From the scion forums, most guys running f/i have been going to much larger injectors. I have 410cc with the s/c now. But these guys are going 550- 700. To me, that seems ridiculous for ~250-300whp.
I don’t know if the few are just lemmings following what they see on the boards, but I am really trying to understand why this is the case.
What they write about is “keeping charge temps down to cool with fuel”…i am no expert but the minimal boost with this centrifugal design…can’t see it being that hot. Or they say they “add fuel to combat a lean condition or possible detonation.”
Someone else said he maxed out 550cc at 5500 on an s/c with 10.5psi. Considering I am at 9.5psi on 410cc injectors, with no supposed problems on the TRD map I really don’t understand this.
But a local tuner in the area said I should be fine with 400ish injectors, and a buddy of mine into suby’s is telling me they probably didn’t detonate from high charge temps, but from being way too rich. He suggests all I need is a 255lph walbro and adding fuel to fight knock will only reduce power and lower knock slightly.
I don’t want to believe everything I read on the googlenets, but most of these guys have gone big. There has to be a reason.
I am going to be adding EMU soon, a couple more pounds of boost and want to understand this whole injector business.
Well unless your injectors are getting maxed out or are working inefficiently going bigger shouldn’t do anything for you.
With a proper tune, a larger injector will just run at a lower rate, giving you less fuel, so unless you are running the 410’s at 100% at some point in your rpm range I don’t see why you would have a problem.
Example: My car is running 30 lbs injectors at about 95%…If I go with a 45 lbs injector and a re-tune it would be running closer to 65%…but that would give me more room to expand.
We’re not being given enough info to answer your question. Maybe that other guy has other mods that aid in breathing like cams, head porting, more efficient blower, etc.
What’s your current duty cycle at redline?
Do you have some manner of control over ignition timing like a piggyback or standalone ECU?
What is your wideband reading at full boost?
What are your CHT or EGT readings like on a 4th gear pull?
Well, you can count on 1 hand the number of people with cams and head porting on the scion tc. One person went to 311whp on regrinds and Crower just came out with some last month for N/A. Although you would be hard pressed to find anyone with them. Incidentally, the regrinds guy went to 700cc injectors. His tuner (Ripp Mods) said they “maxed out” too.
on the scion boards most people are concerned with LED mods and hid headlight conversions. Not so many trying to push performance or have the funds to do so. So I’m not sure if the majority of those who have tuned have come to the same collective conclusion, or you just have a bunch of 17 year olds listening to what 1 tuner has told them. I PMd a guy with a similar setup to my own and asked him what he ran. His response “I could go with 550, but I decided on 700cc…just to be safe”. For 250whp. That floored me. I understand he’s got parasitic loss on the drivetrain and the s/c belt…but it just seems excessive. Is it possible the toyota ecu is just that finicky?
“more efficient blower”…there is none. TRD makes the only s/c. I have a scan of the compressor map if that means anything to you. I will tell you I don’t see a lick of boost until 3k. I can cruise at 75mph and be at 0psi.
Anyway, I like to understand what I am doing before investing and understand the science behind this. Some of the reading I have been doing suggests going too big is a waste if not counterproductive to go big.
I’m not sure if I have (or understand) the additional info you need to help me, but this is what I know…
Returnless fuel system. So no changing fuel pressure unless you go DIY.
How do I determine duty cycle? I have an AutoEnginuity ScanTool, but I don’t see that option. What do I need?
Currently I am running 9.5lb (upgrade over the stock 7lb) on the stock reflash from TRD.
EMU -> Emanage Ultimate. Although that bird looks pretty nasty. Maybe I should add him under the hod.
AFR was 10.5 at WOT if I remember correctly. That was on the dyno. I am in the process of installing my gauges now.
EGT was “normal” from the dyno run. I cannot remember the exact figure. I want to say 1300, but don’t quote me.
I’ll be adding CAI, 12lb pulley and EMU…and plan to find a good tuner - hopefully to tune off of the MAP rather than MAF.
You can calculate injector duty cycle based on pulse width vs. RPM if you can’t log duty cycle directly. Just make sure you get a reading at wide open throttle just before the rev limiter as that will be the highest reading.
That’s going to give us the best idea of the headroom you have left on your current injectors.
Being able to change your fuel pressure would be nice and probably cheaper than bigger injectors. The only downside is reducing the total flow capacity of the fuel pump at those higher pressures, could be an issue if your current pump is not oversized.
Avoid running any extended period of time over 95% duty cycle with ANY injector, the coils can get very hot and can fail.
Spray pattern and particle size can be very important to preventing knock, so just getting more fuel isn’t the answer.
OK, it seems I have to upgrade my autoenginuity with Toyota specific codes to get pulse width. Seems like a good investment since it will provide about 200 other sensors too like fuel trims. I will figure this out and get back.
