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Author Topic: sub piston induction on ST.23 question  (Read 653 times)

Offline MikeMorgan

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sub piston induction on ST.23 question
« on: October 23, 2011, 05:41:09 PM »
hey gang,
i'm new to this site but am an avid enthusiasts of CL for years along with my background in Free Flight competition.
this is a great site and becuase of this site i am able to pursue FF competition again with all the links to specialty items that you guys post here.
i have some Super Tigre .23's that are 1970 series which is basically (i think) the same engine as the 60 and 65 series (60-65 series had SPI) except that the sub piston induction was blocked on the 70 series to allow the use of a muffler.
no doubt the muffler robs these little guys of power, but i am using them now for FF and need all the performance that can be squeezed out of them.
so my question, does sub piston induction give the engine a few more rpm's?
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Offline Tim Wescott

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Re: sub piston induction on ST.23 question
« Reply #1 on: October 23, 2011, 05:57:54 PM »
I'm not a real dyed in the wool expert, but I just know the answer none the less:

It depends.

There.  Does that help?

If all else is equal (intake & transfer areas, intake & transfer timing, crank case volume, etc.), and the intake by itself isn't sufficient for top RPM, then yes, sub-piston induction may help.

In other words, if the engine is optimized for sub-piston induction and they just made the piston taller or the exhaust port bottom higher.

If they rearranged all the timing to match the change in the sub-piston induction, then no, maybe not.
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Offline MikeMorgan

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Re: sub piston induction on ST.23 question
« Reply #2 on: October 23, 2011, 06:18:16 PM »
claer and perfect answer Tim,
ah, out comes the degree wheel.
luckily i have an old 60 series i can measure.

thx for pointing out the obvious and the quick reply.

-mike
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Offline Steve Helmick

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Re: sub piston induction on ST.23 question
« Reply #3 on: October 23, 2011, 06:46:31 PM »
If you look at the Jett Engr. website, Dubby says that his engines have SPI and that's because they run faster that way.  y1 Steve
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Offline Chris Wilson

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Re: sub piston induction on ST.23 question
« Reply #4 on: October 23, 2011, 08:14:12 PM »
Steve,
 the answer is from Jett "Answer:
   Almost all Jetts have this gap. It is called "sub piston induction". Many manufacturers have claimed to use this to enhance power. Unfortunately, it does not make the engine run better. However, during the design of the engine a certain amount of sub piston will allow the engine to be made more compact and thus lighter and stronger. Power is not sacrificed, but a strength and weight advantage is achieved."

So no faster or more powerful.

In the old days racing engines usually lacked the ability to breathe deep enough through the standard intake gas channels so tinkers 'tinked' away with the lower piston skirt in order to lighten the piston and stumbled across slightly better breathing as a result - but this is only valid IF the intake was sub standard to begin with.

SPI (sub piston Induction) can rob needle accuracy because it competes with it as a source of air.

To sum, SPI will give more top end power but only if the intake has been compromised.
Will it make the piston lighter? Yep and that's probably the more modern reason for it.

Cheers.
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Offline Mike Greb

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Re: sub piston induction on ST.23 question
« Reply #5 on: October 24, 2011, 04:16:12 PM »
In a conversation with Richard Oliver at the carrier contest this weekend, he told me that Dubb was starting to take the subport induction out of most of his motors.
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Offline Chris Wilson

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Re: sub piston induction on ST.23 question
« Reply #6 on: October 24, 2011, 05:11:54 PM »
Quote from: Mike Greb on October 24, 2011, 04:16:12 PM
In a conversation with Richard Oliver at the carrier contest this weekend, he told me that Dubb was starting to take the subport induction out of most of his motors.
Mike,
         did Richard state why he was doing this?
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