85 lb injectors too big?

[roachjuice]

I was thinking instead of just maxing out my +40s i have I was gonna buy some 85lb injectors. Goal. 300+whp. Only reason I'm wanting to do this is because these injectors can be bought for cheap.

[BadAssPerformance]

Definitely overkill for 300 as the 52lb/hr should work unless you plan to rev past 7k, but 85pph is not too big as long as your cal is scaled for them. With 300whp goal, 72pph would make more sense and still give you room for more.

[roachjuice]

I don't plan on running past 7k. Just a guy I know says it's nuts to even think about over 20psi of boost with my stock 2.5 engine. I think it wi handle it. Hell I did 24psi on the stock turbo and a stock 86 short block. I'm running 16-18 psi now. I was Gonna say that 20psi was gonna be the limit but I dunno if that will be enough. Plus the 85s I'm looking at are a hell of a deal. I can scale for some injectors. That's not a problem. As long as there is something in there that is close.

[BadAssPerformance]

Yeah, most people think we are nuts... I've seen 27psi with the 42pph injectors in my stock long block 2.2L T2 Shadow, but that was on 100 octane ;)

[roachjuice]

Yea I plan on running 91 pump here. But I will throw some race gas in at the track. I was tellin him Gus and Gary did that all day long back in the day!! I know it's not unheard of to do 20+ psi.

[BadAssPerformance]

Yeah, these cars can take amazing sh!t for a little bit... I remember my first CSX, bone stock except a MP S-II LM and I lost a vacuum line right as I was playing with an early 80's (RWD) Malibu from a light... 18psi on the stock 32pph injectors and 93 octane :eek: I lifted before winding it out in 3rd, that might have been bad, LOL! ....Of course this was back before the 10% ethanol BS :mad:

[cordes]

If you can get them cheap and do your own cals, go for it.

[roachjuice]

I just didn't know if the drivability would suck

[turbovanman²]

I just didn't know if the drivability would suck

If you do a cal for it, then it will run just fine. Agreed that they are overkill though. Hell, I am still running +40's, lol.

Lots of use run over 20 lbs, even on stock shitt. I ran on a basically stock engine for years at 20+, as long as you have the fuel and no detonation, your fine.

[roachjuice]

I think I read somewhere that the 40s max out around 320whp. But If you ground them then 400 is easy lol. No clue. Id be happy with 300+ but the more the better. Ya know how it goes. I'd rather be safe and have big injectors than have barely enough injector to make it.

[cordes]

I think I read somewhere that the 40s max out around 320whp. But If you ground them then 400 is easy lol. No clue. Id be happy with 300+ but the more the better. Ya know how it goes. I'd rather be safe and have big injectors than have barely enough injector to make it.

+40s can be pushed very hard. When you run the numbers the DC is somewhat scary given what many of us are doing HP and RPM wise.

[tryingbe]

I just didn't know if the drivability would suck

I ran 83lbs injectors with my stock 2.5TI with my custom cal. Had to do some tuning to get it run good, other wise, it ran perfect and got 26mpg average.

It's all about the tune. If you want to run 83lbs injector with and adjustable fuel pressure regulator at 20psi with no wideband, you can forget about it.

[roachjuice]

+40s can be pushed very hard. When you run the numbers the DC is somewhat scary given what many of us are doing HP and RPM wise.
Yea. That's why I usually don't to the whole calculation thing and match up things. It never seems to work for me lol. Shitt I throw together seems to work the best in my case lol.

I ran 83lbs injectors with my stock 2.5TI with my custom cal. Had to do some tuning to get it run good, other wise, it ran perfect and got 26mpg average.

It's all about the tune. If you want to run 83lbs injector with and adjustable fuel pressure regulator at 20psi with no wideband, you can forget about it.
Yea I got a wideband and can burn and tune. I think I may give it a shot. See how they work on my setup. My af now is 10:9@17psi of boost. And I'm dead even with a modded 6.0 gto 6 speed. :)

[DodgeZ]

I think people don't take in to account the rising fpr. I have a seen a lot +40s that are rated more at 43.5psi instead of our 55psi so they are more like 58lbs injectors, as you add more boost the fuel pressure goes up making the injector "bigger". Those 85lbs should be rated on the standard 43.5psi so at 55psi they are going to be 95lbs. When you add 20psi of boost it is adding 20psi of fuel pressure. So you'll be at 75psi of fuel pressure which will bump the injectors up to 111lbs injectors. So to answer your question... yes they are too big. Should be a good injector for e85 though

[roachjuice]

Maybe I should run the 40s. See what they can do.

