Tahiti350
08-31-2005, 09:44 AM
I am running a 350 Chevy/OMC 800 combo, 3 years ago turned a best pass of 5200-5300 rpm, 21+ SS tri-blade, minimal fuel, near glass surface, and no passengers. Translates to about 67 mph, which it felt like. Since then the peak RPM has fallen off considerably, to the point that I can only get 4400 rpm with the same conditions. I hope to GPS it this weekend, to confirm the correction for prop slip.
Changes to the original combo are: removed Torquer installed Performer RPM, bypassed thru drive exhaust with 3-1/2" pipes off the risers, and new plugs. Normal tune up items have also been replaced. Compression is good, need to re-run and get this seasons numbers, but they have been consistant in the past, with minimal cylinder to cylinder variance.
Current combo is: 350 4 bolt block, flat top 4 valve relief pistons (standard bore), stock 882 heads, steel shim head gaskets, Edelbrock Performer RPM, HEI w/coil upgrade, Osco cast iron risers w/3-1/2" O/T pipes. Drive is OMC 800 1.36:1 gears, 14-1/2 X 21+ SS tri-blade prop, Timing is: 15* initial, 32-33* @ 3000, no vacumn advance. I run PVC for normal cruising (I know they are pretty much useless at WOT).
I'm thinking the valve springs have gone south. I don't relieve them during the off season, and the boat sat for about 1 1/2 years with just an occasional start-up. I am considering upgrading the cam from around a 268 profile to a 282 profile, and upgrading the springs accordingly. I also have a set of Bassett bell end Stahl pattern headers to install (weight and flow improvements) but still need the Stahl pattern adapters.
Am I on the right track here, or should I be looking at something else for my RPM loss?
Changes to the original combo are: removed Torquer installed Performer RPM, bypassed thru drive exhaust with 3-1/2" pipes off the risers, and new plugs. Normal tune up items have also been replaced. Compression is good, need to re-run and get this seasons numbers, but they have been consistant in the past, with minimal cylinder to cylinder variance.
Current combo is: 350 4 bolt block, flat top 4 valve relief pistons (standard bore), stock 882 heads, steel shim head gaskets, Edelbrock Performer RPM, HEI w/coil upgrade, Osco cast iron risers w/3-1/2" O/T pipes. Drive is OMC 800 1.36:1 gears, 14-1/2 X 21+ SS tri-blade prop, Timing is: 15* initial, 32-33* @ 3000, no vacumn advance. I run PVC for normal cruising (I know they are pretty much useless at WOT).
I'm thinking the valve springs have gone south. I don't relieve them during the off season, and the boat sat for about 1 1/2 years with just an occasional start-up. I am considering upgrading the cam from around a 268 profile to a 282 profile, and upgrading the springs accordingly. I also have a set of Bassett bell end Stahl pattern headers to install (weight and flow improvements) but still need the Stahl pattern adapters.
Am I on the right track here, or should I be looking at something else for my RPM loss?