Mitsubishi 3000GT & Dodge Stealth Forum banner

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.
 
See less See more
#127 ·
plus you WANT that extra timing.

Just figure out a way to control it:

Race gas
Methanol injection

And now, you get all that extra power from the timing :)

I'm going to try and get my timing as close to stock as possible so I don't knock like mad, but advance it a bit (FPR) when I'm going to run meth and race gas etc (mostly 99% of the time)
 
#128 ·
I started out with 450cc injectors and 9b's and decided that I wanted to go faster and wanted to get my feet wet with 650R's and thought 720cc were ideal and at the time didn't realize that would cause too much timing on pump gas. I bought the E-Manage to pull back the excess timing on pump and sold the S-AFC. Now I have the best of both worlds.. maximum timing on pump and race gas without knock.

the only reason your car is faster is because it's a lot lighter and you're running bigger turbos.. don't kid yourself.

200+ lbs lighter and 25psi vs my 19psi with TD05s vs TD04s and Drag Radials vs Street tires.

I wouldn't have any problem picking up 4 tenths 200lbs + lighter and 5 psi more boost alone.
 
#131 ·
all it would take is bigger turbos alone.. I've exceded my goal for this car and just don't have the drive to pursue 10's. The cost is what's holding me back more than anything at this point though. Spending 4k+ just to prove that I have a bigger E-Penis isn't cheap.
 
#132 ·
interesting points... both of you...
 
#133 ·
Mellon said:
Bottom line on these cars is that if you have a piggy back ECU you need to get timing control or you're going to be pulling your hair out. The E-Manage has fantastic fuel control and timing control.. I can't stress enough how easy it would be to fix all of your timing issues with one device and not have to deal with the price of the AEM and the learning curve.
Mellon, timing is not the only thing the EMS has the potential to correct.

The way the stock ECU manages knock is pretty dangerous... especially when everyone boosts they way they do nowadays. The use of race gas to deter detonation allow most to boost more and keep those counts from actually occurring.

...But lets not shy away from the real problem here... and timing is not it.

Its the tuning.
People LOVE to get the most bang for their buck... It will always be that way regardless. But many people end up swapping one part, with a complete disregard to how it affects the whole picture. It's nice to see almost everyone actually paying attention to the WHY's and HOW's to correct these things(i.e. discovering that timing was affected by the fuel corrections and resulting fuel pressure)... other than posting 'MY-ENGINE-BLEW-UP-BECAUSE-VR4-SUCKS!' threads.

Now I'm not saying that everyone that runs into timing problems sucks at tuning. I'm just saying that the timing issue is CAUSED by our bang-for-the-buck attitude... and how the standard piggyback alters STOCK MAS signals before sending it to the STOCK ECU. We are... in the sheer essence of things... J-rigging our stock tune.

Hopefully everyone will agree with me when I say... if given the opportunity... they would go standalone when they get high up there with their horsepower. HOWEVER, most people just don't have the time to deal with learning how to tune and don't care to be EFI engineers... so their only options are to accept what's given to them and live with what they are comfortable with.

I'm sure plenty of people can do MORE with LESS... heck... you will ALWAYS come across it on this forum ;)

And lets not get started on the PSI thing... because low timing/high boost vs low boost/high timing will be an unresolvable discussion. It just boils down to how well you can tune the car right? Just because you can get more HP from jacking up the timing and running lower boost doesn't mean it's the only way to go... or mean the engine isn't working as hard.

If you look at how supra people are tuning when they get into higher boost... you don't see them trying to run 30+psi with 30 degrees of advance.

just some mindless babbling... sorry guys :D
 
#134 ·
pacman3000gt said:
Mellon, timing is not the only thing the EMS has the potential to correct.

Now I'm not saying that everyone that runs into timing problems sucks at tuning. I'm just saying that the timing issue is CAUSED by our bang-for-the-buck attitude... and how the standard piggyback alters STOCK MAS signals before sending it to the STOCK ECU. We are... in the sheer essence of things... J-rigging our stock tune.

