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bass gt · Posted: Thu Feb 16, 2006 10:47 am Post subject: Intake Design

Guy's,

I have read with interest Nicks post from a while ago regarding designing a new intake for the 931. The talk moved on to a diffusor design being an ideal choice. However, these seemed to be based upon a single throttle body.
As you know, i am fitting ITB's, so my question is whether a diffusor type plenum is still advantageous, or a standard taper type single chamber plenum is a better option.
As i have made the plenum back plate, now is the time to decide!

Cheers,

Steve

Lizard · Posted: Thu Feb 16, 2006 12:33 pm Post subject:

you can still have the intake plenum after the ITBs and it will make a difference, but what type of power are you looking for?
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endwrench · Joined: 07 Dec 2002 Posts: 1631 Location: Victor, Montana

The point of the diffuser is to distribute the incoming air to the plenum more evenly so I would "assume" it would serve the same purpose with ITB's. I'm not sure if it is worth the extra effort or not. Audi sure seems to think so!

Todd

sequential · Joined: 18 Nov 2005 Posts: 500 Location: BANNED

The diffusor setup as used by Audi , will take some doing to get right , the idea is to reduce turbulence and promote induction speed , it is not about just distribution. the installation of the trumpets is key as you do not want to crowd them. it will kill flow quickly. make sure the ends and edges are as clear as you can .5 inch off the floor is good and a airbox volume of 1.5-1.7 times engine displacement. remember to extend 1-1.5 inch behind number 4 cyl. ( take your map sensor reading from the back here) remember min3 inchs above the trumpet and i prefer to taper ( as per pic )
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Raceboy · Joined: 01 Mar 2004 Posts: 2327 Location: Estonia, Europe

I'm in a progress of fabricating two intakes (one for my 931, other for my friends 951 3.0 turbo engine) and I'm doing it the diffusor-way. Right now I've cut some pieces and the trumpets are being fabricated in a shop (full-radius types).
Just for fun, here's intake of Carrera GT (not 924 though):
http://forums.rennlist.com/rennforums/attachment.php?attachmentid=99372&stc=1
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'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
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'91 944 S2, sold
'82 924S/931 "Gulf", sold

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Peter_in_AU · Joined: 29 Jul 2001 Posts: 2743 Location: Sydney, Australia

sequential · Joined: 18 Nov 2005 Posts: 500 Location: BANNED

hello guy,s,

I not sure what you are getting at peter, Yes the most important part of the trumpet is the corners , curl , bell, span , etc that is what i said and mean't by suggesting a min of .5 inch of course 1-2 inch is better if there is room. as there is no flow in the center of the bell. also you do not want anything within 3 inchs in front of the bell.

steve when flow bench testing the head , place a finger on one of edges of the trumpets and you will see a drop in flow then put 3 fingers towards the center and you will see no drop in flow.
_________________
928 gts prototype
baby blue engine block
steam in 1,2,3,4 sometimes
cold star issues while on stands
112 whp with new 4 valve head and MIS 2

bass gt · Posted: Thu Feb 16, 2006 7:10 pm Post subject:

Guy's,

here are my TB's. I am thinking of a uniform chamber, with a tapered pipe running along the whole length on the top or side, into which a slot is made to link the two chambers. The tapered pipe will be the air feed from the I/C.
Regarding the trumpets, is there a minimum clearance they require on all sides?

Steve

Peter_in_AU · Joined: 29 Jul 2001 Posts: 2743 Location: Sydney, Australia

My924gtc · Joined: 14 Aug 2004 Posts: 1362 Location: 248

I do believe he was refering to the space in front of the trumpet needing to be 3 in. minimum. "above' might have been the wrong term.

I'm doing the same type of intake for my ITB set up, and all the afore mentioned principles are sound. Don't know about going after the throttle bodies as per lizard's post as it seems like it would kill velocity but I'm no expert.

As it is, I have a tappered plenum housing 4 stacks running directly into the ITB's and then tappered runners going into the head. I think this design should make for excellent velocity as it enters the head and the length of the runners is optimized for the best atomization of the fuel in the charge.

I'm also developing a single throttle body set up with injectors in the runners but that will be going on my 931 later this year.
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sequential · Joined: 18 Nov 2005 Posts: 500 Location: BANNED

sequential · Joined: 18 Nov 2005 Posts: 500 Location: BANNED

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

The slot must be in the area of 30 mm wide (bit more than 1 inch).
_________________
'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.
http://www.facebook.com/vemsporsche