ka24 rod/stroke ratio? - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

azboy · 02-25-2002, 11:46 PM

from what i've found so far the center-to-center length of the OE KA24(D) connecting rod is 165mm and the stroke is 96.0mm which gives a ratio of 1.718.  

can anyone else confirm these numbers?  if this is correct i'd rather buy a turbo for the ka24 instead of doing the sr20det swap.

*Jeff240sx* · 02-26-2002, 02:08 AM

Even if you are correct, what the #### does that have to do with anything?  Including why you'd want a turbo Ka rather than an Sr...
I just dont see the relevance of your math to anything or either engine...
Could you please elaborate is what I am trying to ask <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'>
-Jeff

DuffMan · 02-26-2002, 03:09 AM

Isn't there supposed to be some kind of "ideal rod ratio" or something like that.

crazycuban · 02-26-2002, 07:12 AM

Yeah, ideal is 1.7

EDIT - The ideal rod ratio only means that it would rev higher and better, however...the KA is not built for that, and would need a LOT of work to take advantage of that rod ratio.  Basically, although it does have a 1.7 ratio, that's useless.  If you get the KA, get it for the low end torque, because to make it a high end monster you would need an entirely new valvetrain.

(Edited by crazycuban at 7:14 am on Feb. 26, 2002)

uuninja · 02-26-2002, 07:29 AM

I don't know my high end feels and pulls just fine <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/wink.gif" border="0" valign="absmiddle" alt=';)'>

97S14 · 02-26-2002, 09:31 AM

The ideal rod/stroke ratio is just a fraction of what makes a good high revving engine.  There is a lot more to it then that.

And isn't the ideal rod/stroke ratio 1.65?

azboy · 02-26-2002, 10:25 AM

Here is some info I've found:

"Several things are directly effected by rod/stroke ratio, piston speed, piston acceleration and decelleration, piston dwell time at TDC and BDC, piston side loads, cylinder loading, and bearing loads. Almost everything mentioned as "effected" plays a major role in the way the engine breathes(piston speed, acc., dec.), the combustion characteristics(again piston speed, etc. and dwell time), and friction / wear characteristics(piston side loads, cylinder loads, and bearing loads).
There are many opinions on this subject, but it's generally felt that the lower the ratio numerically, the worse the geometry. As far as I'm concerned 1.75 to 1 is the ideal rod length to stroke ratio, regardless of application, and any number going down numerically is not favorable. If you lengthen the rod relative to the crank and the ratio grows larger, the wear goes down as does the piston speed, but this will contribute to an engine having a very narrow useful torque range. If the number is between 1.8 and 1.7, it's workable."

The reason for this is because of $$$$$ I don't have much of it and turboing the ka24 is a #### of a lot cheaper then doing the sr20 swap. although my dream is to drop in the sr20, I just don't have the finance. I wanted to make sure I understood the matrix of the ka24 engine before adding a major modification like a turbo. That's why I posted about the rod/stroke ratio in the first place.

(Edited by azboy at 10:29 am on Feb. 26, 2002)

9591 · 02-26-2002, 02:33 PM

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Quote: from azboy on 11:46 pm on Feb. 25, 2002
from what i've found so far the center-to-center length of the OE KA24(D) connecting rod is 165mm and the stroke is 96.0mm which gives a ratio of 1.718.

can anyone else confirm these numbers?</td></tr></table><span id='postcolor'>

Yes, those are the correct numbers.

azboy · 02-26-2002, 03:20 PM

THANKS 9591
That's all I wanted to know <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'>

02-26-2002, 04:38 PM

Underpsi, Psi240, and my future engine is using the 171mm length rod. 6.75" vs 6.5" stock length. Try that for the rod to length ratio...

*sykikchimp* · 02-26-2002, 04:59 PM

Is that gonna effect you compression ratio??  What pistons are you going with?  that ratio is a 1.781

azboy · 02-26-2002, 09:30 PM

whats the max and min length on ka24 engines anyway?  6mm above stock sounds kinda long to me but hey if it works.....

02-25-2002, 11:46 PM	#1
azboy Leaky Injector Join Date: Feb 2002 Posts: 52 Trader Rating: (0) Feedback Score: 0 reviews	from what i've found so far the center-to-center length of the OE KA24(D) connecting rod is 165mm and the stroke is 96.0mm which gives a ratio of 1.718.   can anyone else confirm these numbers?  if this is correct i'd rather buy a turbo for the ka24 instead of doing the sr20det swap.

