PSI

[esahuque]

OK, Here's the Q- how can I (ME MYSELF) fig out what PSI i should run with my setup that im getting. I dont what anyone to answer my Q with (you should run X PSI on that set up or it depends on what your looing for) I not looking for a certin amount of hp, i'm not looking for a certin track time. I'm looking to fig this out on my own. (thats the only way i'll learn) im going to get my ECU tunned by Enthalpy and i know he's going to ask at what PSI im planning on running, so he can tune it for that seup at that PSI. So i would like to be able to answer him. what's the formula to fig out what PSI is safe for my setup or any setup. with out running anything at 100%. I want to fig out the most i can safely get out my motor, withuot anyone doing the math for me. i dont want to be hand feed. i like fig things out on my own. thanks for any comments that can help me i better edjucating my self in this matter.

[WDRacing]

That question can't be answered. Its not about how many PSI you can boost. For every turbo it will be different. It depends on what injectors you have, what turbo you have, how good is your intercooler. Everything ties into how much boost you can run.

Boost is the last thing you figure out in an equation. Maxing out injectors and ignition timing are far more important.

Enthalpy or JWT will most likely just burn you a chip for the size injectors you're going to run. Ignition retard will be the same for just about any boost setting over 10 psi.

If I know everything in your setup, then I can give you a rough estimate on how much boost you can run. But without that info, no one can answer your question.

WD

[esahuque]

thats the thing, didnt want any one to tell me what PSI i should run. what do i take in to consideration when tryng to fig that out. My injectors can dump X amount of fuel, My MAF can handle X amount of air intake. I have X size turbo which can move X amount of air? OK never mind, heres my setup what PSI should i run at without maxxing anything out. T3/T4 turbo JGS mani SR20 dp 38mm WG FMIC (E Bay) Size 31"x11"x3" 555cc injectors turboxs BOV Z32 MAF Enthalpy tuned ECU 3" exhaust well thats all the major parts anyway, gauges, TT, FPR, and MBC.

[nissanfanatic]

I'd do 15psi on pump gas and probably whatever it took to make 400whp+ on race gas.

[coolbone28]

Ya you gotta ask yourself how much power YOU are looking for. You are asking how much pressure you should run, but for what? Do you want to hit 250whp? 315? 450? Also, it depends on the specs of the turbo. That will give your ultimate answer of what you CAN run. Ya its a t3/t4 but thats too vague. your efficiancy could be way out of rance at 20psi with one turbo, and another you could take over 30psi. Just read more on what people are hitting on their current/similar setups and maybe do a little research into the compressor maps for your turbo.

[WDRacing]

After re-reading your original post, I'm a tad confused. You want us to tell you what? You don't want us to tell you what boost to run, but you want us to tell you how to figure it out?

I explained exactly why we need to know everything. Because EVERYTHING matters.

I understand you're trying to learn here. Thats a good thing. But I don't know *what* you're trying to learn.

I'll give you the method I use to figure out how much boost I can run. From there, you can try to apply it to yours.

I know you don't care what kind of setup I have, but its a must know if you're going to understand the tuning process and how everything ties together.

If I sound like I'm dumbing things down to much, its not my intent. I'm just explaining exactly what goes through my mind when I tune ANY car.

I installed a SAFCII to control the fuel injectors. I installed a MSD BTM to retard my timing on boost. I have a very efficient T3/TO4E .63 ar hotside and a 50 trim compressor wheel. This turbo is the most proven and runs exactly where the KA24DE should run. I have a MSD inline fuel pump and the S14 fuel pump and I have my base fuel pressure set to 55 psi. By setting the base fuel presure higher, I effectivly make my fuel injectors larger. I simply have to reduce the duty cycle a bit more as I would if I were running say 50lb injectors instead of the 42lb injectors I am currently running. The fuel pressure increase is done via an aftermarket fuel pressure regulator. I have a decent sized FMIC, the exact proportions elude me, its been awhile since the install.

Are you follwoing so far? My setup is goes like this.Aeromotive top feed fuel rail42lb injectorsT4/TO4E turboJGS type manifold(log style)SAFCIIMSD BTM

The first thing I did was set the BTM to pull out 1 full degree of timing per psi of boost. This is similar to what Enthalpy and JWT will do, except they use the ECU timing map. I'm not going to get into detail here, just take my word that its fairly close to the same thing. Reguardless, ignition retard on boost is very important.

