we've all heard the safe limits but i want to know why and what happens...

[hysteria]

so i'm toying with my car lately since i have everything installed now and the wastegate dumped out the side for the time being (damn it's loud)...

i have a wastegate that i don't know the spring rate on. i know it has to be less than 10 psi, because it opens up somewhat early when i give the car throttle (and a little positive manifold pressure ~5 psi). i've been slowly increasing my throttle so i can determine the spring rate of the fmu without overboosting since i have an fmu as my fuel management currently (as many of you know i want to get the new bikirom board and start playing with that when i have some free time... maybe over the summer).

so anyway i'm approaching 7 and 8 psi in my trials (have not touched full throttle yet) and i have not yet adjusted my timing (which i am going to do this weekend when i do some more trials because i may go over 8 psi). i am getting concerned that my spring is set a little too high because i'm going to be running my fmu for at least a month or two or maybe three... or maybe it will be much longer, but i want to be able to boost my car up and have fun so i've been trying to determine the spring rate without blowing up the engine because i've heard that fmu's are only good up to 8 psi...

well so i know the fuel pressure will max out around 8 psi or so and so if i continue to increase boost past 8 psi i will just start leaning out really bad and eventually blow up the engine. i'm wondering what peoples experiences with this have been because i have seen someone (man i can't remember who) that runs 10 psi on an fmu and apparently has been doing it for a while. i guess i'm also wondering what the exact limits of the engine with a fmu as the fuel setup are because chances are that i will accidentally boost up to the spring rate of the wastegate at least once, and that may be more than 8 psi...

i've been doing my trials in 5th gear for the most part because it's the least erratic for this type of thing, so i can ease on the throttle and watch the boost rise slowly rather than in 2nd where it will jump up so fast... the response with this turbo is freaking insane, which is what i wanted since i'm just aiming to balance the car out better as an overall performer, not a straight line car or a dyno car or whatever... this setup was just plain and simple bolt on more power to my car and see how it reacts... once i start tuning with bikirom and what not it will be a different story and i'll upgrade to a different turbo and other things probably. by the way i just have a little t3/t3 (with a freaking tiny exhaust side- .48)...

so anyway back to the answers i need from people...

i've got all my gauges hooked up and everything too and i have become increasingly aware of how lazy my o2 sensor is... i have a 92 fastback, so it's obd1 and it has a 1 wire o2 sensor. it's become a concern as well as i am pushing the limits of my fmu setup and worrying about how lean my car will be under heavy load at higher rpms.

so give me some reassurance or tell me i am on the fast track to blowing it up by pushing it to maybe ~10 psi. i'm not going to be doing this in a racing style way.... not quick shifting and punching the throttle... i am easing into everything at this point because i want to know what the spring rate is.

if you're wondering why i have a wastegate i don't know about all that much, well this is a complete DIY setup and i bought a lot of stuff on ebay. this wastegate is the same as the boost designs wastegate, but i don't know the spring rate. i didn't buy it from them.

i gotta say i am very impressed with this car so far. my friend and i were doing these trials last weekend. we were doing most pulls in 5th like i said while we were on the highway, but then we got off the road and came to a light and the light changed before i stopped so i dropped it to 2nd and eased on the throttleand it threw us back in our seats... he was like "well damn now you're going to have to race the rx7"...

i guess i don't have very specific questions but just read what i've said and let me know what you think i should do, or if i should just put this on hold for a while and ride my bike when i need some speed...

thanks

[Red-KAT]

If it looks the same as the BD WG then just open it up and look at the spring... Far as I know they use the Tail springs... But if you look you will know.

[nismo1003]

so u have 270cc with FMU? I had that setup before, I had hard time playing with the FMU to get the fuel curve right anyways get a wideband so u can moinitor the A/F instead of guessing it, U need it when the Bibirom is out anyways. I also had one of those 0-1v autometer a/f gauge before , they only go up and down, i don't really trust that.I also in Austin area, what color of the 240 u drive?i'm new on here ,let me know if there are any 240sx meet.

[nissanfanatic]

I would definately invest in a wideband.

lol, or just punch it really really quick and see how high it goes!!!! Lol, j/k

Use an air compressor and see how much air it takes for the valve to open. Thats what I did on my evolution. Turns out they labeled my springs wrong. So I'm def glad I checked it.

