85

I was just reading that other thread about someone trying to make 350whp on stock bore K20. It got me thinking, the more over square a motor is, (generally) the higher the rpms along with HP and less torque. when you have a light weight drag car like a honda, how much torque do you really need? looking at all the 600cc street bikes, over the past 7 or so years have been getting smaller and smaller strokes all the way to 2007 where they all have 42.5mm now.

Ive always herd, theres no replacement for displacement but what about the D16 with the D15 crank? im just thinking, lose the TQ and rev the SH** out of the motor with a larger bore

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b20powereDA

so what is ur question? i didnt quite catch that

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85

people seem to be all about the stroked motors. to be blunt, but why not just bore it out and build it with the lightest internals and rediculous valve springs to get the most revs you can out of it. sure you wont have the TQ that you would with the stroker but im sure it would more then make up for it with HP and in theory make more HP the a stroker ever could.

im not sure what your getting at here but why not? OVER SQUARE is better!

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HAMOTORSPORTSUSA

oversquare or high rpm motors shift the torque peak higher. you don't always loose torque.

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mgags7

All other variables the same, a longer stroke will make more torque at peak.

Why not find a happy balance, revving the shit out of a 2 to 2.5 liter engine is not always going to last well.

For drag racers you have a good point, but for anyone who uses their car on a real track having to rev to 10k rpm to make power is just a bit ridiuclous.

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averyvm

can someone explain to me what oversquare means

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mgags7

It is a way to talk about bore versus stroke.

A square motor has the same bore as stroke
Undersquare means the bore is smaller than the stroke
Oversquare means the bore is bigger than the stroke.

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bluedlude

you dont need to lose the torque, or destroke, just make a longer rod and a taller deck . its the rod to stroke that lets you rev the shit out of it.

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DonF

No1. you can only discuss this with the same size motor. 1.6 vs 1.6 or 2.0 vs 2.0.
N02. What is the reason for the larger bore? Stroke really does not come into it except to keep the equal displacement.
Example 81 bore 95 stroke vs 90 bore 77 stroke. Both 4cyl. What would make more BHP and why?

simply

wow learned something new today. Anybody else have any input.

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DonF

Huh?

bluedlude

i was just saying that you can make a motor have any characteristic you want if you could change the deckheight to whatever you want.


and i vote the 90bore 77stroke motor for highest bhp

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FS: centric rotors for 04-06 TSX. new in box.

DonF

Why?

bluedlude

ahha sir, ive learned too much from you all on here. but i just typed to very simple numbers into my calculator and compared the two answers i got for each. just so happens both setups come out rather close, but not exact. do you want me to give away the answer before anyone else gets to it? i guess this is all assuming im right

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FS: centric rotors for 04-06 TSX. new in box.

DonF

They should not be that close. Why?

bluedlude

i made the assumption that both cylinders have the same AFR and a homogensous mixture. so if they have the same displacement, they will have the same force F created during combustion. that force is applied over the surface area of the piston. ill call that my gas force. and that acts like a moment arm . so my gas force times my moment arm gives me my really basic answer. even though using half the strok as a moment arm isnt correct it gives you a general idea.

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NJIN BUILDR

You working inside a predetermined box.People start stroking a b motor because you limited by how much you can go with the bore.The box the bikes work within is a displacement limit.A big bore allows you to increase airflow and decrease piston speed.The trade off is you move the hp and torque peaks farther up the rpm scale.And you increase the strain on the valve train.You have to be careful with bike comparisons though.They change things for the sake of change.Through the late seventies and eighties Honda 250cc dirt bikes changed bore and stroke almost every year.And every year they had a revolutionary reason why the new bike was better.

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85

larger R:S does allow you to rev higher by lower the acceleration of the piston to a extent. having a 3' rod is going to weigh too much for the crank as well as just in general to have any gain. So i see the question here as being, how much can the crank of a K20 handle?

riddle me this...

2 engines = each 1 cylinder, each is the same cc

engine 1 has a 100mm stroke
engine 2 has a 50mm stroke and has a rod length that is twice as long (feel free to change the rod length)

its a perfect world, so during each stroke each engine makes a gas pressure = to C

so how much torque does each engine make in comparison to each other? How much more does the short stroke engine weigh?

And last, if HP=[(rpms x Tq)/5252] then which engine will make more power in the end?

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85

yeah you do have a point there...

just something to make you think about though... if you look at GSXRs from i think 1990 to 1998 (or around there) they shrunk the port size and still managed to increase HP with each change in generation.

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DonF

NJIN is correct more bore, larger valve, more air, more RPM's, more BHP. It may call for a new head design, but these are just air pumps. The K's have a new head, more air flow and can go 90mm, theirfore more potential, same displacement.

DonF

On the TQ vs BHP 200 Lb Ft @ 7000 rpms equals what vs @ 200Lb FT @ 10,000 RPM.

85

well if it were a perfect world,

7,000rpms = 266hp
10,000rpms = 380hp

but with more rpms comes more friction soo...


keep in mind these are nothing more then calculations


Modified by 85 at 10:27 AM 5/3/2007

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