The final word on boost limit with stock EFI?

[Guest bastaad525]

I'm going to try to get to the dyno within the next week (key word TRY) and answer this question for myself. I know it's been said time and again that without an I/C, on stock EFI, 10psi was pretty much the edge of the safe limit you could run.

 

But I dont think I've ever really seen anyone mention what is safe to run after an I/C is installed? I have upgraded my fuel pump, but otherwise my EFI is bone stock 280zxt fare.

 

On the one hand you'd think you could turn the boost up with the colder air charge, but on the other hand, colder means more oxygen means more lean, so maybe you actually have to turn it down instead? I definatley have no way of knowing just how much one cancels out the other.

 

Anyways, I've asked this before but didn't really get a lot of response... I guess a lot of guys have also upgraded their fuel systems by or at the time by which they've installed an I/C, so maybe no one really knows? Surely some other guys here have run I/C's on bone stock EFI and know what the new safe boost limit might be, or at least, what they got away with running.

 

I've turned the boost down a bit since the I/C install, to about 8psi (with a spike to about 10) but can't help but feel that I"m cheating myself of some of the power I could be enjoying with the I/C installed... I dont know if it's just from the additional turbo lag or what, but I will say the car definately feels slower.

[cygnusx1]

Do me a favor, try 13psi on the dyno and see how that works. I run 13-14 with the stock FI system. I had set the FMU to 45psi(fuel) at 13psi boost BUT it seems to run fine without the FMU as well, or on the stock fuel curve. Because of all the mid power I have, I dont really ever go much past 5300rpms. I know the AFM setting plays a role too. I set my AFM spring wheel to give me a smooth, smoke-free, clean-smell, idle. I have the idle mix screw all the way in (rich).

 

I need to line up some dyno time soon. It "seems" to be running good.

 

Good luck on the dyno.

[Guest bastaad525]

I wouldn't mind doing that, except I don't trust the dyno guys enough if I start out at 13 and they're revving it up and it goes lean or something they might not let off in time and there goes my engine... Whenever I do get it on the dyno I'll start low and raise it up from there if air/fuel ratio permits. I get three pulls for my money and can make adjustments in between. I'm pretty shocked that you're can run 13-14 even w/o the FMU, I would expect you to be WAY lean at 5000rpm on up. I also never shift any higher than about 5500... there just doesn't seem to be that much power up there, in addition to knowing the car was getting dangerously lean at that point. About the AFM... I haven't fussed with the idle screw at all, I never do, but I have tightened the spring a couple gear teeth, to try to lean out the super rich 10:1 A/F ratio I was getting last time I dynoed. Idle did go up a bit and smooth out as a result, but any leaner and it starts to get more rough. Even small one-tooth adjustments seem to make a lot of noticeable difference in the idle quality, though not so much any difference noticed in power or driveability otherwise.

 

I'm gonna call the dyno shop today and try to get an appointment whenever they have one available.

 

Funny though, logic tells me I would have to lower the boost with the cooler air, but you're the second person who has said they've run low teens w/o any additional fuel over stock... awfully tempted to crank it up a bit more

 

 

Anyone else get away with 10psi + on bone stock EFI with an I/C?

[Guest Cronic]

yup I ran 15 forever w/o any fuel mods. My friend messed with the AFM a bit, dunno what he did.

 

I now run 20psi, and have 2 secondary injectors, a 1200cc, and a 450cc.

[Guest bastaad525]

heheh yeah you were the first one to mention boost in the teens on stock EFI... really dont know how you got away with 15... did you ever dyno at that setting with the stock EFI and if so what kind of A/F ratio did you get? If you're friend just adjusted the AFM, either the flapper spring tension or the idle mixture screw, I wouldn't expect much of an effect on the top end either way, which is where you should have been running lean. Also, what was your timing set at?

 

 

You know, call me negative, but I'll bet I end up dyno'ing at a lower hp than what I got last time... the car just doesn't feel as fast. Most likely because of the increased lag, but it also just kinda doesn't feel 'right'. Not to mention, I was running a much lighter flywheel the last time I dynoed... so I imagine I'll lose at least a few hp right there. Hopefully the fuel curve stays good and I can run boost in the low teens like you guys did.

[Guest bastaad525]

Aw crud... the dyno shop I had gone to the last couple of times may not be there any more... the number is disconnected. I'll swing by later and see if maybe they just changed it... I hope they're still there, they were the only place I could find close by and they were the cheapest place I found as well.

 

 

Another question, did you guys find you needed to adjust you're AFM's at all after installing an I/C? My car seems to be running a bit more rich now... more smelly exhuast, and I"ve gotten a couple hard backfires when shifting... again, odd, because I would have expected the car to lean out, not richen up.

