rb25 higher compression, missing boost??

[supersayianjim]

so I blew a head gasket , and then this happened.

http://www.240sxforums.com/forums/rb-tech/118679-project-s-rb-11.html

so in a miracle my car runs and drives fine, except!!!!


when I get to a certain psi(13-15) then the cur hit's a hard cut. I thought maybe it's my tune. so I richen it out to 11-10afr right before cutoff, but the cut still happens, I lean it out a little and still I hit a cut.

This happens when I run 91-93 octane fuel. If I got less than premium I would only be able to boost up to 8psi.

then I had my buddy modify my nistune map and do something with the timing. and now even in low octane now I can only get 13-15psi.

I can't get to w.o.t. in boost. I can get over 100mph and I can spool but I have to stay in the 10psi range.

my stock injector duty cycle isn't hitting over 50%. so iam not running out of fuel.

but soon as I spool higher, I hit some cut. now iam not crazy, so on the rpm and mph cut I raised on the ecu. also I was told to adjust my tps. it's from a infinity q45.






and here's the wot tps reading.









so I heard from my head shop guy that since he took off 16 thousands. And if I used the stock head gasket,this would raise the compression. By how much?? I don't know??

well this is what I did, so has me raising the compression cost me some boost pressure???


heres my mods

-rb25det with-

-z32 maf
-nismo fuel pressure regular
-wally 255lph fuel pump
-freddy intake mani
-q45 throttle body
-nistune ecu z32 n/a
-3" exhaust
-front mount intercooler 3"

[Skym]

I think MAF might be maxing out, as stock MAF is only rated to around 300hp (need a Z32 MAF + wired in Z32 MAF plug or a Ford Cobra MAF, plug, which is Fords equivalent to the Z32 MAF and is a MAF option with a Nistune modified ECU). Also check for a intake airleak before MAF, as can cause MAF to max out and hit the boost cut on ECU alot earlier. Also check the boost cut settings on ECU. If you datalog MAF voltage when it happens, it should be obvious that MAF is maxing out (around where the boost cut settings kick in).

[h4X6]

Was going to say it's either maxing out the maf or boost cut is set low on nistune. Same ad skym was saying.

Sent from my Z10 using Tapatalk 4

[supersayianjim]

iam running a z32 maf.




if you can see it, the distance between the maf and cone is non existent. my real concern is that but using the stock hg and not a thicker one, that a higher compression was achieved and thus taking some boost with it. is this possible??

[Skym]

It looks like a clamp onto adaptor type of airfilter (can cause it to hit boost cut if hose clamp is loose, but usually happens at low rpm, around 3000-4000rpm). Solution is a bolt on Apexi airfilter or similar to eliminate it as a cause.

Also, was the boost cut settings reset for the Z32 MAF???? If not, that could explain the boost cut.

Higher compression would dictate the boost level you can run without engine failure (headgasket, piston ring lands, etc), usually under 20psi with stock RB25DET engine if thrashed. But it shouldn't limit the boost level you can run on a dyno.

Also ECU can switch to a knock boost duty map to drop boost level. But not sure if the ECU is controlling boost level on your car via stock solenoid (I presume it isn't, going by what I see in photo).

Other could be internal wastegate is faulty (spring has failed), as that would result in a lower boost level (wastegate open a little bit). But would get a rattling sound on back of turbo (wastegate hat rattling around), due to spring inside internal wastegate actuator bulb not helping to keep wastegate fully closed.

[supersayianjim]

it's a z32 nistune ecu(although a n/a one)





heres my wastegate setup. I beat the wg housing slightly to clear the engine body before I cut and got the arm welded.

[Skym]

It has to be a boost cut if it's hitting a fuel cut. Can't see anything else that would make it cut on ECU side, unless there's 0km/h to ECU and is setting off a rev limiter.

[supersayianjim]

^^ what is a okm/h?? and another funny thing. I set my profec b greddy to about 7psi. and I can still get the damn car to 13psi. whats up with that?? I have it plugged in correctly.

[Skym]

Speed input from dash to ECU. If 0 km/h at ECU it engages a revlimiter. Could be the angle of wastegate arm (looks to be modified) thus not allowing wastegate to open fully.

[supersayianjim]

I see. but I thought you want the actuator tight for it to have more boost?? like in this vid??

https://www.youtube.com/watch?v=p12g1PpIcjE

[Skym]

I see. But spring preload might be too much. It's similar to adjusting BOV where more preload should mean BOV doesn't open properly until higher boost levels and doesn't open properly or at all at lower boost levels. Try backing off with preload a turn or two and see if it improves.