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Tech: My take on injectors vs. timing control vs. HP with the stock ECU

137K views 263 replies 87 participants last post by  RealMcCoy 
#1 · (Edited)
All right guys. I'm kinda bored. I think I'll make a tech post with some of my philosphies. I've posted some of this before so those that were paying attention..this is probably a partial rehash. This is just my opinion on how the world works and is some insight into why I do things the way I do. If you think I'm full of crap post up...you won't hurt my feelings any. I could be wrong...but that doesn't happen very often. :p I'm posting this because some people don't seem to understand how to choose an injector and others seem to think that no cars can make big HP without an emanage controlling the timing. Maybe this will shed some light on the subject and give people some info that they missed. Maybe allow people to see the relationships between things. Excuse my spelling too...I'm going to be doing the mad scientist pouring out my guts thang.

First off learn the equations on this page:
http://www.rceng.com/technical.htm
I'll be using those and I'm not going to show my work. I always use 0.5155 for Brake Specific Fuel Consumption (BSFC). I base this on MANY BPU cars we have running around making roughly 399 crank HP and running mid 108 MPH traps on our stock 360cc injectors (sometimes even on 91 octane). If our BSFC was higher than that then we would not be capable of making that much power on 360's alone.

OK. So first thing we need to know is stock timing. Timing is based on load which is for all intesive puropses the MAF frequency. Load/MAF signal frequency also regulates Injector Duty Cycle (IDC). A stock 1G making 300HP crank is pushing 75.2% IDC. A stock 2G making 320 Crank HP is pushing 80.2% IDC. Personally I like using the 80.2% IDC figure because I believe that stock cars are slightly underrated (maybe 330-335 crank HP for 2G's). It splits the difference.

So OK...we put two and two together. If you have 80.2% IDC then you have the same ignition timing as a stock 2G because the load & MAF signal frequency is going to be the same. It's all tied together if you're running a stock computer. The stock ignition timing (or a slightly more timing retard) should be close to optimal. Now granted optimal ignition timing varies slightly based on rpm and fuel burn characteristics but I think we can all agree that stock timing (or a little less) is definitely in the ball park of what is good. Some will say some advance over stock is good but usually that's referring to while running race fuel.

If your IDC is greater than 80.2% that means your MAF signal frequency is higher than a stock car. When your MAF signal frequency is higher the computer interprets that as more load. When load is higher then the computer retards your timing to match. This a good thing on low quality fuel. On plain premium gas you usually make more power with the "more boost and less timing" combo providing you have enough intercooler and turbo to work efficiently at the higher boost.

If your IDC is less than 80.2% that means your MAF signal frequency is lower than a stock car. When your MAF signal frequency is lower the computer interprets that as less load. When load is lower then the computer advances your timing. It's actually quite excessive too. Even 72% IDC's can translate into WAY too much timing advance depending on how much boost you're attempting to get away with. This is a bad thing when you're not running race gas. Hell, if the advance is excessive enough it could be a bad thing even on the best race gas.

So heres the deal guys...if your MAF signal frequency is so low as to get IDCs below 80.2% at full throttle your timing is advanced further than a stock car. The lower your MAF frequency and IDC get at full throttle the further from optimum (for premium pump fuel) you timing shifts.

So how do you keep your timing in check then? Well that's easy...
Check your ego at the door and choose injectors that reflect your actual HP output then fine tune your fuel pressure to optimize them.
Its not hard to do. Look at other people dynos and trap speeds with you approximate setup. Use Jeff's site www.stealth316.com . He has an air & fuel flow calculator that is AWESOME for figuring out estimated HP numbers. You're going to need this site too in order to get your approximate uncorrected ambient air pressure for your altitude:
http://www.digitaldutch.com/atmoscalc/
Using all these tools will tell you how large of injectors you need. Don't fall into the trap of buying injectors for how much HP you hope you get. Don't fall into the "I'm going to get huge injectors now so I don't have to upgrade later" thing. It's not hard to upgrade later and you can always EASILY sell your old injectors. Also don't fall into the old addage of "trying to compete with the Jones'." Just because Jack T's car needs 720's doesn't mean you do. Approximate ranges are as follows:

360's with stock FPR: 320 - 399HP
360's with adjustable FPR: 305 - 417HP
450's with stock FPR: 400 - 499HP
450's with adjustable FPR: 381 - 510HP
550's with stock FPR: 489 - 610HP
550's with adjustable FPR: 466 - 624HP
560's with stock FPR: 498 - 621HP
560's with adjustable FPR: 474 - 635HP
645's with stock FPR: 573 - 715HP
645's with adjustable FPR: 546 - 731HP
660's with stock FPR: 587 - 732HP
660's with adjustable FPR: 559 - 748HP
720's with stock FPR: 640 - 798HP
720's with adjustable FPR: 610 - 816HP
745's with stock FPR: 662 - 826HP
745's with adjustable FPR: 631 - 845HP


The "adjustable FPR" ranges are based on base pressures of 39-45 psi. Anything under 39 psi base pressure gets you 29 psi at the rail at idle and atomization usually suffers. Maximum rail pressures are usually quoted at 75psi by the injector manufacturers. 45 psi base pressure gives you 28 pounds of boost to play with.

