924Board.org

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

Is there any reason a set of gutted Weber carbs would not be suitable for use as an independent throttle body setup? I can't imagine their flow characteristics being a bad thing!

DCOE-based ITB setups seem like the easiest path to ITBs (assuming one could find a 924-DCOE manifold adapter), but the off-the-shelf solutions are $$$$pendy (e.g. TWM, Jenvey, Extradabody, Omex, etc.).

Bike-carb setups can probably be done for a fraction of the cost of a TWM or Jenvey type setup, but it seems like they involve a lot of custom fabrication and experimentation to get the manifold adapter made, plus the linkages and throttle cams, etc.

Just wondering if DCOE Webers might be a really affordable solution. If you were going to gut the carb bits anyway, the rebuild kit probably wouldn't even be essential. You just need a linked set of throttle bodies with some thoughtfully sized venturis and velocity stacks.

The only drawback I can think of would be the lack of off-the-shelf support for a TPS.

Thoughts???
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erstwhile owner of just about every 924 variant ever made

flosho · Posted: Fri Mar 02, 2012 11:14 am Post subject:

If you can get a decent set of bike ITBs, any decent fabricator could make an adapter for under $200.
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ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

But you still have to fiddle with throttle linkage and spacing and stuff, no?
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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

Also, if you're going to gut a bike carb, why not just gut a weber that has a proven and known configuration (including idle, which I've read can be a bitch to set up with bike carbs). Isn't it the same difference? From what I'm seeing, there isn't much price difference for used webers vs. used bike carbs...
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erstwhile owner of just about every 924 variant ever made

flosho · Posted: Fri Mar 02, 2012 12:08 pm Post subject:

Well if you can find a set of webers for cheap? How abundant are they? Bike carbs are plentiful and cheap (Under $100).
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ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

flosho · Posted: Fri Mar 02, 2012 1:21 pm Post subject:

I was looking at something like this...

http://item.mobileweb.ebay.com/viewitem?itemId=130654418993&index=9&nav=SEARCH&nid=89035507789
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ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Yeah, doing some more research, seems the K2 throttle bodies may be the way to go...injector ports and everything, so no need to gut out the carb stuff.

Hmmm. Wonder if I could get a group buy going to make up some 931 and 924 intake manifold weld plates...
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erstwhile owner of just about every 924 variant ever made

flosho · Posted: Fri Mar 02, 2012 2:18 pm Post subject:

Raceboy · Joined: 01 Mar 2004 Posts: 2327 Location: Estonia, Europe

I have a CAD drawing of the 931 intake and I had the new flange cut out of 10mm aluminium sheet for 30 euros.
Going bike ITB's (GSXR 750-1000 K1 and K2, these are easily separable) is a no-brainer. They are readily available also and have injector ports and TPS already in place.
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'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold

'84 924, turbocharged, sold.
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flosho · Posted: Sat Mar 03, 2012 3:52 am Post subject:

I think you are best off keeping the ITB spacing the same, since you can use all the linkage and the fuel rail and just make an adapter to connect the ITB to 931 inlet ports.. if that makes sense.
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Arvidw · Posted: Sat Mar 03, 2012 5:31 am Post subject:

GSXR-600 K3 throttle bodies & low-cost manifold:

Injectors are good door 240cc/min @ 3bar

Synchronizing butterfly valves is quite easy.

TPS is compatible with Megasquirt

Stroke of throttle linkage is half of what the original 924NA throttle body, you will need to modify the throttle pedal to compensate for the 1:2 ratio. With a modified throttle pedal the throttle bodies react very nice to throttle input, very precise and not too sensitive. Comparable with stock TB.
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Porsche 924 2.0 Kompressor 136.1wHp @ 5650rpm / 201.9wNm @ 3900rpm (dyno @ dp-engineering.nl)

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

Arvid, I already stole those photos!

Arvidw · Posted: Sat Mar 03, 2012 7:15 am Post subject:

Unfortuntately I don't have foto's from the throttle linkage but I made this fantastic sketch:

You just basically move the throttle cable connection point on the throttle pedal cantilever more towards the pivoting point.

You need the guidance wheel to prevent the inter cable wearing out the outer cable near the firewall. I used a guidance wheel of a mountainbike gearing system. You can mount the bracket to one of the mounting studs of your brake booster.

The synchonation of the throttle bodies I did by ear. Take two hoses of equal length, put one end of both hoses in your right and left ear. Place one in the first throttle body, the other in nr 2. Tune adjusting screw until suction sound is equal. Then move hose from 2 to 3 and repeat tuning. I found this much more convenient/faster/accurate than measuring the pressure of all throttle bodies with an external map sensor.
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Porsche 924 2.0 Kompressor 136.1wHp @ 5650rpm / 201.9wNm @ 3900rpm (dyno @ dp-engineering.nl)

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

Perfect! See, it's stuff like this that worries me about "going it alone" on these low-dollar-heavy-fab approaches...but so cool we have the internet and this forum to exchange learning!!! Thx!
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erstwhile owner of just about every 924 variant ever made