JunIntegra

well the topic pretty much says it. ive heard many people say that the nissan KA24de and many other large stroke motors( like the k24 by honda, etc.) are limited to their high stroke (96mm) and in assumption that the r/s ratio is bad because of this. but the ka24de has a comparible r/s ratio to a b16a in 1.7s. (1.716 i think) this is better than an ITR motor that goes to 8400 rpm. so what about a large stoke (and high r/s) is limiting high rpm?
i ask this cuz my ka24de is limited to quite a low redline (6500-7000) and would like to get a higher speed from each gear and top speed. i know that power curve shoukd govern the redline but if the motor can go higher, it will be built to make power there. any help is appreciated

sledgehammer

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JunIntegra &raquo;</TD></TR><TR><TD CLASS="quote">well the topic pretty much says it. ive heard many people say that the nissan KA24de and many other large stroke motors( like the k24 by honda, etc.) are limited to their high stroke (96mm) and in assumption that the r/s ratio is bad because of this. but the ka24de has a comparible r/s ratio to a b16a in 1.7s. (1.716 i think) this is better than an ITR motor that goes to 8400 rpm. so what about a large stoke (and high r/s) is limiting high rpm?
i ask this cuz my ka24de is limited to quite a low redline (6500-7000) and would like to get a higher speed from each gear and top speed. i know that power curve shoukd govern the redline but if the motor can go higher, it will be built to make power there. any help is appreciated</TD></TR></TABLE>

Also take into consideration that as the bore gets bigger the pistons for the most part get heavier and more piston speed w/ a heavy piston puts a lot of stress on the rod bolts.

Mike

HONDA_TYPE_R

The stock materials that your internals are made of may not be able to handle the extra revs. Better pistons (i.e. lighter), better piston rings, and better rod bolts would go a long way, plus some blueprinting.

alloutmotor

not only that, the ka24 head wont flow to the higher rpms

JunIntegra

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by alloutmotor &raquo;</TD></TR><TR><TD CLASS="quote">not only that, the ka24 head wont flow to the higher rpms</TD></TR></TABLE>

stock it cant but can be accomodted with cams. i am building one with wiseco slugs, oe bearings, all studs to ARP and new HG. the crank and rods are forged, has piston oil squirters and blok girde stock

JunIntegra

if this thing can see 7500 rpm happily, i will be happy

notstock93

Think of it in terms of the R/S ratio determines how well the car will operate at higher RPM, while the stroke dictates the maximum safe redline before things start getting wonky.

Wonky is the technical term, BTW.

89mm LS crank-CAN go to 8k+, but the 1.54:1 dictates that not much will be happening without lots of work (even so, 1.54:1 isn't too bad)

the KA24's R/S tells that it would be able to breath efficiently at higher RPM is setup accordingly, but the long stroke is prohibiting it from doing so safely.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by HONDA_TYPE_R &raquo;</TD></TR><TR><TD CLASS="quote">The stock materials that your internals are made of may not be able to handle the extra revs. Better pistons (i.e. lighter), better piston rings, and better rod bolts would go a long way, plus some blueprinting. </TD></TR></TABLE>

weight of the components have alot to do with it, as he said. I guess the best answer to your question would be "all of the above"

JunIntegra

i understand what you say. but i just want to be clear on one thing: why is a larger stroke so bad on an engine with minimal sideload (r/s ratio)?

dscivicdx

as i understand it... the longer stroke increases the piston speed per rev as the piston has farther to go per rev. there is just a limit on the max speed of the pistion due to materials/physics. i may be wrong, but thats how i understand it.
thats why most high rev motors have a shorter stroke and bigger bore.

notstock93

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JunIntegra &raquo;</TD></TR><TR><TD CLASS="quote">i understand what you say. but i just want to be clear on one thing: why is a larger stroke so bad on an engine with minimal sideload (r/s ratio)?</TD></TR></TABLE>

its the length of movement that it takes to reach a certain engine speed. Say an engine with a 70mm stroke is turning 500ft/sec at 6k, while an engine with a 100mm srtoke is moving 30% further at the same engine speed.

You can see where things would start to go bad.

EE_Chris

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JunIntegra &raquo;</TD></TR><TR><TD CLASS="quote">i understand what you say. but i just want to be clear on one thing: why is a larger stroke so bad on an engine with minimal sideload (r/s ratio)?</TD></TR></TABLE>

How can it be minimal (r/s ratio) when the 's' denotes stroke and you throw the phrase "larger stroke" in the same sentence?

Veris

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JunIntegra &raquo;</TD></TR><TR><TD CLASS="quote">well the topic pretty much says it. ive heard many people say that the nissan KA24de and many other large stroke motors( like the k24 by honda, etc.) are limited to their high stroke (96mm) and in assumption that the r/s ratio is bad because of this. but the ka24de has a comparible r/s ratio to a b16a in 1.7s. (1.716 i think) this is better than an ITR motor that goes to 8400 rpm. so what about a large stoke (and high r/s) is limiting high rpm?
i ask this cuz my ka24de is limited to quite a low redline (6500-7000) and would like to get a higher speed from each gear and top speed. i know that power curve shoukd govern the redline but if the motor can go higher, it will be built to make power there. any help is appreciated</TD></TR></TABLE>

Both R/S and Stroke can restrict RPM.

