dashingMax

Peeps running Supercharger & fuel pressure gauge, please help out.
I need to know what
Pulley size:
Boost:
Maximum fuel pressure:

I'm running a SC w/ 3.33 pulley however, I do not have a fuel pressure gauge. I would like to go for the variable intake & assuming that it will add 20-30 wheel hp, I need to know if I need to upgrade fuel injectors.
I consistently see 8psi boost. According to MardiGrasMax 10 psi is the limit for stock fuel injectors. 2 psi = 20-25 whp. MEVI=20-30 whp. Therefore, it is quite possible that I'll max out my injector limits with MEVI.

What fuel pressures do you guys see & at what boost/pulley levels?

Thanks in advance...

Chunger

iTrader: (1)

You might want to include the RATIO of the FMU, too.

dashingMax

ANYONE?!?!?!

Chebosto

iTrader: (1)

if you're running 3.33 go with the 8:1 fuel disc. you'll be fine..


at max boost, max fuel press is 100? i cant tell. i never look at it. too busy trying NOT to run into things.

Confused

iTrader: (4)

I don't believe your theorum of transitivity applies - the MEVI does NOT equal +2lbs of boost. You are effectivly reducing the length of the runners and NOT pumping up the boost. You should be more than fine with the 3.33 and a 8:1 disc. My .02, anyone else?

Stephen Max

iTrader: (59)

Yeah, I thought the same at first, but if the MEVI is helping the engine breathe better, then the ECU has to be giving the engine more fuel, too, based on the additional air that the MAF is detecting. So if the fuel pressure is already up to the limit due to boost, then the additional air due to the MEVI will lean out the mixture if additional fuel can't be added. Am I wrong? Where are the experts?

delio

iTrader: (11)

You want more of an expert than Brett?? Hmmm... anyways. I don't think you need to up the FMU disk at all.. I think on the Stock 6:1 included in the Stillen kit you will be fine. Alot of dyno testing has proven that the 6:1 included in the kit can handle pulley sizes all the way down to 3.125. If you run this setup, put on a dyno or buy some guages and get an idea of what the A/F looks like at Redline, I am going to guess that it will damn close to 12:1 which is almost ideal for a boosted Max. There is alot of fat in the FMU setup, hence the reason people like to go to big injectors, versus a pressure increased system. With the FMU setup, by the time you get into the upper boost levels you are running a ton of fuel pressure, a good portion of which is not getting used correctly because it is overkill. Stillen chose the 6:1 disc with safety in mind, not neccessarily optimum performance. I believe that you could run the SC setup on a 4:1 disc for the stock pulley size and maybe a size below. (That is MY personal opinion... do not take that as gospel without the proper guages or dyno time).

All in all... if you plan on keeping your 3.33 pulley, then get the VI, don't worry about fuel pressure, because the 6:1 has enough fat on the top to burn off... Get it on a dyno and see for yourself. I don't know how people run SC's and stuff, especially bumping down pulley sizes, adding VI's and all this jazz without the right instrumentation at their disposal. Guages are critical. I think any Boosted max planning to go lower than 3.33 (9 psi or so) needs 3 guages. Boost, Fuel Pressure and EGT... others are nice to haves, those 3 IMHO are musts.

Any more thoughts??

Y2KevSE

iTrader: (13)

6:1 should work up to 3.125. 8:1 will actually make you run a little rich with 3.125, but rich is better than lean.

dashingMax

I agree with you Kevin, however, this richnes at very high fuel pressures can cause one or more injectors to sieze up & bye bye engine.

I am leaning towards Stephen Max's hypothesis. The extra air I'm dumping through the MEVI needs the extra fuel. Two possibilities:
(1) The ECU provides the extra fuel based on MAF sensor.
(2) The 6:1 FMU disk provides plenty extra fuel (for safety reasons) to compensate for extra MEVI air.

Unfortunately I do NOT have a fuel pressure gauge. I have EGT, Air/Fuel & Boost. I would like to stay within safe fuel pressure limits. I was told 90 psi is a reasonable limit of our 240cc injectors.

delio

iTrader: (11)

Well if you have an EGT guage you should be able to easily tell how the motor is running, long before you would get to the point of grenading the motor. If your EGT's go up to high for a few seconds it should not cause any long term damage (within reason) I don't see an extra 20-30 HP or potential HP causing that type of damage. Use your guage, run it out to redline for a couple of gears, and you should be able to tell how the car is running and whether you need to bump it up to an 8:1 disc. If you bump up the disc, be prepared for a really rich mixture, probably "forcing" you to go down a couple of pulley sizes

Y2KevSE

iTrader: (13)

If you're REALLY worried about fuel pressure, stick with the 3.33 (always been in the smallest but safest pulley in my opinion) and don't go any smaller. If the pressure was too great, you would've heard about blown motors by now.

dashingMax

Hmm... I see your point. The only blown motor I personally know of is BriGuyMax, running over 100 psi fuel pressure & fried piston rings.

