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5.0GXI Volvo Penta Engine

J

jrichardson

New member
I own a 2007 Four Winns boat with a 5.0GXI engine with only 30 hrs, I am going to have to pull the engine to repair a broken starter bolt, I live in high altitude so this boat is under powered (6,900 ft elevation). I want to have this engine bored to a 5.7L. What will interchange between the two? Obviously I will be purchasing new pistons, but will I need to repalce heads also, etc.

Jeff

Bayfield, CO
 
The only difference internally would be the bore diameter, crankshaft, rods and stroke are the same. So am I correct in stating that if you bore .030ths this engine becomes a 5.7L (350 Cubic Inch)?
 
Jeff, as you may know, there is a .264" difference between the 5.0L and 5.7L cylinder bore diameters.
This would equate to .132" off the cylinder wall!
So boring a 5.0L block safely will not gain you anywhere near 350 cu in!
305 = 3.736" x 3.48" (Gen.I, 5.7" rod)
350 = 4.000" x 3.48" (Gen.I, 5.7" rod)


Since you are operating at higher altitude, you need to make thick air out of thin air, figuratively speaking.

There are several methods that can be used to achieve this.
The least expensive method would be to slightly increase C/R.... (and perhaps a cam profile change)!
Steer yourself as far away from the full dished piston as you can possibly get.
Dished Piston.jpg

Read up on Q/E ("quench effect" or "squish effect") for the Small Block Chevy Marine Engines.
There are many Q/E piston selections that will get you where you want to be!
(Low Comp Q/E, Reverse Dome, D Dish, etc.)

When we select the appropriate piston for the cylinder head combustion chamber volume, and the correct head gasket, we can build ourselves a Q/E SBC Marine Engine.
The concept is simple, yet very effective, and it won't break the bank!

.
 
Last edited:
Jeff, I forgot to mention that nothing else to the engine build needs to be changed.
It can all be accomplished with the correct piston style for the cylinder head chamber volume.
In your case, your chamber volume is very likely 64cc.

This is one of the few areas where I'll site the Hot Rod guys regarding the Quench Effect.
These guys know about this as well.... and many good articles can be found on the subject.

However, it's also where we draw the line regarding C/R's, Ignition Timing, Camshaft Profile, Short Piston skirts/Long Rods, and several other aspects of the SBC Marine Engine build.

Pick up a copy of Dennis Moore's "Small Block Chevy Marine Performance"..... it's a great read, and pertains as much to the our cruiser engine as it does to HP marine!

.
 
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