I have just built a s5 turbo II engine for my kit car. I am initially goint to use the stock turbo, until i get it all running and then look out for a slightly bigger item.

My question is, Do I need to port the wastegate on the stock turbo to prevent boost creep or will I be ok.

I ported the stock exhaust port about 3mm all the way round, basicaly ported out the taper and then put another taper back.

I enlarged the primaries and secondaires but left the runners alone other than polishing a little. Both are between 1 - 2mm bigger all the way round although i raised the secondary port by about 5 mm.

I want the engine ready to make reasonable power when i get another turbo but need it to work with the stock unit.

I am not after huge power as the car only weighs 650 KG's (1350lbs) so 300 - 350 Fly is plenty

 

IIRC my friend Wankel7 should have a thread on here with pictures showing the port that he did on his S5 unit compared to the S4 that BNR did for him, searching....

Found the S4 turbo WG pic, still working on the S5...

 

If you want to read his thread its here: https://www.rx7club.com/2nd-generation-specific-1986-1992-17/s5-wg-porting-dp-wrapping-361144/

From what I remember for WG capacity the S4 unit is preferred over the S5 so if possible opt for an upgraded S4 snail!

 

Port to the edge of the stock flap, leaving enough overlap to achieve a proper seal. If you go further it'll leak and slow boost response. Make sure you take into accounts the way the flap wiggles around a bit on the arm.

The port area of a heavily ported S4 wastegate is still smaller than the combined port area of an S5 wastegate ported to the edge of the stock flap; plus the S5 wastegate lets exhaust escape from both scrolls rather than just one. That combined with the fully divided manifold makes it the better choice.

 

Good info, its been a while since i've brushed up on FC factoids so I yield to you sir!

 

thanks guys, before i do all this, do i actually need to? or will the stock wastegate cope with a mild street port?

 

well i went ahead and did it anyway, it was quite easy, i also took some meat out of the cover to allow the door to open a little more. I dont think mine are as big as the pics above but there is a lot that can be taken out.

 

You might want to separate the turbine housing from the turbo so that the metal shavings don't collect in the turbo. It's also easier to manipulate and clean once you're done porting. RETed has a good writeup on his website for WG porting. Check it out!