Turbo Advice Needed: S13

[Thoughtful_One]

I am looking to turbo-charge my car within the next summer and am on a budget. I don't plan to ghetto-rig either. I have been searching, but many posts are based on here-say and no proof, or are just flat-out arguments. What I am not sure about is the electronics portion and whether I need certain things or not.

My Plans/Goals:- ~220 WHP- Should be quick spooling and have useable power- I don't plan to exceed 7 PSI of boost- Hoping to use stock injectors (supposedly maxes out beyond 7-8 PSI of boost) Parts I Plan To Use:- SR T25 turbo- Maybe a RevHard or other used manifold- eBay S.S. downpipe- Either custom 3" mandrel-bent exhaust, or 3" eBay exhaust- Using stock injectors and staying at 7 PSI of boost- eBay FMIC with couplings and piping- Brand name BOV- Oil lines- Boost, water temp, A/F guages- Walbro 255 liters/hour fuel punp

--Do I need to use a FMU? This maintains stock fuel pressure off boost and increases fuel pressure with increasing boost, correct?--Is the SR internally waste-gated and air-cooled?--Will this setup give me what I want? --What is and do I need a SAFC? (super a/f controller, right)--Is there any special prep work I should do? (ie water pump, clutch, ...)--What else do I need to get this project going?

The IAP stage 1 kit does not offer any special fuel parts except for the choice of the Walbro pump OR the Vortec FMU. I would prefer a used and nicely priced IAP stage 1 kit but piecing my own kit together is more fun, less expensive, and I will learn more about the parts that I will put into my car.

[Dustin240]

I'm runing 7.25psi with a FMU 10:1,walbro, and stock injectors works great.Go with a T3 if u can and there's no real lag.

I'm geting 206whp on a built motor but I ran a 13.8 1/4mile.

[Thoughtful_One]

So the FMU is needed? Is my expectation of 220 WHP too much? I have searched for information, but too much of it is just here-say. I don't know anyone with a 240SX, let alone a KA-T. Please help me.

[Dustin240]

Ya u need a FMU,

walbro 255 and a 10:1 FMU= great air/fuel ratio's .Thats all u need for fuel.Works great for me. Dont go over 8 or 9psi with this setup. And trust me when u feel 7psi u'll fall in love.

PS, do it right the first time ( realy )

[Thoughtful_One]

My main question is: Will these parts get me the power I am looking for??

[boznuttz]

wow, that af is pretty damn rich....

[Dustin240]

What are u talking about? (10psi of fuel for every pound of boost) for the FMU (rrpr)

[Dustin240]

U should reach your goal with 9psi. Just watch your a/f's.And use a blow threw mafs setup=near the TB, and place the air temp sensor in the piping also. I had bad idle problems until I switched to the blow threw setup.

[Thoughtful_One]

Isn't the air temp sensor only on the S14; I have the S13. The IAP kit says that either the Walbro fuel pump or the FMU will provide enough fuel. Thanks to ka-t.org, I know have SOME idea of what I need, but it says for 200WHP I should use 370CC injectors, Greddy eManage and SAFC 2. In my understanding, if I use the stock injectors, I won't need the eManage right? Also, why then would I need the SAFC? Tuning is expensive and I will avoid if if I can. I don't plan to make 300 WHP, just something like 220.

[C-Kwik]

The stock injectors will start getting lean about 4 psi. You'll be very lean by 7 psi. With a fuel pump that's working as it should, I'd opt for the FMU before the fuel pump. But if the pump is marginal, do both.

I'd personally go no smaller than a T3. The T25 is very small for a KA. The SR's turbo is internally gated and water-cooled Turbos are either considered oil-cooled or water-cooled. Though, technically, water-cooled turbos are cooled by oil and water. Perhaps the exception might be a VATN turbo, but that's a different subject altogether.

[Dustin240]

No need for a Greddy eManage or SAFC 2. My s13 has a air temp sensor and u might get away with just a FMU but be on the safe side (110$ for a walbro 255 or the chance of BOOOOOOM) your pick.

[24DSXY1]

What is this "FMU 10:1"? Do you mean the vortech fmu or something else?

[Dustin240]

Just a rrpr, fmu or vortech fmu your choice. Same thing, just 10 to 1.

[Jookmasta]

get injectors, fuel pump and safc..................

[24DSXY1]

Just a rrpr, fmu or vortech fmu your choice. Same thing, just 10 to 1.

