Best Option, RB24??, 25 0r 26

[Roy]

You say valvesprings in your experiance have you found them to be a weak link???

My experrience....no i havent played with near enough cars/engines to be saying my experience. But despite my engine still going strong at 185,000kms, there are things that i would be looking at replacing when doing any sort of overhaul work. Valvesprings being one of them.

Valvesprings lose tension, and can hurt performance when they age. I dont think its so much a matter of needing different/aftermarket valve springs, its more a matter of needing new fresher ones. Just think of the job of the valvespring, its a pretty tough old job in a pretty hot old environment. No metal component with that sort of cyclic duty is going to work optimally forever.

As for RB26 crank and rods, they arent that expensive as there isnt really a market for them, and not hard to get courtesy of all the people that have gone aftermarket 2.6/2.7/2.9/3.0L bottom ends, or blown pistons and just abough an import motor etc etc.

Whether that justifies the purchase or the sensibilites of it, its up to the guy with the chequebook i suppose

[Sydneykid]

Hi Joel, you posted "The RB30 has the supposively near perfect 1:1 rod to stroke ratio. 86mm bore x 85mm stroke"

That's not actually right, the rod to stroke ratio is the length of the rod (152 mm for an RB30) and the stroke is as you said (85 mm), So 152 / 85 which is 1.78.

Maybe what you are thinking of is the bore and stroke ratio, that's 86 / 85 = 1.01 or what we would call slighty over square.

Some people believe that rod length stroke ratio is very important in determining where an engine makes it's power. Since Smokey Yunick proposed it in the '60s, this has been somewhat controversial. There have been several back-to-back tests in various magazines over the last 20 years using a number of otherwise identical Small Block Chevies eg Hot Rod, Circle Track etc. A few tests showed that a 'short-rod' engine made slightly more power up top while the "long-rod" made more power (around >2%) down lower in the rev-range. What it breaks down to is, changing rod length will not likely make much difference in power unless you also optimize intake & exhaust length/dia. A long-rod motor also has a little less cylinder wall friction due to the 'better' thrust angle.

Hope that helps

[the phantom]

Hey Sydneykid,

Is your Rb31's ability to rev to 8500 due to the mysterious concept of 'overbalancing' you speak of

Apologies for meandering off topic, I cant resist... Sydneykid never quenched my curiosity... :wassup:

[Cubes]

Sydneykid,

Maybe what you are thinking of is the bore and stroke ratio, that's 86 / 85 = 1.01 or what we would call slighty over square.

Yep thats what I was talking about..