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Stroker vs Big Bore
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The Noof
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PostPosted: Thu Mar 08, 2007 3:26 pm    Post subject: Reply with quote

Thank you... Cool
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Stripped66
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PostPosted: Thu Mar 08, 2007 3:50 pm    Post subject: Reply with quote

To illustrate John's point,

[email protected] wrote:

While it is true the longer stroke engine has "more leverage" due to the longer stroke, IT HAS A SMALLER PISTON PUSHING ON IT. So, it's a wash.


Let's say you have 200 psi of cylinder pressure during a combustion event on 2 different engines, a 1904 (74 x 90.5) and a 1914 (69 x 94):

200 psi acting on a 90.5mm piston = 1994 lbs of force
200 psi acting on a 94mm piston = 2151 lbs of force

The moment-arm length changes as the crankshaft rotates, but it is never more than 1/2 the stroke; so, let's assume that these cylinder pressures occur at peak moment-arm length.

Maximum moment-arm length using a 69mm crank = 0.1132 feet
Maximum moment-arm length using a 74mm crank = 0.1214 feet

Torque = force x distance (the length of the moment-arm)
1904cc engine: 1994 lbs x 0.1214 ft = 242 ft.lbs
1914cc engine: 2151 lbs x 0.1132 ft = 243.5 ft.lbs

Anyway, hypothetical situation so that we can visualize how a given cylinder pressure produces torque under two similar displacements. Yes, it would be nice to have 240+ ft.lbs of torque, and yes, cylinder pressures are much higher than 200 psi. Before you go tearing down why the psi/torque numbers are off, remember that cylinder pressure is near it's highest *around* TDC, but this is where the moment-arm length is nearest to zero (at TDC, the moment arm length is zero). As the crank rotates and the piston moves down in the cylinder, pressures diminish quickly (remember, pressure is inversely proportional to volume). So, no...the pressure is not representative of anything in particular, but is merely a simple example to demonstrate the relationship between displacement and torque.
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66brm wrote:
Bodacious wrote:
Why not just make a custom set of wires with a Y splice in them. Then you could just run one distributor.

I don't think electrickery works that way
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veedubcrazy
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PostPosted: Thu Mar 08, 2007 4:01 pm    Post subject: Reply with quote

I would like to see Jeff Denham type all this stuff... Laughing
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[email protected]
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PostPosted: Thu Mar 08, 2007 4:51 pm    Post subject: Reply with quote

the difference is almost .75%! Oh snap.......

lets find some other <1% janx to worry about......

I will go on record and say a small bore stroker will not be hurt as much by a tightwad putting on some crappy heads as much as the big bore engine will, LMAO.

Build the small bore stroker if you want a tractor motor. Razz


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Stripped66
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PostPosted: Thu Mar 08, 2007 5:09 pm    Post subject: Reply with quote

[email protected] wrote:
the difference is almost .75%! Oh snap.......


The difference is about the same % as the difference in displacement...about 0.5% Very Happy
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66brm wrote:
Bodacious wrote:
Why not just make a custom set of wires with a Y splice in them. Then you could just run one distributor.

I don't think electrickery works that way
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[email protected]
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PostPosted: Thu Mar 08, 2007 5:10 pm    Post subject: Reply with quote

WTF do we know, everyone knows strokers make more torque

Laughing


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[email protected]
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PostPosted: Thu Mar 08, 2007 5:15 pm    Post subject: Reply with quote

you wussy, you should have at least an 86 crank in that thing Matt.......

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matt davis wrote:
[email protected] wrote:
People wake up!

Build the biggest BORE you can, and after you have done that if you have $ leftover, then stroke it.


Which is why my street engine is 101x74

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redhot
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PostPosted: Thu Mar 08, 2007 5:16 pm    Post subject: Reply with quote

Then what I believed is correct.... The simple laws of physics still apply, and that`s good to know Smile


A follow up question: what would impact on how the torque/hp relates to RPM? Are there any variabels there that should be considered?