Do you have a link to one of these so I can see what it looks like? Does it adjust automatically?

[boznuttz]

yeah, ment lean, esp on stock injectors

[hannibal]

Here's Vortech's FMU

http://www.vortechsupercharger....html

A 10:1 fuel mgmt unit (FMU) or rising rate fuel pressure regulator (RRFPR) increases fuel pressure 10psi for every 1psi increase in boost. Its probably the crudest form or fuel mgmt for a turbo car. This is one area where you dont want to be cheap.

A fuel pump ($100), 370 injectors ($100), and used SAFC ($150?) is a much safer solution.

[Dustin240]

Using injectors, fuel pump and safc is beter (than a FMU) but if tuning is'nt your thing (just put in a FMU). I realy dont think u'll be lean with a pump and 10to1 FMU, seams I'v been runing just that for 5months with good a A/f mix.

[24DSXY1]

So for a stock injector turbo set-up, 10:1 is better than 8:1?

[WDRacing]

I'll toss in my two cents on this matter. The S13 fuel pump is garbage, change it out no matter what you decide to go with...trust me here. Any boost creep at all and the pump itself will cause you to go lean with bigger injectors or an FMU.

The FMU is old, its crude, its ugly, it doesn't have any cool bling bling lights on it...but it works great. The SAFCII and bigger injectors can be purchased later, but you'll need a new turbo by then anyway, cause the T25 is way to small.

Summary: Buy the fuel pump and buy the 10-1 FMU and don't run more then 7 lbs of boost.

WD

[Dustin240]

The 10 to 1 FMU works great and a 8 to 1 might make u run lean. It's beter to go a little rich than lean.

[boznuttz]

ugh, that seems to be what i may be lookign into with a starion intercooler, lol

[C-Kwik]

The 10 to 1 FMU works great and a 8 to 1 might make u run lean. It's beter to go a little rich than lean.

It's doubtful it will make a difference . At 7 PSI on a 10:1 FMU, you're going to need to have a fuel pump that can actually hit 70 psi over the stock fuel pressure while still being able to flow enough fuel to keep the A/F in check. At best, a 10:1 will supply a little more fuel than an 8:1 as boost comes on until the injectors fail wide open. At this point or shortly after, it's likely the fuel pump's capacity will determine how much fuel will be going in. With an FMU, typically, the engine runs like stock off boost, then goes rich as boost starts and then leans out as you approach redline. The primary concern will be keeping the A/F in a safe range at all times, but is considered a crude tuning device since it will run rich most of the time(reducing power output). NSport used to provide a 7:1 FMU with their kits and I've never heard of any problems with detonation with their set-up. 8:1 worked fine with the XS Engineering Kit(S14) I used with the only detonation occuring from boost creep from a failing wastegate. Ran a whole day at the track in the middle of July(Hot Day) with the kit without any problems.

[crzycav86]

Revhard doesn't make a t25 manifold for the ka(as far as i know).

A better manifold would be the ssautochrome bottom mount from ebay. It's tubular, cheaper, and it works well with the sr t25(it allows you to use sr-spec intercooler and exhaust components which eliminates the need for custom piping, etc). Oh yeah, the turbo is internally wastegated at 7.5 psi.

[crzycav86]

Anyway, 8 psi on a t25 will be around 220whp. Good sized injectors for that power level would be 370cc/min(injectors rated at 43 psi). Since you want to use a rrfpr instead of getting new injectors, you will want the fuel flow through the stock 270's at 8 psi w/ rrfpr to match those 370cc/min injectors.

The way you do this is by the following injector pressure-flow formulanew_flow = old_flow*(new_pressure/old_pressure)^.5

you want to find out what the new fuel rail pressure should be to flow the same amount of fuel as 370cc/min injectors...

370cc/min = 270cc/min * (n_p / 43.5)^.5n_p = (370/270)^2 * 43.5 = 81.7 psi.

so what's the rrfpr ratio? 81.7/8, which is 10.2:1, or most closely 10:1. EDIT: This is wrong. Correction is below.So the fuel rail pressure needs to be 81.7 psi. The rrfpr adds pressure above base pressure, so the added pressure is 81.7 - 43.5, which is 38.2 psi. 38.2/8 gives a ratio of 4.8:1. A 5:1 ratio would be ideal. /correction

Anyway, those are some basic equations you can use again if you think a less fuel flow will be sufficient, or if you want to run higher boost pressure.. etc.

