UNDER SQUARE vs OVER SQUARE

CAN SOME ONE EXPLAIN THIS. LARGE BORE SHORT STROKE VS SMALL BORE LONG STROKE


ACE

Bigger Bore short stroke engines seem to like higher rpms,longer stroke seem to be more torque oriented. I'm not a expert,just what I've observed.

Big bore = more room for the valves. Unless one is restricted by rules run a big bore & stroke   

Lem Evans wrote:Big bore = more room for the valves. Unless one is restricted by rules run a big bore & stroke   

^^^^^No replacement for displacement.   

bbf-falcon wrote:Bigger Bore short stroke engines seem to like higher rpms,longer stroke seem to be more torque oriented. I'm not a expert,just what I've observed.

This is what I've been told as well, but those pistons are heavy compared to long stroke so what gives? Heavy pistons for high reving? Still doesnt go together.

Square seem to be right (for what its worth).

I also like a square engine also.....4-5/8" X 4-5/8".

622" works for me   

As long as you got head flow to support that.

Dave De wrote:As long as you got head flow to support that.

Exactly.....people think just because one has a short stroke an engine will make a lot of power at high RPM.

It also takes a lot of cyl. head flow to make big power at very high RPM with a smaller engine.

powerstrokeace wrote:CAN SOME ONE EXPLAIN THIS. LARGE BORE SHORT STROKE VS SMALL BORE LONG STROKE
ACE

Only in a volume as long as "War and Peace".

The BB/SS 538" that Jim Kuntz built that made 1150/800+ said that the heads Flowed 450 int. Thats not Huge #'s these days for a Ahead. So,I don't know the details about the rest of the engine,kinda wonder what it would have made w/BIG flowing heads  

sometimes I think I know something, other times Im sure I don't.....

bbf-falcon wrote:The BB/SS 538" that Jim Kuntz built that made 1150/800+ said that the heads Flowed 450 int. Thats not Huge #'s these days for a Ahead. So,I don't know the details about the rest of the engine,kinda wonder what it would have made w/BIG flowing heads  

Valve shape , valve job angle, chamber work, etc. are additions to flow. Flow is not the only measure of performance.

Lem Evans wrote:

bbf-falcon wrote:The BB/SS 538" that Jim Kuntz built that made 1150/800+ said that the heads Flowed 450 int. Thats not Huge #'s these days for a Ahead. So,I don't know the details about the rest of the engine,kinda wonder what it would have made w/BIG flowing heads  

Valve shape , valve job angle, chamber work, etc. are additions to flow. Flow is not the only measure of performance.  

Why is it that only Pro Stock guys and Competition Eliminator guys are the people I hear who say this stuff about "flow numbers" not being the "end all" of performance...?

They probably know something which the general racers / bench racers / wanna-be racers only THINK they know.

As you change bore and stroke while maintaining the same RPM and cubes.... you will be changing piston speed, a longer stoke will increase piston speed, (must cover more distance within the same amount of time) Knowing, manipulating and designing the entire package with the understanding of how piston speed and air flow coincide are important for building and engine to its full potential.....

rmcomprandy wrote:Why is it that only Pro Stock guys and Competition Eliminator guys are the people I hear who say this stuff about "flow numbers" not being the "end all" of performance...?

They probably know something which the general racers / bench racers / wanna-be racers only THINK they know.

I guess this is why I listen to the professionals and not get hung up on flow numbers. Heck, I never flowed my A heads after doing mild clean up to remove the casting flash on the little 488ci motor. I couldn't be happier with it after all the help I recieved here considering its making way over 800hp @7200 and is that small!

hookin78 wrote:As you change bore and stroke while maintaining the same RPM and cubes....  you will be changing piston speed, a longer stoke will increase piston speed, (must cover more distance within the same amount of time)  Knowing, manipulating and designing the entire package with the understanding of how piston speed and air flow coincide are important for building and engine to its full potential.....

That is the main reasoning that short stroke / big bore engines get associated with higher RPM; long stroke engines can't GET to that same very high RPM. That advantage won't mean a thing if the valve train and the rest of the engine can not get up there either.

Interesting thread.   

"Why is it that only Pro Stock guys and Competition Eliminator guys are the people I hear who say this stuff about "flow numbers" not being the "end all" of performance...?"
 
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"Not being the 'end all' of performance"
 
Randy, that's a very good way to express it. But, some people take it to mean that flow numbers mean little or nothing.
 
I.m.o. a guy could bet his ass that the P/S & C/E guys do have a lot of flow but, are not willing screw up a package that is mechanically correct to get the next 12-15 cfm.

