Reply With QuoteValve springs would do it. I bought some new 781 heads off Ebay with the story of fresh valve job, springs and so on. Springs ended up being weak. Only gained about 150 RPMs after changed. Weak springs it would back fire once in a while at WOT.
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?
Valve springs would do it. I bought some new 781 heads off Ebay with the story of fresh valve job, springs and so on. Springs ended up being weak. Only gained about 150 RPMs after changed. Weak springs it would back fire once in a while at WOT.
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?
Have the dist. checked or just replace it it worked for me.
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.
Worst thing you can do, check the springs!.. If I let mine sit for a week I back them off!..
Worst thing you can do, check the springs!.. If I let mine sit for a week I back them off!..
Yep!! If you don't back them off at least turn the motor over every couple of days.
Thanks guys,
I figured that was it. Had a Plymouth back in my circle track days that had weak springs, did the same thing, kept dropping max rpm. Never really missed, just kind of rolled over and quit pulling, same as the boat is doing now, although I was fighting a miss and occasional backfire when the secondaries tipped in. I am hoping to upgrade to Vortec heads, along with a cam change in Jan/Feb, If I can put the money back.
Yep!! If you don't back them off at least turn the motor over every couple of days.
Yeah that helps but no matter what position, there's always some that are fully compressed and for what "good" springs cost and how much time it takes to run the valves, fk it I just back them off!, LOL..
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