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Old 07-29-2009, 02:36 PM   #1
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Default Forced Induction Stroke/Bore Preferences?

Has anyone heard of or noticed that their turboed/supercharged engine is partial to an oversquare/undersquare/square bore:stroke setup?
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Old 07-29-2009, 02:37 PM   #2
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I triangulate my bores.
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Old 07-29-2009, 02:42 PM   #3
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Moar detail please?
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Old 07-29-2009, 02:49 PM   #4
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He is joking.

A higher bore to stroke ratio is always going to be better for making more top end power, no matter what, but its effects are negligible in anything short of an extreme setup. The F20C from the s2000 which can rev to over 9k stock is undersquare.
Rod ratio is far more important in a high performance engine...
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Old 07-29-2009, 03:07 PM   #5
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The turbo sees gas flow and pressure and therefore doesn't care much as long as the displacement of both engines makes the gas volume being expelled the same. The engines themselves will produce very different torque curves if one is small bore long stroke and the other is large bore short stroke. What are you asking zackly?
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Old 07-29-2009, 03:13 PM   #6
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For a supercharger, what would be the ideal rod ratio and if I am looking at total area under the curve as opposed to just an extremely steep curve with a high peak, would I be better off with a larger bore and shorter stroke or vise versa?

(BTW: NA 1.8L with a '99 head)

EDIT 2: Doesn't anyone make a twin screw blower for the Miata?

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Old 07-29-2009, 03:35 PM   #7
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Quote:
Originally Posted by MegaSquirt My Face View Post
For a supercharger, what would be the ideal rod ratio
Does it really matter in this case or are you planning on dropping $3K on a crank? I guess my point is, we have the hand that we are dealt unless the pockets are deep.
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Old 07-29-2009, 03:39 PM   #8
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True dat. So unless I am springing for an obscenely priced piece of machined billet steel (a.k.a. crankshaft), longer rods are pretty much not usefull?
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Old 07-29-2009, 03:48 PM   #9
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Quote:
Originally Posted by MegaSquirt My Face View Post
True dat. So unless I am springing for an obscenely priced piece of machined billet steel (a.k.a. crankshaft), longer rods are pretty much not usefull?
Correct. Well, unless you are going for diesel compression ratios.
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Old 07-29-2009, 04:56 PM   #10
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Our engines just happen to be designed for mid-range torque instead of low or high rpm torque peaks, so you happen to be in luck.
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Old 07-29-2009, 06:40 PM   #11
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Should I get the 1.33L or .87L Kenne Belle supercharger?
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Old 07-29-2009, 09:17 PM   #12
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Quote:
Originally Posted by MegaSquirt My Face View Post
Should I get the 1.33L or .87L Kenne Belle supercharger?
Probably doesn't matter because a small turbo will make more torque at the same low rpms for a lot less money and still make better torque on the top end, too.

I know you are stuck on superchargers and I get it. I was stuck on them, too. They were much easier for me to get my head around. They seemed to make more logical sense regarding their operation and there were less variables to master. Please look at this thread before you pull the trigger:https://www.miataturbo.net/forum/t26641/
And read the dyno sheets Dynos and timesheets - Miata Turbo Forum - Home of the turbo Mazda Miata. for people running 2554 and 2560 turbos and see at what low RPMs the torque starts to rise, how high it goes (both RPMs and max torque numbers), and of course the corresponding rear wheel horsepower numbers.

People are getting very early spool with the right turbo and getting much, much higher power than the superchargers. And most importantly, they are getting a tremendous bang for their buck. After all, we are all just looking for the best bang cheap.

Please. Do it for the children.
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Old 07-31-2009, 06:13 PM   #13
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Go here:
Bell Experimental Group - BEGi

If you are gorilla-glued to the idea of a supercharger, Corky has one brewing.

- L

(BTW - When first venturing into forced induction, I too was looking at an S/C solution. A couple of conversations with Corky and I am driving a custom built turbo...)
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