12psi fun but should I go higher? Can I? some questions...

[Guest bastaad525]

I've been loving the new setup a lot lately... running much better and quicker with the I/C, and not worrying about running too lean after dynoing with the FMU... it's been sweet. But... well you know how it goes... fast starts to feel slow again, and the urge to crank the boost just a liiiiiittle bit more keeps creeping up on me.

 

 

Well I have some questions for you guys. Some kinda random.

 

 

First off... how is it any of you guys have run more than 15psi of boost on the stock T3 turbo's? I remember two times now I've had the signal hose to the wastegate blow off... so basically NO wastegate action at all, and the boost hit exactly 15psi, no higher. I've also read stuff from others here that showed about the same thing... so I got the impression the turbo would just spin no higher than 15psi... yet I see guys running 17, 18 or even 20psi on the stock turbo's... how is that?

 

I'm thinking of turning my boost up to about 14-15psi, but what about efficiency? I have a Trust I/C... dunno what it's efficiency is, but seems to work great. At 14-15psi would I not be heating the air so much as to cancel out the I/C's effect? Or if not cancelling it out, either way wouldn't it be heating the air too much to be safe any more? Does anyone have the map for the stock T3 that they can post and can show efficiency at 15psi of boost? How hot will it be getting the air at that level?

 

Is running that high a level of boost greatly shortening the life of the turbo itself?

 

What about spiking? After installing the I/C and upping boost from 10 to 12-13psi, I get a lot more of a spike than I used to... used to only spike about 1psi before settling on 10, now it sparks up to 14 or sometimes even 15psi before settling at 12-13 (gear dependent). I dunno if this is an issue with the grainger valve boost controller, or because I'm now getting my signal to it and the wastegate actuator from the intake manifold, or if it has something to do with the I/C or what. I also dont' know if it's a linear spike. In other words, will it always only spike 2-3psi now? or will the amount of spike be proportionate to the amount of boost I"m running i.e.: higher boost = more psi of spike. I'm gonna guess that setting it to 15psi and spiking to 18psi is really not good for my turbo or engine. What if I do have the fuel to support it though? Is there anything I can do to cut the spiking, short of buying an electronic boost controller? I've already got the signal line hoses cut as short as I can possibly make them. Maybe change to a different spring in the boost controller? Should I go stiffer, softer, shorter, longer?

 

As most of you know I'm running a BEGI FMU to get the extra fuel I need. Right now it's set to run at about 65psi at WOT/max boost, which is only an increase of 12psi over what it was running with just the stock FPR. I'm also running an upgraded fuel pump. On the dyno, this setting provided enough fuel to keep me in the 12:1 air/fuel range all the way up to redline at 12psi of boost, with no falling off in pressure or fuel curve (fuel pump kept up fine). I've heard of guys running 70 or even 80psi of fuel pressure w/o issue... but I wanted to ask you guys. There's been lots of allusion to running 'too much fuel pressure' being dangerous, but no one has really said exactly how much pressure is too much pressure? I'm running 65psi which is a very small rate of gain, about 2.5:1 (2.5psi of fuel pressure for every 1psi of boost). Guys running the FMU on N/A cars that have added turbos run much more pressure than this, 4:1 or 7:1, getting pressures well over 100psi... so how much pressure is too much? The math equations given to me by Sean73 say that by upping the fuel pressure to 75psi (additional 10psi) my stock injectors should provide enough fuel for about 250hp to the wheels, about 15psi of boost. His math was VERY accurate, as it predicted I needed 65psi to get about 230 at the wheels, and I got 226 at the dyno running a little bit rich at that fuel pressure. So is another 10psi too much?

 

 

What should I do guys? I'm thinking I can get really close to my ORIGINAL goal of 250hp at the wheels, and do it more or less safely, by running 15psi... but what do you guys think?

