Marti

Hi

I was looking for feedback on increasing the size of the throttle body butterfly on the S4/GT/GTS inlet manifold for a S4 engine running the Colin’s cams and MSMD headers with a X pipe and remaining exhaust system being standard. The car is also running shark tuner and uprated injectors.

As bolt on replacement performance manifolds are not quite there yet I am working on modifying the S4 manifold to clean up the airflow as best I can which I hope will help. I am trying to investigate options on fitting a larger butterfly. I believe the existing butterfly is 75mm and some people have increased this size, i would like to know what size is possible and where parts are sourced

I am working on the theory that with the increased airflow now being sought by the engine that this may be worth doing especially since I have the parts off the car at present.

Many thanks

SwayBar

With those cams, x, and proper tune, you can expect 330+ rwhp with a 5-speed.

However, after reading many threads on this topic, as well as being in-process of mocking-up an intake, I wouldn't waste any time/money on the stock intake, including a bigger TB.

Runners 5 and 8 are mangled beyond repair with their 180 degree bends. Runners 2 and 6 flow the best, thus run the leanest for batch fire, and everyone is forced to tune for them which includes pulling timing to minimize knocking on those cylinders. Lots of hp is left on the table as a result.

IMO, this knocking is the root cause of 2/6 bearing failure on the 32v, and not the oiling system.

A completely new intake which allows all cylinders to fill equally will enable a much more aggressive tune while being safer at the same time.

KenRudd

Don't forget to polish your plate...

Strosek Ultra

https://rennlist.com/forums/928-foru...ughout-30.html
https://rennlist.com/forums/928-foru...reets-118.html
I made a larger number of 80mm butterfly valves for Tuomo (Ptuomov). He might sell you a valve. He has got all the tooling for the machining of the throttle valve housing.
Åke

V2Rocket

http://www.maxbore.com/

like $120, quick turnaround, nice work.

i had a 944 TB taken from 55 to 60mm there.

i had a 928S3 tb in hand a while back, it looked like it could go bigger (80?)

ptuomov

V2Rocket

no but the hole should drill the same despite the weird shape of the S4 TB "housing"

they did somebody's 928 TB up to 82mm (1/3 down)
http://www.maxbore.com/europeanpictures.html

SeanR

Sterling did his a good sized larger than stock. Once he changed up to ITB's he sold his to Roger and I installed it in his GTS. Would like to have one for my car also.

ptuomov

The problem is that just replacing the throttle valve isn't going to increase flow much. And neither does just welding and porting the throttle body without replacing the valve. One needs to do both, and that's extremely time consuming. Then, there's the flow demand chart that lists how much hp one should expect to gain from the change, which isn't much for near-stock motors. Take a look at what Ake posted in two threads on this, plus my estimates of hp gain.

ptuomov

His setup can't do a S4 throttle body. I asked.

SeanR

Oh heck with all that. I just want one so I can say "Hey, I've got a large throttle body"

Marti

I generally dislike the standard S4 manifold to, however until there is a ready replacement for it I can only really tinker with this to make what ever improvements possible. I am hoping GB will move to some limited production version of the manifolds he has been testing

ptuomov

PorKen

Basic by-cylinder retard tuning patch (for ST.BINs):
https://rennlist.com/forums/928-foru...ard-patch.html

ptuomov