72 lb/hr fuel injectors overkill for 330 whp???

[MarkEmark]

Here's the deal:

I have a JWT ECU programmed for 370 cc injectors, S14 MAFS, MT, etc....to get it retuned it'd take probably 6 weeks, and my engine will be done a lot sooner than that...and I can't just swap a stock ECU in there because of the fuel injectors, and I don't feel like going through the hassle of reinstalling stock fuel injectors and then some RRFPR just to break the engine in...

Enthalpy's ECU's are out of the question because apparently there's a 3-4 month wait on a part he needs to tune S14 ECU's (convenient, huh?)

So I figured I'd have much better luck just finding someone with a JWT ECU already tuned for 50 lb or 72 lb/hr fuel injectors and a larger MAFS, and then install this with new injectors and sell my existing setup to re-coup much of the cost. The problem is, JWT ECU's tuned for an S14 MT with 50 lb injectors and a cobra MAFS are few and far between....It seems that the ones tuned for 72 lb injectors are far more prevalent.

I found someone selling a JWT ECU tuned for 72 lb injectors and the MSD 72 lb injectors themselves for $600 (not that bad of a deal, but not that good either considering klattr1 was selling this same ECU, the same injectors AND a MAFS for this price a while back...).

My question is, would 72 lb/hour fuel injectors be overkill for my goals? I'm planning on running around 330 or so whp on a fully built engine..I can't see myself EVER wanting more power, nor is it feasible/practicle/safe to have so much power on the street with street tires. I know 50 lb fuel injectors are said to be good past 350 whp, which is why i wanted them...but are 72 lb/hr fuel injectors necessarily worse if I'm not going for the huge numbers one can achieve with such injectors? I know Jeff @ cip motorsports is running the 72 lb program for a 16 psi, 340 whp tune...

Here's my concern: people using a JWT ECU tuned for 72 lb fuel injectors are going for much bigger numbers (400+ whp) than I am, meaning the ECU would be tuned even MORE conservatively than the 50 lb tune, in both fuel map and timing, meaning for the amount of power I want to run, the tune would be far too conservative and rich (correc tme if I'm wrong here). The engine is being fully built with forged 9:1 wiseco pistons and all that good stuff but that doesn't mean I want to get the absolute limit out of it and go looking for 400 whp, because I know I'll be plenty satisfied with anything around 330. Also, I'm severely low on cash. Rebuilding an engine costs a LOT of money, as does upgrading the fuel system. So I am not going to have the $250 to fork over for a S-AFC II, at least not for a pretty long time (I'll pretty much be in debt the whole summer). All that I have to "tune" is an adjustable fuel pressure regulator, and I'd rather not use tha to tune, because lowering the base fuel pressure can adversely affect the spray pattern of the injectors.

Also, I take it 72 lb fuel injectors would be even MORE of a ***** to have pass emissions with compared to 50 lb fuel injectors...I already passed emissions with my KA-T and 370 cc fuel injectors....

Next question: What's the main difference between high and low impedance fuel injectors, besides, obviously, the impedance? I know the 50 lb/hr fuel injectors are high impedance, and the 72 lb/hours are low-impedance. What else is needed to make the 72 injectors work, besides the injector harnesses? What's the difference in regards to passing emissions?

Final question: Does JWT tune an ECU going in a car with 8.5:1 compression pistons differently than a car with 9:1 compression and differently in a car with 9.5:1 compression? I would hope they do because there's a substantial difference between 8.5:1 and 9.5:1 when it comes to being safe and preventing detonation. But, JWT's site is absolutely terrible and has pretty much NO information.

Let me know your thoughts...

-Marc

[Structure240sx]

first i think the 72 program would be good (lucky u found one i jstu sent in a jwt ecu to get retunned for that). you talk about being safe so why not have plenty of duty cylce left? it adds fuel based on readings from the tps and maf to find laod. so it should run about the same from 8psi to 24 psi besides the turbo flowing differently.

#2 difference is the resistence. hihg is about 12ohms while low is (mental blaco) just a few ohms. to run the low IMP you need to wire in inlien resistors or a resistor pack. the inline resistors are $20 shipped

the jwt tunes from lower compression are more aggresive ont iming. i have a 9:1 engine and ordered a 8.5 tune. im prolyl going to add a couple degrees also depending on what timing it pulls at WOT.

[HolyShiznit]

I know this isn't going to add anything to the discussion but I would gladly buy those 72lb injectors from you if you don't want to use them cause I really need/want some.

[DRIFTEADOR]

may not be of big concern but by using a maf meant to read twice the amount of air, you're effectively lowering its resolution in half.