[cygnusx1]

Yes, I spent weeks trying to get the mixtures "right" after the IC install. I think that was due to the FMU though...but not sure. I definately ran rich when I was done assembling it. The problem is that I don't know what fixed it.

 

1) AFM tweaking

2) FMU tweaking

3) Cleaning Connectors

4) Fixing vacuum leaks

5) All the above.

 

Answer: Don't know what it was.

[Jersey]

I was running about 14psi with the warlbro pump and 3/8" feed from the tank, stock injectors and NPR. I was probably running a bit lean on top at that level but never put it on a dyno to verify. I would think you'd be safe to the 12psi range as long as your getting that air cooled nice and there isn't much of a drop across your IC. Are you taking your PSI reading right at the intake? Also, you might also want to think of putting in the cheap MSD-2222 before you go to the dyno. This way, if you find out you are running lean on top, you can crank down on the pressure a little bit to possibly squeeze a little more out of the stock injectors. Yes, it will make you run richer down low and mid throttle but you'll be safer when the urge to pin it to the firewall arises Just some ideas.

[Sean73]

Anyways' date=' I've asked this before but didn't really get a lot of response... I guess a lot of guys have also upgraded their fuel systems by or at the time by which they've installed an I/C, so maybe no one really knows? [/quote']

 

In my opinion, there's never any final word on how much boost can be run on the stock fuel system. It's probably possible to find out if you measured it scientifically in controlled conditions, on a new OEM engine. But there are too many variables from one car to the next to say anything definitive.

 

You know the anectdotes, that non IC cars can run about ~10 psi, give or take. Adding an IC will shift that number up if you have the fuel to support 10+ psi, and down, if you don't. Regardless, the flow rate of stock injectors running at 100% duty cycle, only supports crank 270 HP safely. The amount of boost it takes to make 270 crank HP varies from one setup to the next, but it should hover around 12 psi at sea level. Some people's personal experiences may yield different results, because of factors like fuel grade, weather, IC efficiency, intake efficiency, injector performance, turbo efficiency, altitude, and the list goes on.

 

In my personal experience, I have been able to run 8 psi consistently with an NPR IC in 100 degree weather. I also have a static compression ratio of 8.8:1 and Z31 ECCS. I've run 12 psi bursts with no ill effects, except ruining the stock clutch. I won't try anything above 12 psi, because - see above HP limit. I personally flow tested my injectors, and asking them to flow more fuel than they can, would be a foolish thing to do. A trip to the dyno may tell me something else. I use an in-car A/F meter as a general safety device, I haven't done the wideband yet.

 

PS - does your dyno use a tailpipe sniffer, or do they plug into a secondary O2 sensor port at the downpipe? I've heard the former is innaccurate from some local dyno shops.

 

 

Sean

73 240Z, L28ET, 8.8:1 CR, T3/T04E, NPR IC, 8 psi, Z31 ECCS

(still breaking it in).

[Guest Cronic]

I had a 10:1 a/f ratio until about 4500 when it leaned out to 12.8:1. I made 198whp, and 242wtq at 15psi. This was without any fuel upgrades.

 

Once I got my 2ndary injectors in (2x450cc) and raised the boost to 16.5psi I made 206whp/274wtq. I installed a larger injector, 1200cc, and raised the boost to 20, and Im currently making 266whp/324wtq. The boost dropped to 16 @ 4000rpm unfortunatly and that's why I didnt make my target hp, of 280whp, and about 350wtq.

 

I am still using the stock afm/injectors/pump/lines/rail. Everything on the EFI is stock except for my SDS EIC and 2 extra injectors.

[fl327]

did 12psi for a long time on stock injectors (good ones) 50psi fuel pressure, npr intercooler, porsche fuel pump, stock timing, stock ignition, stock ngk plugs, good for high 13s 2-ish 60fts on Afshins old swastikas with the original tires .

no issues, except no hook

[Guest bastaad525]

 

Regardless' date=' the flow rate of stock injectors running at 100% duty cycle, only supports crank 270 HP safely. The amount of boost it takes to make 270 crank HP varies from one setup to the next, but it should hover around 12 psi at sea level. Some people's personal experiences may yield different results, because of factors like fuel grade, weather, IC efficiency, intake efficiency, injector performance, turbo efficiency, altitude, and the list goes on.

[/quote']

 

 

All of which baffles me completely. Because on my first dyno runs, I was definately going way lean on the top end at 10psi. There was no sign of detonation, just a really lean fuel curve past 5000rpm. BUT, I only put 200hp to the wheels, which is definately quite a bit shy of the 270 crank hp the stock injectors are supposed to be good for. And I've seen a few other L28ET setups dynoed on stock EFI that did the same thing. This was with 10psi non intercooled. After the first dyno session, a lot of guys here thought that it was the stock fuel pump that wasn't able to cut it and the cause of the lean top end, so I promptly replaced it with a better one, and headed back to the dyno, and got pretty much the exact same results.

