Increasing bore and stroke

[xlosinghopex]

What exactly are the pros and cons of increasing bore and increasing stroke? From what I have read increasing the stroke will lower top end HP but heighten tow end torque. I've also read that a longer stroke makes and engine less efficient and reliable. Seems to be more of a domestic approach and not in my plans but maybe there's other factors I missed so that's why I'm asking. As for the bore how will an increase affect how the engine produces power? I remember seeing on some car show the guy said not to go over like 84 or so mm when using gasoline because the flame speed isn't fast enough to go further or something like that, maybe it was just for that specific engine because some engine have 100mm bores. Also would the effects be different depending on whether you're running NA or FI?

[Bronco2]

Generally speaking,longer stroke means more bottom end torque.Boring an engine will increase the piston size but only by a few CC. or CI.Example is .30 over on a 350 Chev. gives you 355 C.I. Stroking an engine will also increase the displacement,but balance becomes critical.The more weight and inertia {remember the piston/connecting rod has to change dirrection} limits the engine speed.I hope this helps,if you can imagine all those pieces turning at 7+

[xlosinghopex]

But how does the increased bore affect performance? Does it do top, bottom, or full power band increases? Any effect on engine speed or reliablity? Any info you can think of will be useful. I'm considering increasing the bore, especially if I go with iron sleeves but I need to know exactly how it will affect my eninge. Obviosuly there must be some downside to it or all enines would have over 100mm bores.

[whtteg]

I don't think 100mm bore is possible in a honda motor. You are limited by the distance between the cylinder walls.The larger the bore the closer the cylinder wallls get to each other, and the space between them gets thinner, and weaker, so there is a limit to how far you can go. The power increase comes from the extra displacement, lets say you have a B18B1 and you bore it to 84mm then you will end up with the same displacment as a B20.
As far as stroking the motor this can have down sides , having a longer stroke will throw off your r/s ratio and cause the piston to push on one side of the cylinder wall more, this increases wear and also lowers the rpm levels that you had before.

[xlosinghopex]

So increased bore has no performance downside? The only bad thing is that the walls will be weaker? The redline will remain the same, and the entire power range will be increased?

[whtteg]

Yes in a nutshell you have the correct idea. But the max you can go is 84mm on a b series block without resleeving it. Don't forget that you also have to buy new pistons and rings and the machine shop work won't be cheap either, it is not as cheap as most may think.