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Talk about engine building here. New products, tricky questions or showcase your work - If it's engine building related it's welcome here.
what is the difference between a stroker engine and a de-stroked engine, if so which is better, especially for a drag/street build?
People often stroke to increase the displacement and compression ratio of the engine. You have to be careful of the resulting increase in maximum piston speed and the corresponding forces accelerating and decelerating the piston. Engines are destroked for for the opposite results. Lower piston speed may allow a higher maximum RPM resulting in more power at high RPMs -- compression ratio losses are compensated for with different piston dimensions.
As David said.
Sometimes de-stroking is done to meet engine capacity limits, or one may be able to use an engine block variation with a larger bore with the shorter stroke for a similar reason*.
Usually, though, the engine will be stroked for extra capacity, with the advantage that the components used are usually much better than the OEM stuff.
Some engines have a poor rod-stroke ratio, and a shorter stroke and longer rod can reduce side-loads on the bores, or the changed piston acc'ns work better with the engine's breathing characteristics.
*Back in the day, the small block Chev' engine was made in 8 different engine capacities, from 265 to 400CID. Seven of which used the same crank main bearing bore and the 400 could with the other's cranks with special "spacer" bearings, or the crank mains turned down for a long stroke crank in the others. With at least 5 different OEM bores, and at least 4 OEM crank strokes, one could mix and match for many different capacities. The 302, 327, and 350 all used a 4" bore but with different wrist pin heights to work with the 5.7" connecting rods all but the 400 used. This sort of thing also meant different rod lengths could be used with 'off the shelf' pistons.
If you are operating without any form of capacity limit, generally the bigger capacity the better. If you want to stay with you current block and can't bore it out any further, stroking is the only option left to increase capacity. Bigger capacity will lead generally increase to more torque over a greater RPM range.
If you have a capacity limit to work too, destroking a larger engine is an "easy" way of getting more optimal bore/stroke/rod length/maximum valve size for higher RPM/power.
For a road/drag car using a wide RPM range good torque over a wide range is probably more important. For a circuit racing car mostly operating within a very narrow RPM range, you only need good torque over a small window and the higher the better to take advantage of gearing. If you have ever driven a peaky race engine with a narrow power band, they are horrid on the road.
Stroking or destroking an engine is a complex thing that involves a few other issues to consider- required power level, RPM limit by mean piston speed, Rod to Stroke ratio, transmission type and gears ratio, turbo size (if force inducted)
I'll try to give you an example- Mitsubishi Evo 4g63 engine with 2L displacement and 88 mm crankshaft and manual transmission. It's a great engine capable of making tonns of power with right components and revving up to 9000+ RPM. But let's say I'm not reving the engine that high and need more power sooner than very high RPM range. I would then go for 94 mm crankshaft to increase engine displacement to 2.2 L (+10 percent potential additional power because of added displacement) by trading top RPM limit dictated by piston mean speed- now i wouldn't rev the engine much past 8300-8500 RPM but still getting up to 10 percent additional power sooner.
Next thing up is installing 100 mm crankshaft making engine displacement 2.3L. Another 5 percent of additional power on top of 2.2L engine but again there is no free cheese in the fridge- you will need to give up top RPM limit - I would not rev it more than 7700-7800 RPM. With 100 mm crankshaft and short rod combination your get huge increase in torque at low and mid rpm range and terable Rod to Stroke ratio wich lead to constant problem with breaking parts in manual transmission and excessive cylinder wall wear. That is why that combo is not popular. However, if you swap for automatic transmission - it's almost perfect. Automatic transmission usually isn't that effective comparing to manual so additional torque at low and mid rpm range compensats for that and torque converter absorbs all the shift switch hitting that reqular manual transmission cannot withstand...
Next thing up is using 4g64 engine block (which is 6 mm higher) with 100 mm crankshaft making it 2.4L. It's almost the same as 4g63 with 100 mm crankshaft but can have a better Rod to Stroke ratio if longer rod is used with conjunction to shorter piston. Still tonns of torque at low and mid rpm range but should not be reved very high. Still perfect match for automatic transmission wich doesn't like to be reved high either...
Next thing is 4g64 block with 88 mm crankshaft (from 4g63)- this is a classic destroker going from 2.4L to 2.1L but gaining incredible high top RPM limit of 9000+ ( since RPM is a part of making power equation) . It will give you the best power up top but will be very boring to drive at low and mid RPM range...
I hope it gives you an idea what the difference between stroker and destroker is and which one is better for a particular purpose...