[:: orion ::]

The JWT timign curve is almost identical for all the ECU's I've logged...370cc, 50lb, 72lb. That's B.S. IMO...

...and as for injctors, the 72lb'ers are peak-n-hold...as compared to the saturated 50lb'ers.

So that means at idle...it's MUCH harder to get it smooth, since the voltage delivery needed to open/close the injector in the proper (short) time can't be done (basically, it opens TOO much at idle, so it idles rich and rough).

So that's a problem with low impedence, peak-and-hold injectors...and your emmisions test location won;t like that.

Plus, JWT uses a Cobra MAF with a reducer circuit to get it to handle over ~350rwhp...which makes things weird IMO.

...

In short...I don't like the JWT 72lb program. I also don't like the 370cc program (too little timing).

The 50lb/Cobra MAF program is pretty good for a stock block KA and less than 350rwhp, and the only JWT program I reccomend.

- Brian

[:: orion ::]

See here for saturated versus peak-and-hold injector differences:

http://www.msdignition.com/fuel_3.htm

[huguetpj]

But there are 50lb/hrs (or at least 550cc) injectors in low and high impedance. I've seen drop in inyectors, that would be high impedance, for 550cc and 750cc. And of course there are plenty 50lb and 72lb injectors with low impedance... so they are usually cheaper.

Now, I do believe 72lbrs are overkill. Impossible to tune with a SAFC2, specially the idle since the ECU has a minimum injector cycle time which it will not go below even if you set the SAFC to -50%. Now with a JWT ECU I bet they lower this duty cycle so you'll probably not have any issues (a part from maybe a rough idle as orion says). Dunno about passing emissions dough. I know I can pass them like a charm with 50lb's with the SAFC2, but dunno about 72lb's.

[MarkEmark]

The JWT timign curve is almost identical for all the ECU's I've logged...370cc, 50lb, 72lb. That's B.S. IMO...

...and as for injctors, the 72lb'ers are peak-n-hold...as compared to the saturated 50lb'ers.

So that means at idle...it's MUCH harder to get it smooth, since the voltage delivery needed to open/close the injector in the proper (short) time can't be done (basically, it opens TOO much at idle, so it idles rich and rough).

So that's a problem with low impedence, peak-and-hold injectors...and your emmisions test location won;t like that.

Plus, JWT uses a Cobra MAF with a reducer circuit to get it to handle over ~350rwhp...which makes things weird IMO.

...

In short...I don't like the JWT 72lb program. I also don't like the 370cc program (too little timing).

The 50lb/Cobra MAF program is pretty good for a stock block KA and less than 350rwhp, and the only JWT program I reccomend.

- Brian

Damn, well emissions is a very real concern for me (no sense in having a nice car if it's not even legal to drive), so I guess that completely rules out the 72 lb injector program...how come MSD or anyone else doesn't make 72 lb injectors in high impedance? How come anyone would ever even want to switch from high to low impedance, considering stock injectors are high impedance?

Anyway, so you tested these different JWT programs and found that the timing isn't substantially different between, say, the 72 lb program and the 50 lb program?

Interesting.

Also, does it piss anyone else off that companies like JWT have nissan ECU's monopolized for those people who are unknowledgeable about tuning/modifying their own ECU? I mean $600??!?!? Honestly...their programs are FAR from customized, and they use the same routine for every ECU they re-tune depending on the program....I'm sure it takes them VERY little time and effort, although I could be wrong. $600 is just friggin' ridiculous. My wiseco piston and rings were only $450, and a helluva lot more R&D and manufacturing costs/materials went into them...

[deezlins]

Im waiting on my teacher from EFI University to get back from Australia and he's supposed to give me a link to the peak-and-hold injector drivers he makes/sells so you can use peak-and-hold injectors on a saturated ecu. I can give you the link after i get it if youre interested.

[Frozen240]

...how come MSD or anyone else doesn't make 72 lb injectors in high impedance? How come anyone would ever even want to switch from high to low impedance, considering stock injectors are high impedance?

A saturated injector is one that is always full of voltage and has a high resistance. Somewhere between 7-14ohms. Because the resistance is high in these injectors, very little current is used to open them.

A peak and hold injector is one that must be fed a signal of high current in order to quickly open to it's maximum flow point, and then uses a slightly lower amount of current to hold it open. This is usually found on higher flowing injectors, because of the higher magnetic load required to open the larger injector coil. the extra current helps to get the job done.

