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Stroker vs Big Bore
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redhot
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PostPosted: Wed Mar 07, 2007 12:47 pm    Post subject: Stroker vs Big Bore Reply with quote

Hi,

Searched the threads, and read a lot. But one thing still puzzels me: why should I build a stroker instead of at big bore engine?
Best example would be maybe 76x90,5 vs 69x94. Being 1904 vs 1914, they show nearly the same displacement.

One has a larger arm, while the other one pushes with more force. Should they not compare directly using the same heads, cam, carb and such, and show the same torque and HP curve on the dyno?

As for ease of the buildup, the 1914 should be much simpler, but is there somehting I`m missing?



Read this post and that`s the background for my question:


2 engines of similar displacement will have similar outputs. For example, a 1914 and 1905 are almost the same thing. I see guys all the time say the 1905 will be "torquier" because it's a stroker, but that's bullocks. The 1905 may be a stroker, but the bore is smaller so it's not pushing as hard on the crank as the 1914 is, the result is 6s.

My advice (as always) is to bore the engine to 94s first, next get heads 2 steps better then you can afford, and if you have $ leftover get an 82mm crank. Do not bother with the in-between 74-80mm crankshafts, waste of $ IMO.

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http://www.thesamba.com/vw/forum/viewtopic.php?t=206234&highlight=stroker+john
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veedubcrazy
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PostPosted: Wed Mar 07, 2007 1:33 pm    Post subject: Reply with quote

If it were me, I would go for stroke over bore. Anytime. And if your going to stroke the engine, then stroke it big... Cool
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PostPosted: Wed Mar 07, 2007 1:34 pm    Post subject: Reply with quote

I say, do both. That's why I went 2180. Not too big, not too wide.
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redhot
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PostPosted: Wed Mar 07, 2007 1:39 pm    Post subject: Reply with quote

veedubcrazy wrote:
If it were me, I would go for stroke over bore. Anytime. And if your going to stroke the engine, then stroke it big... Cool



But why? What is the part I`m missing?

Glenn: Wise words... Rumor has it that once started with big engined VW`s you wont ever go back Smile
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veedubcrazy
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PostPosted: Wed Mar 07, 2007 1:41 pm    Post subject: Reply with quote

All I can say is, if you have never driven a stroked vw, just wait. When you do, you will wonder why you waited so long to do it. I will never go back to 69mm.
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Stripped66
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PostPosted: Wed Mar 07, 2007 2:33 pm    Post subject: Reply with quote

veedubcrazy wrote:
All I can say is, if you have never driven a stroked vw, just wait. When you do, you will wonder why you waited so long to do it. I will never go back to 69mm.


It's not so much the stroke, but the displacement. Heroics aside, a street VW is usually limited to a 94mm bore. Therefore, there's only so much you can do with the stock stroke. John Connolly's post is right on the money...torque = Brake Mean Effective Pressure x DISPLACEMENT. That's the mathematical equation for torque in an internal combustion engine. So, not stroke but DISPLACEMENT. That means, for a given cylinder pressure and displacement, torque is going to be the same regardless of whether it's small bore x large stroke, large bore x small stroke, or something in between.

A 1904 or a 1914...go with the 1914. It will be cheaper and easier to assemble. But if you want something larger, then YES, GO WITH A STROKER! It's not so much the stroke as it is the much larger displacements you can achieve (and the inherent inability to build a 2.2-2.4 liter engine WITH a stock crank).
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mailman
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PostPosted: Wed Mar 07, 2007 5:05 pm    Post subject: Reply with quote

Isn't it true, though, that increasing the stroke will move the power band lower in the RPM range? If so, then with a stroker you'll be able to utilize your power without revving the hell out of the engine.
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Loopole
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PostPosted: Wed Mar 07, 2007 5:43 pm    Post subject: Reply with quote

you need to do some more reading and learn some about rod ratios, you are basically locked in wth a stock crank, not so with a stroker, the ideal engine now for daily ride is probably a 2180 with the thick wall cylinders, nice heads, good exhaust and idf 44s, i am driving a 2110 i got from chico and absolutely love it, runs cool, gets decent mpg and is a kick in the butt to drive, the torque you get from a stroker is night and day.
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The Noof
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PostPosted: Wed Mar 07, 2007 6:19 pm    Post subject: Reply with quote

Strokers rule...don't let ANYONE tell you otherwise.
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veedubcrazy
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PostPosted: Wed Mar 07, 2007 6:23 pm    Post subject: Reply with quote

The Noof wrote:
Strokers rule...don't let ANYONE tell you otherwise.