[cordes]

I think people don't take in to account the rising fpr. I have a seen a lot +40s that are rated more at 43.5psi instead of our 55psi so they are more like 58lbs injectors, as you add more boost the fuel pressure goes up making the injector "bigger". Those 85lbs should be rated on the standard 43.5psi so at 55psi they are going to be 95lbs. When you add 20psi of boost it is adding 20psi of fuel pressure. So you'll be at 75psi of fuel pressure which will bump the injectors up to 111lbs injectors. So to answer your question... yes they are too big. Should be a good injector for e85 though

There are less and less of the higher flowing +40s as a percentage of the whole these days. It's been a while since I've seen someone post up and have that be the case with a new set.

Why are they too big? I would concede that they are more than is needed in this case, but if he can get them for cheap what's the problem?

Also, what does the rising FP have to do with anything when comparing injectors. They all see the same rise in rate giving a uniform increase as a function of boost pressure. What am I missing there?

[DodgeZ]

Maybe I should run the 40s. See what they can do.

lots of big numbers out of them. kind of shocking but with the fuel PSI going up with every PSI of boost it helps.

Here is a stock bottom 2.5 and 25psi.


http://www.youtube.com/watch?v=IyU1lkEBn44

[roachjuice]

Ok I just did an injector calculator and what dodge z said is correct. 75pph injectors will do 360 hp. So that's why the 40s can do good numbers.

[turbovanman²]

Maybe I should run the 40s. See what they can do.

I am probably the last guy to use, lol, but I am running 2x255 fuel pumps, hollowed fuel rail and even at 30 psi, still have lots of fuel, lol.

[roachjuice]

lots of big numbers out of them. kind of shocking but with the fuel PSI going up with every PSI of boost it helps.

Here is a stock bottom 2.5 and 25psi.


http://www.youtube.com/watch?v=IyU1lkEBn44
wow. what mods are done to that car?

[shackwrrr]

I think people don't take in to account the rising fpr. I have a seen a lot +40s that are rated more at 43.5psi instead of our 55psi so they are more like 58lbs injectors, as you add more boost the fuel pressure goes up making the injector "bigger". Those 85lbs should be rated on the standard 43.5psi so at 55psi they are going to be 95lbs. When you add 20psi of boost it is adding 20psi of fuel pressure. So you'll be at 75psi of fuel pressure which will bump the injectors up to 111lbs injectors. So to answer your question... yes they are too big. Should be a good injector for e85 though


I thought you were smarter than that. The 1:1 rising fuel pressure is only to maintain the pressure differential between the fuel and intake. If you did not have that as you have more pressure in the manifold thats more pressure that the fuel has to overcome to exit the injector. So without it your fuel pressure would effectively drop pressure by the amount of boost you are making. Same reason why alky injection pumps are so big and expensive, they have to overcome the boost pressure but still have enough pressure to atomize the water/meth.

[DodgeZ]

I thought you were smarter than that. The 1:1 rising fuel pressure is only to maintain the pressure differential between the fuel and intake. If you did not have that as you have more pressure in the manifold thats more pressure that the fuel has to overcome to exit the injector. So without it your fuel pressure would effectively drop pressure by the amount of boost you are making. Same reason why alky injection pumps are so big and expensive, they have to overcome the boost pressure but still have enough pressure to atomize the water/meth.

Do you know how the fuel pressure works on an SRT4?

[roachjuice]

Do you know how the fuel pressure works on an SRT4?

It's a rerurnless system from the factory correct?