You want proof of what the so called "too-small" injectors are good for? Matt Monett went 10.65 & 134.44 mph on 660's with the pressure turned up. The above numbers aren't just pulled out of thin air. The injectors that some of you guys think are much too small are capable of much more than you've been led to believe by people regurgitating the same crap they heard from another idiot.

So are those numbers surprising to anyone? Keep in mind that you need to make the minimum HP for the injectors you're choosing during the worst possible conditions. Unless you want to cripple your car on daily driver fuel that means on the worst fuel you run, during the hottest weather you see, and at the highest altitudes your drive at. So...to run 720's and have good timing that means you need to make 640 crank HP if you have a stock FPR. I don't know about you guys but I don't make quite 640 HP on 94 octane here at 3075' altitude when its 112F outside. That's just not going to happen.

On another note...put your adjustable FPR to work. Use it in your math when you're figuring out how much injector you're going to need. to fine tune your IDC's and get them right where you want them. It works great.

So here's the beauty of it...if you get it right you'll be golden. Take my ride for instance. Latest tune is 38.4 psi base on 645's. That gets me a range of 542 - 676 HP. 542 HP is roughly what my car should make on 94 octane and alcohol, 17.5 psi, 112F ambient temps, here at 3075' altitude. I'll never see any more timing advance than a stock car. Obviously I've been flirting with fuel cut on the 676 HP side but at least that way I'll be running less timing which will be the safe way to go about it when you're running over 28 psi.

So like I said...if you're trying to avoid adding an emanage to your ride check your ego at the door when you're picking injectors. Don't BS yourself...you will pay for it later.

Personally I don't want timing control. I quite enjoy my two dimension fuel vs. boost tune that I have right now. Very simple. Simple is good. Throw in timing control and you now have a three dimensional setup. Do you realize how difficult that can be to get right? I have big respect for people that do good things on standalones and emanage setups. The thing is that for every person that's successful with a 3D setup like that there's 8 people that are going nowhere floundering around like a fish trying to figure it all out.

And another thing...people are always saying "those injectors are good for XX psi on that turbo." That's bull. Injectors are good for a certain amount of fuel flow and that fuel will make a certain amount of power. Now I can understand people factoring in someone's mods and saying a statement like that but we all know theres a HUGE difference between a set of 650R's at 20 psi on an otherwise stock motor and a set of 650R's at 20 psi on a motor with full intake & exhaust, manifold work, built heads, an overbore, and headers. It's apples to oranges. Injectors are good for XXX crank HP...not XX psi.

So anyway...that's my take on things. I hope this helps somebody to make the right decision while ordering injectors or tuning their car. Sorry if I went in about 10,000 directions at once.
 
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#77 ·
gotcha.
 
#78 ·
RobBeck said:
I assume by the pics you have no porting done, but only polishing of the combustion chambers :confused: Usually porting is more oriented to the Intake and Exhaust runners (which are not pictured), and deshrouding (usually only with bigger valves) and polishing on the Combustion Chamber.

Rob
Intake pics

I "think", my intake running have just been ported and my combustion chamber was left alone. I have never seen any heads in person but my own, so I'm not a good judge. Also, I bought this car with this gtpro engine in it, so who knows what they did to it. Either way, the heads if the combustion chamber hasn't been touched or done correctly, may be my cause of low boost (15psi) knock. The other culprit could easily be timing, but I see others successfully running 15-18psi on pump with 720s. I'm hoping my race gas experiment will shed some light.

I'm really curious to know what others do for tuning on low boost due to the IDCs? Surely everyone doesn't just say, ok I need approx 23psi to get the right IDCs, here goes nothing! :)
 
#79 ·
I'm really curious to know what others do for tuning on low boost due to the IDCs? Surely everyone doesn't just say, ok I need approx 23psi to get the right IDCs, here goes nothing!
I was sort of thinking the same thing. right now i'm barely able to run 10psi without gettting knock in the teens. My IDC's are only 60% max. I was thinking that if I cranked up the boost then i'd be making more power making the IDC's higher, then timing would be in check.