So, to conclude:
3.33" + MEVI = NO Injectors, 8:1 disk.
3.125" ONLY = NO Injectors, 8:1 disk, Blitz BOV.
3.125" + MEVI = Injectors, ??:1 disk, FPR, profe$$sional tuning costs.
2.87" + MEVI = Please stop me from even thinking about it

delio

iTrader: (11)

Bobby,

I have to disagree with this..

3.33" + MEVI... Stick to the 6:1... And watch the EGT guage...
3.125" Only... You can probably continue on the 6:1...
3.125 and VI 8:1 for sure, and that is PLENTY of fuel... no real tuning involved
2.87" + MEVI 8:1 should still be plenty... if not, this is the point at which I would seriously consider going the injector route. with the 3:1 FMU disc.

I have run the 10:1 disc, and am not at all hyped up on the thought of running that high fuel pressure. Hence my investement in the below items:




Let the EGT guage be your friend. And let it be your guide to your homebrew tuning. Professional tuning is not always needed.

Y2KevSE

iTrader: (13)

No blow motors by SC guys besides Loren (not related) and BrianV.

3.33" + MEVI = NO Injectors, 6:1 disk.
3.125" ONLY = NO Injectors, 6:1 disk (8 if you want to play safe), Blitz BOV.
3.125" + MEVI = Injectors, 6:1 disk (8 if you want to play safe)
2.87" + MEVI = Please stop me from even thinking about it


You definitely want to tune after swapping pulleys, but you can't tune unless you have an adjustable FPR or AFC.

Chunger

iTrader: (1)

Del,

What size are those injectors?

Y2KevSE

iTrader: (13)

370cc

delio

iTrader: (11)

Ding ding ding.... We have a winner... BTW Chung, expect a delivery soon buddy

Y2KevSE

iTrader: (13)

Chunger

iTrader: (1)

Where's my cookie? with the delivery?

I was thinking about RC Engineering and getting 280-300cc sized ones... about $80 per injector?

dashingMax

I like that remark made by Confused, "theorm of transitivity". I couldn't resist but research a little more on fuel injectors. Mathematically speaking:
Lets take our stock 240cc/minute injectors & convert to lbs/hr:
To convert cc / min to lbs. / hr. - Divide by 10.5 = 22.86 lbs/hr
Now, using the formula:
lbs/hr = (BHP X BSFC) / (Number of injectors X Duty Cycle)
Assumptions:
BHP = Crank Horsepower assuming 17% drivetrain loss. Therefore, BHP = 1.17 X Wheel HP.
BSFC = 0.53 is a safe, reliable estimate for SC cars. Perfectly stoichiometric.
Duty Cycle: 80% or 0.80 is industry accepted standard.
240cc/minute = 22.86 lbs/hour
---------------
Using the Formula:
BHP = (22.86 lbs/hr X 6 injectors X 0.80 duty)/0.53 BSFC
BHP = 220 = 187 wheel hp. This is at a static flow of 43.5 psi.
To obtain 300 wheel hp from 3.125 or smaller pulley:
300 whp = 355 bhp requires
370cc injectors
@80% duty cycle
@53 psi system fuel pressure
---
Currently, on my stock 240cc injectors, I am pushing things over 85psi fuel pressures to obtain 270 whp.

Does anyone know where I can rent Delta Dash or similar OBD-II diagnostics tool? Would like to measure my duty cycle. I bet it is over the recommended 80% limits...

dashingMax

To further backup my findings, I did some digging on 300ZX Twin Turbo upgrade path.
The stock 370cc injectors are okay upto 450 crank HP. After that most tuners recommend 555cc injectors. Why? We'll using the same formula:
Up to 450 bhp at 0.54 BSFC pushing 90 psi fuel pressure at 80% duty cycle requires 370cc injectors.
Any more HP & you will risk running unsafe fuel pressures or duty cycles or both.

JAY25

iTrader: (38)

going to the Z injectors is a good idea, I do know you have to change your FMU disk. Which one I am not sure, you have to ask Matt (Mardigrasmax) or call Vortech and they can help you with that. I am running very rich. At 10 PSI my fuel pressure is 100PSI. That is the reason why I ordered the SAFC. The fuel pressure I got a direct reading straight out of the FMU hose that connects to the top fuel rail, and ghetto rigged it and took it on a spin on the highway. Since you are planning on going w/the smaller pulley dont forget to shave down that plate therefor your belt wont touch. Look below your pulley see that part where one of the bolts go thats the spot you will shave down. Wont take you that long 15mins tops. Also since your doing all these major upgrades hell you need to upgrade that intake to a CAI. Just my opinion. Snow is right around the corner so you can leave that project for March something like that.

iansw

iTrader: (7)

I am running a 3.25 and getting 9PSI with the MEVI.

Using a Cartech FMU (it does not use disks), my FP is 65-70PSI Max, and I'm tuned on a Dyno to 12.5:1 across the powerband.