[ToplessZ]

Well I believe I have read that 14psi is the max for stock injectors. I dont know this for sure though. Looks like you are getting into the relm of the 370cc injectors though. I may be selling a set soon if your interested. Im going with the 420cc mercedes ones. Sounds like that fmu is working nicely maybe I will have to get one

[Tim240z]

I think it was a week or so ago that I remember you saying that you were happy with the car and were done with any more adjustments/mods?

 

I think you have the disease...but good!!

[Guest bastaad525]

I think it was a week or so ago that I remember you saying that you were happy with the car and were done with any more adjustments/mods?

 

I think you have the disease...but good!!

 

I admit it, I've caught the bug well but you know my ORIGINAL goal all along was to put 250hp to the wheels on stock stuff, at whatever boost level it took really I lowered that goal when some guys here put the scare into me about running 'too high' of fuel pressure and about spinning the turbo too high, and a few other things so decided to lower that to 230hp to the wheels instead. But then I look around and see lots of guys running 14-15psi of boost happily all day long... so I think okay if I've got enough fuel for that then why not me as well? heheh but enough of my excuses you got me red handed. By the way Tim, I tried some of that Seafoam, and I'll be damned if it doesn't seem to be idling just the slightest bit smoother. Still a little bit of misfire but it's very light now, the pop-pop-popping not nearly so pronounced. I've only driven about 50 miles after dumping it in there... hopefully it will help even more.

 

ToplessZ - actually I've never heard a max amount of boost that the injectors would be good for, only a max amount of hp. Stock 260cc injectors at stock fuel pressure are only good up to about 270hp at the flywheel at 100% duty cycle, which equates to about 205hp at the wheels at 90% duty cycle, which I've already exceeded by far. That power came at about 10psi of boost btw, so bone stock injectors are actually only good to about 10psi. Which is EXACTLY what I saw all the times that I dynoed before the FMU... even after adding the I/C and upping the boost from 10psi, power just did not want to climb much above 200rwhp, even though torque had gone up by nearly 40 ft lbs at the peak! With increased pressure the injectors can support a lot more, but the problem is figuring/finding out just how much increased pressure can be run w/o breaking/damaging anything. At 80psi of fuel pressure for instance (WOT/full boost) they can support upwards of 250hp at the wheels... nearly 50hp increase, and flow about as much as a 330cc injector. But can the fuel system put up with 80psi? The FMU IS working nicely, it does exactly what it's advertised to do. I love it. My goal has always been to try to pull as much power as possible, reliably, out of the stock EFI, injectors and turbo. I still say I can do 250hp on this setup safely... we shall see. Having bought the Sentra to drive as my daily driver/beater has given me a lot more guts to try things on the Z... if it breaks now at least I'm not stuck w/o a ride

 

 

Well I decided to go ahead and bump the boost up a bit, now it hits 13.5-15psi (gear dependent). I did answer one of my questions myself, about the spiking. It actually seems to spike LESS now... only going as high as 16psi, so only a 1-2psi spike. Fuel pressure should be up in the 75psi range at max now, but I have no way to verify that. I'm gonna see about talking the wife into an in-car fuel pressure gauge to go along with my WB O2 this Xmas

 

I imagine hp is up to at least 240rwhp, though I didn't really feel any difference, my wife swears she does... then again I probably didn't feel any difference because I had her extra weight in the car. I may not leave the boost there though... of course not knowing what the air/fuel is at now, I dont' really want to risk anything, though the math says it should be more than enough fuel. The FMU should be adding about 3-8 psi of fuel pressure, on top of the extra 3psi of pressure the stock FPR is adding. Graaar maybe I need to work on talking my wife into getting me my xmas present early??

 

I bet money I'm actually running perfectly safe and still in the mid 12:1 a/f ratios like this.....

[Guest bastaad525]

Turned it back down a little to 13.5-14psi... and drove to work tonite sans wife it's definately faster for the extra 2psi. Getting easier and easier to break the tires loose in SECOND gear... that's new. I wonder how much power one psi is good for this far outside of the T3's efficiency range... definately a noticeable increase.

