BFives

The Audi 5000 Big Bore TB fits the 12v intake manifold like a glove. Some minor modifications are required but nothing extreme. I've been running it since June with no issues. Makes for an easy upgrade for those who would like a little more room to breath! No honing, boring, epoxy, etc needed.

punkbomb138

what mods were needed to make it work? and where may some fo us find this big bore tb at?

CRAZY_RUSSIAN

got 2 5k at the local junkyard, will be yanking them:-)
what differences did you notice?

CRAZY_RUSSIAN

ok, so im holdin 3 TB's in my gand right now, first of all, how did u mod the TPS to mount, 2nd what did u do with ISV passages? they will bolt on, but i dont c a way to mod those 2 things

BFives

Ok so here's the deal. It's probably best to get both a 5k big bore TB and a spare stock 12v to start. Just completely strip down the 5k TB. pull the TPS off and remove the butterflies and shafts. At this point you should just have a bare shell. As you'll note in the picture I previously posted the 5k TB comes with a TPS sensor, however, its incorrect for our applications. But lucky for us the mounting points for the TPS braket are the same for both the 5k and 12v TB's. So remove the TPS and bracket from your spare 12v TB this will swap over to the 5k TB. Next you'll note that the primary butterfly shaft is also incorrect for running the 12v TPS. So in order to make this work you'll need to swap out the butterfly shafts from the stock 12v TB and install them in the 5k TB. Once you have installed the butterfly shafts, TPS and bracket, and aligned everything properly you will be holding a big bore TB that will directly bolt up to the 12v manifold with the correct TPS. Thats step one.

You are also correct that the ISV inlet passage will not line up. This will be bypassed. Cap off any unused vacum ports and turn the idle screw on the 5k TB all the way in as to close it off. The car will run if you just bolt it on as is and supply air via the idle screw. Essentially this eliminates the ISV. This will make for hard cold starts and best results are had by creating a proper bypass route to allow the ISV to function properly.

I'll have to create a second post with pics describing how to bypass the ISV. I'm not at my computer now so can't upload them. It will be easier to follow with visual aids.

What i can tell you is that the intake manifold will need to come off. So it is also a good time to port match, clean up your intake, and replace the gaskets if you haven't done so already, and if you have already then even better, you are already familiar with the intake and should be able to do the job quickly.

More to come

BFives

To bypass the ISV passage you need to pull the intake manifold. Once you have removed it. Flip it over and drill a 7/16" hole into the ISV passage on the intake manifold at the red spot shown in the picture below. This hole can then be threaded with a 1/4-18 NPT tap. Purchase a Hose Barb Fitting, Male; 3/8"; 1/4" NPT(Found at NAPA) Once you have drilled and tapped the hole wrap the threads on the hose barb with some Teflon tape and thread it in. You have now completed the intake manifold. Now to supply air to the ISV via this new bypass you need to purchase some 3/8 hose and run a line from your air intake. This procedure may vary from person to person depending on your current setup, but the general idea is to thread another 3/8 hose barb into your current air intake setup (after the MAF) and use the rubber hose to supply air from that point to the ISV, bypassing the TB ISV passage. I personally fabricated new aluminum intake piping using some mandrel bent elbows and fitted it with hose barbs that were welded flush to the piping to support the ISV bypass and the breather hoses from the valve covers. I then used a rubber cobra head elbow to clear the firewall and connect my air intake to the TB. I was able to maintain my stock engine covers and appearance. Like I said, I have been running this setup now for about 5 months with no issues. This modification is by no means a direct bolt on. However, I think it is an easy option for those DIY'ers out there looking to run a larger TB at an economical price. All it will cost you is a junkyard 5k TB, intake gaskets, 3/8 hose barbs, 3/8 hose, and time.