Compression test on 7.4L, are these numbers ok?

[tpenfield]

Re: Compression test on 7.4L, are these numbers ok?

Yes, sounds like the engine may be OK. If you drop about 10% in pitch (1-2"), then you should get in the 4400 range at WOT, which will help your lower end speeds and planing, etc.

 

[OldNBold51]

Re: Compression test on 7.4L, are these numbers ok?

my 4000 lb 23 foot wellcraft '95 model with a 19P prop will only turn just over 4000 rpms. My manual says it should be able to turn 4500 rpms but mine just feels like it ran out of cam as it accels smoothly and quickly to 4000 and then just foes flat without a hint of bog or engine note change.

coming on plane doesn't sound much different fully loaded or unloaded. The engine just kinds of chugs up and chugs down. i was expecting a much quicker rev when throttle quickly pushed to WOT. Engine just chugs on up like a truck engine. I had 3 guys and 9 (bigger)women on the boat 1 time and it planed out not much slower than with just me, and revved to about 3900. It cruised easily at 2800. I'm thinking that this is just the characteristics of this motor and cam profile.

 

[kleake]

Re: Compression test on 7.4L, are these numbers ok?

Mine revs to about 3k right off, and holds there until I reach about 25mph, then slowly climbs as I gain speed. With the heavy load I had, I couldn't get on plane without moving one or two people up front. While we tried the wake board (yes, big boat to be wake boarding with, but we just wanted to try it) I had 6 people on deck and one on the board. I could hit 15mph, but could not plane out even at WOT until 2 people moved up front. Once up to speed I can back off the throttle enough to get out of the the secondary's on the carb, but I can't back off much or I start losing speed. It just really feels like there is a huge amount of prop slip and not much bite. I have an old 15 pitch that is a larger diameter from a different boat I might try just to get a feel for the difference before I commit to one. It rode really nice at 30mph, so if I can get a good cruise right there without too much throttle, that would be ideal.

 

[Don S]

Re: Compression test on 7.4L, are these numbers ok?

You may very well be over propped. Might want to post over in the Prop Forum and include your prop size, and other info requested in the prop forum stickies.