Hopefully everyone will agree with me when I say... if given the opportunity... they would go standalone when they get high up there with their horsepower. HOWEVER, most people just don't have the time to deal with learning how to tune and don't care to be EFI engineers... so their only options are to accept what's given to them and live with what they are comfortable with.

I couldn't agree more.. the AEM EMS is clearly superior.. the price and learning curve scare most poeple away. My issue is the price and the fact that I'm doing pretty well with my piggy back. I don't think I'd gain any performance with it and that's what I'm most interested in. I watch my knock counts like a hawk and have the palm setup to alarm me audibly so I feel confortable beating on the car.
 
#135 ·
Bump.

This thread answers a few new posts.
 
#136 ·
I had a hard time finding this thread so I bumped it for good Luck.

I finished the install on my adjustable fuel pressure regulator and I am installing my 510CC injectors this weekend. REALLY! I swear I am actually going to do it this time.

I am trying to minimze my timing issues so I went with smapller injectors than most people get. If I can TRUELY max these out and make 500HP I will gladly pay to upgrade to larger injectors if needed.
 
#138 ·
That's probably a good idea. I wish my car had slightly smaller injectors, like maybe 580's. I'm never gonna make enough power to even get close to maxing 660's on my current setup. I have to retard timing 10 deg. just to run 12psi w/ no knock.

still selling your car John?
 
#139 ·
sombody help me out here, please give me some feedback. this is the general activity i'm seeing. i'm using mmcd which clint swears has accurate idc.

at wot, it takes until 5k rpm for my idc to hit 80%, at that point timing is 18-20 degrees. at wot below 5k rpm idc is less than 80% and timing is 12-17 degrees, dependent on rpm. at 6500 rpm wot i've generally got idc ~95% and timing at 25 degrees.

how does this sound? am i reading this correctly and basically you should tune for 80% idc for optimal timing :dunno: i can do this, but right now i'm tuned for my a:f ratio, if i adjust the maf signal down (from -20% to say -25% theoretically) at 6500 rpm won't that 1) affect timing since the maf signal is being changed and 2) make me run pretty lean up top?

does anybody have any logs i can compare to? i can't upload my logs off my datalogger, it just locks up my system :mad:

the car is running 15lbs, 450cc injectors and 13g turbos and using an afc for fuel management.
 
#140 ·
You should be fine as long as you're able to hit at roughly 80% IDC somewhere in your sweep while holding your target air-fuel ratio. Don't deviate from your target AFR just to change your IDC's. Get your IDC's in the optimal range by changing your fuel pressure or injector size, then re-tune for your target AFR.
 
#141 ·
Mellon said:
all it would take is bigger turbos alone.. I've exceded my goal for this car and just don't have the drive to pursue 10's. The cost is what's holding me back more than anything at this point though. Spending 4k+ just to prove that I have a bigger E-Penis isn't cheap.
so 4 months go by and now you want a bigger "E-Penis"?
 
#142 ·
eyeluvmy3kgt said:
so 4 months go by and now you want a bigger "E-Penis"?
LOL! Yeah, that's pretty much how it goes... You convince yourself that it is good enough, but then something gets you thinking you are soooo close to being that next step quicker... Then the wallet comes out and all hell breaks loose. :D
 
#143 · (Edited)
Trevor said:
You should be fine as long as you're able to hit at roughly 80% IDC somewhere in your sweep while holding your target air-fuel ratio. Don't deviate from your target AFR just to change your IDC's. Get your IDC's in the optimal range by changing your fuel pressure or injector size, then re-tune for your target AFR.
this is good news. i don't think i can adjust my idc's any, since i don't have any timing adjustments and have not yet upgraded my fpr. i'm not sure i want to since i'm staying with 13g turbos. i don't think i want to change my injectors either since the 450's will result in the smallest adjustment to the maf signal. i may have to go to 550's if i want to run more than 15lbs, but for now i'm content. thanks for the clarification trevor :)
 
