forged or cast?

[bengalcharlie]

hi

I am looking at some pistons for my Stromberg big valve engine rebuild. head is 4 3/4 inch thick.
have piper bp270 cams ( fast road) and thinking of fitting a light (fidanza??) flywheel. Otherwise stock engine
Anyway had the block measured and it needs a re-bore and consequently I need new pistons.
Looked at a few of the usual outlets in the UK and the US but it seems everybody is selling forged pistons these days??? according to my limited knowledge forged pistons do require more clearance so increased changes of pistons slap??They need more time to heat up hence the reason they are used in race engines but cast pistons are better for road going applications??.
Therefore I tend to look for cast pistons but where can I find 2nd overseize cast piston? And am I right that for the slight improvements I will make to my engine cast pistons are the right choice?
cheers Robin

[StressCraxx]

Forged pistons have come a very long way. The alloys have improved, heat treatment is better, less thermal growth and much improved design. I have used both the old Hepolite pressure cast (the ring lands really take a beating from the revs) and the CP forged pistons. I run the same clearances with both. I can not hear any sign of piston slap when cold with the newer forged pistons.

http://www.cp-carrillo.com/Tech/PistonTech/tabid/74/Default.aspx

I also used the CP forged pistons in my Formula Ford (same rotating assembly as a twink, but longer stroke and higher deck. The rod angles are worse than the twink, but the pistons lasted more than 60 hours of racing with no discernible wear in the ring lands, only some scuffing on the skirts. I could have reused them if the crank hadn't broke in 4 places!

I think you would be very pleased with the workmanship and performance of a modern set of forged pistons.

Regards,
Dan

[rgh0]

I don't think you should have any problems with piston slap with forged pistons if you install them with the specified clearance for a road engine. Competition engines tend to be built with wider piston to bore clearances to allow for greater piston expansion under continuous full load racing conditions but even then I don't have any issues with piston slap when cold.

New forged pistons are certainly very durable and they typically use modern lightweight ( i.e. thin) piston ring designs and this leads to much less piston ring land wear and also better combustion pressure sealing.

cheers
Rohan

[bengalcharlie]

Thanks Dan and Rohan for your replies. I have heard similar re-assurances from the engine reconditioning place and the various lotus suppliers, but before I jump in, I like the opinions of the people here on the elan net.
Another example technology has caught up with me! still looking for that smartphone!
cheers robin