frEEk
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posted November 25, 2006 12:14 PM
max stroke?
not necessarily specific to the 12r... at what point does increased stroke actually burt HP and/or TQ? i don't mean while keeping the same displacement, because obviously that would mean any increase in stroke woudl mean a decrease in peak HP. but given a fixed bore and a variable stroke, at what point does HP & TQ (assume it will happen at different ponts) decrease?
   
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Y2KZX12R
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posted November 25, 2006 12:49 PM
Thats a complex question. But stroke doesnt reduce HP it increases it. Because it increases the displacement and thus increases HP.
But I think your asking at what point does stroke reduce the rpm you can rev the engine to and thus reduce the HP before you cant rev the engine.
If thats the case then every engine is different. And even the same basic engine (zx12r) would vary based on how good the rods etc. are that were used and what rpm they can take.
The zx12r could rev to the limiter 11,625 with a stroke longer that the 60mm Muzzy puts in thier 1375 kit. And thats with stock rods. I'd have to crunch some numbers to tell you at what stroke piston speed and ring seal would become the limiting factor. But it would be a few mm longer than 60. At that point then if you traded off stroke for bore and kept the displacement the same you could then rev the engine higher and make more HP then the same displacement engine with a longer stroke.
Sounds confusing but bottom line.... these big stroker inline 4's arnt at the limits of stroke where too much stroke is an issue.
The 12r at 61mm stroke is a can of worms becasue the rods will hit the block. Thats why 60 mm was chosen by Muzzys.
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entropy
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posted November 25, 2006 04:11 PM
With the 60mm stroker crank & Carrillos, the rod bolts hit both the case and the starter gear, but no giant problem to fix.
I have not had the crank hitting the cyl block
(yet... give me time, I can break anything  )
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supra5677
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posted November 25, 2006 04:56 PM
all things being equal more stroke equals more torque, more bore makes more h.p.
classic example zx12r vs hayabusa.. the 12r makes more horsepower even though its
giving up 7.6mm on the stroke.. F1 engines have relatively short strokes and are
half the size of Nascar Engines yet the still make more horsepower. 3.0L for
F1 and 5.7 Liters for Nascar.
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frEEk
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posted November 26, 2006 08:52 AM
Y2K, that's surprising that it is so little more on the 12r, but i suppose that's more cause of physical constraints than anything. what i was asking was more theoretical though. like if you had pretty open specs, but a set bore, what is the max stroke before peak HP decreases? i figured RPM to be a limiting factor as u pointed out, after all a 3ft stroke on a 3" bore aint gonna work too well (is it?). i was actually thinking that at some point you simply wouldnt have enough fuel to produce such a long flame front, but then i realized u'd just increase the combustion chamber to pack more and more fuel in. i guess the limiting factor then may become the amount of ring friction due to having so much wall surface for a given displacement. what it comes down to, is there are several limiting factors i gues,s but i dont know which one would be the primary one, and at what point it would kick in.
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Y2KZX12R
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posted November 26, 2006 09:25 AM
Well if you had a target RPM limit, then you would know what the maximum stroke could be with a given rod length.
Thats what would determine the maximum stroke.
The bore? Well the bigger the better. More displacement makes more power. Wether its stroke or bore, increasing the displacement increases power.
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frEEk
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posted November 26, 2006 02:47 PM
no RPM target, just this:
given a fixed bore of X, what stroke would give the highest peak HP?
i figured it was a well known rule that builders all knew about. if there' snot a clear answer, don't worry about it. the question is jsut for my theoretical curiousity anyway.
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Y2KZX12R
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posted November 27, 2006 01:41 PM
 Edited By: Y2KZX12R on 27 Nov 2006 14:06
quote:
no RPM target, just this: given a fixed bore of X, what stroke would give the highest peak HP?quote:
Well you need a HP or RPM target. So becasue you have no RPM target you need a HP target. Once you have a HP target then you need to calculate the rpm you need to "pump" that amount of air. But thats a somewhat sketchy formula with lots of variables. But average air flow or the average cfm on a flow bench =1.67x hp per cyl. But the maximum intake air flow rate for one cylinder will be about 2.5 times the average. Remember the intake valve is open only about 40% of the total cycle.
Heres an example of a 440 hp small block chevy. The power is 55 hp per cylinder.
average air flow = 1.67 x hp = 92 cfm
average intake rate = 2.5 x 92 cfm = 230 cfm
peak intake rate = 2.5 x 230 cfm = 575 cfm
I have software that does all the thinking and math and formulas so it makes things much quicker and easier to play " what if ".
I've run out many senarios of the zx12r engine and believe it or not its a very well balanced design aimed more towards peak HP and less importance on low and mid range torque.
If you had more information on the engine rules of the class you were building an engine for, you could get more specific on what stroke would be best.
So its not a static answer its very dynamic.
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frEEk
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posted November 28, 2006 01:14 AM
not too surprising really. well, i'll just have to keep wondering. or i'll have to expiriment one day by chopping up my engine and putting a 1fy frank extension on it 
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bossman12r
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posted December 06, 2006 06:13 PM
Ok the zx14 has a 61mm crank and a 84 piston, not sure if the rods are the same lenth as a 12 but on another site I am getting beat up about a 12 running with a 14. I don't see why a 1394 zx12 can't run with a 2mm over bore zx14. Should I just get a 14 or is their hope for my 12?
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NINJA12
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posted December 08, 2006 06:02 AM
The stock zx14 has not dynoed 200 yet!
I know of a few 1361/1375 that have.
I think most of those guys were thinking you were starting from a stock bike wanting
to spank the zx14. That is not economically wise, but with the base you have
I feel the motor investment will work until the zx14s start to go bigger.
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TRNorBRN6001
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posted December 08, 2006 06:55 AM
ZX14 has already gone bigger........................5mm over crank (must be some real short rods for that kit!).
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ozzy
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posted December 08, 2006 09:14 AM
quote:
not necessarily specific to the 12r... at what point does increased stroke actually burt HP and/or TQ? i don't mean while keeping the same displacement, because obviously that would mean any increase in stroke woudl mean a decrease in peak HP. but given a fixed bore and a variable stroke, at what point does HP & TQ (assume it will happen at different ponts) decrease?
depends on how long your rod is
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entropy
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posted December 08, 2006 10:34 AM
quote:
quote:
not necessarily specific to the 12r... at what point does increased stroke actually burt HP and/or TQ? i don't mean while keeping the same displacement, because obviously that would mean any increase in stroke woudl mean a decrease in peak HP. but given a fixed bore and a variable stroke, at what point does HP & TQ (assume it will happen at different ponts) decrease?
depends on how long your rod is
i don't understand what you are getting at???
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Y2KZX12R
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posted December 08, 2006 01:37 PM
Edited By: Y2KZX12R on 8 Dec 2006 17:14
My above posts were assuming the same rod length. But rod length does play a role in piston speed and acceleration.
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Ozzy
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posted December 08, 2006 04:44 PM
quote:
My above posts were assuming the same rod length. But rod length does paly na role in piston speed and acceleration.
I don't care to find out how long ones rod is
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