As far as pump. I believe it is 190. Some have upgraded to 250lph walbro…still with no regulation. I would have to install a fuel return system to make that happen.
With the little I know i agree that “just getting more fuel isn’t the answer.”
But in a general sense…would you think that a 2.4L 4 banger lucky to push 250 to the wheels would need 550ccs or higher? Granted I have drivetrain loss, auto trans loss and s/c belt loss which could mean the 250 is actually closer to 300 at the crank. I know I am losing a lot.
But it seems a lot of guys on this board are pushing more with less on different platforms…trying to find the correlation. Or am I mixing apples and oranges?
there are many factors that go into deciding what injectors will give you what power. Volumetric efficiency, parasitic losses, bsfc, fuel timing, spark timing, fuel pattern/size, stoich, combustion chamber geometry, air temp, altitude, etc.
the easiest way to figure out what you need, is copy someone else’s work that you believe to be sound. no math required on your part, but you will need to know more info than you have now.
Thinking off the top of my head I think 660cc and 750cc are upgrade injectors for SRT-4 Neons. I know it isn’t the same case, but its a similarly sized 4 banger FI.
very general ballpark, 550’s should be ok. most ppl just go oversize so they dont have to keep stepping up to a larger injector and losing money buying new/selling used etc. thats only if u can adjust ur fuel maps tho.
most 300whp 4 cylinder cars will run 550 or so injectors, but that is with a rising rate fpr
i would think 550 would be good for 250whp pretty easily but it all depends on how efficient your motor is and how much drive train loss you have
most injector companies will recommend no higher then 80% injector duty cycle
why do you want bigger injectors if your car is running fine right now? do you plan on upgrading and making more power? if so i would just go with 750 or something close to that so you wont ever have to worry about upgrading them again while your supercharged
stock 370, with the non-intercooled trd s/c kit: 410cc. By comparison, Greddy sells an intercooled turbo kit with 440cc tuned for about 6psi.
I’ve played with those online calculators, but it’s best guess right? BSFC, VE…hard to peg those down. Plus they work on peak HP requirements…how often are you at WOT. I could be wrong, but on a non-race car…I question how much the 80% rule applies for the .01% my car will be at that.
Even with those calc’s i still don’t get why a 310whp tc needed 700cc injectors. One guy says you need the injectors to deal with duty cycle. Another guy says you need it to “cool the charge” or “reduce knock”. “Well which is it?” is my rhetorical question to these guys. Without the science, it’s just guessing.
So let’s assume that perhaps the toyota/trd isn’t very efficient, and that the ecm isn’t cooperative. That would be the reason to go bigger?
The VE as I understand it is not that great on the s/c. For my 9psi it doesn’t currently start building until 3k. If that means anything. And perhaps I have much more at the crank than I think because of all the drivetrain loss. Guesstimate is 17% for trans, and another 10% for the belt driven charger?
This is the compressor map for the Vortech F Trim.
Car is running fine but i plan to add a little more power. I plan on upping to 12psi, cold air and engine management. I want to understand the why/how of additional fuel.
Does going bigger than necessary do anything detrimental? Will it be too rich? Waste too much fuel…or do you just manage that with the piggy back?
I found a decent article that seems to explain this, and also suggests that going huge isn’t always an efficient thing.
I have to get a s/w upgrade for my autoenginuity to read toyota specific codes: the pulse width and about 200 other sensors like fuel trims which will be useful. Once I get that in I will post.
yeah the ve/bfsc is all hard to know but u take an educated guess and estimate on the high end.
even if you are WOT 1% of the time, if the car needs that much fuel, and you can’t deliver on small injectors…well…boom!
u can use any size injector u want, as long as u have a means of adjusting your fuel maps/tables. The freedom you have is limited with a piggy back cuz some can’t really handle a huge injector upgrade…most engine management systems allow you to recalibrate/re-scale your fuel maps for larger injectors so you maintain driveability/idle etc. the extra fuel to cool/prevent knock is SOMEWHAT true, but its not like a HUGE factor…it wont make up for a shitty intercooler or a turbo/SC that is past its efficiency range and just pushing hot air. I was never a fan of that whole deal cuz its more of a bandaid than anything to cool with extra fuel…waste gas…do the setup right and u wont need to dump the extra fuel.
So yeah if u just throw 750cc’s on there, you will run super rich cuz the computer is telling the injectors to pulse/deliver as much fuel as your stock 310’s would have…when you realistically only need to deliver 1/2 the fuel now on the larger injector. Along these lines, you have basically double the capacity (power wise) of your old injectors, and thats why ppl go big…cuz u always wanna make more power, and it sucsk to to run out of fuel
