Chris, do you have any objective data or seat-of-the-pants comparison between steel and carbon?
- Starting/idling issues
- RPM where gains begin
- Max power/torque gain
- Usable RPM range
- Life/durability
- Ability to conform to used housings
Thanks,
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In my experience...
Carbon don't start as well cold. They require a shot of ether in the morning. After that they're golden for the day. The carbon seals require a bit more clearance than a stock type seal and I'm guessing that's where the cold starting becomes an issue. They also don't run quite a spring pressure as a steel seal so there again cranking compression suffers. Idle is same as anything else.
I'm not so sure you're going to see an big gain in power over stock seals within the powerband of an IT engine. The gains will be near the power peak and above. The reason I like them is because they are much easier on the rotor housings. Iron seals start to skip across the housing north of 7k. After some miles you'll actually be able to see lines running perpendicularly across the surface of the housing where the seals are skipping. This a) causes a loss of power because of blow by, and
eventually ruins an otherwise good housing. So there is a possibility for a slight gain but it's in an area where the power has already peaked and is begining to fall off. Now if you're shifting passed the power peak (say 8500) to optimize average HP then the carbon seals will be an asset in longevity and provide a slight power bump.
Comparing a dyno chart that we have on one of our carbon sealed engines with a dyno chart supplied by a customer on a iron sealed engine we're showing about 4-6lb/ft advantage from 5k+. Though that, IMO, is within the realm of dyno calibration and any of a multitude of differences in the cars themself.
Carbon seals have spun over 10k. No issues with an IT engine. The word on the stock seals is 8500. I think that's optimistic. The Renesis spins to 9k but those seals are about half the height (half the weight...) of a Cosmo seal. There is also not an exhaust port for the Renesis seal to skip across.
There is a guy on nopistons who used to campaign a GT3 RX-7. He's reused his set of carbon seals in several engines. That said, I'm not that thrifty and would opt for new seals if I were building a new engine. The set that came out of my last IT engine when I tore it down after two years measured out at as-new height. I gave them to a friend and we put them in his j-bridge engine. The real deal plus is rotor housing life. Not only are the carbon seals easier on the surface in general they are one piece. The lack of the corner assist piece that likes to dig a groove around the circumference of the housing is a plus. Rotor housings, the real expensive part, should last longer.
Not really sure on their ability to conform with used housings. You really should up for new anyway.
So by your interpretation I can adjust my oil pressure to 78 PSI @ 3000 rpm like my FSM says I can--right? Mine is right on the money so yes, I think I am Legal. I never said anything about different pumps being legal--just pressure.
