I kinda understand why a good rod/stroke ratio is important. I know that certain length rods are better for revving high, but I'm not clear on how you get the "1.75" number. What is it made up from?

-Steve

 

I believe its rod length / stroke.

 

Correct....i.e if your rods are 135mm and the stroke is 75mm you have a r/s ratio of 1.8

Edit: the 1.75 is the ideal rod/stroke ratio for a STREET driven car.


[Modified by Spade, 11:39 AM 12/26/2001]

 

Cool, I didn't know that.

Now here is the technical question. Why is 1.75 the best for street cars? I understand that certain rod/stroke combo's are more "rev friendly" than others, but I dont really understand the mechanics as to why.

-Steve

 

It has to do with the sideload on the cylinder walls.
The higher the R/S ratio the less sideload, wthere fore you can rev higher. Although it also changes the characteristics of the engine, the way it makes power and the powerband. The higher the R/S ratio the less torque and the higher the power will be in the powerband.

Alot of people also say that R/S is a bunch of bullshit and it really doenst make a differance.

 

Lol. You all are so right about the Rod/Stroke ratio. That is exactly why my friend is using the b16 internals to go in a b20/vtec engine with the Type R gear ratio. He will be all motor and wants to rev high (or have the piston hit TDC as much as possible compared to the other motors).

Just doing something different.

 

1.75 is the best r/s the because it is the perfect time that the piston dwells at the combustion chamber. all it is it rod lengh devided by the stroke.

 

The higher the ratio, the slower the piston moves. You WANT this cause when your piston start moving to fast you introduce huge tension and compression loads on your rods. Also a piston that moves to fast will cause cavitation during the intake cycle, you don't want this cause now your VE goes down and that means less power.

You can go to big on rod/stroke ratio too, 1.75 is a good number, but only the B16 has that and it's actually 1.72. Only other Honda automobile engine with a higher rod/stroke ratio is the S2000, but it's not that much more.

 

Actually, the B16 has a R/S of 1.74:1 and the B16B (Civic TypeR) has a R/S of something like 1.8ish. Once I find out the true R/S I will post.