What's everyone running. Currently I'm running about 13psi got a boost cut defender and was thinking 17?

 

17 psi will be your max assuming you have the right fuel support ..... beyond that , turbos are on borrowed times

 

^^ This. Although you can have those twins rebuilt with steel turbine wheels if you wanted to. That takes the fragile ceramic turbine wheels out of the equation. For JDM twins there is a standard steel wheel rebuild available and then the much more expensive "STU Hybrid" rebuild/upgrade (not to be confused with the very similar "standard" and "STU GT28 Hybrid" rebuild options for USDM twins).

Other than that you shouldn't go higher than Gerrb's recommendation and even then I think it shortens the useful lifespan with those ceramic wheels at 17 psi? The USDM twins in stock form are supposed to be fine up to 17-18 psi all day long but I thought owners of the JDM ceramic versions (in stock form) wouldn't want to keep boost that high all the time. Gerry, please correct me if I'm wrong about this.

 

You are right Craig , they should not be abused at 17psi all the time otherwise those ceramic wheels will be gone. But they can be pushed to 17psi just to answer the OP's question if he just want to try them at that boost level. If the turbos were properly maintained like no oil coking or shaft play .. they should survived at that boost level but you are shortening their life as you have said. Turbo's life span depends a lot on how they were maintained and used. Most of the time we have no idea how these JDM motors and their components have been used. I have been boosting up to 17psi on my 1992 SC300 with stock twins. Well , not too worried about them cause I have 4 sets of them around.. hahaha.

 

what is the right fuel support for 17 psi? The car has stock 440cc injectors and Supra Fuel pump. I was under impression thats usually good for 375 give or take RWHP and limited by the 440s?

 

depending on your setup , like manual or auto trans , exhaust size ... etc , it is easy to ramp up the boost and get more power but you have to make sure that you have good fuel . Overdoing your fuel system is the best . You never want to go lean while boosting. I always want to be within 80 to 85% duty cycle or less of my fuel system (injectors / pump / fuel line size) capability. In that way I have a safe buffer cause getting lean while on boost is catastrophic.

you have to differentiate that 375RWHP .. with auto trans , there was some power robbed by your trans so actually are getting more. At 17psi , I would say 550cc injectors with a Supra TT Denso pump is the least I would say I should have. An optimized setup could get 450rwhp at 15psi on a single turbo on pump 93. It really depends on the setup so overdoing your fuel system is the best .

 

I'm talking manual numbers, its a w58 car so i'm trying to stay away from 450rwhp. I do have a denso pump.

 

technically , when you say 440cc injectors , at 100% duty cycle .. they can support 440RWHP. So at 375RWP you are within 85% duty cycle which is safe.

But what I am trying to say is that 375rwhp depending on how effective your setup can be achieved with less than 17psi which means if you boost at 17psi you can actually get more rwhp .

I have given the example .. geauxsimon's SC (now my Black Pearl) made 450rwhp at 15psi on a R154 / 2jzgte . If we had 440cc, they would have been maxed out. What more if it was pushed to 17psi..... the 440cc won't make it. Engine will go lean and there goes the engine. That is why they always say , always over do or you can never go wrong overdoing your fuel system.... more fuel is better. It is a good insurance from getting lean which can be catastrophic.

if you are trying to stay away from 450rwhp because you want to preserve your W58 , which actually is on borrowed times beyond 350rwhp , then stay lower on boost. Going to 17psi is asking for trouble for the W58.

 

I would just go up a couple psi at a time and watch the wideband. the 440's might make it to 16 psi cause the fuel pressure regulator raises pressure with boost but it only gets you so far before it leans out as Gerrb said. safest is 550cc and a piggyback but I would at least try 14 that should be safe but do check the wideband don't take anyones word for it.

 

Well turned the boost up to 15-16 psi and larger turbo only lasted all of 2 days. The small turbo comes on and builds boost up to 10 psi car feels like it did when it was in sequential mode only its not. Boost keeps going past 10psi but larger turbo is dead I'm pretty sure. I ordered a s366 and log manifold...I saw it coming just thought it would last a little longer

 

Ouch! I'm sorry it happened so quickly, MDSC. That's awful news :/

I don't know what that means for the rebuild potential of your #2 turbo but it sounds like you're going single anyway. Regardless you'd be able to find some JDM Aristo twins fairly easily if you wanted to try steel wheel sequential twins a second time.