Yesterday I put in an Apexi ITC, i've got the timing retarded about 10 degrees across the rpm's. I'm still not happy. I turned the boost up to 14psi and still get knock in the teens at various rpm's. Now I don't know what to do. I've only got another 5 degrees of retard, but from looking at other people's settings with the ITC, I shouldnt need to go that far for a measely 15psi of knock free boost.

I figured i'd post this since there are a few knowledgeable people watching this thread. Any tuning advice guys. Besides throw all my shit in the trash and get a AEM.

BTW my a/f is about 11.0 right now. kinda rich but I only have 3% correction left to go in the safc above 4k rpm.
 
#80 ·
Quick question...

Since we are going in to detail about what IDCs we need to see, I think it would be a good idea to openly say what timing values are considered low, OK, good, great and then too high. Where do we draw the ling on timing? is 35* too high? 25* too low? Since it's all a balancing act anyway, might as well get a better grasp of the variables...
 
#81 ·
ukyo said:
Quick question...

Since we are going in to detail about what IDCs we need to see, I think it would be a good idea to openly say what timing values are considered low, OK, good, great and then too high. Where do we draw the ling on timing? is 35* too high? 25* too low? Since it's all a balancing act anyway, might as well get a better grasp of the variables...
half the battle is getting people to realize what their timing actually is.. loggers displaying wrong. people with the wrong base timing etc.. throw the discussion into a tailspin often.
 
#82 ·
eyeluvmy3kgt said:
I was sort of thinking the same thing. right now i'm barely able to run 10psi without gettting knock in the teens. My IDC's are only 60% max. I was thinking that if I cranked up the boost then i'd be making more power making the IDC's higher, then timing would be in check.

Yesterday I put in an Apexi ITC, i've got the timing retarded about 10 degrees across the rpm's. I'm still not happy. I turned the boost up to 14psi and still get knock in the teens at various rpm's. Now I don't know what to do. I've only got another 5 degrees of retard, but from looking at other people's settings with the ITC, I shouldnt need to go that far for a measely 15psi of knock free boost.

I figured i'd post this since there are a few knowledgeable people watching this thread. Any tuning advice guys. Besides throw all my shit in the trash and get a AEM.

BTW my a/f is about 11.0 right now. kinda rich but I only have 3% correction left to go in the safc above 4k rpm.
my IDC's only see around 65% max on pump gas ~ 16-18psi and I pull up to 14 degrees and my a/f is 11.7:1

using fuel to quell knock is old school... pull some timing and get that a/f right.
 
#83 ·
ukyo said:
Quick question...

Since we are going in to detail about what IDCs we need to see, I think it would be a good idea to openly say what timing values are considered low, OK, good, great and then too high. Where do we draw the ling on timing? is 35* too high? 25* too low? Since it's all a balancing act anyway, might as well get a better grasp of the variables...
The best way to find that out is to log timing advance on a stock car. I've done it with TD05s running stock injectors, stock correction, and wastegate boost. You see a big dip in timing as boost comes on, which is caused by airflow shooting up. I wish I had been able to test it with stock turbos because the dip wouldn't be so damn high up. :p

-Chris
 
#84 ·
It is humbling to imagine the factory team designing these systems within fiscal constraints pretty much from scratch 15-20 years ago. Folks will always want to make changes/tradeoffs in the interest of performance, but when used within its intended parameters, which is sufficient for the vast majority of owners, the stock configuration handles just about any condition imaginable. Temperature, humidity, elevation, fuel quality, etc., etc., etc. That it even marginally accommodates extreme boost pressures and manipulated sensor signals is downright impressive.

This has been an interesting and insightful thread, but it's a shame we can't pick a designer's brain for a few days rather than continuing to rever$e engineer such a complex system by trial and error. I look forward to the day when standalone ECUs are available that offer programs as robust as the stock ECU's. In the meantime, this sort of thread is indispensable for making the most of what we have to work with now.
 
#85 ·
With my car, timing advance sometimes goes as high as 33-35 degrees at WOT and then I get knock as low as 14psi only 1x near 5200rpm, then the ECU pulls a couple of degrees and all is well till redline. Thats the loggers represented timing, so I dont know if its real or not, but I would say for the most part, you would want timing to be no higher then 30 degrees and even as low as mid to low 20s if your trying to boost close to 19-20psi on pump gas.

Sam

Sam
 
#86 ·
I was playing around with MMCD on the way home and watched timing drop when I stabbed the gas pedal.. it went from 35 to 25 instantly .. I can't imagine it had any significant increas in airflow that quickly. well it probably went from -7psi to 0 if anything.
 
