What causes power to pick up when piston to cylinder wall clearances are increased? I hear many Cup and drag teams run 9-11 thousandths - on the verge of breaking skirts? It is counter-intuitive because one would think piston rock would actually increase friction and compromise ring seal.

Also, does anyone know about thermal droop and why the ring lands should droop down instead of getting pulled up by the tensile forces at TDC? As I undrstand it, tensile forces at TDC are larger than any other force the components of an NA engine see.

 

I'll take a stab in the dark at the first part of your question. Keep in mind, I'm no expert here, so I could be way off base. My idea would be that by keeping piston to wall clearances on the larger side you actually reduce frictional losses. The lower the frictional losses the more HP are theoretically achieveable. Now that being said, running .009"-.011" clearance might be right on the verge of piston rock, as you called it. But it still may be enough to keep the piston "upright" provided the rod/stroke ratio is maintained.

As far as thermal droop, you've got me on that one man, but I'm keeping this topic at the top, as I'd love to know the answer too


Clayton

 

 

Keep in mind that the pistons in cup cars and big drag engines are going to "swell" more than the typical engine. I was curious about this also...search the web for "thermal expansion."

 

bump

 

 

I agree with Clayton. One thing, this increase hp comes at a price: longevity.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Clayton &raquo;</TD></TR><TR><TD CLASS="quote">I'll take a stab in the dark at the first part of your question. Keep in mind, I'm no expert here, so I could be way off base. My idea would be that by keeping piston to wall clearances on the larger side you actually reduce frictional losses. The lower the frictional losses the more HP are theoretically achieveable. Now that being said, running .009"-.011" clearance might be right on the verge of piston rock, as you called it. But it still may be enough to keep the piston "upright" provided the rod/stroke ratio is maintained.

As far as thermal droop, you've got me on that one man, but I'm keeping this topic at the top, as I'd love to know the answer too


Clayton</TD></TR></TABLE>

wouldn't that clearance be too much?? but then again, when i was researching on this topic, it was for a street car