Preach it, brother!!!
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Eaallred
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PostPosted: Wed Mar 07, 2007 8:16 pm    Post subject: Reply with quote

Strokers rule ONLY if the bore has already been increased.

Think about it. A 1904 and a 1915 are moving the same amount of air through them at the same rpm's. Period. The two motors, given that everything else about them is the same, will make the same amount of power (actually the 1915 will make slightly more power).

Now, seeing as you're going to make the same amount of power, which way would be the better route? Well, lets look at it this way. If you go with a 1915, you can run larger heads, blowing the power a 1904 would away. The 1904 would never be able to touch it at that point because the head work wouldn't be there. Also, a small bore stroker motor is more difficult to build than a big bore, stock stroke motor. Cheaper too!

Where's the benefit of a small bore, long stroke motor? There isn't one.
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The Noof
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PostPosted: Wed Mar 07, 2007 8:30 pm    Post subject: Reply with quote

Eaallred wrote:
Strokers rule ONLY if the bore has already been increased.

Think about it. A 1904 and a 1915 are moving the same amount of air through them at the same rpm's. Period. The two motors, given that everything else about them is the same, will make the same amount of power (actually the 1915 will make slightly more power).

Now, seeing as you're going to make the same amount of power, which way would be the better route? Well, lets look at it this way. If you go with a 1915, you can run larger heads, blowing the power a 1904 would away. The 1904 would never be able to touch it at that point because the head work wouldn't be there. Also, a small bore stroker motor is more difficult to build than a big bore, stock stroke motor. Cheaper too!

Where's the benefit of a small bore, long stroke motor? There isn't one.



Who is gonna build a stroker 85.5 bore? The WHOLE point is power, when you start the bigger motor adventure.I'm sure there are a few dudes that doob too much and ponder these things, but there's no point to stroking a small bore. Your point is well made, and well taken.


Last edited by The Noof on Wed Mar 07, 2007 8:31 pm; edited 1 time in total
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jamestwo
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PostPosted: Wed Mar 07, 2007 8:30 pm    Post subject: Reply with quote

Thank you.

One thing the stroker has, is a shorter rod ratio, which can increase low end torque.

But for pure HP, the bigger bore is as you decribe


Eaallred wrote:
Strokers rule ONLY if the bore has already been increased.

Think about it. A 1904 and a 1915 are moving the same amount of air through them at the same rpm's. Period. The two motors, given that everything else about them is the same, will make the same amount of power (actually the 1915 will make slightly more power).

Now, seeing as you're going to make the same amount of power, which way would be the better route? Well, lets look at it this way. If you go with a 1915, you can run larger heads, blowing the power a 1904 would away. The 1904 would never be able to touch it at that point because the head work wouldn't be there. Also, a small bore stroker motor is more difficult to build than a big bore, stock stroke motor. Cheaper too!

Where's the benefit of a small bore, long stroke motor? There isn't one.

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PostPosted: Wed Mar 07, 2007 10:00 pm    Post subject: Reply with quote

The Noof wrote:
Who is gonna build a stroker 85.5 bore? The WHOLE point is power, when you start the bigger motor adventure.I'm sure there are a few dudes that doob too much and ponder these things, but there's no point to stroking a small bore. Your point is well made, and well taken.


Hasn't HotVW's magazine been building a 88x76 engine the last 5 months? In one of the last issues it sounded like they were putting out HP in the 90's and torque in the 100's. A stroker has much more torque at a lower RPM.
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krusher
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PostPosted: Thu Mar 08, 2007 1:00 am    Post subject: Reply with quote

There has to be more to it than said here, if stroke to bore ratio bears no impact on the engine why do we have things like short strokers for high rpm like motorbikes and race cars?

Is it all just about piston speed and rod ratio, or does bore to stroke have an impact on the engine? Confused

Here is some interesting reading http://me.engin.umich.edu/autolab/Publications/P2000_07.htm

All vw motors have a short stroke ratio, so its all kinda one side of the fence.

