Hey guys!

Tried searching for this but didn't get a good answer to my question. So I've read the wastegate spring for s4/s5 turbos is 5.5psi and is internal. But when upgrading to say a RacingBeat RevTII it essentially raises it to about 10psi if I remember correctly. How is this done without adjusting the spring? Would a boost controller work to keep it at the stock boost level? Sorry if this sounds dumb I'm just thinking about a weird project as I have a few too many disassembled parts and not enough running stuff

 

A boost controller cannot turn boost down below stock levels. Only used to raise boost, or control it at a certain level. To lessen boost you would need to restrcit airflow.

 

So the wastegate spring isn't adjustable at all and is completely dependant on airflow? So I couldn't use a boost controller to keep the stock turbo at 5.5psi with a free flowing exhaust?

 

the boost is rising because not enough air can bypass the turbo through the wastegate.

a boost controller only bleeds air out of the line going to the wastegate so the wastegate thinks there is less boost than there actually is (which raises boost).

 

Ok so only way to keep boost down is restrictive exhaust?

 

Or port the wastegate.

 

So porting the wastegate allows for better control of the boost. And with a free flowing exhaust the S4 turbo makes around 10psi. I'm sure there's some math behind porting to boost level, any idea how large it would need to be ported to safely maintain 10psi and below? I can't imagine very much. Car would be running basically unrestricted exhaust. Trying to see if I could frankenstein an S4 turbo to VR6. I have a complete S4 t2 engine and a complete vr6 sitting in the garage. VR6's hold about 10psi safely on stock internals so that would be the max

 

oh if you change the engine that matters. the stock wastegate will probably be ok on a piston engine, piston engines are lazy, and it isn't going to move any air

 

Stock TII HT18S-2S turbo is a pretty BIG turbo/exhaust side for a VR6.

No need to do anything to keep it at 5.5psi on a VR6, it will be huffing its lungs out trying to spool the HT18.

HT18 will max at 400wheel on VR6, but for that power level the engine would be better off with a smaller exhaust side to spool the turbo faster.

Any 4cyl turbo car stock turbo would be better suited.

HT18 exhaust wheel is 64mm and the primary+secondary scroll AR combined is 1.00AR.

The compressor wheel is 63mm (yes, rotaries like big exhaust wheel).

 

For example the popular 250-360rwhp GT2860RS "Disco Potato" aftermarket turbo is-

60mm compressor wheel
54mm exhaust wheel in 0.64 or 0.86ARs

 

Hmm ok completely forgot to count in rotaries love spooling. It would be nice to get a different turbo, just tryig to do a bit of a hackjob/budget diy build just because. Although I have considered finding a turbo from a 1.8t and slapping that on. Options... Thanks guys!

 

just research porting the wastegate.

 

Extreme S4 Wastegate Porting

There you go.

 

i would recommend being a little more picky about the flapper cover material if modding the wastegate that large though, the first try i made at it the washer wound up disintegrating under the heat.

 

Yeah ^^ I used an exhaust valve out of a boinger.

 

Exhaust valves work, or thick stainless washers.

The turbo I used for the writeup is still in use after all those years with the galvanised washers still holding up.