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Old 01-15-2016, 12:45 PM   #1
JMlegacy
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Default Engine stroke and turbo spool

So I've read somewhere on here (can't find it back) that the stroke of an engine will more affect spool than the displacement. This was in the context of a 2.0 vs 2.1 vs 2.35 vs 2.5L. The poster said that the 2.35 and the 2.0 would spool the same, while the 2.1 and the 2.5 would spool the same.

I've having a hard time processing and accepting that as fact, as my brain is telling me that more displacement means more volume, means more gases to spool the turbo.

Does anyone have any take on this?
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Old 01-15-2016, 04:38 PM   #2
DisoDisp
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From experience that statement isn't entirely correct.

Yes, stroke does come in to play, but with an increase in stroke, you also get an increase in displacement.

I.e
2.0 -> 75mm stroke x 92mm bore
2.1 -> 79mm stroke x 92mm bore
2.2 -> 83mm stroke x 92mm bore

The 2.2l will spool the best out of those options.

I'd also say a standard EJ22 with a 75mm crank spools better than a 2.1l stroker (slightly)
But a 79mm stroked EJ22 (2.35L) outspools the standard motor noticeably.

I've never built a destroked EJ25 (2.35L so can't compare to a stroked EJ22) but I'd say that if the volume is equal, the longer stroke will aid in "spool" due to the torque band being further left on the longer stroke engine.
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Old 01-15-2016, 06:50 PM   #3
JMlegacy
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Oh.

Well, seems I'll be still building a full 2.5 then.

I ran it through an engine sim and you and i are on the same page.
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Old 01-16-2016, 02:06 PM   #4
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Well i'm sure to get jumped for this but i do feel the 2.1 spools more like a 2.5 than a 2.0. Not to sure about the 2.34 its not done just yet.
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Old 01-17-2016, 09:16 PM   #5
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Having played with these motors the 2.1 (92mm bore x 79mm stroke) spools up like the 2.2L (97mm bore x 75mm stroke) but produces more torque due to the stroke. The 2.2L has more pick up than the 2.0L but they seem to rev smoother.

You definitely notice the more aggressive exhaust pulse of the 2.1L.
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Old 01-18-2016, 12:09 PM   #6
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Stroke, or bore is meaningless. A turbo sees mass flow, it has no idea where or how it was made or why it's moving in one direction. It only knows a certain mass flow is going a certain way and it drives impellers in the process.
All things being equal more displacement will get it up to speed quicker, but you're feeding more displacement too.
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Old 01-18-2016, 02:33 PM   #7
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Quote:
Originally Posted by rtv900 View Post
Stroke, or bore is meaningless. A turbo sees mass flow, it has no idea where or how it was made or why it's moving in one direction. It only knows a certain mass flow is going a certain way and it drives impellers in the process.
All things being equal more displacement will get it up to speed quicker, but you're feeding more displacement too.
I used to think that too but after installing the same turbo on 2.0, 2.1 and 2.5 builds i found that not to be the whole picture. The exhaust is delivered to the turbo in pulses. The pulses are different lengths depending on stroke. This must come into play on the spool. Like I said the 2.1 spools much more
like the 2.5 than a 2.0 but is closer in cubes to the 2.0.
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Old 01-18-2016, 06:03 PM   #8
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Quote:
Originally Posted by rtv900 View Post
Stroke, or bore is meaningless.
"Your stroke, bores me"

-she

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Old 01-19-2016, 06:17 AM   #9
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Quote:
Originally Posted by mod maniac View Post
I used to think that too but after installing the same turbo on 2.0, 2.1 and 2.5 builds i found that not to be the whole picture. The exhaust is delivered to the turbo in pulses. The pulses are different lengths depending on stroke. This must come into play on the spool. Like I said the 2.1 spools much more
like the 2.5 than a 2.0 but is closer in cubes to the 2.0.
eh
that's my point, comparing 'spool' on different size motors, different turbo, same turbo, etc. . .is a meaningless comparison.
I'm quite certain if you did a valid test (waste of time anyway) with two identical turbos NOT feeding the engine, on two different motors, and just measured their rpm rate of increase blowing into some metered device you'd find stroke or bore don't make a lick of difference.
Pulsing is affected by a host of variables, stroke and bore being about 100 down the list.
Valve timing, aggressiveness of cam ramp, total lift, port shape, length, header length, etc, etc, etc
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Old 01-20-2016, 11:07 AM   #10
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I was intrigued by this, so I did some quick math.
I put together some python to calculate cylinder volume given crank angle for engines with different bores and strokes: http://pastebin.com/2h4E74kw

For this calculation I used discrete strokes of subaru EJ engines: 65.8, 75, and 79 mm
I kept the volume constant, so I also varied the bore. This means at bottom dead center the volume of the cylinders will be the same: 511 cm^3, so the engines in question would all have a swept volume total of 2.044L.

I then graphed volume with respect to crank angle:


Hmm. Doesn't show much. What about change in volume with respect to angle. This would, purely geometrically, show what volume is being pushed out the exhaust port throughout the exhaust stroke.


Hmm. The EJ25 crank has a higher peak difference in volume, as expected, but since the TOTAL volume is the same it must sacrifice that change somewhere.
Much of the force pushing exhaust gases out of the cylinder has to do with the higher pressure of the gases due to combustion rather than piston motion. I was just curious if there were a substantial volumetric difference between strokes. There is not.

Someone please check my math, though. I didn't spend too much time on it.
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Old 01-22-2016, 08:21 AM   #11
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Quote:
Originally Posted by FuJi K View Post
Having played with these motors the 2.1 (92mm bore x 79mm stroke) spools up like the 2.2L (97mm bore x 75mm stroke) but produces more torque due to the stroke. The 2.2L has more pick up than the 2.0L but they seem to rev smoother.

You definitely notice the more aggressive exhaust pulse of the 2.1L.
Would you recommend an 83mm stroked 2.0->2.2?

I seen someone did it and complained about oil consumption. Then someone else did it and didn't find that. What's the consensus about this option?
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Old 01-22-2016, 09:14 AM   #12
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it was probably me
when we built another one we approached it differently, by using sleeves without the wrist pin holes... takes a creative approach to put everything together, but no more oil issues



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Old 01-22-2016, 09:24 AM   #13
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nice, hyper
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Old 01-22-2016, 10:49 AM   #14
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Yes it was. Now if I can only find someone who did a 83mm in a 2.0 to tell me how they got around that oil consumption issue (without Hyper's sleeved block method)
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Old 01-22-2016, 12:47 PM   #15
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We've done one, MPS have done a few and IIRC hyper is the only one to have excessive oil consumption.
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