Bore - Stroke Square - Oversquare (rectangle?)

[DSC]

I was reading up on the CA vs SR thing over here (http://www.zilvia.net/f/cgi-bin/ikonboard.cgi?act=ST;f=1;t=7826) and I didn't think my question should go in that thread, so I started a new one.

First tell me if I'm wrong on this, Bore is the diamater of each cylinder, or the diamater of each hole in the head (4 for us) rather? Stroke is the distance the piston travels up and down?

Alright, so my main question, what are the advantages/disadvantages to haveing:
More bore than stroke
More stroke than bore
or haveing stroke = bore
Umm and why...

[240meowth]

don't quote me on this, but since no one is responding thought i might take a stab at it.

more stroke you have, you get higher compression, which ultimatly leads to more hp per liter, yet leads to higher octang as well.  also, your redline will decrease?

bore... don't have a clue... i assume it increase the displacement, and you get more displacement outta the engine, which means more fuel, more power

don't know if that did anything...

all i know is, the F1 cars have fat ass bore and tiny ass stroke, so their car revs to like 14k rpm as redline?

[HotRodGuy]

Yep, that's pretty much my understanding of it also. Except that the bore is in the block, not the head.

However, you also git increased displacement from increasing the stroke, too.

I don't pretend to know exactly how it all comes together, it's all in the math, that much I do know.

Here's the formula to figure out the Cubic Inch Displacement:

(Bore x Bore x Pi x Stroke x No. of Cyl.)/4

This should work on any engine although I got it out of an AMD engine building book.

If you increase the bore and keep the stock stroke then your redline should stay about the same. You'll just have more power building in the piston chamber. (bigger piston = more power)

If you increase the stroke then your compression goes up and your redline goes down. (longer stroke = less revs)

If you decrease the stroke then your compression goes down (but can be corrected with dome top pistons) and your redline goes up. (shorter stroke = more revs)

Now, if you want to build a Turbo engine with lots of boost then you want about 8:1 compression (not sure what the KA's is stock) I believe that you can put a turbo on a stock KA with little boost (7-8 psi?) and it'd be ok, but don't quote me on that as I haven't built mine yet.

Hope this helps. If I'm wrong on any of this someone please correct me. I don't want to steer anyone wrong.

[dsjunkie]

in the '89 ka sohc the compression is 9.0:1
in the '90 ka sohc the compression is 8.6:1
and in the '91 and on dohc the compression is 9.5:1

so you would need to do some work on changing compression eventually but light boost is acceptable

[White240sx]

Compression has to do with piston design and combustion chamber shape, not stroke.

The main advantage to a larger bore is that it allows for bigger valves, which flow more at high engine speeds. But at low engine speeds you lack intake velocity with large valves, which translates to less power in the lower rev range. A smaller bore uses smaller valves which creates high velocities for low-end power, but the can't flow enough to make power at high engine speeds.

Stroke wise a longer stroke gives more leverage and thus more torque, but it is limited on how fast in can travel and it has more side thrust. A shorter stroke engine can move faster but it doesn't generate the leverage of a longer stroke.

So a motor with a long stroke and small(er) bore will have more lower end power but not as much revability, and a short stroke large® bore engine will have more high end capability as well as faster engine speed potential.

[9591]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (dsjunkie @ April 01 2002,11:47)</td></tr><tr><td id="QUOTE">in the '89 ka sohc the compression is 9.0:1
in the '90 ka sohc the compression is 8.6:1
and in the '91 and on dohc the compression is 9.5:1

so you would need to do some work on changing compression eventually but light boost is acceptable</td></tr></table><span id='postcolor'>
Early '89 was 9.1:1. Later '89 was 8.6:1, same as the '90.

[camppain]

there was a topic strared exactly like this on fa dsc i cant find it though i was reading it this morning and now i cant find it <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/confused.gif" border="0" valign="absmiddle" alt='???'> it was good too didnt finsih readin ti all

nerr mind i saw you replied in that topic

[DSC]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (camppain @ April 03 2002,01:17)</td></tr><tr><td id="QUOTE">there was a topic strared exactly like this on fa dsc i cant find it though i was reading it this morning and now i cant find it <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/confused.gif" border="0" valign="absmiddle" alt='???'> it was good too didnt finsih readin ti all

nerr mind i saw you replied in that topic</td></tr></table><span id='postcolor'>
Yeah, I was talking to someone on AIM about it and he thought it would be a good idea to post the question there also...he was definately right.

Here it is (http://forums.freshalloy.com/forum/ultimatebb.php?ubb=get_topic;f=9;t=012628) for those of you who are interested...2 pages already

[HotRodGuy]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (White240sx @ April 02 2002,12:47)</td></tr><tr><td id="QUOTE">Compression has to do with piston design and combustion chamber shape, not stroke.</td></tr></table><span id='postcolor'>
Well, duh! I knew that. *smacks forehead*

Don't know what I was thinking about when I said that changing the stroke changed the compression. When you change the stroke you have to get new pistons that have the wrist pin in a different location from stock, so the top of the piston will still be at the top of the cylinder bore.

Yer right, compression is all determined by piston shape (dome, flat, dished) and combustion chamber size and shape. It has nothing to do with the stroke.

Thanks for the correction! <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/wink.gif" border="0" valign="absmiddle" alt=';)'>