My next step was to tune the car for proper idle. I have a wideband O2 meter. Without one, you simply can not tune a car properly. So I set the idle at about 15:1 AFR while idling. My next step was to lean out the off boost rpms but add fuel back in as the turbo spools up. I estimated that the turbo would spool by 3000rpm. So I pulled out fuel until that point, gradually increasing it until I hit 3000 rpm. Then I added fuel back in.

I drove the car around with the wide band hooked up, tracing the AFR's and tuning the SAFCII as I watched the mixture get to lean or to rich.

The tuning process takes a bit to get semi good. But I'm going to skip to where I had the fuel tuning set to where I wanted it. Which was about 11.5:1 AFR on boost and 15:1 at idle. There are alot of particulars I'm leaving out of SAFC tuning, but there isn't any need to go into those at the moment.

With the fuel set, I set my BTM to pull .5 degree's of timing per lb of boost. If the tuning is done semi decent, you don't need anymore retard then that.

Here's where you figure out how much boost you can run for your particular setup. You increase the boost while you're tuning. You'll reach a point where you can't add enough fuel to keep up with the boost. By that I mean, you can't keep the AFR where you want it. But that is running your unjectors close to 100%. So back the psi down 2 psi and that would be your max.

All of this depends on if you get knock also. If you get detonation, then you've rached the max point of somthing in your system. Perhaps the FMIC is heating up, or maybe you have reached the maximum boost for that octane fuel. Reguardless, thats the basics for tuning.

I hope that helps you understand what you're asking us.

WD

[esahuque]

yes it does. thank for the info,all of you. this is my calculation for my turbo at 12 PSI. so now i need to fig out what size injectors would be sufficient. I know that the 555cc injectors will supply enough fuel along with walbro 255 fuel pump b\c thats what i was told by everyone here at NICO. CFM = L x RPM x VE x Pr 5660

Where L = engine capacity in litersRPM = maximum engine speed (we'll adjust this later)VE = engine volumetric efficiency. From A. Graham Bell's book Forced Induction Performance Tuning some good values for VE are:Stock 2-valve = 85%Stock 4-valve = 90%Street modified = 93%Competition = 105%Pr = pressure ratio

To calculate the pressure ratio you need to know what boost pressure you want to run and then plug that into the following formula:

Pr = 14.7 + Boost 14.7

At 12 PSI

[esahuque]

I know the turbo can handle 12 PSI, I know the fuel/ air flow can handle the PSI (with a Z32 MAF) but can the stock motor handle it. and do i need a FPR or can my stock one handle the fuel flow? OH, sorry the motor has 41820 on a rebuild. very tight motor.

[WDRacing]

Its Corky Bell, not Graham Bell, you're thinking of Alexander Graham Bell...lol.

Anyway, exactly what turbo are you going to use? Do you know all of the specs?

As a reference, I was running 14psi on my 42lb injectors at 43psi base fuel pressure with no issues at all.

[nissanman04]

I know the turbo can handle 12 PSI, I know the fuel/ air flow can handle the PSI (with a Z32 MAF) but can the stock motor handle it. and do i need a FPR or can my stock one handle the fuel flow? OH, sorry the motor has 41820 on a rebuild. very tight motor.

it'll prolly run ok w/o a fpr, but it is nice to be able to fine tune the pressure. Its not like the are that expensive, and it's a useful tool.

[esahuque]

I'm going to be running a Turbonetics .50 trim T3/T04E turbo w/.48 A/R

[WDRacing]

Well, with that turbo, anything over 20 psi will turn it into a heat pump. SO there ya go...with that turbo and a .63 Ar, Fiznat made 420 WHP at 20 psi.

[nissanfanatic]

I know the turbo can handle 12 PSI, I know the fuel/ air flow can handle the PSI (with a Z32 MAF) but can the stock motor handle it.

Yes.

Stock FPR will do the job just fine.

[Edub1]

You're not going to need any of that information. Once you correct for your larger fuel injectors and trim the tune, the ECU will maintain the correct injector pulse for any level of boost. That's the beauty of the hot wire MAF system. Timing unfortunatly does need to be re-tweeked unless the tuner blankets the map with major retard as some do.

Anyway, there is no set boost level. With 550cc injectors you can run over 25lbs or about 450HP. It's more a matter of what your internals will handle. On stock internals I plan or running about 325HP which is ~12lbs on my setup.

Also, 2.4L is a big 4 cylinder. I wouldn't run anything smaller than a .63 AR, stage III exhaust. Anything smaller will cause backpressure.

BTW, you are using the compressor map correctly. If you multiply the X axis numbers by 10 it will give apx HP at that boost level - over 300 in this case. But, the small exhaust section will hurt your top end.
Modified by Edub1 at 11:16 AM 1/27/2007