[DodgeZ]

It's a rerurnless system from the factory correct?

yep and it is a static 58psi no matter what the boost. When you do the "math" I don't think the common formulas take in to account 1:1 regulators. I mean, the SRT guys and us are both using the same formula to pick injectors size. Clearly it is incorrect for one of us. I'd say it is wrong for us since we have see +40s flow 400whp when on paper they should only support 300ish crank. So maybe I am wrong but someone needs to explain why the math is so far off on the +40's.

[Aries_Turbo]

kevin, you are wrong. :)

if there is 20psi at the tip of the injector (boost) and 20psi more fuel pressure at the inlet, the fuel flow is still equivalent to having 55psi (or whatever your base pressure is) at the inlet.

the SRT cal adds pulsewidth to compensate for pressure at the tip of the injector.

do guys SRT tunes suddenly become rich when they add the return line and a 1:1 regulator with no other changes? They should.

Brian

[roachjuice]

yep and it is a static 58psi no matter what the boost. When you do the "math" I don't think the common formulas take in to account 1:1 regulators. I mean, the SRT guys and us are both using the same formula to pick injectors size. Clearly it is incorrect for one of us. I'd say it is wrong for us since we have see +40s flow 400whp when on paper they should only support 300ish crank. So maybe I am wrong but someone needs to explain why the math is so far off on the +40's.
See this is why I don't calculate anything lol. It just makes me question more questions. I've done stuff that guys said can't be done (not on here) like someone told me that the small can wastegate can't hold over 17psi. Shims fix that. It held 24psi. Someone told me that the turbo is just blowin hot air over 17psi. Well when I turned it up on the stock turbo it went faster. So I guess the hot air worked. Someone told me my stock fuel pump wont support alot of boost. Again i did 24psi on it. Someone told me that I can run high boost on 91 pump. And I need meth. This is why I started this thread. Someone told me that I'm runnig out of injector right now at my level. I'm still on the stock pump. I'm gonna change this pump this week and change nothing else. And see if the af changes. Then I will turn the boost up to 20psi. On the 40s. I think I really wanna see what the Max power I can run on 40s and pump 91.

[Juggy]

aaron miller made 407 whp on +40 injectors with a 255 walbro.....

[DodgeZ]

do guys SRT tunes suddenly become rich when they add the return line and a 1:1 regulator with no other changes? They should.

Brian

They do, which is my point you add more fuel pressure you get more fuel out of the injector. My comment is directed to the fuel injector calculators. If you use the calculator does it take in to account the 1:1 regulator or not? When I use the calculator to size my injectors it is the same calculator for SRT (static) and the Shelby Dodge (1:1). It is clear that they are not the same. The calculator has to be wrong for one of them, so which one is it?

I am not sure I believe the boost pressure vs the pintle pressure. While sounds good I don't see it in the real world. Is there a source other then thedodgegarage that has factual information about this? I have a hard time believing my SRT drops down to 34psi of fuel pressure when I am running 24lbs of boost.

[wallace]

Injector flow is calculated on a pressure differential between the fuel system and intake tract. with 55 psi of fuel pressure and the intake at atomosphere (engine not running) you have 55 psi of differential across the pintle of the injector. At 20 lbs boost with 1:1 rising rate regulator you have 75 psi of fuel pressure and 20 psi in the intake. 75-25=55. The 1:1 regulator does nothing more than maintain the base differential pressure of the fuel wrt intake pressure/vacuum. At idle with vacuum in the manifold (less than atmospheric) the 1:1 regulator DROPS the pressure accordingly and maintains that same 55 psi of diff. Injector size does/should not change with the 1:1 setup.

[roachjuice]

aaron miller made 407 whp on +40 injectors with a 255 walbro.....

16v?:confused2:

[DodgeZ]

Injector flow is calculated on a pressure differential between the fuel system and intake tract. with 55 psi of fuel pressure and the intake at atomosphere (engine not running) you have 55 psi of differential across the pintle of the injector. At 20 lbs boost with 1:1 rising rate regulator you have 75 psi of fuel pressure and 20 psi in the intake. 75-25=55. The 1:1 regulator does nothing more than maintain the base differential pressure of the fuel wrt intake pressure/vacuum. At idle with vacuum in the manifold (less than atmospheric) the 1:1 regulator DROPS the pressure accordingly and maintains that same 55 psi of diff. Injector size does/should not change with the 1:1 setup.

