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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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#103 ·
RussianVR-4 said:
never had a problem with SX/aeromotive regulators.
btw, SX/aeromotive - same stuff.
Sorry Eugene, that statement is incorrect.

Aeromotive is a comapny founded by an Ex SX employee.
SX FPRs can hold higher PSI
SX FPRs are made in an ISO9000 regulated facility, Aeromotive is not.

They are Similar yes, they however are NOT the same.

and yes, I sell both.
 
#104 ·
ditto, been running the SX FPR kit from IPO for a long time now.. it's awesome.
 
#108 ·
i love science and equations to go along with hp and 1/4 mile claims :)

i did a work up on the RC page to verify that my 550s would be correct for my set up with stock fpr
it said 559 cc so i think that it should be perfect
great thread
 
#110 ·
DRIFTIR said:
I will be running dr-650r's with 550cc injectors. Thanks Trevor.

:rolleyes: enjoy your rediculously high IDC's and low timing
 
#111 ·
Mellon said:
:rolleyes: enjoy your rediculously high IDC's and low timing
Depends on what boost he's running typically and on what gas. I just replaced my 720s with 550s, and for a starter, the car runs 5x smoother than before. No more low RPM bucking, and overall, the car just drives more like stock car. As for IDCs, I'm testing at 1 bar and seeing IDCs as low as the 50s. The plus is that IDCs (and indirectly timing) are within my control using the FPR. I can run from 33-53psi to see what works best, and drastically change the IDCs to my advantage. Granted this isn't as convenient as your emanage or other methods of direct timing management, but it is better than the 720cc problem--super low IDCs, super high timing, and not a thing you can do about it.

All this is of course related to running pump gas which we all know sucks. If you're running c16 all day, then get big injectors, pull the wastegates, and have fun.

On a side note---As an update to my post above, I ran almost pure VP101 and was able to run 1.4 bar without any knock. Needless to say, it was fun.
 
#112 ·
2root4u said:
Depends on what boost he's running typically and on what gas. I just replaced my 720s with 550s, and for a starter, the car runs 5x smoother than before. No more low RPM bucking, and overall, the car just drives more like stock car. As for IDCs, I'm testing at 1 bar and seeing IDCs as low as the 50s. The plus is that IDCs (and indirectly timing) are within my control using the FPR. I can run from 33-53psi to see what works best, and drastically change the IDCs to my advantage. Granted this isn't as convenient as your emanage or other methods of direct timing management, but it is better than the 720cc problem--super low IDCs, super high timing, and not a thing you can do about it.

All this is of course related to running pump gas which we all know sucks. If you're running c16 all day, then get big injectors, pull the wastegates, and have fun.

On a side note---As an update to my post above, I ran almost pure VP101 and was able to run 1.4 bar without any knock. Needless to say, it was fun.
so you're going to change the fuel pressure and re-tune when you go to c16 and when you're done, change the fuel pressure back for pump tune. that's a nasty way to adjust timing. And by the way. 720cc injectors don't cause low rpm bucking.. poor tuning does.
 
#114 ·
Mellon said:
so you're going to change the fuel pressure and re-tune when you go to c16 and when you're done, change the fuel pressure back for pump tune. that's a nasty way to adjust timing. And by the way. 720cc injectors don't cause low rpm bucking.. poor tuning does.
No, I'm going to just enjoy 9 psi with 720s, because that's all it'll run without knock :rolleyes: I never said it was pretty. Bottomline is piggy backs aren't pretty, including emanage. I recognize piggyback limitations, and I'm doing what I can with them until I get real solution--aka AEM.

I'd love to hear your tune advice for getting rid of bucking since my car was so poorly tuned.
 
#115 ·
2root4u said:
No, I'm going to just enjoy 9 psi with 720s, because that's all it'll run without knock :rolleyes: I never said it was pretty. Bottomline is piggy backs aren't pretty, including emanage. I recognize piggyback limitations, and I'm doing what I can with them until I get real solution--aka AEM.

I'd love to hear your tune advice for getting rid of bucking since my car was so poorly tuned.
bucking is due to a lack of fuel .. with large injectors if you don't add some fuel down low the ecu practically sees no airflow so as you're tooling around the parking lot the gas pedal will basically become and on/off switch. you give it some throttle, the rpm try to rise but there's not enough fuel so it shuts off.. surging back and forth.
 
#116 ·
Just from experience what I had to do with Farhad's car, 720cc injectors, emange and stock maf, i pulled a few degrees of timing from about 2500-3500 at the mid levels (going by airflow in HZ) and the knock totally disappeared, I didn't really have to do anything up top, he was running a stock fuel pressure regulator too and stock lines. 15-18 psi on 91 octane, 0 knock. Its going to the dyno on Monday to see how many pump gas HP we can squeeze out.