[akeizm]

Turned it back down a little to 13.5-14psi... and drove to work tonite sans wife it's definately faster for the extra 2psi. Getting easier and easier to break the tires loose in SECOND gear... that's new. I wonder how much power one psi is good for this far outside of the T3's efficiency range... definately a noticeable increase.

 

You sure thats not your tyres getting balder and balder

[cygnusx1]

This should be a sticky!

Warning, a turbo Z conversion is highly addictive and may cause obsessive behaviors along with short quick spurts of mometary satisfaction. Generally these moments are accompanied by the desire to invite friends, spouses, and/or random strangers for a ride in the Z. Within hours of passing peak satisfaction, thoughts are quickly realigned towards seeking information, funding, and the nearest screwdriver in an attempt to reinforce the fixation with more boost. The only known cure is four days of honda civic. Note: the honda cure will only last two days once victim has returned to Z.

 

Turn it up Baast!

[mobythevan]

But then I look around and see lots of guys running 14-15psi of boost happily all day long

 

If I run 14psi(and that is what I am running right now on stock fuel pump) it is only like a person at sea level running 11psi. So I figure that is safe on the stock fuel pump. IF someone says they run xx psi on any engine setup you need to know more about their environment, especially their altitude. To start off with it would be good to know their absolute pressure which is atmosphere + turbo boost.

 

sea level

atmo 14.7 + boost 14psi = absolute pressure 28.7 psi in intake manifold

 

me (6400)

atmo~ 11.7 + boost 14psi = aboslute pressure 25.7 psi in intake manifold

 

You may know this stuff already and don't take this post the wrong way. I did not understand this concept through most of my turbo swap and tuning(maybe I'm just slow that way ), so I put the post in hoping to help someone else that may be like I was. Really only important to high altitude people, but it becomes more important when all of us start comparing boost numbers that people are able to run with certain stock components or any components for that matter.

[Guest bastaad525]

You sure thats not your tyres getting balder and balder

 

ROFL!!!

 

You know what's funny, I'm running on some $25 a piece, Just Tires specials. 195-60-14's, all weather radials... and these things have put up with a TON of abuse and still show plenty of tread. I've had these tires for like 3 years now, and have done so many burnouts, especially when I had my N/A engine with the 3.90 gears, would dump the clutch at 3000rpm and the tires would spin all the way thru first and halfway thru second. But I still have tread left to spare. On the flipside, they are actually pretty grippy tires... Even when I was pushing 270ftlbs of torque at the wheels (when I was running a bit too lean and making more power because of it) getting them to spin from a launch still takes a lot of provocation... so much so that for a long while I was convinced something was wrong with the car and power was way down because of how hard it was to get the tires spinning!

 

 

Cygnus - driving the '91 Sentra SE-R I just bought puts a whole new perspective on things... I mean, that car was or is considered to be 'quick'... and it's a fun car. But it is a definate 'cure' for whenever the Z starts to feel 'slow' again. A couple days in the Sentra and the Z feels as fast as ever.

 

Cygnus I know you're running 14psi right? I have one big question for you if you could please check for me when you get a chance? On your FMU, I'm just really curious how far out/in you have your bleeder screw adjusted. Could you count the number of turns you have it set in from fully out for me? Also did you ever recheck the fuel pressure with your compressor setup to see exactly what your final pressure under WOT/full boost would be? I know every setup is different, but from everything you've told me so far, I'm gonna bet you are probably running too lean. Remember it took me 65-70psi of fuel pressure at WOT/full boost, to get into the low-mid 12:1 a/f ratios on the dyno at 12psi of boost. And on top of that you're running a much more efficient turbo, so running even leaner because of it.