#87 · (Edited)
Mellon said:
I was playing around with MMCD on the way home and watched timing drop when I stabbed the gas pedal.. it went from 35 to 25 instantly .. I can't imagine it had any significant increas in airflow that quickly. well it probably went from -7psi to 0 if anything.
Throttle position should also have an effect on timing. Most of the discussion here assumes WOT the whole time, so that factor is taken out.

[edit]
except not. sorry.
[/edit]
 
#88 ·
#89 ·
#90 ·
2root4u said:
With this injector/FP/IDC issue in mind, I've wondered if there is a problem range of boost when running 720s but still tuning at lower boost. If tuning at lower boost and you see knock, then typically you're not going to turn up the boost. But what if turning up the boost would increase IDC thus decrease timing and get rid of the knock. I don't have the balls to just crank it up to 20+ psi and pray for high IDCs/lower timing, so I'm going to take the race gas approach. Increase the octane and see if it helps.
Old thread (well, not that old), but it's full of good information so I'm reviving it. Mainly because of the quote above by 2root4u that no one responded to. It's a very interesting question and something I wondered about myself today before I happened across his post.

Like you, I just don't have the balls to try it and am thinking about the racegas approach, hehe. Did you ever give this a shot?
 
#91 ·
JRink said:
Old thread (well, not that old), but it's full of good information so I'm reviving it. Mainly because of the quote above by 2root4u that no one responded to. It's a very interesting question and something I wondered about myself today before I happened across his post.

Like you, I just don't have the balls to try it and am thinking about the racegas approach, hehe. Did you ever give this a shot?
I'm almost out of my old May 04 fuel. This weekend I'm getting my safety inspection done and put in VP101. I'll report back how it goes.
 
#93 ·
SHiVeR-91VR4 said:
2root4u, how does timing look on your car? I'm going to have about the same setup, but I have 660's now. Looks like I will probably hit fuel cut as I start getting close to 30psi. Do you have any fuel/timing problems?
My timing gets into the 30s and my IDCs are in the 50 or 60s (can't remember). I start seeing knock at 15 psi typically. Those were my observations from last year. From that, I assume that I am.

I tried a few tricks like reducing fuel pressure to raise IDCs but no luck. I'm anxious to see if race gas cures the problem.
 
#94 ·
ok, I read that whole thing. Helps explain a lot for a novice tuner such as myself. With my mods I/E/P, 650's, and 720cc's with ARC-2 and pocketlogger.....the question I have would be: should I get an aftermarket FPR, and a fuel pressure gauge for fine tuning? I want the 2 dimensional tuning like you have so I do not have to mess with time. I have a EGT, Boost, and air/fuel gauge. Basically what I am getting at; would a wideband, FP gauge and FPR also be benefitial? And keep me in the 2D tuning?
 
#95 ·
JRink said:
Old thread (well, not that old), but it's full of good information so I'm reviving it. Mainly because of the quote above by 2root4u that no one responded to. It's a very interesting question and something I wondered about myself today before I happened across his post.

Like you, I just don't have the balls to try it and am thinking about the racegas approach, hehe. Did you ever give this a shot?
I did something similiar a few weeks ago. I was running about 13psi and getting IDC's in the low 70's to high 60's, with timing at redline around 34-35degrees. I decided to turn the boost up to ~16psi, and my IDC's jumped to the 80's, with timing peaking at 29-31 degrees at redline. I get less knock at 16psi then I did at 13psi on 91 octane. The #'s might not be exact since I don't have my logs in front of me.

Another thing I could have tried since I have an AFPR was turn the fuel base pressure down and richen up my high setting to raise IDC at the same boost level.
 
#97 ·
Raising the boost when your already getting knock is counter-intuitive, but if the cause of knock is low IDC's and high timing then it does the trick. I love my AFPR because adjusting the fuel pressure allows you to do many different things (scale injectors, adjust timing, fine tune high setting).
 
#98 ·
Stealth 222 said:
Raising the boost when your already getting knock is counter-intuitive, but if the cause of knock is low IDC's and high timing then it does the trick. I love my AFPR because adjusting the fuel pressure allows you to do many different things (scale injectors, adjust timing, fine tune high setting).
I tried 18psi with low-as-you-can-go FP and managed to get better IDCs (mid/high 70s i think), but still I had knock. As you put it, cranking the boost higher is definitely counterintuitive.
 
#101 ·
2root4u said:
I'm almost out of my old May 04 fuel. This weekend I'm getting my safety inspection done and put in VP101. I'll report back how it goes.
I barely got to test today after filling up with VP101, but I'd figure I report back since I successfully made a .9 bar pull at 11.5. Nothing wild I know, but I say successful because I had no knock as I usually do. Tomorrow should be my tuning day to finally crank this pos up after 3 years.
 
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