The larger the stroke the larger the max piston velocity/acceleration.
The shorter the R/S ratio the larger the max piston velocity/acceleration.

Here is an analysis I did earlier this year. It explains it in detail.
http://www.ftlracing.com/tech/engine/rsratio.html

mmuller

R/S ratio is overrated, what really comes into play in rev capabilities is the piston speed.

ex:
b18c piston speed at 8k would be 4577 (stroke of 3.433)
b16 at 8k= 4041(stroke 3.031)
b18a/b at 8k=4670(stroke 3.503)
b21 at 8k=4986(strke 3.74)

and if you have a 96mm stroke piston speed at 8k would be 5038
just to add, revving a 96mm strke motor to 8k would have pretty much the same pistons speed as a b16 at 10k

crazy hugh?

Lsos

If there's a longer stroke, the piston has to travel further per each revolution. This means the piston speed as well as the acceleration will be higher...even if you have a 10:1 r/s.

Inertial loading on the rod is quite extreme at high revs. Lets say a b16 piston weighs 1 lb. In order to move this piston at 8000rpms (thus accelerating it at about 3500gs), the rod has to apply a force on it of about 3500lbs. This is not counting that the rod also has to accelerate itself. Using a beefier rod will probably mean it will be heavier, so more stress. Add to this the fact that this stress rises exponentially with rpm, then throw in vibration issues, and the result is that it's not so easy to just rev a motor to whatever you want. This is all without even looking at the r/s....

Veris

You aren't looking at max piston speeds just average pistons speeds. The speed limit on the road isn't a limit for your average speed it is a limit on the max. Same idea here.

Rod failure doens't occur due to average piston speed! That is why R/S has a role to play.

Read the link, it'll make more sense then.

http://www.ftlracing.com/tech/engine/rsratio.html

builthatch

lets not forget about weight of valve train components/ rotating assembly bits, induction efficiecny in terms of the porting and cam profile/ timing...alot of this stuff decides rev potential beside simply r/s-stroke...

danimal

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Veris &raquo;</TD></TR><TR><TD CLASS="quote">Rod failure doens't occur due to average piston speed! That is why R/S has a role to play. </TD></TR></TABLE>

nice page

what you are saying makes sense, but it's kind of difficult to interpret the data you have there, because piston acceleration is usually expressed as feet per second squared, not feet per minute... the page talks about piston acceleration, but then appears to list piston velocity instead(??).

when you look at it as a function of piston acceleration instead of piston velocity, what do those rod ratio differences look like?

Veris

There are two types of graphs on the page; Velocity and Acceleration. Velocity graphs are in ft/s and acceleration graphs are in g's (g-forces; 1g = ~32ft/s^2).

Hope that clears things for you.

danimal

i shoulda known about the g-force conversion!

thanks.

JunIntegra

thanks for all the great replies guys. i understand alot more about the subject.
what would you say to be the highest redine/piston speed i should attempt with my build?
Wiseco forged pistons 9:1
stock forged rods and crank
Full arp studs
new OE bearings
cometics HG
oh and it does have main block girdle and piston oil squirters

i was hoping to get atleast 7400-7500 RPM out of it

Veris

At 7500RPM the max G's of a K24 is -4126G's. (99mm stroke not 96mm.)
http://www.acura.ca/AcuraEng/M...tions

For reference a B20Vtec is -4218G's at 8000 RPM.
At 8000rpm the K24 is -4695G's.

In a B20 motor I'd suggest ARP rod bolts for those RPM/stresses. I'm not sure about the K24 rod bolts so I can't comment specifically, but 7500 on those stock internals will be pushing things.

My best GUESS is 7500rpm is ok with APR rod bolts & 8000rpm would be ok with all aftermarket-forged parts.

JunIntegra

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Veris &raquo;</TD></TR><TR><TD CLASS="quote">At 7500RPM the max G's of a K24 is -4126G's. (99mm stroke not 96mm.)
http://www.acura.ca/AcuraEng/M...tions

For reference a B20Vtec is -4218G's at 8000 RPM.
At 8000rpm the K24 is -4695G's.

In a B20 motor I'd suggest ARP rod bolts for those RPM/stresses. I'm not sure about the K24 rod bolts so I can't comment specifically, but 7500 on those stock internals will be pushing things.

My best GUESS is 7500rpm is ok with APR rod bolts & 8000rpm would be ok with all aftermarket-forged parts.
</TD></TR></TABLE>

please keep in mind that i am talking about the nissan ka24de with 96mm stroke...

Veris

My bad...

Send me the bore, stroke, and rod length and I can calculate your max g's at 7500 rpm.

JunIntegra

cant remember rod length but it is 89mmx96mm

LudeyKrus

Wow, there's a lot of misinformation in here.....