 

Moby - you're absolutely right. Though I have always been aware of that, you're right in that I don't always think about it. Whenever I do find people running setups similiar to me I usually PM them and get as much info from them as I can, see what they did the same, see what they did different... but you're right that "what altitude are you at" is not ever really on the list of questions

 

Well, this morning I turned the boost back down to where it was (12psi)... due in part to the kinds of things Moby is talking about... basically I can't trust that just because five other guys have run 14psi means that I can do the same thing and not blow something up. I tuned at the dyno for 12psi at mid 12:1 a/f ratios, and that's where I'm gonna leave it for now. Next step is to get my own wideband O2 and then I can tune w/o worry. THEN I'll try 14psi and see what I have to set the fuel pressure to to sustain a nice rich fuel curve... if the pressure gets too high I'll back off. I MAY even be picking up a set of 370's after all

 

I'm such a liar and a hypocrite

[Guest bastaad525]

Does anyone know (I'm sure more of Sean73's math could solve this), if I turn up the boost 1psi, but dont' change the fuel supply at all, how much does this lean out the a/f ratio? Or how much extra fuel you need to compensate for an additional 1psi of boost to keep the a/f ratio constant?

[Sean73]

12 psi is pressure ratio of (12+14.7)/14.7 = 1.816

13 psi is a pressure ratio of (13+14.7/14.7 = 1.884

 

The percent change from 12 to 13 is 1.884/1.816= 1.0376

 

So, you need roughly 4% more fuel

 

If you turn up the boost, without addressing the fuel, then your A/F will go leaner by 4%, all other factors being equal.

 

Rounding up, and solving for fuel pressure: (1.04)^2 = 1.08

 

Ok, so I haven't read this whole thread (no time). But you need 8 % more fuel pressure to go from 12 to 13 psi, all other factors being equal.

[Guest bastaad525]

w00t thanks Sean was hoping you'd pitch in here! Every equation you've given me has gone into a handy little .txt file on my desktop that gets viewed on an almost daily basis! Another very useful equation that will save me some dyno money I GOT to get an in-car fuel pressure gauge ASAP at the very least....

[Sean73]

just be careful, it's the "all other factors being equal" clause that's important to keep in mind. the math is there as a guideline, but isn't always accurate when the rubber hits the road.

 

I would invest in a in-care A/F meter. Even a narrow band one will at the least give you some warning sign of a lean condition. I use mine all the time. Sure, it's innacurate. But absolute accuracy is sometimes not as important as relative accuracy. I try to keep the lights in the middle of the green (rich) at WOT. If I make an adjustment, and the lights are in the yellow, I know something is wrong and I need to back off. I also get the immediate gratification of dancing lights (when the ECU is in closed loop), as a constant reminder that the ECU is getting all the right inputs.

 

It's all moot right now for me, as I try to find the time to put in my 2400 lb RPS clutch. it's going to suck driving it for 500 miles to break in the clutch, that's going to feel like an eternity.

 

Sean

73 240ZT

[Guest bastaad525]

Well I've put a wideband O2 meter at the top of my christmas wish list. I don't put much stock in the in car, narrowband O2's, I've talked to three different guys who've had them now, and then had their car on a dyno with a wideband, and the wideband was showing that they were running lean, while the in car gauge was showing they were still well in the rich.

 

I do know not to trust 100% in just the math alone, though your initial equations that you gave me gave a predicition that ended up being just about spot on once I got down to the dyno. I was amazed just how accurate those equations ended up being. I keep going back over my dyno sheets... my A/F curves on the last run were actually way in the rich, averaging 11:1 a/f ratio, but there's a lean 'spike' at about 5600rpm, after which it starts to richen back up, but that lean spike was at about 12.5:1, and I was trying to keep the leanest point of the fuel curve right there. Sucks about that spike otherwise I could easily up the boost a bit w/o adjusting fuel at all, but I absolutely am putting safety above all else. I dunno what I can do about that spike... it was exactly the same even before I installed the FMU, so I dont feel that's the cause. The FMU really didn't change the fuel curve much at all, other than just richening the whole thing, but it still follows the same lows and peaks. Stock '82 ZXT ECU really does suck......