One more thing I want to mention is that you definitely MUST upgrade your fuel pump if you use a rrfpr, moreso than setups with larger injectors. This is because fuel pump flow decreases dramatically at higher rail pressures. Look at this graph for "high pressure" walbro pumps.



At 80 psi, Your walbro's max flow will be 110 L/H. This is equal to 1833cc/min. Divide that flow between 4 injectors, and you have a max flow of 460cc/min per injector. That's within the 370cc/min scope that you need, so the fuel pump will work well at 80psi.

Look at the pump's flow at 100psi. It drops down to practically zero - the pump stops. Having said all of this, what do you think the stock fuel pump would do at 80 psi?
Modified by crzycav86 at 1:06 PM 10/27/2006

[C-Kwik]

The pressure you need if you assumed 220 HP maxed the injectors is correct. However, an RRFPR raises fuel pressure over the base pressure. So if you need to reach 81.7 psi, then you need to increase fuel pressure by 38.2 psi (81.7-43.5 = 38.2). If you need this pressure at 8 psi, then,

38.2/8 = 4.775.

So essentially, you really only need 5:1 RRFPR. Tuners will tend to play it safe though and run a bit rich.

On the flipside, if you run a 10:1 RRFPR at 8 psi of boost, you'll be seeing 80 psi + 43.5 psi = 123.5 psi. Few, if any, fuel pumps will be flowing much at that pressure. As I stated previously, at some pressure level the pump used will no longer be able to flow enough to increase pressure and will simply just max out at a specific pressure and flow a specific amount of fuel through the 100% duty cycled injectors. At lower RPM's where this occurs, the motor will run richer than at higher RPM's. Higher rate RRFPR's in this case will simply ramp up the fuel pressure quicker leading to a richer mixture before max fuel pressure is reached and the injectors fail open.

I would agree with your recommendation to replace the fuel pump. The stocker is good enough to flow fuel for about 7 psi with a RRFPR, but that's assuming it's new and in great condition. Since 240's are at least 8 years old at this point, it's better not to play with fire. A high flow aftermarket would probably be cheaper than a OE fuel pump so might as well go that route, but a new factory pump would be fine as well.

But essentially, my message is 10:1 RRFPR is overkill here.

[crzycav86]

The pressure you need if you assumed 220 HP maxed the injectors is correct. However, an RRFPR raises fuel pressure over the base pressure. So if you need to reach 81.7 psi, then you need to increase fuel pressure by 38.2 psi (81.7-43.5 = 38.2). If you need this pressure at 8 psi, then,

38.2/8 = 4.775.

So essentially, you really only need 5:1 RRFPR. Tuners will tend to play it safe though and run a bit rich.

On the flipside, if you run a 10:1 RRFPR at 8 psi of boost, you'll be seeing 80 psi + 43.5 psi = 123.5 psi. Few, if any, fuel pumps will be flowing much at that pressure. As I stated previously, at some pressure level the pump used will no longer be able to flow enough to increase pressure and will simply just max out at a specific pressure and flow a specific amount of fuel through the 100% duty cycled injectors. At lower RPM's where this occurs, the motor will run richer than at higher RPM's. Higher rate RRFPR's in this case will simply ramp up the fuel pressure quicker leading to a richer mixture before max fuel pressure is reached and the injectors fail open.

I would agree with your recommendation to replace the fuel pump. The stocker is good enough to flow fuel for about 7 psi with a RRFPR, but that's assuming it's new and in great condition. Since 240's are at least 8 years old at this point, it's better not to play with fire. A high flow aftermarket would probably be cheaper than a OE fuel pump so might as well go that route, but a new factory pump would be fine as well.

But essentially, my message is 10:1 RRFPR is overkill here.

Yes, you are absolutely correct. It adds pressure over base(duh), otherwise it wouldn't have any effect until the boost pressure * rrfpr ratio was over the base pressure. Good call.

I made a similar post on our local forum a while ago, and I came to a 4:1 ratio. I was wondering why I didn't get a similar result in this case. Good call. I will make the correction.

[Dustin240]

If a 10:1 FMU is over kill why am, I not runing way to rich at any boost level.(1 to 7.25psi)

[Chezedik]

It depends on total volume. I believe the POA was that it was a T25, unless I am wrong.

[nissanfanatic]

I ran a 8:1 on my T04B setup and ran 12-12.5:1 AFR. If I ran a T04E, I would probably run a 10:1. If I ran a T3, I would probably do a 6:1.