Why did honda make the d15z1 (vx motor) have a unique 1.62 r/s ratio
Thread Starter
B*a*n*n*e*d
Joined: Mar 2003
Posts: 9,783
Likes: 47
From: Greenville, South Carolina
Why did honda make the d15z1 (vx motor) have a unique 1.62 r/s ratio
Something that I've been wondering for a while is why honda chose a unique rod/stroke ratio for their d15z1 vx motor. The motor is a complete freakshow in comparison to the other d-series. It along with the jdm d15b are the only d-series motors that honda made with the 84.5 stroke / 137 rod combo. All the other d15s have 134mm rods and all the d16s have 137mm rods.
r/s ratios
d15 = 1.59
d16 = 1.52
d15z1/jdm d15b = 1.62
Now I realize that efficiency is well efficiency. Several tweaks that are made to increase efficiency yield gains in both mpg and hp. But Still. The d15z1 is optimized for low rpm use. The transmission says so. The small ports on the head say so. The low redline says so. The small valves say so, and the tiny intake manifold and throttlebody say so.
yet it uses a r/s ratio that seems to be optimized for high rpms. I thought lower r/s ratios were better for low RPMs?
r/s ratios
d15 = 1.59
d16 = 1.52
d15z1/jdm d15b = 1.62
Now I realize that efficiency is well efficiency. Several tweaks that are made to increase efficiency yield gains in both mpg and hp. But Still. The d15z1 is optimized for low rpm use. The transmission says so. The small ports on the head say so. The low redline says so. The small valves say so, and the tiny intake manifold and throttlebody say so.
yet it uses a r/s ratio that seems to be optimized for high rpms. I thought lower r/s ratios were better for low RPMs?
Honda-Tech Member
Joined: Jul 2002
Posts: 812
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From: Peg City, 204
Re: Why did honda make the d15z1 (vx motor) have a unique 1.62 r/s ratio (Bense)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bense »</TD></TR><TR><TD CLASS="quote">Something that I've been wondering for a while is why honda chose a unique rod/stroke ratio for their d15z1 vx motor. The motor is a complete freakshow in comparison to the other d-series. It along with the jdm d15b are the only d-series motors that honda made with the 84.5 stroke / 137 rod combo. All the other d15s have 134mm rods and all the d16s have 137mm rods.
r/s ratios
d15 = 1.59
d16 = 1.52
d15z1/jdm d15b = 1.62
Now I realize that efficiency is well efficiency. Several tweaks that are made to increase efficiency yield gains in both mpg and hp. But Still. The d15z1 is optimized for low rpm use. The transmission says so. The small ports on the head say so. The low redline says so. The small valves say so, and the tiny intake manifold and throttlebody say so.
yet it uses a r/s ratio that seems to be optimized for high rpms. I thought lower r/s ratios were better for low RPMs? </TD></TR></TABLE>
there's one more big variable in the mix that you overlooked... The cam.
Also, the longer rod makes the rotating assembly more mechanically efficient, the piston has better mechanical leverage on the crank, and less energy is wasted pushing on the cylinder walls...
Other than that... maybe they just had a lot of 137mm rods hanging around the factory lol
r/s ratios
d15 = 1.59
d16 = 1.52
d15z1/jdm d15b = 1.62
Now I realize that efficiency is well efficiency. Several tweaks that are made to increase efficiency yield gains in both mpg and hp. But Still. The d15z1 is optimized for low rpm use. The transmission says so. The small ports on the head say so. The low redline says so. The small valves say so, and the tiny intake manifold and throttlebody say so.
yet it uses a r/s ratio that seems to be optimized for high rpms. I thought lower r/s ratios were better for low RPMs? </TD></TR></TABLE>
there's one more big variable in the mix that you overlooked... The cam.
Also, the longer rod makes the rotating assembly more mechanically efficient, the piston has better mechanical leverage on the crank, and less energy is wasted pushing on the cylinder walls...
Other than that... maybe they just had a lot of 137mm rods hanging around the factory lol
Thread Starter
B*a*n*n*e*d
Joined: Mar 2003
Posts: 9,783
Likes: 47
From: Greenville, South Carolina
Re: Why did honda make the d15z1 (Justin Jones)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Justin Jones »</TD></TR><TR><TD CLASS="quote">
there's one more big variable in the mix that you overlooked... The cam.
Also, the longer rod makes the rotating assembly more mechanically efficient, the piston has better mechanical leverage on the crank, and less energy is wasted pushing on the cylinder walls...
Other than that... maybe they just had a lot of 137mm rods hanging around the factory lol</TD></TR></TABLE>
the vx uses an exclusive rod. Why do they say a lower r/s ratio is better for lower rpms though?
there's one more big variable in the mix that you overlooked... The cam.
Also, the longer rod makes the rotating assembly more mechanically efficient, the piston has better mechanical leverage on the crank, and less energy is wasted pushing on the cylinder walls...
Other than that... maybe they just had a lot of 137mm rods hanging around the factory lol</TD></TR></TABLE>
the vx uses an exclusive rod. Why do they say a lower r/s ratio is better for lower rpms though?
Honda-Tech Member
Joined: Jul 2002
Posts: 812
Likes: 0
From: Peg City, 204
Re: Why did honda make the d15z1 (Bense)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bense »</TD></TR><TR><TD CLASS="quote">
the vx uses an exclusive rod. Why do they say a lower r/s ratio is better for lower rpms though?</TD></TR></TABLE>
I was joking about the rods hanging around in the factory...
Lower rod ratio=faster piston speed for a given crankshaft rotational speed, quicker dwell events. This is good for a low RPM motor, it allows faster gas velocity for a given port design... Therefore allowing for larger ports and valves. Also, with less dwell time faster combustion events can take place, and detonation can be avoided.
Short rod ratios are good for some high-RPM applications as well... ie: NHRA pro stock where the piston speeds are faster than imaginable.
the vx uses an exclusive rod. Why do they say a lower r/s ratio is better for lower rpms though?</TD></TR></TABLE>
I was joking about the rods hanging around in the factory...
Lower rod ratio=faster piston speed for a given crankshaft rotational speed, quicker dwell events. This is good for a low RPM motor, it allows faster gas velocity for a given port design... Therefore allowing for larger ports and valves. Also, with less dwell time faster combustion events can take place, and detonation can be avoided.
Short rod ratios are good for some high-RPM applications as well... ie: NHRA pro stock where the piston speeds are faster than imaginable.
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Mar 27, 2006 08:47 AM
