toddk911

I do know that stock injectors will flow more than many say on here. With 18psi, the LR 75, stock AFM (yes, MAF makes a big difference) and 3" exhaust(about 270-280whp) my stock injectors were registering at 80-85% duty cycle. When everyone was telling my my injectors would be maxed.

However, stock injectors on this 400+whp setup is certainly pushing it.

toddk911

I still have a magazine that was showing a "200mph club" and how hard it is to hit 200, etc. And Huntley was in there with their 911 cab and a 951. I think they got pretty close to 200 in both of thier cars.

toddk911

Karl is a celebrity!!

Karl, with you already having an article published by Excellence once, you think you could get the 951 back on their pages/cover again??

Maybe a "The 944 turbo....20 years later..."

Touch on the growth of the car and the 951 commmunity and how the values are really going up now and the limits being pushed WAY beyond what many thought possible.

Any chance???

Porschefile

That's odd. Maybe the 37# rating is a bit conservative. What fuel pressure are you running?

Andial951

+1

toddk911

3BAR then and now. But now I have 450cc and MAF and 19-20psi.

I think, from what I have seen in many forums, a lot of injector's ratings are on the conservative side. Also, the formulas to determine what injectors should be used I think are also on the conservative side.

How much is the fuel flow affected, or need to be increased, based on rpms alone???

billindenver

You have checked this or you read it and believed it? At what PSI fuel pressure? Again, I go off of what I see myself, not what I'm told and the stock injectors flowed plenty of fuel at over 400hp. Enough in fact that if I was wide open and turned the injection up (huntley) I could flood the engine enough to shut it down. The injectors simply are not as 'tiny' and incapable as you have been lead to believe. If I were running them at 100%..they could not have flowed enough to shut me down, nor would they have lasted 4 years + at that horsepower output. I only went up in size as a precaution since the injectors are original...not because they ever showed signs of stress.



Ok, since you have personally seen this I will take your word for it. But, I would like to know how you determined the realistic max. What were your testing criteria? What % of their max flow were the injectors running at and is the injector in the non 944 cars you refer to the same injectors we use? You say that 300hp is the realistic max based on non-944 cars but are you comparing apples to apples? I am not attacking you, just trying to understand your viewpoint. I can prove the 951 will deliver on stock injectors well past 300hp and do so for years on injectors that are 20 years old. I can put my old ones in and show you that. I have yet to see someone prove the injector is 'maxed out' at 300hp....though if you do so I'll take your word for it.



Very true. The real question however is..are they really risking blowing their motor? Who says they are and what testing criteria have they used to show it...other than 'well everyone knows - it says so on the internet'. Again, please don't take this as criticism....only a questioning banter between car guys.

Bill
89 GT-3s

George D

My previous 951 was hitting 340 wheel hp and 360 tq using the stock injectors. They were hitting close to their peak duty cycle according to Chris Cervelli at Technodyne when running at max boost on my car. Chris Cervelli owned Technodyne Racing in Phoenix and was one of the best 951 drivers in our area or anywhere.

His race car had one of the original 3.0 motors from the factory 968 turbo cars. He ran in the unlimited division in NASA. He was always in the top point bracket for the year. I used to love to see his 951 compete in the unlimited division.

His shop took care of my car and built some awesome engines for our cars. He was involved with PowerHaus on the technical side of things. He had 2.5 951 400whp cars almost ten years ago.

He was interviewed by European auto with David Rains from PowerHaus about 10 years ago about the awesome 951's.

George

DFASTEST951

Hey, just saw the thread. I'm using only 52lb injectors on my motor by David Raines. At 21psi, I pull 480 to the wheels, running rich. That's 564 crank. I can go up to 24psi and I'm at 600 crank. I have AutoThority chips, stock intercooler, stock size exhaust, and still get these numbers. He's a hell of a builder.

So it can be done but I want to go bigger...everything. I am looking at different tuners to complete my motor. David is retiring and he said he'd work on my motor until he couldn't wrench any more but I'm still looking. Some day, if I keep my car, someone is going to have to take over. My motor is fine, I just need some upgrades that weren't around when my motor was built. Whether it was ten years ago or a year ago, the guy builds some of the best motors out there.

Chris as well. He was the first 951 builder to get the garrett turbo's working on our cars. They'll both be missed.

Porschefile

To convert lb/hr units into CC's, multiply by 10.5: 37# x 10.5 = 388.5. I said 370cc to be a bit conservative as there can always be differences in flow from an injector to injector. The stock injectors are rated at the stock fuel pressure of 2.5 bar AFAIK. Running 3 bar will increase the flow capability of the injectors a bit. Here is an official source if you want to double check my math :

RC Engineering

That page also has an equation for determining how increases in fuel pressure increase the flow capability of injectors. Basically, in short you divide the new fuel pressure (3 bar = 43.5psi) over the old one (2.5 bar = 36.25 psi), then take that number and determine the square root of it. Take that square root and multiply it by the original flow rate in cc's (388.5) and you have your approximate new flow rate:

43.5 / 36.25 = 1.20, sqrt of 1.20 = 1.0954451150103321, 1.095 x 388.5 = 425.58.....