I don't think you'll need bigger injectors with a 3.33" Pulley.
At least I don't, but maybe the FP needed is different with a Cartech FMU.

dashingMax

CAI is definitely on the pipeline for future mods, but I don;t have the luxury of warm weathers. After this SNOW season, I'll get it done.

100 psi.
I think it is a general consensus among people on this board, 300ZX TT peeps & boosted IS300 folks that 90 psi is reasonable maximum FP. Anything more is pushing things. If you think about it, stock Maxima pushes 43.5 psi fuel pressure at WOT at max horsepower. Essentially what they told me is that you can somewhat safely double this pressure on good quality fuel rails & injectors. They started bragging about how their IS300's are essentially a Supra in sedan's clothings & their **** is better...anyways...

Better get that FP down as soon as possible. To run at 0.50 BSFC mixture, you need no more than 90 psi at 80% duty cycle.
Currently you are at 85% duty cycle on 100 psi.
Fuel Injector Calculator

dashingMax

To obtain 267 fwhp = 310 bhp on 240cc injectors @ 80% duty cycle, and 0.48 BSFC (pretty much stoichiometric, but a tad bit on the lean side) you need 80 psi fuel pressure.

There are three possibilities using pure physics & mathematics:
(1) Your FP gauge is off by 10psi.
(2) You're not running 12.5:1, but actually running slightly on the lean side.
(3) Your injector duty cycle is exceeding the safe 80% limits.

Of course, my math could be wrong. Find out for yourself:
Fuel Injector calculator

iansw

iTrader: (7)

No, it's probably the MEVI that's it.

Without the MEVI, I'm only 231hp.

IanS

iansw

iTrader: (7)

No, it's probably the MEVI that's it.

Without the MEVI, I'm only 231hp. I don't believe the MEVI changes FP.

IanS

dashingMax

Well, the fuel pressure is regulated by the Vortech FMU. Assuming that you are running the 6:1 disk and your boost gauge is registering 9 psi boost, then essentially your fuel pressure should be:
(9psi X 6) + 43.5 psi = 97.5 psi fuel pressure.
Since you're only seeing 70 psi, something (either a smaller FMU disk or AFC) is leaning out the fuel pressure.

iansw

iTrader: (7)

I don't have a Vortech FMU, I have a Cartech FMU.

I know I tuned ito n the Dyno. 12.5:1 across the band.

IanS

Stephen Max

iTrader: (59)

There's something here I'm not quite understanding. How is it possible to adjust air/fuel ratio without the ECU readjusting it back based on what the O2 sensors are telling it? Or does this work only when you are needing so much fuel (due to increased air from boosting) that stock fuel pressure can't supply enough fuel? Maybe I just answered my own question.

Y2KevSE

iTrader: (13)

[(9 psi) X (6 from FMU disc)] + [(36psi base pressure) / 2] = 72 psi

dashingMax

How did you come up with 36 psi base fuel pressure?

Y2KevSE

iTrader: (13)

34... 36... close enough (FSM).

dashingMax

Now THAT I did NOT know...
I believe you, however, your 5th gen stuff might be slightly different. Do you have 4th gen FSM?
From what I was told the 4th gen 240cc injectors are rated at 43.5 psi max. fuel pressure. This is at WOT (zero vaccumm/atmospheric pressure).
At idle (full vaccumm) the fuel pressure should be:
43.5 - 14.7 atm. press. = 28.8 psi.
If only I had a freaking fuel pressure gauge...

Y2KevSE

iTrader: (13)

Your idle fuel psi is also 34 psi. 43 at WOT.

MardiGrasMax

iTrader: (14)

I was at 100% duty cycle at ~5750rpms when I was running a 3.125 pulley with the MEVI on stock 240cc injectors. I could see the change in the O2 graph on my dyno plot becaue I would start lean out even with an 8:1 from ~5700rpms up and the Fields AFC adjustments had no effect. IMHO the stock MAF is only good to ~300bhp

dashingMax

Matt...it makes perfect sense. You are absolutely right.

And what is this about MAF choking on us?!?!?!
Will we need a different MAF sensor? or worse a bigger throttle body??

I'm definitely making more than 300 bhp with my setup on stock MAF...

Y2KevSE

iTrader: (13)

Were you leaner than this?

http://boostedmaximas.com/jane97se/i...ynos/dyno5.jpg

MardiGrasMax

iTrader: (14)

Yea, IIRC ~13.5:1 at 6300rpms when the dyno operator cut it off.

FWIW the car ran fine though, no detonation that I or the dyno operator coud detect.

Y2KevSE

iTrader: (13)

Weeeeeeeeeeird. Were your injectors okay at the time (dirty? clogged?)? Was this with 8:1 or 6:1?

Jane's 8:1 without Cartech:
http://boostedmaximas.com/jane97se/i...ynos/dyno3.jpg