924Board.org

bruni · Joined: 26 Jul 2008 Posts: 114 Location: South Africa

Interesting design, however it looks like a variable volume plenum chamber not variable length intake runners, I'm not sure what effect this would have. In any event if you are looking at a forced induction motor there are several relatively simple anti lag strategies that can increase boost at lower revs without resorting to such complexity.
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1982 931
1975 harley sportster

Rich H · Posted: Fri Feb 20, 2009 8:01 pm Post subject:

Plenum volume has a similar effect to runner length on a single throttle intake, how much differnece it will make on a mult throttle I don't know.

I know this to be true as a plenum design change on my Elise robbed some the mid range torque!
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1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

It is also the same approach used on the BMW. In addition, I found a couple of sources online that indicated that changing the plenum volume, when done in this fashion or as with the "folded plenum" design, works essentially the same as changing runner length. In any event, it would be quite easy to take this design and weld three plates parallel to the end plates in between each of the runner ports, which would effectively create individual runners within the plenum...

The goal of this exercise was not necessarily to come up with an anti-lag method. It was merely to see if a rudimentary design could be constructed with off-the-shelf materials. Seems pretty doable...but whether it would be worth it or not, and what the results would be, all remain to be seen.
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erstwhile owner of just about every 924 variant ever made

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Refined the drawing of the latest design just a bit to take into account how this thing would have to be assembled.

I think I've also devised a fairly simple but effective way of retaining the bearings. The plenum end plates would have four bosses welded on outside the circumference of the sealed bearing. The bosses would subsequently be drilled and tapped, and simple bars could be bolted in place to retain the bearings. When installing the bearings, the would be sealed with RTV against the end plate, and for additional sealing, the seam along the circumference could be sealed further using a two-part epoxy as described earlier. End plates would look something like this looking straight on:

The same technique could also be used at the point where the fixed inlet pipe would connect via a flange, which on the opposite side could be configured in the same fashion to secure the outermost sealed bearing. This approach could also be used to accommodate a single throttle body if desired (rather than the ITBs depicted above).

I'm still struggling to come up with an elegant and easy way to fabricate and attach the diffuser plenum inside the 60mm rotating tube. The cylinder makes creating baffles a bit of a challenge. The only thing I can come up with is to have two 60mm pieces of tubing, use one to make a cone as I did with my current custom manifold diffuser, cut a slot in both the outer tube and the diffuser cone, and then somehow try to weld the slots together.
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erstwhile owner of just about every 924 variant ever made

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Maybe the diffuser doesn't have to be made of alu...could toy around with some alternate materials and means of attachment...
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erstwhile owner of just about every 924 variant ever made

Rich H · Posted: Mon Feb 23, 2009 7:14 pm Post subject:

The diffuser tube doesn't haev to run up the middle of the rotating tube, cant it over so the slot in the tapered fiffuser meets the edge of the tube and weld the edges together, that way woul don't have a long slot from the diffuser to the tube the diffuser just empies straight into the plenum.
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1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Rich H · Posted: Mon Feb 23, 2009 11:34 pm Post subject:

Fiberglass using lost foam to make the taper? make your internal shape using blue insulation foam and then wrap it in parcel tape, cover in PVA adn then allow to dry, cover in fiberglass + epoxy, allow to dry, pout gas on the foam and it'll dissovle out of the middle leaving the fiberglass taper.

then take your outer 60mm tube and glass the taper in place using flat sheet either end and glass tape on the seams.
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1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

A related and very interesting article in this month's AutoSpeed, originally published in 2004. Hadn't seen this one before:

Split Port Intake Manifolds

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erstwhile owner of just about every 924 variant ever made

Min · Posted: Thu Apr 22, 2010 12:57 pm Post subject:

This definitely perked my interest, would be interesting to see if we could setup a computer model to design one of these for the 924.

Min
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Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting.

Mike9311 · Joined: 14 Dec 2004 Posts: 1798 Location: Chicago-ish

I know I am coming in late here but is this for a turbo or NA?

I think I am seeing my answer here a way back "for NA".
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1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car

Rocco R16V · Joined: 03 May 2009 Posts: 497 Location: PNW

This is really cool and if it gets built will be one of, if not THE coolest homemade mod to a car I’ve ever seen.

Mike9311 · Joined: 14 Dec 2004 Posts: 1798 Location: Chicago-ish

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

velocity and short runners are antithetical. So regardless of boost, the variable intake runner should be of benefit on a forced induction setup. They are more common on normally aspirated cars because the effect is more pronounced without having to go to the expense of forced induction.
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erstwhile owner of just about every 924 variant ever made

snakoil · Joined: 09 Feb 2010 Posts: 362 Location: Montreal, Canada

all those fancy words for something that has been available on the toyota 4AGE engine since 1985!
was also reborned in 1997 on the Ford SPI engine in the escort.

This used to be better for NA engine. Was providing better torque at lower RPM and higher power at higher RPM
on the 4age the 2nd set of runners where closed up to 3500rpm, once they opened you felt a second life in your engine and the sound changed drastically.
Was also a good way for low consumption as if you where going under the secret barrier, engine was not drinking at all.
However, the second people started to modify this engine, this was the first thing to be removed to always have both plennum fully opened at all time.
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1979 924 NA