Thanks for the many replies! Guess it`s a topic that many have interest in
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The Noof
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PostPosted: Thu Mar 08, 2007 6:21 pm    Post subject: Reply with quote

[email protected] wrote:
WTF do we know, everyone knows strokers make more torque

Laughing


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ROTFLMAO...he finally said something I can agree with.
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eng-man
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PostPosted: Fri Mar 09, 2007 8:32 pm    Post subject: Reply with quote

Ther is no match for cubie inches except more like big blocks rule
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PostPosted: Sat Mar 10, 2007 8:49 am    Post subject: Reply with quote

eng-man wrote:
Ther is no match for cubie inches except more like big blocks rule


Not in the VW world. Heads reign supreme when looking for power.
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eng-man
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PostPosted: Sat Mar 10, 2007 6:29 pm    Post subject: Reply with quote

You can put the best heads in the world on and engine and help it . But realey all the wright parts must be put together to make things run. one part is good but when you get BIG bore Long stroke Good heads You syill have to have a good intake &carbs and good exhaust. and it all needs to work together . but the more CC the better
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PostPosted: Sun Mar 11, 2007 9:28 am    Post subject: Reply with quote

eng-man wrote:
You can put the best heads in the world on and engine and help it . But realey all the wright parts must be put together to make things run. one part is good but when you get BIG bore Long stroke Good heads You syill have to have a good intake &carbs and good exhaust. and it all needs to work together . but the more CC the better


I'm just making it clear to anyone reading for info that the more displacement is not going to make the most power. That is what you are making it sound like.

It is very easy to build a 1776 that will spank a 2110. We see it all the time. Someone buys a big cc motor thinking they'll reign supreme while some guy with a "smaller" motor is spanking them all over the dunes.

Displacement is secondary. Leave that mentality to the V8 world.
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matt davis
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PostPosted: Sun Mar 11, 2007 10:16 pm    Post subject: Reply with quote

[email protected] wrote:
you wussy, you should have at least an 86 crank in that thing Matt.......

John
Aircooled.Net Inc.

matt davis wrote:
[email protected] wrote:
People wake up!

Build the biggest BORE you can, and after you have done that if you have $ leftover, then stroke it.


Which is why my street engine is 101x74


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krusher
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PostPosted: Mon Mar 12, 2007 10:12 am    Post subject: Reply with quote

So what makes good low end TQ?
high air speeds at low rpm= good chamber charge fill

And if so does a longer stroke crank to bore ratio promote this is any way?

Confused
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[email protected]
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PostPosted: Mon Mar 12, 2007 10:44 am    Post subject: Reply with quote

http://aircooled.net/gnrlsite/resource/articles/t1hpeng.htm

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runslikeapenguin
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PostPosted: Mon Mar 12, 2007 2:07 pm    Post subject: Reply with quote

i learn so much from topics like this one. its good to be able to read stuff like this.
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PostPosted: Mon Mar 12, 2007 2:17 pm    Post subject: Reply with quote

the biggest hurdle is trying to overcome the "I read it on the Internet so it must be true" rubbish that is flying around all over the place.

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PostPosted: Wed Mar 21, 2007 1:07 am    Post subject: Reply with quote

[email protected] wrote:
the biggest hurdle is trying to overcome the "I read it on the Internet so it must be true" rubbish that is flying around all over the place.

John
Aircooled.Net Inc.


How about some "real world" experience with these two engines? From what I know a 1915 is a BUG engine, and a 1904 is more of a BUS engine. And here is a good example I have witnesses myself, keep in mind both buses are splits and both have same size tires and RGB's and carbueration: one buddy has a 1915 in his splitty Bus, it goes along pretty good, but the second he hits a hill, it's game over and falls on it's face and chugging along in third gear.... the bus with the 1904 following the 1915 bus on the hill can easily pass and even accelerate up the hill past the 1915 bus like he's standing still. Keep in mind the 1915 bus is a bare empty panel and weighs hardly anything....the 1904 bus is a pop-top westy fully loaded, now how do you explain that? The 1915 bus runs perfect and is in tune too, and is actually damn near brand new. Both the 1915 and 1904 are damn near identical, Kadrons, 110 cam, standard header, etc. Now explain that one to me. Question From what I read, Aircooled John seems to think the 1915 is more powerfull or at least the same as the 1904, no way! Exclamation
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PostPosted: Wed Mar 21, 2007 8:53 am    Post subject: Reply with quote

Boo hoo!
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