So you are saying the calculator is incorrect for the SRTs (static) and correct for the Shelby Dodges?

[shackwrrr]

The calculator would have to be wrong with the SRT. How many actually run the stock regulator setup with bigger injectors? I know that the stock setup makes tuning difficult because of the non linearity of injector flow. To calculate injector flow for a srt with the stock setup you would have to take your maximum desired boost and subtract it from the 58 psi, then use that pressure to calculate the flow of the injectors.

Looks to me like other srt guys dont understand it either.
http://www.srtforums.com/forums/f187/srt-4-common-injector-flow-math-info-chart-77812/index3.html

[DodgeZ]

aaron miller made 407 whp on +40 injectors with a 255 walbro.....

Clearly something is wrong....

29298

[DodgeZ]

aaron miller made 407 whp on +40 injectors with a 255 walbro.....


The calculator would have to be wrong with the SRT. How many actually run the stock regulator setup with bigger injectors? I know that the stock setup makes tuning difficult because of the non linearity of injector flow. To calculate injector flow for a srt with the stock setup you would have to take your maximum desired boost and subtract it from the 58 psi, then use that pressure to calculate the flow of the injectors.

Looks to me like other srt guys dont understand it either.
http://www.srtforums.com/forums/f187/srt-4-common-injector-flow-math-info-chart-77812/index3.html

I run a static system and 750cc injectors. It is running out of fuel at 440ish crank horsepower which is roughly what calculator says.

[shackwrrr]

Clearly something is wrong....

29298

I think the biggest thing here is the BSFC. .6 does't cover every turbo engine very well. BSFC can change greatly depending on how the engine flows and the engine design.

who knows what he was running for a base pressure but it looks like it was pretty close.29299

[roachjuice]

I think the calculator isn't jdm enough. Needs more vtec. Honestly I think something is wrong with it or our cars are bad --- and just make shitt happen.

[cordes]

kevin, you are wrong. :)

if there is 20psi at the tip of the injector (boost) and 20psi more fuel pressure at the inlet, the fuel flow is still equivalent to having 55psi (or whatever your base pressure is) at the inlet.

the SRT cal adds pulsewidth to compensate for pressure at the tip of the injector.

do guys SRT tunes suddenly become rich when they add the return line and a 1:1 regulator with no other changes? They should.

Brian

That's what I've thought, but I've seen a couple people post up what Kevin did and it made me think that I was misunderstanding how it worked all this time.


Clearly something is wrong....

29298

That BSFC number is way to high for any math I've done with our motors for one.

Kevin, I know nothing about the SRT4 stuff other than what has just been posted here. It sounds reasonable to me that increasing inj. pulse width with boost could work as well as a 1:1 RRR. Could you give me some examples of the problem you are seeing?

It's been a long time since I've crunched any numbers regarding injector size, DC etc.


ETA: When guys throw out numbers Like Aron's etc. I think it is important to remember that their BSFC must be dramatically lower due to the efficiency in their system. Just look at how much less boost those guys do it at than most everyone else.

[wallace]

So you are saying the calculator is incorrect for the SRTs (static) and correct for the Shelby Dodges?

I'm sayng the calculator assumes the flow rate of the injector does not change...83 lb/hr is 83 lb/hr at all intake manifold pressure/vacuum conditions. So an 83 lb/hr injector (at 55 psi differential) potentially flows 83 lb/hr at idle and 30 psi boost because the pressure differential is maintained, the varying pulsewidth from the ECU determines how much of that 83 lb/hr is delivered at any given time. I'm thinking the SRT4 uses a returnless type system (most mfg's dropped return style around 98') and still varies the fuel pressure (with voltage adjustment to the fuel pump) to compensate for vaccum/boost and all points in between this would make sure the flow rate of the injector stays the same just like in a 1:1 mechanical return style regulator deal.

[roachjuice]

I wanna know how make big hp
With 40s that aren't supposed to support that kind of power.