#144 ·
mjannusch said:
LOL! Yeah, that's pretty much how it goes... You convince yourself that it is good enough, but then something gets you thinking you are soooo close to being that next step quicker... Then the wallet comes out and all hell breaks loose. :D

11.50's on 20psi to redline.. I have to see what it will run with 10psi + more boost and better VE :D
 
#145 ·
bjmsam said:
O2v Front = .90 V
O2v Rear = .92 V
Knock Count = 0
RPMs = 6844
TPS = 96%
IDC = 122%
Timing = 22 Deg
J-Ville VR-4 said:
You are using the datalogger IDC count. Its not accurate; it shows a higher IDC than you really have. Its physically impossible to have above 100%IDC.
bjmsam said:
Right. So how do folks tune for 80.2% IDC? Can the values my logger reports be simply scaled by 100/122 = 82%? Perhaps Shiver can add that factor to the next release.

Would timing remain within spec if I upgraded from 9B to 13G (250 to 324 practical max CFM = 29.6%) and from 360cc to 450cc (25% + some fuel pressure)? All I'd need is a SAFC-2?
Multiades said:
"Within spec"? Timing will be higher, but not unreasonable with that injector upgrade and the necessary correction. An S-AFC can easily take care of that.
Before I install a SAFC-2 and finally (after nearly nine years of ownership) try my hand at tuning, I just want to make sure I understand the basics well enough.

My ECU appears to report not IDC, but deviation from ideal IDC. When boost is limited to stock pressure, the logger reports a value of 100 at peak horsepower; if 100 represents 80.2% IDC, then 100% IDC would result in a value of 125, similar to the 122 logged above when the stock fuel system was maxed out.

Increasing fuel pressure via my AFPR and reducing metered load via an SAFC-2 should result in lower IDCs and higher timing advance, generating more power. I won't be able to increase fuel pressure enough to achieve the target value of 100, but I should see the numbers moving in the right direction. 450cc injectors flow 25% more than 360cc injectors, so they, along with slightly lower fuel pressure, should properly correct my current 22% overrun and achieve the 100 target value.

13G turbos flow 29.6% more than 9B turbos, which will once again throw the system out of balance. 550cc injectors flow 22.2% more than 450cc injectors, so they, along with slightly higher fuel pressure, should properly compensate for the change.

I'm getting something wrong here, as folks have stated that 450cc injectors are sufficient for 13G turbos (presumably "sufficient" means they flow enough to achieve 80.2% IDC), but hopefully I've grasped the general idea. TIA for clarifications!
 
#148 ·
eyeluvmy3kgt said:
so 4 months go by and now you want a bigger "E-Penis"?

Haha! Chris got owned! :D
 
#149 ·
Interesting.. I just posted this in the dyno/spool thread but its right inline with your post:

Right now at 18psi@6500rpm the IDCs are 105 @ 11.3ish AFR with slight knock onset at 5800+RPM (EVO7 560s at 48psi base so around 590cc)..... timings showing around 29-30 on hybrid logger on 93 pump gas. Gonna have to log fuel pressure to make sure the Supra doesnt need more voltage.... cause I didnt think I would be maxxing out the injector this quick.


Rob

Quick Vr4 said:
logged my car last night and thought i would share. i have a hotwired supra pump and Rc 550s in the car now. at 18psi at redline my IDCs are at 81.
 
#150 ·
on 660's and a denso pump on stock wiring right now @ 17psi my IDC's are 100 with low 11's A/F.

I just got my relay in the mail, so i'll be doing the re-wire this weekend. We'll see how much the IDC's drop when the fuel pump is getting 14volts and i've re-tuned.
 
#151 ·
Quick Vr4 said:
IDCs are at 81
RobBeck said:
IDCs are 105
eyeluvmy3kgt said:
IDC's are 100
Is everyone stating IDC as computed from IPW rather than what's reported by loggers so that the figures can be compared?

IDC = RPM / 1200 * IPW
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top