8.2 cast pistons, more efficient intake and exhaust manifolds, 330cc low injectors, sodium filled valves, some neat mild cams and serpentine belts all round. oh and the rods are BEEFY like B6T. hmm you can take B6T rods and put them in GTX BPT that's the solve right there.
OK one major problem with the two engines, keyway failure, this means, the key in the crank pulley breaks with added torque so the crankshaft is spinning but your pulley is not. the solve for this is to take the crank from either a B6-DE or BP-ZE from a 95 323F BH and put it in, these cranks have no key to break. (mazda solve the prob)
Soooo.....here is the summary, the B6T is more reliable but harder to modify, the BPT is weaker but it can be modified easily but you have to go inside.
Hope I have helped a little. Oh if you want a B6T i can get one now , PM me nah.
