stephen thomas
Diamond
- Joined
- Jun 3, 2001
I'm trying to top a VW type 1 based 2276 av-conversion.
The exhaust valves are stainless, supposedly Manley.
According to the logs, the engine has less than 35 hrs on it, although it was "moteur neuf" in 2013. (could mean new, or could mean just "fresh") It is possible that the heads were re-used when the engine was removed for OH & re-barreled due to failed Nikasil cylinders; so # hrs on valves might be longer.
Anyway, 4 exhaust stems are barreled .0025" to .0035" under the center diameter, at each end of the travel.
The bronze guides are wallered some .020" to .035" at opposite ends over the center ID.
To replace the guides, there seem to be at least 3 options.
Scat sells "manganese" bronze. Other vendors sell "silicon" bronze.
Another very respected vendor sells "aluminum silicon bronze" as a performance up-grade, but for intakes only. When questioned why not for exhaust, the answer was that the performace derived from being shorter and better flow & also (implied) less friction, but that would limit durability in the exhaust app. It is unknown whether a full length guide in that material would wear better or worse than the other options.
This is a slow revving engine, 3600rpm tops, 3300 or so typical cruise. VW guides are simple.
Is there a preferred alloy for long term durability in the exhaust?
Is 64200 the alloy for aluminum silicon bronze guides, or something else?
How about the straight silicon bronze, vs manganese bronze performance and specific alloys?
Scat sells stainless "racing" valves with chromed stems.
Is there any reason not to use chromed stem valves?
It would seem that would be best with any bronze material, but then maybe the failure mode is not good?
Thanks!
smt
The exhaust valves are stainless, supposedly Manley.
According to the logs, the engine has less than 35 hrs on it, although it was "moteur neuf" in 2013. (could mean new, or could mean just "fresh") It is possible that the heads were re-used when the engine was removed for OH & re-barreled due to failed Nikasil cylinders; so # hrs on valves might be longer.
Anyway, 4 exhaust stems are barreled .0025" to .0035" under the center diameter, at each end of the travel.
The bronze guides are wallered some .020" to .035" at opposite ends over the center ID.
To replace the guides, there seem to be at least 3 options.
Scat sells "manganese" bronze. Other vendors sell "silicon" bronze.
Another very respected vendor sells "aluminum silicon bronze" as a performance up-grade, but for intakes only. When questioned why not for exhaust, the answer was that the performace derived from being shorter and better flow & also (implied) less friction, but that would limit durability in the exhaust app. It is unknown whether a full length guide in that material would wear better or worse than the other options.
This is a slow revving engine, 3600rpm tops, 3300 or so typical cruise. VW guides are simple.
Is there a preferred alloy for long term durability in the exhaust?
Is 64200 the alloy for aluminum silicon bronze guides, or something else?
How about the straight silicon bronze, vs manganese bronze performance and specific alloys?
Scat sells stainless "racing" valves with chromed stems.
Is there any reason not to use chromed stem valves?
It would seem that would be best with any bronze material, but then maybe the failure mode is not good?
Thanks!
smt