Re: OMC 5.7 advice
Hey....., You are very welcome.
NOTE: whether building to OEM specs, or id donig a Q/E SBC, does not mean spending much more money..... I just want to be clear on that for you.
The gain is well worth it!
Like said, this involves a piston selection change ONLY.
While we can make additional changes, nothing else absolutely needs to be done or changed....., other than taking advantage of the Q/E by using the correct deck height and head gaskets.... of which must be done anyway.
(no one puts an engine together without checking deck height)
Read up on Quench Effect to better understand what this means.
Here is a great article on "Quench Effect" by Jeff Smith. (lots more if you were to search this topic)
Jeff speaks primarily of automotive.... and I'll be the first to suggest that we
NOT use Automotive build info when building a Marine SBC!
However, this is one area that nicely
crosses over into SBC Marine.
One difference being that for Marine, we can close the Quench down to approximately .038", due to the lower operating RPM.
Other than that, Jeff's info is worth reading.
See Dennis Moore's book also. Well worth the read!
BTW, the 5.7L engine can use a single valve relief F/T pistons, when used with the 76cc chamber heads.
This gives us the Q/E (or "squish"), yet maintains the correct C/R for Marine use.
Something like this Low Compression Quench piston, or a "D" dished piston, can be used with the smaller 64cc chamber heads.... of which you likely have.
Again, the C/R remains correct for Marine use, as long as the correct piston p/n is used.
(i.e., dish volume. The smaller chambers require that the dish volume control C/R)
With any Quench Effect combustion chamber, C/R can be increased some, yet with little to no affect re; Detonation potential..... of which is what we're combating in the first place.
The Full Dish piston w/ ZERO quench, offers very little resistance to Detonation.
Quite frankly, it's the worst piston that could be used in a SBC Marine Engine!
As for Bayliner..... this is not a typical Bayliner issue. It just seems to be more so with that particular model, and a few others only. Otherwise, it's a non-issue .... no more/no less than with other boats!
As for the word "Investment" and "Boat" being used in the same sentence.... Hah!
Boats are rarely investments, and are almost always expenses only.
We just use it up in the form of enjoyment as we watch the smiles on our children's faces.... (if you have kids!)
If you were to look up Boats as an Investment, and search the words
"Financially Up-Side Down".... you'd see a cartoon with a picture of me and my old restored 2850 SDN F/B boat..... LOL!
But I knew this going in.... I don't mind it one bit!
As for Prop selection:
You won't be able to correctly prop this, until you have all your ducks in a row. I.E., engine in full tune, hull clean, drive ratio correct, etc.
(you may want to pitch down for your break-in duration!)
Then you must perform a WOT RPM test, just as you would with any boat. Stay within your OEM WOT RPM specs, and you'll have the correct prop pitch.
(you are limited to diameter with the Cobra drive.)
I would find a prop shop that will allow you to test several props.
Anything else is a crap shoot that may damage your engine by over-burdening it.
Keep us updated!
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