So, we can see from those calculations that the stock injectors are probably flowing around ~425cc's or around 40.4lb/hr at 3 bar. That's just simple math though. In reality there are lots of other variables which can have an effect on these numbers though it should be a good ballpark number.

300whp was a ballpark number. Generally, in my experience, it's a safe bet. On alot of the 4 cylinder Nissan's I've messed with, they tend to run lower fuel pressure around 2.5 bar. I won't mention the 6 cylinder stuff as that would introduce too many variables to make a worthwhile comparison. Anyways, the stock Nissan Sr20det (2.0l dohc i4, turbo, Japanese 240sx motor) runs 370cc injectors (35#) and generally around ~280-300whp people see duty cycles around 90% if not more. Around 300-350whp people usually upgrade to 500cc+ (~47#+) injectors to keep the duty cycles below 80%. This isn't speculation, it's a proven fact. I've seen this enough times with my own eyes to believe it. I have several friends with 240sx's and various other 4 cylinder turbocharged cars making anywhere from below 300whp up to around ~480whp, so I've seen my fair share of what's possible. One friend has several 240sx's with varying builds and power levels. The few he has around 320-340whp are running ~550cc (~52#) injectors and he is seeing duty cycles around ~70% (give or take a few) I believe. His friend's car is making ~390-400whp and running ~750cc (~71#) injectors, and I think his duty cycles are quite a bit lower like around 60%. Sorry, I can't remember definite numbers. I've personally seen/helped set some of these cars up as well as have seen them tuned, including datalogs showing injector duty cycles among other things. Most of them were using either a Greddy E-manage piggy back (don't be fooled, this "piggyback" is practically a standalone with all of it's capabilities) or an Apexi Power FC which is a plug and play aftermarket standalone. I've seen these same typical results with a large variety of other different 4 cylinders from different manufacturers, and enough times personally to formulate my own opinions.

There are always variables from motor to motor, such as BSFC, which will effect things however generally most 4cylinders will have the same ballpark fuel restrictions of other 4cylinders. Porsches are no different, despite what some may have you believe. There are probably differences in injector resistance, definite differences in BSFC, differences in spray pattern, etc. The list goes on, but the same general limits are there. In my experience, 37# injectors are nowhere near sufficient for any 4 cylinder running 400whp. Did you ever dyno your car to verify it was actually making that hp? 400whp is about 460fwhp. To determine the hp flow capability per injector, multiply the injector size (lb/hr) by the max duty cycle (in this case 1.0= 100%, .8= 80%, etc) and divide by the BSFC: 40lb/hr x 1.0 / .35bsfc = 114.28... Multiply that by 4 (number of injectors) to determine the max flow capability and you come up with ~457hp. This is assuming you were running 3bar fuel pressure, in which case the injectors would be flowing ~40# as we previously saw. Also, these calculations are assuming a 100% duty cycle. There is no possible way you could be running less of a duty cycle at that power level and under these conditions. Also, I determined the necessary BSFC for all of these results to be acheived using the calculator in the link above. 0.35 is the approximate necessary BSFC when considering 460fwhp, 100% duty cycle on 40# injectors. .035 BSFC on a forced induction motor is unrealistic and pretty far off, so technically none of this should be possible.

Please do prove it! Seriously though, I have never seen these kind of recommendations anywhere except here. I find it strange that every other non-Porsche car group out there is following some sort of rules that seem to be different (completely different in some cases) from what I hear here. Sorry, it just doesn't add up. I mean, we can beat this question to death with math, however I have personally seen enough to tell me that what you suggested shouldn't be possible. In fact, I have the perfect example. My Carrera was running oem 951 injectors when I first bought it. With the crappy rising rate fpr it came with, I'm seeing up to 6.8bar fuel pressure. My car put down 431whp (~495fwhp assuming 15% loss). Even on a 6 cylinder running such high fuel pressure, I was seeing 100% duty cycles and the injectors were completely maxed out. This was very apparent considering above ~4.5k rpm my a/f's were anywhere from 13.5-14:1!!!! Needless to say, I stopped driving the car until I put in the 55# injectors. Anyways, a 6 cylinder will generally require a smaller injector to support the same hp level as a 4 cylinder since it has more total injectors. 30whp is not that far off from 400, and I had 2 more injectors plus a ton of fuel pressure. Sorry Bill, what your saying just doesn't add up in my experience.

