61.55mm stroke, can it handle 91mm pistons?

[Joe Goldberg]

I know that bigger pistons mean more compression but I am still thinking if it's possible... JUST PHYSICALLY... for the 61.5mm stroke handle 91mm pistons in the S2R 800 barrels? Is it gonna be peaky if this short-stroke big-bore engine succeeds or what? What do I need to do for tuning?

 

[SZA]

I know that bigger pistons mean more compression but I am still thinking if it's possible... JUST PHYSICALLY... for the 61.5mm stroke handle 91mm pistons in the S2R 800 barrels? Is it gonna be peaky if this short-stroke big-bore engine succeeds or what? What do I need to do for tuning?

Physically yes. You will have an oversquare engine tho. Less torque at low RPM and more power at high RPM, so unless you're planning on cruisin at top speed, why are you gonna do this?

 

[Tossie]

Uhm but have you considered the potential impact on valve clearance and compression ratio with those larger pistons? It might require some modifications to ensure everything runs smoothly without interference.

 

[TheMonster]

You've made some solid points. Physically, it can definitely work, but as mentioned, you'll end up with an oversquare setup, meaning more power at the high end but less low-end torque. Plus, you'll definitely want to keep an eye on valve clearance and compression.

I actually helped a friend fit some big pistons into an old DRZ once, and we spent weeks sorting out valve problems. It could really rip at high RPMs, but it was a bit of a slug under 4,000. Still, it was a fun project. Are you putting this together for track days or just for the challenge of it?

 

[n0tlike0therdrivers]

The best thing you can do is to have a proper ECU mapping along with checks on injector size and cam timing to match the new airflow, and don't forget to check the cooling and spark plug heat range.

Make sure to use a proven 90 mm or 91 mm kit designed for your heads and have the cylinders bored and plated to fit.