02-26-2002, 02:08 AM	#2
Jeff240sx I hate you too... Join Date: Jul 2001 Location: Tampa, FL Age: 41 Posts: 5,828 Trader Rating: (0) Rides Gallery: Jeff240sx Feedback Score: 0 reviews	Even if you are correct, what the #### does that have to do with anything?  Including why you'd want a turbo Ka rather than an Sr... I just dont see the relevance of your math to anything or either engine... Could you please elaborate is what I am trying to ask <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'> -Jeff

02-26-2002, 03:09 AM	#3
DuffMan Post Whore! Join Date: Oct 2001 Location: in a cardboard box Posts: 2,517 Trader Rating: (0) Feedback Score: 0 reviews	Isn't there supposed to be some kind of "ideal rod ratio" or something like that.

02-26-2002, 07:12 AM	#4
crazycuban Zilvia Junkie Join Date: Nov 2001 Posts: 526 Trader Rating: (0) Feedback Score: 0 reviews	Yeah, ideal is 1.7 EDIT - The ideal rod ratio only means that it would rev higher and better, however...the KA is not built for that, and would need a LOT of work to take advantage of that rod ratio.  Basically, although it does have a 1.7 ratio, that's useless.  If you get the KA, get it for the low end torque, because to make it a high end monster you would need an entirely new valvetrain. (Edited by crazycuban at 7:14 am on Feb. 26, 2002)

02-26-2002, 07:29 AM	#5
uuninja Zilvia Addict Join Date: Dec 2001 Location: Reston, VA Age: 46 Posts: 812 Trader Rating: (0) Feedback Score: 0 reviews	I don't know my high end feels and pulls just fine <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/wink.gif" border="0" valign="absmiddle" alt=';)'>

02-26-2002, 09:31 AM	#6
97S14 Join Date: Feb 2002 Posts: 36 Trader Rating: (0) Feedback Score: 0 reviews	The ideal rod/stroke ratio is just a fraction of what makes a good high revving engine.  There is a lot more to it then that. And isn't the ideal rod/stroke ratio 1.65?

02-26-2002, 10:25 AM	#7
azboy Leaky Injector Join Date: Feb 2002 Posts: 52 Trader Rating: (0) Feedback Score: 0 reviews	Here is some info I've found: "Several things are directly effected by rod/stroke ratio, piston speed, piston acceleration and decelleration, piston dwell time at TDC and BDC, piston side loads, cylinder loading, and bearing loads. Almost everything mentioned as "effected" plays a major role in the way the engine breathes(piston speed, acc., dec.), the combustion characteristics(again piston speed, etc. and dwell time), and friction / wear characteristics(piston side loads, cylinder loads, and bearing loads). There are many opinions on this subject, but it's generally felt that the lower the ratio numerically, the worse the geometry. As far as I'm concerned 1.75 to 1 is the ideal rod length to stroke ratio, regardless of application, and any number going down numerically is not favorable. If you lengthen the rod relative to the crank and the ratio grows larger, the wear goes down as does the piston speed, but this will contribute to an engine having a very narrow useful torque range. If the number is between 1.8 and 1.7, it's workable." The reason for this is because of $$$$$ I don't have much of it and turboing the ka24 is a #### of a lot cheaper then doing the sr20 swap. although my dream is to drop in the sr20, I just don't have the finance. I wanted to make sure I understood the matrix of the ka24 engine before adding a major modification like a turbo. That's why I posted about the rod/stroke ratio in the first place. (Edited by azboy at 10:29 am on Feb. 26, 2002)

02-26-2002, 02:33 PM	#8
9591 Leaky Injector Join Date: Feb 2002 Posts: 122 Trader Rating: (0) Feedback Score: 0 reviews	</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Quote: from azboy on 11:46 pm on Feb. 25, 2002 from what i've found so far the center-to-center length of the OE KA24(D) connecting rod is 165mm and the stroke is 96.0mm which gives a ratio of 1.718. can anyone else confirm these numbers?</td></tr></table><span id='postcolor'> Yes, those are the correct numbers.

02-26-2002, 03:20 PM	#9
azboy Leaky Injector Join Date: Feb 2002 Posts: 52 Trader Rating: (0) Feedback Score: 0 reviews	THANKS 9591 That's all I wanted to know <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'>

02-26-2002, 04:38 PM	#10
'91 D21 beater Guest Posts: n/a	Underpsi, Psi240, and my future engine is using the 171mm length rod. 6.75" vs 6.5" stock length. Try that for the rod to length ratio...

02-26-2002, 04:59 PM	#11
sykikchimp WOW addicted Join Date: Dec 2001 Location: the moon Age: 43 Posts: 6,525 Trader Rating: (0) Feedback Score: 0 reviews	Is that gonna effect you compression ratio??  What pistons are you going with?  that ratio is a 1.781

02-26-2002, 09:30 PM	#12
azboy Leaky Injector Join Date: Feb 2002 Posts: 52 Trader Rating: (0) Feedback Score: 0 reviews	whats the max and min length on ka24 engines anyway?  6mm above stock sounds kinda long to me but hey if it works.....