R/S ratio
 

hey im currently building my motor and am exploring the options for d series. i have a question concerning rod/stroke ratio. is it better to have this ratio as close to 1:1 or is it hte farther away from one another the better?

Re: R/S ratio
 

this will start a heated debate for sure, rod stroke ratio, is the relationshp between the connecting rod length and crankshaft stroke. 1.75 is seen as being optimal for small displacement engines. rod/stroke ratio also is effected by deck height. the longer the stroke and the shorter the rod, the lower the ratio will be, and vice versa, the shorter the stroke and the longer the rod, the rod/stroke ratio increases. with a short stroke engine (long rod) the piston will remain at TDC longer and at BDC for a shorter period of time. with a long stroke (short rod) engine the opposite is true, the piston will remain at TDC for a shorter period of time and at BDC for a longer period of time, this is due to the time it takes for each rod to swing through it's arc as the crankshaft spins. longer stroke engines have higher piston speeds as compared to a shorter stroke engine in which the piston speed begins to drop. the D15B maintains a 1.63:1 rod/stroke ratio through the use of a longer than normal rod than any of the 1.5's or 1.6's. the d16z6/y8/y7/a6 have a rod/stroke ratio of 1.52:1, but the D15's maintain a 1.59:1 ratio. i prefer engines with a ratio coming closer to 1.75:1, but the difference in wear between an engine with 1.52 and 1.59 is nill, work with what your budget will allow.

Re: R/S ratio
 

can you give an example of a 1.75:1 r/s ratio?...just curious

but anyways, longer r/s ratio for more power.

Re: R/S ratio
 

good example is a b16 at 1.73:1 just take your rod length and divide it by your stroke (make sure in same units)

Re: R/S ratio
 

This topic started a pretty heated debate between myself and JD on here not too long ago. Although I'm still pretty partial to the 1.75:1 ratio, I have to say I've been leaning more towards JD's take on things, which pretty much boils down to Honda rotating assemblies are so light in design, that the normally accepted 1.75:1 ratio is pretty much meaningless. In the real world it prety much comes down to lower r/s ratio will give you more drivable/streetable torque. And seeing that horsepower is a measurement of torque multiplied by rpm, it pretty much explains why the b16 motor can make such a high horsepower per liter (in n/a form stock) but have a torque number that's lower than your run of the mill d16. You've got 2 choices...either go n/a and end up having to rev to the moon in order to make hp, or turbo it and not give another thought to r/s ratio ;D

Re: R/S ratio
 

r/s ratio really only matters for NA cars and not so much for FI.

Re: R/S ratio
 

Exactly my point above...get a turbo matched to the powerband you spend most of your time in and you'll be golden. Who wants to spend most of their time above the 6k rpm mark to try and make a little power...that's why b16's blow ass. :-X

Re: R/S ratio
 

TDC dwell is going to be the same as BDC.




Not even close. Regardless of the setup, you are going to want to maximize the power for your particular operating rpm. That means setting up R/S, turbo, cams, pistons, intake manifold, exhaust, etc, etc.


Having a low R/S ratio combined with a huge turbo is not ideal. The turbo's operating range will not match the engine. Matching is the key. Having all your components complement each other is the way to go.


Now, this being HMT and trying to make big power cheap we are not going to be bothered with the R/S as changing it is expensive. Getting more torque at higher rpm's can be done with cams and porting. R/S won't do ---- w/o these anyway.

Re: R/S ratio
 

Bottom statement should be more along the lines of "getting more torque at higher rpm's can be done by adjusting cam gears and porting." We're mostly broke-asses here at HMT...last time I bought an aftermarket cam for was my old A20 motor...cost me $159 from Web Cams years ago. :P

Re: R/S ratio
 

"Cams" includes adjusting them with cam gears.


Also, cam gears are cheap as ---- these days.