[LEMHEAD16]

CAll boost deisgns. PJ probably has some .5 bar springs laying around he would part with super cheap. Then you would know exactly what pressure it is

[nismo1003]

what u can do is get one of those brake bleeder (its like 40 bucks at autozone) . it got two end ( one end for vaccum the other end is for boost), hook up to a boost gauge then put a T- fitting to the wastegate, I tried it with my Blitz SBC , the max it reads at 22psi , so u should be able to tell what's the psi ur wastegate should open at

[Structure240sx]

what ratio is the fmu you have? i had an 8:1 at 9psi with a to4b and it ran great. never got a wideband on it with the fmu tho. put some race gas in and floor it to see how much it boosts

[hysteria]

well since i didn't get a new fmu i am running really rich with the 12:1. because it's only a temporary setup i decided to just not buy another fmu with a better rising rate that would fit my app better... you know i don't even know where to get race gas around here. when i lived in florida they had it at a few of the gas stations (lol back when race gas cost as much as i pay for premium now, no kidding) and you'd see guys gasing up their ferraris (oh that f50 was soo nice) and lambo's... there was a guy there with a mclaren f1 but i never saw it on the street i don't think... maybe once.

i was thinking about that you know... just T ing off the wastegate and adding a charge side boost reading just to see what it is doing on that side... because at half throttle the manifold pressure and the charge pipes are definitely not the same...

the wastegate is opening at like 3 psi of manifold pressure, so i was just guessing that the spring was probably ~10 psi... on the way over here i boosted it up to 7 psi in 5th but i'm reluctant to go past that because when i looked at my speed i was already at 100 mph.... funny how that number just comes up now.

i'm going to get the wideband for sure because i can't do a bikirom solution without one... but for the tiome being i have this one wire thing... does anyone else still have one of these on their kat with an fmu? i never knew how lazy it was until i hooked up am a/f gauge...

nismo1003 i drive a champagne (not a pretty 1992 fastback right now.. i have hatch rust i am repairing right now so the car looks kind of crappy. my brother drives a dark purple greyish 240 with some 18's. his car is much cleaner than mine right now... he has an s14 sr swap. he goes to van's (on 183/research blvd) on saturday's sometimes, and i knew some good guys that used to go out there (and still do sometimes) but that place has gone to hell lately.... it's just trashy now for the most part...the people suck now. i used to ride over there and meet up with some cool bike guys that rode suzuki sv's (like me and my friend) but one of the guys got in a wreck so they haven't gone for a while. we kind of stopped going for the most part and we just work on the cars usually on saturday nights then go get a beer or something, but sometimes we still go out there... usually i go when my brother wants me to go, but usually we avoid that place now.

anyhow thanks for all the replies guys, i appreciate the input. hopefully i won't have to worry about this fmu and lazy o2 for too much longer.... just waiting on biki now. man they need to make the day longer.... i think an extra 24 hours per day would be nice...

any more info? post it up!

[nismo1003]

I just got a 240sx just couple months ago, it's a white coupe, I live around UT area , when you guys going to a saturday meet, let me know, I usually hang out with my friend's WRX group , they have some STi and Legacy at van's , I haven't been there long time, but I would go if there are some Ka-T 240 . I am new to 240sx, i'm going to turbo my Ka-E this summer. anyways, let me know if u are going.

[hysteria]

will do... it'll probably be in the summer though cause now i'm studying for finals and finishing up my work for the semester... lots of crap to do...

there are a whole bunch of people who post on these forums that live in or around austin... it seems like almost every time i create a new thread i get responses from people who live close to me. my brother and his friends used to organize all these nissan meets and things, but i was never a part of that really. my brothers friend used to have a full s13 conversion (exterior and engine) but he sold it and he saw my kat now that he's back from basic training and he likes it... haha within 2 days of moving back he bought another 240sx and now that he's seen my kat he might just do that instead of getting another sr.

anyhow this weekend i am going to study a lot and then see if i can either use another boost gauge to see what pressure i read in the charge pipes when the wastegate opens, or i'll rig up some kind of leak detector to try and do the same thing, and to check for leaks...

[SunshineAcid]

ahaha rock oni live in austin toowe all need to get together. i need to get mine turboed, and i would definately like to take a peek at your setup

[hysteria]

we're all just coming out of the woodwork...