Rod Stroke Ratio! R/S
02-25-2003, 02:21 PM
#1
Thread Starter
Join Date: Sep 2002
Location: Orange County, CALIFORNIACATIONATED, USA
Posts: 1,769
Likes: 0
Received 0 Likes
on
0 Posts
Rod Stroke Ratio! R/S
Rod Stroke Ratio!
^To help people better understand R/S ratio^
Just came across it and thought i might post it up..
Off subject: Can someone give me the Part Number for the ITR oil pump (seached but sites wont give me the part number)??? (yes, i know ITR & GSR are the same)
Sorry, if your guys cant read it here it is...
Rod/Stroke Ratio Guide
By: Brian Cummiskey
Rod/Stroke Ratio, or R/S, is the ratio of the length of the connecting rod to the length of the piston stroke. In other words, it is the distance the piston travels from the top to the bottom of its stroke. Don't ask me who came up with it, but there is such a thing as a perfect, or ideal R/S ratio. This ratio is 1.75:1.
Most motor's aren't perfect. The lower the R/S ratio gets from 1.75:1, stress on engine internals increases exponentially, killing long-term reliability. A low R/S ratio means the rod is positioned in more of a horizontal angle on its upstroke, resulting in a force pushing the piston horizontally, rather than vertically. This causes stress on the sides and center of the rod, leaving it more prone to breakage than if stress were on the end of the rod. In addition to the rods being prone to damage, the cylinder walls also see a greater strees. Remember, the rod is pushing more horizontally, and guess what's there- the walls. Because of this, the piston may be pushed right through the wall, or the wall will flex to better fit the poor cycle. If this happens, start singing "Here come's the Oil". However, higher R/S motors aren't in much better shape. While they may last longer and are less prone to mechanical problems, the piston moves slower because of the lesser angle, resulting in less power output.
Remember: Horsepower = (torque x RPMs) / 5252
Here's a few B-series motors and their R/S specs:
B16A:
Rod length: 134 mm
Stroke: 77 mm
R/S: 1.74:1
B17A:
rod length: 131.87 mm
Stroke: 81.4 mm
R/S: 1.62:1
B18A-B:
Rod length: 137mm
Stroke: 89mm
R/S: 1.54:1
B18C:
Rod length: 137.9 mm
Stroke: 87.2 mm
R/S: 1.58:1
Standard Disclaimer
We attempt to provide accurate information at all times on everything we publish. However, mistakes can and do happen, and we simply cannot know everything. If you feel there is an error on this or any page, please contact us and let us know so that we can address the matter. As always, all content is subject to our standard disclaimer.
[Modified by 10K2HVN, 3:29 PM 2/25/2003]
^To help people better understand R/S ratio^
Just came across it and thought i might post it up..
Off subject: Can someone give me the Part Number for the ITR oil pump (seached but sites wont give me the part number)??? (yes, i know ITR & GSR are the same)
Sorry, if your guys cant read it here it is...
Rod/Stroke Ratio Guide
By: Brian Cummiskey
Rod/Stroke Ratio, or R/S, is the ratio of the length of the connecting rod to the length of the piston stroke. In other words, it is the distance the piston travels from the top to the bottom of its stroke. Don't ask me who came up with it, but there is such a thing as a perfect, or ideal R/S ratio. This ratio is 1.75:1.
Most motor's aren't perfect. The lower the R/S ratio gets from 1.75:1, stress on engine internals increases exponentially, killing long-term reliability. A low R/S ratio means the rod is positioned in more of a horizontal angle on its upstroke, resulting in a force pushing the piston horizontally, rather than vertically. This causes stress on the sides and center of the rod, leaving it more prone to breakage than if stress were on the end of the rod. In addition to the rods being prone to damage, the cylinder walls also see a greater strees. Remember, the rod is pushing more horizontally, and guess what's there- the walls. Because of this, the piston may be pushed right through the wall, or the wall will flex to better fit the poor cycle. If this happens, start singing "Here come's the Oil". However, higher R/S motors aren't in much better shape. While they may last longer and are less prone to mechanical problems, the piston moves slower because of the lesser angle, resulting in less power output.
Remember: Horsepower = (torque x RPMs) / 5252
Here's a few B-series motors and their R/S specs:
B16A:
Rod length: 134 mm
Stroke: 77 mm
R/S: 1.74:1
B17A:
rod length: 131.87 mm
Stroke: 81.4 mm
R/S: 1.62:1
B18A-B:
Rod length: 137mm
Stroke: 89mm
R/S: 1.54:1
B18C:
Rod length: 137.9 mm
Stroke: 87.2 mm
R/S: 1.58:1
Standard Disclaimer
We attempt to provide accurate information at all times on everything we publish. However, mistakes can and do happen, and we simply cannot know everything. If you feel there is an error on this or any page, please contact us and let us know so that we can address the matter. As always, all content is subject to our standard disclaimer.
[Modified by 10K2HVN, 3:29 PM 2/25/2003]
03-17-2003, 01:31 AM
#2
Join Date: Mar 2002
Posts: 3,281
Likes: 0
Received 0 Likes
on
0 Posts
Re: Rod Stroke Ratio! R/S (10K2HVN)
higher R/S motors aren't in much better shape. While they may last longer and are less prone to mechanical problems, the piston moves slower because of the lesser angle, resulting in less power output.
03-17-2003, 07:24 AM
#3
New User
Join Date: Mar 2001
Location: Wayland, MI, US
Posts: 2,462
Likes: 0
Received 0 Likes
on
0 Posts
Re: Rod Stroke Ratio! R/S (J2turbo21)
I think the way that's worded at the end is a bit confusing. The piston moves slower on the b16 because the stroke is 77mm not because the r/s ratio is 1.74:1. A 77mm stroke means that the piston has to travel less distance each revolution than a piston in a motor w/ an 87.2, 89, or 95mm stroke resulting in lower piston speeds in the b16 than the other Honda motors. Having the rod closer to vertical will always be better because the combustion will be pushing the piston downward in a more linear fashion. The way that's worded it implies that a superior r/s ratio wouldn't be better for power & reliability w/ the same stroke, and I believe that to be incorrect. For instance if you could fanagle a 152mm rod into a b18c1 then you'd have an r/s of 1.74:1 while maintaining the 87.2mm stroke. I suggest that this hyopthetical motor would be more efficient, more powerful, and more reliable. Unfortunately the deck height would have to be about 7mm higher.
03-17-2003, 11:16 AM
#5
Honda-Tech Member
iTrader: (2)
Join Date: Mar 2002
Location: Woodbridge, NJ, Middlesex
Posts: 5,828
Likes: 0
Received 1 Like
on
1 Post
Re: Rod Stroke Ratio! R/S (10K2HVN)
yup, the longer the rod the more HP period !!!
the trick is getting the head to flow in relation to the ratio, i.e. the longer the rs ratio the less cfm flow needed ... for a b-series head the magic number is 1.81 on a stock ported headflow ... only upgrade is more cuts on the valve seat and exhaust port reshape.
greg
the trick is getting the head to flow in relation to the ratio, i.e. the longer the rs ratio the less cfm flow needed ... for a b-series head the magic number is 1.81 on a stock ported headflow ... only upgrade is more cuts on the valve seat and exhaust port reshape.
greg
Thread
Thread Starter
Forum
Replies
Last Post
