Lost RPM
 

At the start of season running 5200-5300 rpm. I have not run wot until recently now 4400-4600 wot. Engine is supercharged 502 6lbs boost. Runs good at idle,runs good at 4400-4600 no misfire. Timing ok,compression check ok leakdown check ok. Pulled valve covers off no broken springs have not checked seat pressure.
Any input as to other things to check. Engine has 150 hours.

Prop, dirty hull, weight, air temp, humidity. Wher the heck is Hiram? Do you boat in Lake Erie?

Has anyone experienced lifter problems? such as they are not noisey,but when I push on the pushrod by hand the center of the lifter sinks down .125-.150 within 15 minutes after running.

ttt

Im having the same problem. I have a 1995 38 Scarab with twin 502's and 3psi pro-chargers. It would hit 4800-5000 rpm wot. I just had both pro-chargers rebuilt because one came apart. Changed fuel filters and oil. Now Im only getting 4200-4400 wot. Thoughts I had super charger problem. Good boost from both chargers. Any thoughts.

Do you have a boost gauge ?
If so, is the boost the same as it was
earlier in the year ?

jt

Boost is almost same I attrbute difference to rpm. I checked valve springs and replaced no difference.

What about humidity?? Fuel load? Type of Fuel? One of these isnt going to equal a loss of at least 500 RPM, but they could all contribute.

This is pretty hard to trouble shoot over the board. If you ease in to the throttle does the motor RPM up to a point and just stop or RPM up and lay down. How does it run out of the hole under heavy power? I would think if you had a lifter problem you would hear it or you would see slight increase in boost. Here what I would check first.

Spark Plug reading.
Fuel pressure.
Bad fuel. (Are you sure it is not detonating?)
What ignition are you running. Any type of RPM limiter?
Is this a carb or EFI motor. (sorry I do not know your application.)

If the motor is mechanically sound you probably have a fuel or ignition problem. I know you said you can not here it mis but unless headers are dry sometimes it is hard to hear. Just my .02 for what it is worth.

I forgot, how old are the plugs/plug wires? If they werent replaced this spring, I would go do that and see what happens. Last season I was only getting 4400. Replaced plugs, got about 4450. Was really pissing me off, this spring decided to change the wires, nail 5k any day.