[cordes]

I wanna know how make big hp
With 40s that aren't supposed to support that kind of power.

Do a search for 8valves posts. IIRC he and I actually talked about +40s, DC, and FP headroom in a couple of threads.

[DodgeZ]

I think the biggest thing here is the BSFC. .6 does't cover every turbo engine very well. BSFC can change greatly depending on how the engine flows and the engine design.

who knows what he was running for a base pressure but it looks like it was pretty close.29299

Why doesn't the BSFC need to be the recommended settings? Also you need to look at crank horse power not whp. Figuring in 15% for drivetrain loss put him at 468chp. which bumps up the need to 63.5lbs injectors. I think the calculator need to be tossed in the trash at this point. Seems like it is just a shot in the dark.

[turbovanman²]

16v?:confused2:

8 valve, lots and lots of R@D, careful parts selection and tuning.


Clearly something is wrong....

29298

We all seem to run +40's way past the "magic" number, lol.


I wanna know how make big hp
With 40s that aren't supposed to support that kind of power.

See above, :p

[DodgeZ]

I'm sayng the calculator assumes the flow rate of the injector does not change...83 lb/hr is 83 lb/hr at all intake manifold pressure/vacuum conditions. So an 83 lb/hr injector (at 55 psi differential) potentially flows 83 lb/hr at idle and 30 psi boost because the pressure differential is maintained, the varying pulsewidth from the ECU determines how much of that 83 lb/hr is delivered at any given time. I'm thinking the SRT4 uses a returnless type system (most mfg's dropped return style around 98') and still varies the fuel pressure (with voltage adjustment to the fuel pump) to compensate for vaccum/boost and all points in between this would make sure the flow rate of the injector stays the same just like in a 1:1 mechanical return style regulator deal.

The SRT has a FPR right on the end of the pump located in the tank. Any fuel above 58psi gets dumped right back in to the tank. They add fuel by adding pulsewidth like Bryan said. The computer doesn't change fuel pressure by giving more voltage to the pump.

[shackwrrr]

Why doesn't the BSFC need to be the recommended settings? Also you need to look at crank horse power not whp. Figuring in 15% for drivetrain loss put him at 468chp. which bumps up the need to 63.5lbs injectors. I think the calculator need to be tossed in the trash at this point. Seems like it is just a shot in the dark.

assuming that he had the +40s that flowed 58lbhr and he was running about 65-67 psi base pressure then that is enough.

IT could also mean that aarons engine was more efficient thermally.

lower bsfc = better thermal efficiency.

[wallace]

The SRT has a FPR right on the end of the pump located in the tank. Any fuel above 58psi gets dumped right back in to the tank. They add fuel by adding pulsewidth like Bryan said. The computer doesn't change fuel pressure by giving more voltage to the pump.

I don't know that much about the SRT4. I did a google search and come back with a discussion on how the stock returnless fuel system is limited due to flow restrictions of no return line and vaying PW to the fuel pump to maintain the pressure differential....sounds like the SRT4 works just like any other returnless fuel system all the mfg's of cars started using around model year 1999.
Thread: http://www.srtforums.com/forums/f187/why-return-fuel-setup-high-horsepower-203555/

[DodgeZ]

I don't know that much about the SRT4. I did a google search and come back with a discussion on how the stock returnless fuel system is limited due to flow restrictions of no return line and vaying PW to the fuel pump to maintain the pressure differential....sounds like the SRT4 works just like any other returnless fuel system all the mfg's of cars started using around model year 1999.
Thread: http://www.srtforums.com/forums/f187/why-return-fuel-setup-high-horsepower-203555/

That post is from 2005 which was before they could adjust the tunes in the SRT4s correctly. They had to use AFPR and piggybacks (map clamp) to trick the car for a tune. Now that you can adjust the cal you can toss that crap away.


The SRT4 service manual doesn't say anything about change pulsewidth to the fuel pump to control fuel flow.

29300 29301

[roachjuice]

So have we all come to the agreement that +40s are magic and work with everything from stock to 400whp?

[cordes]

So have we all come to the agreement that +40s are magic and work with everything from stock to 400whp?

