but if one wanted to get more torque... wouldnt you have to get a bigger crank if u can? i noticed with Mazda, not trying to diss them, their older motors seems to be more workable than the FSDE... maybe because the FSDE wasnt meant to be an all out race motor unlike the KL and the Rotaries could be...
for a mid-range torque power gain, the lighter pistons and stronger rod would be really still be effective, right? and would monster cams still be drivable in the street? what makes it a monster cam? just bigger lobes? just trying to gather my information before going to a shop... what material would you suggest for the Pistons?
ok for starters, the KL isn't meant to be an all out race motors.... hell toyota's 2JZ isn't meant to be a race motor. Some engines are more adaptable than others - designed for higher end street performance/sports car applications. The KLZE, and BPT etc fall into these brackets, but they are not without their own problems.
The FSDE is more or less an economy engine - why they slapped it into the P5 when they could have used the FE-DOHC (which is a far better 2L engine, probably the best 2L 4cyl engine mazda ever developed) we will never know.
Now torque....why is everyone so hung up on masses of low end/mid range torque? the FASTEST circuit cars in the world are high RPM, top end power monsters. if you do the maths, you will find that the LATER your torque curve occurs (that is, the less "low end" you've got in relation to top end), the faster you will accelerate, due to gearing.
To boot, engine torque is only a small part of the equation - gearing is what matters. Higher RPM = better gearing advantage for any given gear. Also the thing that makes your wheels spin is ROAD FORCE - that is engine torque multiplied by total gearing. Without touching the engine, you can increase the amount of effective force at the wheels by simply changing the rotating diameter of your wheels (with smaller rims, and smaller tires).
NA builds on small capacity atmo 4 bangers is always ALWAYS going to be a question of compromise. they do not build masses of torque like large 6 cyl and 8 cyl engines, so all you can really do is make them spin faster, build more top end power, and use the gearbox for what it was designed to do.
Going to a bigger stroke will SLIGHTLY increase the pumping capacity of the engine (nowhere near like what increasing bore will do), but the trade off is going to be a lack of RPM to take full advantage of it. The best performance motors in the world are either "square" (that is, bore and stroke are equal), or "over square" (that is, bore exceeds stroke). Our motors are badly "under square", and stroking the engine further is only going to make matters worse. Your already sh!t rod ratio becomes even more sh!t, your piston speeds and piston acceleration goes through the roof, and you'd be lucky to spin the thing to stock redline let alone anything further.
Sure, a bigger stroke will mean you'll be able to ingest more fuel and air at lower RPM when compared to the stock stroke, but you'll brick wall at around 6000 to 6500 rpm because the rods just wont be able to take the abuse. Now, for a turbo build where 6500rpm is probably all you are going to need, a stroker kit would probably be something to consider - personally I still wouldn't do it, but its at least a legitimate mod on a FSDE that is boosted. For NA, stay well away.
It is totally false to think that a high revving, top end heavy NA motor will not have "lots" of torque - torque and power are related. Relative to power, the torque may not be as high, and the point in the rev range where the torque "comes on" might be higher - but because power and torque are related, you'll still make it.....and you'll make it in a more useful rev range for almost any form of motorsport you can imagine. Sure it might not be so nice for quiet sunday drives, or trips to pick up the shopping, but lets be honest - if you are out to build an Atmo rocket, its not going to be something you drive your mother/wife/sister to the shops in, is it?
Rods, and high comp pistons are still highly recommended for any "serious" NA build, regardless of where you are going with it - Rods because the additional strength, plus the extra rod length means you can get more revs out of the engine if you want to (as long as you meet all the other criteria i posted previously), and pistons because you can push your compression up - which in turn means you can run bigger cams with more overlap, with little or no ill effect.
What makes "monster" cams? well....a few things. Its not just "bigger lobes"...there are 4 things that come to mind:
1) Lift - how much the cam lobes physically open the valves
2) Duration - how many degrees the valves stay open
3) Ramp Rate - how fast the cams open and shut the valves
4) Overlap - how many degrees both the intake and exhaust valves are open simultaniously
Overlap plays a part in dynamic compression (which is why higher compression pistons allow for more overlap - the additional "loss" in compression due to overlap is counteracted by the fact that you are producing more compression to begin with).
Cams are essentially the "brains" of an engine. They control when, and by how much, the valves open. Playing with cams can have massive effects on drivability. Big monster cams sound cool, but can lead to a rough ride at low speed where the engine is essentially running in a state outside of where the cams are useful.