I'm running the JWT 72lb, Z32 maf, 8.5:1 comp program. I have a built motor with 8.8 comp pistons. I haven't put a lot of miles on yet, so my review of the ecu might be a little premature. It does idle quite nice, holds the 700rpm pretty steady. I haven't had much trouble at all with it stalling at intersections. The idle, and cruise afr's are 14.7~15. Under spool they will run around 11.5~12. Under wot full boost they are 10~10.5. I haven't had the car on a dyno so I'm not sure of the results I'm getting. Currently, I'm boosting to 7psi from a T04 turbo. The power delivery is quite smooth. I wish I had some charts to show, I have yet to get it to a dyno. Hopefully next month. I'm satisfied with my ecu, and the price was right. $350 shipped. I don't think I would ever pay retail for the product, I'd rather save up a little more and go with AEM.

[Jookmasta]

how much are looking to get for that jwt ecu with the sr injector program? also, im assuming it would only work with an s14 right? couldnt by chance work with the s13? o wait, ur OBD II right? if so, n/m.

Back on topic, my friend runs the 72 lb jwt program and he idles just like stock. everyone i know praises the 72lb program for its idle. and yes he is running the cobra MAF. As for ur power goals, like what was said earlier, y not have the extra room for playing around..........And as for emissions, just start praying about it from now. Have you been passing emissions b/f?

[DRIFTEADOR]

doesnt jwt use obd1 ecu's plus a conversion harness for s14's?

[hannibal]

the jwt tunes from lower compression are more aggresive ont iming. i have a 9:1 engine and ordered a 8.5 tune. im prolyl going to add a couple degrees also depending on what timing it pulls at WOT.

Great info! I wouldnt have thought of that...

[klattr1]

the driveability on my JWT ecu tuned for cobra mafs and 72lbers was good. it had very minor funky issues (half throttle building wastegate spring level boost would studder some).

you can get your ecu programmed for 72lb injectors and Z32 mafs with very little downtime since they'll just send you out a chip (with core charge). I would imagine it would take 1-2 weeks. Im not sure how the driveability is on this one though.

the reason why there's more downtime with the 72lb/cobra mafs program is that they implement a subtractor circuit which gets more potential out of the cobra mafs.

I ran my JWT ecu/72lb/cobra setup on 7 psi all the way up to 26 psi.

[:: orion ::]

doesnt jwt use obd1 ecu's plus a conversion harness for s14's?

No...they add a daughterboard and a chip socket to an S14 ECU.

...

As for the idle quality with 72lb'ers...good news. From what I saw with DaveEEE's car...it was not so hot. I always attributed it to the big injectors, but I'll admit that car had other funky-ness that could have contributed.

Anyone with the JWT 72lb program had emmisions testing done?

- Brian

[MarkEmark]

There's a big difference between a smooth idling car and a car that is emissions-efficient at idle...just because the idle is smooth does not mean that the engine is abnormally high on NOx or HC emissions...and that's what they test...and if what's been said about 72 lb/hr injectors is true (I have no doubt that it is), they just aren't going to be efficient at idle.,..again, I'm not going to have the luxury of an S-AFC II to "tune" it, at least not for a long long time. (I will be in debt at least 1/2 of the summer).

So what's the difference between the Z32 72 lb tune and the cobra MAFS 72 lb tune besides MAF sensors? Does anyone really need something larger than a Z32 MAFS?

If I were to get a "new program" or reprogram my ECU through JWT, i'd go with the 50 lb program, because they are high impedance injectors and because they should be better for emissions....

Jookmasta...the ecu is only for S14 manual transmission'd 240's. And yes, I HAVE passed CT's emissions legitimately and legally with the JWT ECU and 370 cc injectors...but once I get even larger injectors, especially ones that aren't even nissan-specific, and a completely different MAFS that also isn't from a Nissan, I know I'll run into problems with emissions.

Frozen240: 10:1 AFR under boost seems far too rich for my taste...I'd rather have 12:1 and an efficient intercooler, 94 octane gas, and alcohol injection (all of which i have), or at least 11.5:1. But 10:1, while it definitely gives you a large margin of error, is also causing considerable power loss....

What MAFS does JWT program the 50 lb fuel injectors for? The Z32 MAFS? The Cobra MAFS? or both? I've ruled the 72 lb/hour program out after reading what's been said on this thread....

It's weird though, reading that MSD site, the 72 lb fuel injectors are clearly more complex and technologically advanced than the saturated 50 lb injectors, and also react quicker to the ECU's inputs...one would think that they'd therefore also be more fuel efficient and environment friendly...guess not though.

[turtl631]

Will your alcohol injection setup affect ECU tuning at all?

[klattr1]

at idle, my setup ran stoich (14.5:1-15:1) with the 72lb injectors.