Flow bench and dyno are tools and in the right hands can advance ones cause. Physical design characteristics matter a great deal too. If Pro stock was allowed to run a 4V DOHC head, but limited to the same max flow numbers think the pushrod 2V stuff be competitive?

As for bore and stroke, years ago you had long strokes and small bores and common belief was the long stroke gave you more leverage and hence made more torque. We are talking flat head days. Reality was the designers used a long stroke/small bore because it resulted in less surface area for a bad design.

When the OHV stuff came around you saw bigger bores and shorter strokes come into favor. Larger bore helps the breathing with limited 2 valve stuff and shorter stroke keeps the piston speed down. Better design put the flat head stuff on the shelf beating it both in torque and HP.

Now a days see a lot of near square stuff. Not convenient for OEM's run big bores a lot of times because of packaging requirements. 4 valve cylinder heads takes care of breathing and DOHC's let them rev as well as optimizing port location.

Not uncommon today for a stocker to turn 6,500 - 7,000 rpm just kicking down into passing gear and they do it without breaking a sweat or running out of breathe. Some of this new stuff makes some power too. Coyote 5.0L 412 HP. That is 1.36 hp/ci.

Lem Evans wrote:"Why is it that only Pro Stock guys and Competition Eliminator guys are the people I hear who say this stuff about "flow numbers" not being the "end all" of performance...?"
 
==================================================================================================
 
"Not being the 'end all' of performance"
 
Randy, that's a very good way to express it. But, some people take it to mean that flow numbers mean little or nothing.
 
I.m.o. a guy could bet his ass that the P/S & C/E guys do have a lot of flow but, are not willing screw up a package that is mechanically correct to get the next 12-15 cfm.

YES ... Exactly part of it. Those flow numbers DO have meaning which is of importance; especially the curve, not the outright maximum air flow capability. Just make it bigger and it WILL flow more total air.
Air Flow is simply one measure of the capability of the power output a cylinder head package could provide. It is certainly NOT the ONLY IMPORTANT measure and shouldn't be treated as such.
A lot of people wrongly see it as the ONLY measure of importance.

The NHRA P/S stuff has long since turned into a rpm fest and I suspect the engine guys are focused on the valve train for performance gains. After all they already have the bigest intake valves that the 4.900" bore spacing rule will allow so there aint much to get on that front at this point.

The teams that are at the front of the field my be the ones that are winning the battle for valve train stability.

rmcomprandy wrote:

Lem Evans wrote:"Why is it that only Pro Stock guys and Competition Eliminator guys are the people I hear who say this stuff about "flow numbers" not being the "end all" of performance...?"
 
==================================================================================================
 
"Not being the 'end all' of performance"
 
Randy, that's a very good way to express it. But, some people take it to mean that flow numbers mean little or nothing.
 
I.m.o. a guy could bet his ass that the P/S & C/E guys do have a lot of flow but, are not willing screw up a package that is mechanically correct to get the next 12-15 cfm.

YES ... Exactly part of it. Those flow numbers DO have meaning which is of importance; especially the curve, not the outright maximum air flow capability.   Just make it bigger and it WILL flow more total air.
Air Flow is simply one measure of the capability of the power output a cylinder head package could provide. It is certainly NOT the ONLY IMPORTANT measure and shouldn't be treated as such.
A lot of people wrongly see it as the ONLY measure of importance.

If you change the discharge direction of the air you could go backwards, even if you see a gain or better "curve". Just doing dry flow will not tell all. How a port is designed matters just as much if not more IMO.

466cj wrote:

rmcomprandy wrote:

Lem Evans wrote:"Why is it that only Pro Stock guys and Competition Eliminator guys are the people I hear who say this stuff about "flow numbers" not being the "end all" of performance...?"
 
==================================================================================================
 
"Not being the 'end all' of performance"
 
Randy, that's a very good way to express it. But, some people take it to mean that flow numbers mean little or nothing.
 
I.m.o. a guy could bet his ass that the P/S & C/E guys do have a lot of flow but, are not willing screw up a package that is mechanically correct to get the next 12-15 cfm.

YES ... Exactly part of it. Those flow numbers DO have meaning which is of importance; especially the curve, not the outright maximum air flow capability.   Just make it bigger and it WILL flow more total air.
Air Flow is simply one measure of the capability of the power output a cylinder head package could provide. It is certainly NOT the ONLY IMPORTANT measure and shouldn't be treated as such.
A lot of people wrongly see it as the ONLY measure of importance.

If you change the discharge direction of the air you could go backwards, even if you see a gain or better "curve". Just doing dry flow will not tell all. How a port is designed matters just as much if not more IMO.

AGAIN ..."air flow is simply ONE measure of the capability of the power output a cylinder head could provide".