Very Happy
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PostPosted: Thu Mar 08, 2007 1:29 am    Post subject: Reply with quote

Hasn't HotVW's magazine been building a 88x76 engine the last 5 months? In one of the last issues it sounded like they were putting out HP in the 90's and torque in the 100's. A stroker has much more torque at a lower RPM.[/quote]

It's actually 85.5x76mm, 1745cc. Their building it for mileage. The stroke idea is to make things easier on this freewaybound cruiser engine. I've been following the article and eagerly await the mileage results. That thing had a 1 3/8 header, mexican heads with 33x32mm valves, dual weber 34 ict's and made a heck of a debut on the dyno! Shocked
But everybody knows that a longer lever is a more effective one all forces being equal. Strokers get off the line quicker, whereas a bigger bore increases top end performance. If the race is long enough the 1914 might win. Smile
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PostPosted: Thu Mar 08, 2007 6:15 am    Post subject: Reply with quote

Power is in the heads. Larger pistons can use larger valves thus creating the potential for more power. The 1915 will blow away a 1904 on the drag strip.
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PostPosted: Thu Mar 08, 2007 9:16 am    Post subject: Reply with quote

krusher wrote:
There has to be more to it than said here, if stroke to bore ratio bears no impact on the engine why do we have things like short strokers for high rpm like motorbikes and race cars?


1) short stroke crankshafts are lighter
2) for a given RPM, a long-stroke crank will produce greater piston velocities and accelerations than a short-stroke crank...there's only so much force (via the accelerating mass of the piston) the connecting rods and piston/wrist pin can take at high RPMs
3) larger bores ultimately allow for better head flow and cylinder filling. Let's take two engines of similar displacement...you build a 69x87 combo and I'll build a 59.5x94 combo. I think I'll run a set of CNC-ported Comp Eliminators with 48mm intake valves and 40mm exhaust valves. What heads are you gonna run? Wait...doesn't matter...you've already lost.


The problem with any of these bore vs. stroke arguments are that there are so many factors contributing to the torque and HP an engine produces...displacement, head flow characteristics (not just flow, but velocity), VE across RPM, camshaft, induction, exhaust, etc. Too many people focus on "stroke" when really it's stroke's effect on displacement plus all of the other factors they changed. Even if the only thing a person changed was the stroke and nothing else, the increased displacement is going to improve VE across the RPM range, up to the point where the rest of the components max out.

If some of you folks are still stuck on the dogma of more stroke = more torque, go buy a Honda Laughing Their engines are all LONG-stroke and small-bore, but they have certainly demonstrated that there are (way) more factors to producing torque than just stroke.
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PostPosted: Thu Mar 08, 2007 9:26 am    Post subject: Reply with quote

[quote="Stripped66]
1) short stroke crankshafts are lighter
[/quote]

How is a shorter stroke crank lighter than a longer stroke crank? If the journal is 2.165 diameter on an 82 or a 69, weight wise how does the crank know it has been moved 13mm?
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PostPosted: Thu Mar 08, 2007 10:19 am    Post subject: Reply with quote

vwracerdave wrote:
Power is in the heads. Larger pistons can use larger valves thus creating the potential for more power. The 1915 will blow away a 1904 on the drag strip.


Are you sure about this, Dave? Sure the power can be harnessed a lot in the heads, but that is NOT all you get it from. It will be interesting to test these two engines and see for sure...all else being equal.

These 2 engines are very close in displacement, but I think the 1904cc will get my vote.

It is a question of "leverage"...stroker or not. The more leverage, the less the energy needed to do work.

Everything has a limit or optimum stroke/bore combination. Bulldozers have strokes measured in FEET! But they turn only 1200 RPM to do their work. Very Happy

For the money spent on an engine, the 1915cc will be very good. Stroker cranks are much more in cost and work to install. NOt to mention all the necessary machine work you have to do to the case.

The combo has to make sense and should complement each other.

One thing I will add though once you have driven stroker engines, it is very hard to go back to good o'le 69mm stocker. NITE and DAY difference in power output. That iddy-biddy 74mm stroke will make your day.
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