Variable length inlet runners

pork

pork

Club Member
Was watching wheeler dealers other day, saw a Porsche 993 come up.

Had variable length inlet runners, long at low rpm...shortened at high rpm

It wasn't 2 sets of runners with a valve between the two, the trumpets actually shortened, via a vacuum piston.

If something could be constructed simalar to this, (I like making things)
What length of runners would work.
Also......worth it?


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Sure we could cobble something together on the cheap lol!

So I take it the runners are inside the plenum and shorten on boost, longer of boost?


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they just broaden the powerband eh neil, long and thin like a bunch of banana,s for added grunt (like the k12) and short runners for topend power
231_02_18.jpg
 
How's the switch over operated,
Vacuum piston type thing, rcu


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The engine in my Honda has 2 intake runners on the inlet manifold.
The butterflies are controlled by a vacuum and open at 6k.

Supposedly keeps low down torque (lol) and opening the other runners for more high end POWAH
 
Frank I (wrongly) thought you were doing this when you were playing round with Toyota corolla manifolds, I was kinda hoping you mighta run with the idea. ;)
http://www.micra.com.au/community/message.php?messageid=69926 Search for ACIS ACIS is toyota's name for it, no telescoping manifolds but at least enough to do something useful?


Anyway the spacing on 4EFE, 4EFTE, 5EFHE etc is close enough to the micra spacing and they are a relatively suitable size so could be cut and shut...

Here's the links:
http://board.tercelonline.com/viewthread.php?action=printable&tid=23606 (Shows the various available ACIS and non ACIS manifolds)

And here's how to make it switch over and tune it:
http://tercelreference.com/articles/acis_activation_options/acis_activation_options.html

It actually seemed reasonably simple from memory.... It's not gonna fit my mini so someone go do this!
 
Last edited:
fuzzy-hair-man said:
Frank I (wrongly) thought you were doing this when you were playing round with Toyota corolla manifolds, I was kinda hoping you mighta run with the idea. ;)
http://www.micra.com.au/community/message.php?messageid=69926 Search for ACIS ACIS is toyota's name for it, no telescoping manifolds but at least enough to do something useful?


Anyway the spacing on 4EFE, 4EFTE, 5EFHE etc is close enough to the micra spacing and they are a relatively suitable size so could be cut and shut...

Here's the links:
http://board.tercelonline.com/viewthread.php?action=printable&tid=23606 (Shows the various available ACIS and non ACIS manifolds)

And here's how to make it switch over and tune it:
http://tercelreference.com/articles/acis_activation_options/acis_activation_options.html

It actually seemed reasonably simple from memory.... It's not gonna fit my mini so someone go do this!
Click to expand...
yes i still have it mate "equal length" rather than variable tho eh , the engine ran mega lean even with the red QG injectors, but i cant see me ever going N/A again tho

78081.jpg
 
It would also be easier to construct if the runners were inside a plenum and the throttle pre plenum.....or would it not work, and need to be more like itb's



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i guess that would work ok neil :) you are just trying to overcome the air reversion created by the inlet valves closing after bottom dead centre eh
the piston pushes some of the intake charge back up the inlet tract because the inlet valve is still closing, and a long narrow tract will resist that reversion (small bore = faster inflow)
 
Also, while I'm at it, was thinking about injector placement, like pre trumpet

Bit like this ......

240135f3928dd2f7af77904ab204b341.jpg


Or would be a huge fire risk?
 
Or possibly use something like arduino which does pwm very well. You would need to get a rpm signal from your ecu, maybe a tach signal output.
 
That's what the chap I bought the ecu recommended too,

Never played with anything like that though, so would have to figure that out


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Seems cheap enough,

I've got a mate who's into all of that stuff, so il pick his brain.

There's some linear actuators that go with it on eBay that are cheap too, have to see how smooth the runners move with the seals to see how powerful the motor needs to be I gurss


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