question's in the title but let me show with an example

block 1:
b17a bored over to 85mm, stock 81.4mm stroke
displacement comes out to about 1847cc

block 2:
b18a stock 81mm bore, stock 81mm stroke
displacement is about 1834cc

both have custom pistons that will achieve 11:1cr with a pr3 head

same pr3 head used on both motor

which motor would produce more torque, horsepower and what rpm's. im not looking for an exact number. more of, "block 2 will have torque due to its long stroke and peak torque will occur earlier than block 1". you guys get me? im just trying to understand the effects of the stroke.

BTW: does rod angles come into play here, determind how much and when torque/horsepower come in?

editted cuz i put the wrong stroke for the b17


Modified by gutted at 12:36 AM 2/4/2004

 

more stroke = more angle = more torque

 

so how does the stroke affect the HP? because to get horsepower its a mathimatical to torque in some way, right?

 

hp = (torque * RPM)/5252

More torque means you will make peak hp earlier in the rpm band.

 

More torque the engine is making at a given RPM, the more HP the engine will make at that RPM.


Take engine #1 for example and say it is making 115 lb/ft at 8000 RPM, the HP of the motor will be 175.1.


Engine #2 is making 145 lb/ft at 8000 RPM, the HP of the motor will be 220.86.

More torque = more HP at a given RPM.

Thats why I am ditching my 77.4mm stroke (b16) and going with a 87mm stroke (b18)

 

hp=(torque*RPM)/5252

torque and horsepower are direct..if torque goes up...horspower goes up...but at the same time..torque and rpm are indirect (inverse)...so if the torque goes up RPM goes down...

simple if you increase the stroke which inturns increases the torque..you will make more power but at a lower revolutions, or the mid to low part of your powerband...

 

Which is why LS/VTEC kicks *** !

 

Horsepower = Torque * RPM / 5252

The more torque you have at any given RPM, the more horsepower you have at that RPM. However, your peak horsepower depends on your TORQUE CURVE!

If your torque curve dips down faster than the value of RPM, then you start losing HP.

If you make 163 lbs-ft of torque at 6800 RPM, but you make 155 lbs-ft at 7200RPM, you still make more horsepower, because you make 211HP at 6800RPM and 212HP at 7200RPM. But after that RPM on an H22A, the torque curves dips sharply, and you lose horsepower.

Now, a longer stroke means more torque, but it usually reduces your REDLINE, because at 6000RPM for example, a longer stroke means a faster piston speed. That's why a B16A can rev up so high so easily. At 9000RPM, the piston speed is slower than an H22A at 8000RPM.

 

The volumetric efficiency of the motor is what increases your torque. Volumetric efficiency (at low rpm) goes up when your rod:stroke decreases because it pulls the air in harder. A motor with an 89 mm stroke and 137 mm length rod will have a broader powerband, more low rpm power, cleaner burn and better throttle responce than a motor with a 89 mm stroke and 150 mm rod (if the bore is the same).
Changing stroke doesn't have as much effect as changing rod:stroke ratio, but since they usually come hand in hand, people mistake changing stroke as making the changes.
Changing Bore will increase the time it takes for the flame wave to pass accross the piston, and give you a smoother engine. Engines which spend a lot of time in high rpm (s2000 and b16) have large bores and small strokes because a high rod:stroke and and oversquare design (larger bore than stroke) makes the engine smoother.

Increasing the bore

 

I have some friends that want to make their B16s in their civics rev to 10.5k and make power all the way up. They can do that and I will laugh when I build an LS/VTEC that only has to rev to 8.5k at the most and it takes forever for them to catch up.

 

you can rev an ls/vtec to 9500+ if you know what your doing

 

but its pointless unless you have cams that make power up that high....

 

.....and on the 8th day the good lord created.....JUN 3's.......

 

yeah no ****, wanna teach me how to print money?