If you could drop the pressure down and make them say 680cc injectors it may make a big difference for ya. I agree with mellon on that one, if you adjust your fuel pressure for race gas then back to normal for pump gas its never going to the exact. but with an arc 2 its not really that big of deal to adjust it by a click or two.
 
#117 ·
Mellon said:
bucking is due to a lack of fuel .. with large injectors if you don't add some fuel down low the ecu practically sees no airflow so as you're tooling around the parking lot the gas pedal will basically become and on/off switch. you give it some throttle, the rpm try to rise but there's not enough fuel so it shuts off.. surging back and forth.
Trust me, I've flooded it down load multiple ways--ARC2 load based and SAFC2 TPS/RPM based. It does help, but its no where near as smooth.

If you could drop the pressure down and make them say 680cc injectors it may make a big difference for ya. I agree with mellon on that one, if you adjust your fuel pressure for race gas then back to normal for pump gas its never going to the exact. but with an arc 2 its not really that big of deal to adjust it by a click or two.
I tried lowering my FPR down to about 35ish. For me, the improvement was not much. For now, I'm going to max out 550s and crank up the FP as needed. If it runs like a great and can handle more timing, then I'll buy some 680s. Right now, I'm attempting to just make the car enjoyable on 93 without making the jump to AEM. I don't plan to be switching between race and pump a lot. My last stop after messing with 550s is propane/alchy. If that doesn't work, I'm really don't want to mess with an ITC or emanage--I'll just sell all the electronics and get the standalone. Lets hear it for our money pit on wheels....w00t.
 
#118 ·
I feel sorry for you guys that would rather fiddle with crude a/f adjustment such as the arc2, safc and on top of that limiting your injector size to keep knock away yet trying to make them bigger with a fuel pressure regulator. Could you be more in the stone age?? get with the times guys. The E-Manage can handle massive injectors and shave off any excess timing.

do yourself a favor and sell all of that gear and get yourself an e-manage and get back to enjoying your car. You'd thank me later I guarantee it.
 
#119 ·
Mellon said:
I feel sorry for you guys that would rather fiddle with crude a/f adjustment such as the arc2, safc and on top of that limiting your injector size to keep knock away yet trying to make them bigger with a fuel pressure regulator. Could you be more in the stone age?? get with the times guys. The E-Manage can handle massive injectors and shave off any excess timing.

do yourself a favor and sell all of that gear and get yourself an e-manage and get back to enjoying your car. You'd thank me later I guarantee it.
:stupid: The idea is perfect, and your ways are fine Trevor, and the rest of you guys, I haven't read all this thread, but Mellon has a point, E-manage makes life a lot easier.
 
#120 ·
Mellon said:
I feel sorry for you guys that would rather fiddle with crude a/f adjustment such as the arc2, safc and on top of that limiting your injector size to keep knock away yet trying to make them bigger with a fuel pressure regulator. Could you be more in the stone age?? get with the times guys. The E-Manage can handle massive injectors and shave off any excess timing.

do yourself a favor and sell all of that gear and get yourself an e-manage and get back to enjoying your car. You'd thank me later I guarantee it.
Its not like the ARC2 is a turd that has never ran good times. FYI, my SAFC2 is tuned to straight zeros. I bought the SAFC2 because of rumors like what you posted about how crude the ARC2 is. It was $300+ wasted. The ARC2 is amazingly easy to tune, but it is true that timing is an issue. It came with my car, so I'm trying to make it work. Given the price of an ARC2 (new) vs Emanage, the emanage is a better option.

Timing is the issue at hand and the whole point of this thread. If I sell my equipment, I'm going for the AEM not another piggy back. I've had enough of "tricking" our ECU.
 
#121 ·
Since I'm new to the world of tuning (a/f) I took well to what trevor suggested. Going with 550cc, supra pump hotwired, and an AFPR stock 43 psi. Where I live we dont have 93 either..Highest down here is 91 pump gas
:( Money is not an issue either in terms of what to get. I just don't know much on the other systems..e-manage-AEM-and so forth. I read about 30 pages of posts on the map ecu system so I feel more comfortable actually buying it.
 
#122 ·
2root4u said:
Its not like the ARC2 is a turd that has never ran good times. FYI, my SAFC2 is tuned to straight zeros. I bought the SAFC2 because of rumors like what you posted about how crude the ARC2 is. It was $300+ wasted. The ARC2 is amazingly easy to tune, but it is true that timing is an issue. It came with my car, so I'm trying to make it work. Given the price of an ARC2 (new) vs Emanage, the emanage is a better option.

Timing is the issue at hand and the whole point of this thread. If I sell my equipment, I'm going for the AEM not another piggy back. I've had enough of "tricking" our ECU.
I know a lot of people are tired of piggy backs but keeping in mind what kind of equipment they've been dealing with.. I don't blame them. ARC2, SAFC, MAF-T MAP ECU etc.. they all focus on fuel contol with no regard for the nasty timing issues they cause.

