Finally putting my 5.0L Hybrid back in this weekend. However I just got a 90mm Throttle Body from a Q45 that lines up real well with my set up. I'm thinking about swapping it out. It will need a plate fabricated I can attach to the lower plenum to fit the new mounting screws. Since the Q45 TB (Silvia/Skyline) is hot amongst the tuner crowd for huge turbo set ups there are plenty of universal plates available, you weld just them on. I will also have to dremel out the bottom plenum to make the larger hole. On the top plenum I am going to port out the bottom hole making the walls thinner. Looks like it will line up nice. I already have a nice coupler to join the TB to the upper plenum I am already using.

The stock Euro S TB is about 75mm if I remember correctly. I'll measure when I get it off. As a side note, my Euro S heads have been ported, polished and gasket matched with a valve job. I have JE race springs with a cam simular to Carls new S+ cam. Tiny bit less lift on intake (.503 instead of .506) with slightly less duration (243* vs 246*), however exhaust lift and duration are higher (.503@243* vs .480@234*). Also have MSDS headers, no cat, 3" Magnaflow "X" into 2 afterburners with turn downs. All 3" from headers on. CIS has been modified for more flow as well, along with 3an fuel lines and new mercedes injectors.

So do you think the 90mm TB will help at all or are there other restrictions farther down the line with a 16v Euro S spider that are choking things more than the TB? Going from the USA TB to the Euro S TB makes a small improvement so I'm hoping another 15mm will also help.

The Q45 TB has just enough vacuum ports for me. One before TB and after for the 2 lines on the WUR. I don't run vacuum to my Distro. No smog pump, so no vacuum to diverter valve. Only issue I will have is modifiying the TB for the deceleration valve, though I think I can make it work. Unused ports and cooling inlet will be blocked off.

A side benefit it has a TPS which I can use to trigger the giggle gas instead of the awkward noid switch I currently have.

 

Here is a picture of my 80 Euro S throttle body, I would say its at least 80mm:

 

I don't know if the extra few (less than 10) mm's on the Q45 TB will make any difference over the Euro one. I would doubt if you would get a significant gain, and it does sound like a bunch of work. Carl (at 928 Motorsports) seems to think the spider is a restriction to H.P. levels over about 400.

My thought/comment relates to your mention of the Deceleration Valve (Vacuum Limiter in Porsche-speak). Many of us have removed this part with nothing but good results. They often are worn, and cause a vacuum leak. A new one is not cheap. A properly functioning decel. valve can make rev's drop so slowly during a shift that it can limit how fast a rev-matched shift can be made. This is the reason Mark K cites for deleting his.

It's you call, but I'd leave the Decel. Valve off.

 

Thanks for the info on the decel valve. Sounds like it's going in the circle file.

I'm not at 400RWHP yet so I'm thinking it may help. Not a lot of work really. Carl is under boost so things are different. I'm still below 400hp at the crank.

Since it's basically just attaching the bottom adaptor plate and I have an extra bottom plenum I'm going to give it a try. Got the TB for free, so why not. What I need to do is dyno before and after to know for sure. Extra 10mm is still the same jump a Euro has over a US. We'll see.