How important are forged rods and pistons?

[rustymav1974]

I'm on alot of mustand forums and such where 5.0's are kings some of those guys are running cast internals with 100 shots of n20 or blown in some other way and they don't seem to have problems that often. Are they doing something special to avoid doing damage to their engines? If they are will the same techniques work on our inlines? Is there any amount of boost that would be safe to run on a stock 74 block 200?

 

[Anlushac11]

Normally aspirated not that big a deal. Cast works fine below 5500-6000rpm.

Turbo or nitrous, big deal. Must have over 6,000rpm.

If you can build every aspect of your engine and control every variable to absolutely prevent detonation or pinging, sudden lean out, etc. then you can run cast iron rods and cast aluminum pistons.

However we dont live in a perfect world and such variables do exist.

Forged pistons can be killed by bad conditions in a engine as well. but forged pistons are much more forgiving and give you a extra safety margin when running nitrous or turbo. With cast pistons they are not likely to survive a mistake or problem that might pop up.

For everyday driver and mild performance cast rods are fine. IMHO I would avoid the cast iron rods at all cost. Ford factory 170/200 Forged rods last I knew were easy to find on Ebay.

 

[80Stang]

If the question is to be evaluted thru mean piston speed, then we end up with these figures for the 200cid six:

considering "safe" mean piston speed for cast iron internals ("stock") 3500 feet per minute, for 200's 3.126" stroke, would be 6717rpm.

considering "safe" mean piston speed for all forged internals 4000 feet per minute, for 200's 3.126" stroke, would be 7677rpm.

With mixed conditions, figure out something between 3500-4000 fpm.

Since we don't have forged crankshafts, main bearing caps and pistons very readily available we have to live with that 6700rpm in our minds. The calculation formulas do not take rod-ratio as a factor, which in our sixes is bad, and thus I would tend to lower the "safe" RPM.

If we consider 6700rpm a limit there seem not to be very many 200's around with power peak anywhere near that rpm. More engines need be built and results evaluated.

All power adders are a tale of their own, and forged stuff will do good in all those buildups.

 

[rbohm]

8) most of the time forged internals are not needed, even with boosted engines. there are limits though, piston speed, boost pressure, air/fuel mixtures all need to be with in the performance envelope of what ever piston and rod you are using to avoid problems.

for instance, lets say you are running 8.5:1 compression and you have a turbo that you are limiting to 10psi boost pressure, and you are limiting your engine rpms to a maximum of 6000 rpm with a proper rev limiter. as long as your air/fuel ratio keeps you out of detonation, cast pistons and rods will do just fine. however, exceed 6000 rpm for too long, or run lean too long, and the engine will tear itself apart. forged internals will increase the life of the engine under less than optimal circumstances.