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If I remember right from my '02 readings, one of the ways Honda bumped up the horsepower was to increase the compression ratio to 10.0:1. Is that indeed the case? What was it previously? And, most importantly, was the compression ration change achieved by changing the head or the pistons? Have there been any changes in the block of the 3.5 V-6 over the last few years?

Yes, this does have to do with my getting a new short-block. I can imagine lots of older short blocks floating around the warehouse, but '02's?

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'02 Redrock Pearl EX
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Been a long time since I thought about this, but would they not change the stroke of the crankshaft to change the compression ratio without changing displacement.
 

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Just guessing, I would say they got the extra compression by changing the cylinder heads, since they changed to a more elaborate V-Tech system, which would probably require different head castings.

Jerry O.

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2001 Odyssey GG LX
 

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<font face="Verdana, Arial" size="2">Originally posted by nds:
Been a long time since I thought about this, but would they not change the stroke of the crankshaft to change the compression ratio without changing displacement.</font>
Changing (increasing) the stroke (assuming the same bore) changes (increases) the displacement.
 

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You are right. I did a little research. They probably did reduce the displacement just a little to get the increase in compression ratio. Easiest way to do it is to reduce the volume in the head cavity, and we know they changed the heads. The required reduction in overall displacement is only on the order of 1%, which the increased compression ratio would more than compensate for in terms of power. Also, since they only report displacement in liters rounded to the nearest tenth, the 1% change does not change the claim of 3.5 liters.
 

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NO! Changing the Compression ratio alone DOES NOT affect displacement. All other factors being equal, changing the stroke will affect displacement and compression ratio but this is typically not the way it is handled.

Most likely, Honda either changed the design of the combustion chamber and/or the top of the piston.
 

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Here is Honda's explanation of the HP increase:

2002 Honda Odyssey Drivetrain

The Odyssey's 3.5-liter SOHC V-6 now produces 240-horsepower and 242-lb.-ft. of torque on regular unleaded fuel (an increase from 210 horsepower and 229-lb.-ft. of torque for the 2001 model on premium fuel). This increase results in quicker acceleration and improved drivability. The increased power is achieved with improved high-flow intake and exhaust components, a new 6-piece intake manifold, larger bore throttle body (55mm to 64mm), a 3-rocker VTEC system (previously 2-rocker VTEC system), increased diameter intake and exhaust valves and a 10.0:1 compression ratio (previously 9.4:1).

The 3-rocker VTEC system expands horsepower and torque capability by adding increased throttle response at low engine speeds and top-end power at higher engine speeds. Horsepower peaks at 5,500 RPM and torque peaks at 4,500 RPM. Even with the power increases, the 2002 Odyssey is projected to maintain its best-in-class overall fuel economy as well as its 50-state LEV emissions rating. Regular unleaded fuel meets the octane requirements for the engine's increased horsepower and compression ratio (10.0:1) thanks to a highly sensitive engine knock sensor that prevents pre-detonation in the cylinder chambers.




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Neo Fender is correct. Displacement has nothing to do with head design or size. They did not change the pistons or stroke on the 2002's. I do not know 100%, but I'm pretty sure they left the block alone. No literature I've read says anything about a new block. Rarely will an auto maker mess with the engine block on an established model... especially mid-run (Honda's five year model cycle). They will opt, as Honda has done, to change "lesser" components... intake manifolds, valve design, etc.
 
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