 

 

PS - does your dyno use a tailpipe sniffer' date=' or do they plug into a secondary O2 sensor port at the downpipe? I've heard the former is innaccurate from some local dyno shops.

[/quote']

 

 

Funny you mention this, I went to the dyno again yesterday... a different one than I've been going to unfortunately as that guy has gone out of business... but anyways, they were using the tailpipe sniffer, a bosch wideband, and there was some pretty weird stuff going on with my A/F ratio there. I'm going to post in a bit here, the last of four dyno runs showing some odd stuff going on there.

[slownrusty]

Man...awesome thread....Great reading from each reply...thanks to all and Bastaad525 for starting it!

 

Yaisn

[Sean73]

 

Regardless' date=' the flow rate of stock injectors running at 100% duty cycle, only supports crank 270 HP safely. The amount of boost it takes to make 270 crank HP varies from one setup to the next, but it should hover around 12 psi at sea level. Some people's personal experiences may yield different results, because of factors like fuel grade, weather, IC efficiency, intake efficiency, injector performance, turbo efficiency, altitude, and the list goes on.

[/quote']

 

 

All of which baffles me completely. Because on my first dyno runs, I was definately going way lean on the top end at 10psi. There was no sign of detonation, just a really lean fuel curve past 5000rpm. BUT, I only put 200hp to the wheels, which is definately quite a bit shy of the 270 crank hp the stock injectors are supposed to be good for. And I've seen a few other L28ET setups dynoed on stock EFI that did the same thing. This was with 10psi non intercooled. After the first dyno session, a lot of guys here thought that it was the stock fuel pump that wasn't able to cut it and the cause of the lean top end, so I promptly replaced it with a better one, and headed back to the dyno, and got pretty much the exact same results.

 

In order to make 270 crank HP at sea level, you need ~10-11 psi in ideal conditions. In reality you didn't have ideal conditions. The lack of intercooler, probably cost at least 15% power loss. The ECU might be capping the duty cycle at 90-95% or your injectors might be faulty. Put it this way:

 

270 crank HP

-15% air density penalty from lack of IC

-15% drivertrain loss

= 195 HP.

Even if my numbers are off, they are in the ball park, and I think your non IC dyno is in the ball park. Adding an IC takes most of the air density penalty away, and I can see that 230 RWHP may be possible with a perfect IC on stock injectors. If the ECU caps duty cycle at 90 or 95%, than this number would be even less.

 

You might say that some of the personal experience out there gets better results. More power is definitely possible out of the stock injectors, it just depends on what the engine's tolerance for leaning is. Fuel is the bottleneck: You will start to lean at 9-10 psi no matter what, because of the injector imposed limit. Anything above that, is a gray area that should not be visited for long periods of time.

 

Sure, some people can run 12+ psi w/ an intercooler on the stock EFI. But I doubt they run 12 psi, at 6500 RPM, in 4th gear, uphill, in 100 degree heat, for longer than 30 seconds.

[Guest ON3GO]

maybe you guys can help me on how much boost is to much.

right now im running stock 5psi.

 

its a 82 L28ET with a 77 ecu and harness with a MSD 6AL BTM w/ Blaster 2 coil, downpipe, fmic, FMU, walbro 255 fuel pump, fuel rail, and other things like 60mm t-body and such.

 

i was thinking 14 or so psi.

i have 370cc injectors but they leak so count them out.

 

mike

[Jersey]

525 - have you checked your injectors to see if they're all spaying a nice clean pattern? Could be part of your leaness on top as well. Just a thought.

[fl327]

Sure, some people can run 12+ psi w/ an intercooler on the stock EFI. But I doubt they run 12 psi, at 6500 RPM, in 4th gear, uphill, in 100 degree heat, for longer than 30 seconds.

 

 

Youre probably right.

but I was at 12+daily driving and not scared to WFO at any time.

every run at Sears point ive ever done is 90 degrees out side at least, but no, im not going for the Sean73 test of man turbo-athalon..

[Guest bastaad525]

yeah well if my dyno results are right (the most recent dyno, see my other new thread) you wouldn't need to run 6500rpm WOT uphill 100 degrees etc., to ping... the A/F ratio went so lean (higher than 18:1) that I was amazed the thing actually got me home! This was even at 9psi!

 

Well after all this, I think it's safe to correct the current oppinion... the stock EFI, or rather the stock injectors at the least, are NOT good for much more than 190-200rwhp, at a safe A/F ratio, no matter what the circumstances. I've seen too many dyno charts by now that just show lean running on top at anything above 190rwhp, and NOT ONE dyno chart that showed more than this on stock injectors w/o getting leaner than 12.5:1.