I don't believe they are magic. I do know that many people have used them to make 400HP though.

[roachjuice]

Well I guess I'll stick with the 40s then. No use in spending money on injectors I don't need. Changing pump this week and going to 20psi. Should haul a$s

[cordes]

Well I guess I'll stick with the 40s then. No use in spending money on injectors I don't need. Changing pump this week and going to 20psi. Should haul a$s

Sorry, I must have missed where you already had +40s. No reason to go with anything else at 20PSI.

[roachjuice]

Yea. I was gonna buy the 85# injectors but after reading all this im gonna stick with the 40s. I just have a stock fuel pump in there right now

[DodgeZ]

Hello Kevin,

For turbocharged applications using a 1:1 fuel pressure regulator, you
would use the formula like you normally would and use the base fuel
pressure. If the fuel pressure does not reference boost manifold, then
the base fuel pressure minus the boost pressure is what the injector
would actually see. The BSFC value does not take into account fuel
pressure.

Thank you for your interest in RC Engineering. Please feel free to call
or e-mail us with any further questions you may have.

RC Engineering, Inc.
20807 Higgins Ct.
Torrance, Ca 90501
T (310) 320-2277
F (310) 782-1346
rceng.com

[roachjuice]

say 20# of boost with a 55psi fp and its boost referenced so it would be 75psi? am i reading this correctly? you would use the formula but at 75psi?

[DodgeZ]

say 20# of boost with a 55psi fp and its boost referenced so it would be 75psi? am i reading this correctly? you would use the formula but at 75psi?

He is saying that the formula is correct for shelby dodges but is incorrect for SRTs.

[roachjuice]

He is saying that the formula is correct for shelby dodges but is incorrect for SRTs.
ah ok

[DodgeZ]

ah ok

After looking at it and playing with the calculators I wouldn't use them. The B.S.F.C. plays a big part and I don't think we really know what the B.S.F.C. should be. If you move the B.S.F.C. around it can make huge differences in what the injectors "support".

Here is another email I got.

The calculator is a bit conservative and is only a guideline to make sure
that you are in the ballpark. It is the standard calculations that is in
most books and used by most everyone.
The fuel pressure across the injector stays the same with a 1:1 regulator
since it is referenced to the intake manifold vacuum / pressure.
I plan to redo the calculator since very few people actually know what the
BFSC really is. I will redo it so one just has to enter their target A/F
ratio, I just need to find the time and drag out the books again, maybe
after tax time is over.
Thanks for reminding me...


Regards,

Gordon
WitchHunter Performance / Injector Services
206-919-0794

[roachjuice]

After looking at it and playing with the calculators I wouldn't use them. The B.S.F.C. plays a big part and I don't think we really know what the B.S.F.C. should be. If you move the B.S.F.C. around it can make huge differences in what the injectors "support".

Here is another email I got.

The calculator is a bit conservative and is only a guideline to make sure
that you are in the ballpark. It is the standard calculations that is in
most books and used by most everyone.
The fuel pressure across the injector stays the same with a 1:1 regulator
since it is referenced to the intake manifold vacuum / pressure.
I plan to redo the calculator since very few people actually know what the
BFSC really is. I will redo it so one just has to enter their target A/F
ratio, I just need to find the time and drag out the books again, maybe
after tax time is over.
Thanks for reminding me...


Regards,

Gordon
WitchHunter Performance / Injector Services
206-919-0794

Yea I have no clue what the hell bsfc is on my car. I doubt anyone truly knows.

[cordes]

Yea I have no clue what the hell bsfc is on my car. I doubt anyone truly knows.

Playing with various calculators on the net I would put a stock TII motor at about .52 or so. Guys making the big power must be at a .48 or slightly lower.

[roachjuice]

What exactly is that number? And why does it say for supercharger and turbo applications use .60?

[cordes]

In short, it's how efficiently the engine turns the fuel into power. The better the BSFC (the lower the number) the more power the car will make with less fuel.

http://en.wikipedia.org/wiki/Brake_specific_fuel_consumption

[roachjuice]

Ahhh ok makes total sense now why the 40s do awesome.