Are you talking 400 flywheel or wheep horsepower? I personally find 400whp hard to believe unless you were running quite a bit more fuel pressure then 3 bar. As far as injectors flooding the motor, under what conditions? Some injectors you can run at 100% for extended periods of time and they can take it. Some injectors, under those conditions, can fail in the stuck open position causing the motor to flood out at idle! Honestly, I think we really need to see dyno charts, datalogs, and/or wideband datalogs when making claims like this. People could be browsing, read that 400whp is fine on stock injectors, and then they might go out and do it. What if you're wrong? That could lead to alot of blown motors.

Rogue_Ant

I agree with the ~300rwhp ballpark number. I estimate my rwhp to be ~330hp, and my stock injectors are maxxed. And I'm running ~55psi of fuel pressure.




The V Out 2 is the Maf signal going to the DME. As you can see I hit a peak of 4.98v. I do like to run rich, but am about .2 higher then my target A/F of 11.5, as it leaned out to ~11.7x by redline. So some might be willing to run leaner and get more power out of the same injector, I prefer the extra safety margin.

BTW I saw a peak Airflow of 290gms/sec, or about 38lbs/min on that run.



Rogue

billindenver

At what fuel pressure? Lower fuel pressure=more duty cycle. Raise the pressure and you work the injector less.

Bill

billindenver

Ok, that is fair. I said I put down 340 at 16psi on stock injectors so I should put up the dyno for it.



After this dyno I removed my boost control. Boost is limited by my wastegate spring. It holds about 22 psi, 23 on a cool day with the planets aligned. You seem like you enjoy math, so I'll let you figure out the HP with 7 more PSI of boost. I never bothered to re-dyno it. As far as my being lean...I'll state it again. 180k miles...completely original bore, pistons, rings, head....lean? Not a chance.

I'm not saying your math is wrong, I'm saying your assumptions are wrong. You are doing the math with figures supplied by someone else. Take an injector, put it in a test system and tell me what it flows. You also quoted some fuel pressure numbers...is that at idle? Do you know what the fuel pressure does under boost?

Again, I'm not saying you are wrong. I'm saying I doubt that bosch tested and rated their injectors based on a fuel pressure figure supplied to them by Porsche. I don't know what pressure bosch tests their injectors at...but I doubt Porsche has any input. It is very easy to make assumptions like you did and throw an AFAIK at the end. But people will read it like it's gospel....like you did when someone told you that 300hp is the limit on stock injectors. That's just plain incorrect...and rather than have a math duel with you, I'll just point at my car and say there is my proof.

You are right, we can play mathmatics all day long and back in college or back at chrysler where I designed fuel systems for a living, I may have had some fun doing so. The truth is where the rubber meets the road however. Tell you what. In the spring, we will pick a track between you and I. I'll bring my stock injectors and plug them in...and if you smoke me down the straight....well, I will buy the beer that night. That's about as friendly a gentlemen's wager as I can imagine. We're just two guys disagreeing here, not having a fued....

Bill
89 beastie

333pg333

"You are right, we can play mathmatics all day long and back in college or back at chrysler where I designed fuel systems for a living, I may have had some fun doing so. The truth is where the rubber meets the road however. Tell you what. In the spring, we will pick a track between you and I. I'll bring my stock injectors and plug them in...and if you smoke me down the straight....well, I will buy the beer that night. That's about as friendly a gentlemen's wager as I can imagine. We're just two guys disagreeing here, not having a fued...."

Now that sounds like a fair challenge Trav. Unfortunately you won't have your car ready in time will you? I think if you do, you may just get drunk on Bill's money that night. lol

Porschefile

Bill, so you mean to tell me that you removed your boost controller and your car is now running wastegate spring pressure of ~22 psi?!?! You DID upgrade your WG spring with a 22psi spring, right??? It's physically impossible to run less boost than the WG spring pressure. Unless you upgraded the spring at the same time, that statement doesn't make any sense.

Look, I'm not repeating anything that was told to me. I've been involved with enough cars to have experienced these things first hand, so I know these things from personal experience. Actually, to be honest I really don't like math all that much. I'll gladly take you up on your offer, though I doubt if my car will be done in a timely manner as it will probably take 6 to 8 years!

On that note, I'd like to know who else here in the 951 community has or is willing to run stock injectors with that much hp? Sorry Bill, what your saying just doesn't add up, not with my personal experiences and what some industry standard/accepted simple calculations show. By saying that the math is flawed, you're pretty much saying that a large and well known injector manufacturer doesn't know what the heck their talking about. 340hp @ 16psi on stock injectors, I can believe that. That's not too far fetched though that would be stretching the limits pretty far and risking some problems. 400whp just isn't possible and I haven't seen any substantiating evidence to suggest otherwise.