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.
 
#123 ·
the theory in this thread is that you need to pick the right size injectors to keep knock away and scale the injector size with a fuel pressure regulator to get the IDC close to a max of 80% so that timing isn't too high. If you need larger injectors later, just sell yours and buy larger ones later.

a few things this thread doesn't mention:

1) you're going to have to buy a fuel pressure regulator, the stock one isn't adjustable.

2) fuel pressure regulators don't come with a fuel pressure gauge so you'll need to buy that too.

3) to adjust the fuel pressure you're going to have to loosen a nut and turn the adjusting bolt with an allen key..by doing this and watching the fuel pressure gauge (if you have one) you can get the base fuel pressure where you want it.. it isn't very precise with an analogue gauge.


let's say you've bought 550cc injectors and adjusted the base fuel pressure after some tweakin to where you end up with ~ 80% IDC's and no knock on pump gas at 16psi. That's great. Now let's say you're ready to go to the track and put in race gas...you crank the boost up and you're IDC's are through the roof and you're timing isn't near 30* by redline as it should be for best power. No problem right? Just crank up the base fuel pressure so the IDC's lower and the timing increases right? how far? who knows, keep trying until you get it right. Oh damn, now the a/f has changed since the fuel pressure was touched and you're going to have to tune it again.

Now you're done at the track you may or may have not been able to dial it in like that, but you need to go back to pump gas. So you have to set your base fuel pressure as close as possible to your "pump gas" setting you had earlier. Because adjusting the base fuel pressure isn't exact the tune is slightly off now so you'll have to tweak on that otherwise you'll be a little lean or a little rich more than likely.

is that really acceptable? personally I see that as a huge pain in the ass because if you go to the track frequently you'll constantly be tuning. It might be fun at first but trust me that will get old fast.

My advice.. buy the E-Manage.. make one fuel/timing map for pump gas and another for race gas. Changing from one to the other is a click of a button. You don't even need an aftermarket fuel pressure regulator. Now you can run large injectors and simply shave off any excess timing that sets off knock on pump gas and you can ramp up the timing on race gas for more power.

for instance on pump gas with 720cc I end up with rougly 44* of timing by 7k.. way too much for pump gas but I simply pull that much out in the timing map on the e-manage and get 0 knock and effectively 30* at redline like factory.

when I go to the track I load up my saved race gas tune which is significantly leaner a/f and no timing pulled since I'm running c16 and again see at least 30* at redline.
 
#124 ·
A few things that I've probably said before but you never seem to have an answer to:

- Not everyone knows what to do with timing or wants control of it. Have you seen the questions some of the owners on this board ask? Do you really think they're ready for timing control and capable of of making the most of it (or even keeping their motor together while playing with it for that matter)? Most can't even get the fuel thing right...let alone fuel, boost, timing, and RPM all intertwined.

- I have one (1) fuel map that works great for all boost and fuel quality levels. I haven't touched my adjustable fuel pressure regulator in months.

- 100% IDC timing is not retarded enough to slow the car down all that much. The results speak for themselves. 552 at the wheels at 23.2 psi, 127.6 mph at 25.6 psi, and it will probably running about 129.3 once I get a clean pass at 28.6-30.5. You ran 119.7 mph? Timing control, C16, and DR650R's? I was going 119.9 years ago. I had 210 lbs on you at the time so you are defintely going faster (relatively) but my car had alot of handicaps that negate that 210lbs....no timing control (a massive handicap from what you've said), unclipped 15G's, 105 octane, 550's, an ARC2, and no datalogger whatsoever...just tuning off of my butt dyno and trap speeds. You'd think the difference would be larger seeing how you're telling us timing control is essential.
 
#125 · (Edited)
my point is why buy a fuel pressure regulator and deal with that when you could put your money towards an E-Manage and not have to worry about perfectly sized injectors and don't have to buy another set of injectors later should you want to upgrade the turbos a bit.

if you're goal is to keep it simple for novice tuners then why would you even mention the MAP ECU + FPR that would be a nightmare to tune for the beginners.

It's just my opinion but I think it makes more sense to buy one piggy back that can do it all and you don't have to worry about going a little big on the injectors, it's cheaper and can scale up easily.
 
#126 ·
The MAP ECU a nightmare, please. Once you understand how it works its a cake walk.

And no response on the other two points...

Am I the only one who sees what's behind all this?

You're using the emanage to fix a problem that you could have avoided in the first place.

All that work because you made a mistake when choosing your injectors. That mistake (and that's what it is) has forced you into a corner where you require timing control just to be able to punch it on 93 octane at 13-14 psi without knocking your ass off.

You're wrestling with a monster of your own creation.
 
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