GTR Forum banner

1 - 19 of 19 Posts

·
Registered
Joined
·
818 Posts
Discussion Starter · #1 ·
Hi all,

Was wondering if anyone could help me on this one. I am thinking of putting larger injectors in my engine in preparation for some cams and more power. Currently my Apexi is mapped on the standard injectors (440cc?) so obviously if i put bigger ones in its going to run rich.

I noticed on the apexi FC commander that one page in the 'Settings' has injectors listed 1-6 all set at 100% with an 0.04 advance? on all of them. If i put in larger injectors say 550cc ones could i reduce this 100% down to 80% (i.e. 440/550 *100) to compensate for the larger injectors? Im guessing that this would limit the bigger injectors to a max of 80% of their duty cycle and effectively make them act as 440cc injectors?

I assume that injector duty is directly proportional to fuel flow? so would this 'fudge' work across the entire fuelling map or do i need to get the car remapped? Or am i talking complete rollocks!

Any help would be appreciated
Cheers
 

·
Registered
Joined
·
8,804 Posts
yes, 100% is for the stock JECS 444cc injectors. You just need to put in the injector correction (calculation is correct), find out what the lag time is for your new injectors and correct for that, and then you are good to go.

caution: if you have an adjustable fuel pressure regulator, have it set at normal pressure (2.5bar at idle), as injector rating is variable with fuel pressure. Sometimes you'll have to fiddle with the settings if your calculated settings don't work out perfectly. checking with an AFR would be a good idea to see if you're rich or lean. But your fuel map should be fine once your injectors are dialed in via the injector settings menu.
 

·
Registered
Joined
·
380 Posts
Set the injectors at 80%

Not sure on lag time ??

The fuel map will need adjustment aswell...........



REgards



Barry
 

·
Registered
Joined
·
818 Posts
Discussion Starter · #5 ·
Thanks for all the replies guys, looks like i wasnt talking complete rollocks afterall. Ill get the injectors and then have a play. The link to the Apexi site was very informative too cheers

Was thinking if i do it myself (i do have an after market adjustable fuel pressure regulator set up already by Rod Bell) is there an easy way to set these back to standard fuel pressure i.e 2.5bar as kismecapitain says? i.e. x mm of thread of the screw showing or something or an easy way to measure fuel pressure?
 

·
Registered
Joined
·
1,273 Posts

·
Registered
Joined
·
818 Posts
Discussion Starter · #7 · (Edited)
Cool thanks for all the advice.

In the interim if I fit the Injectors (550cc Greddy ones I've sourced - anyone now the advance for them??), adjust the PowerFC injector settings down to about 80% and dont mess with the adjustable fuel pressure regulator (until i get my fuel pressure measuring gear) whats the worst that can happen? By my reckoning im just going to run a bit rich for a while which is better (i.e safe no damage) than running lean and its just going to hurt my petrol money piggy bank?

Speaking of the adjustable fuel pressure reg is there a rule of thumb for 0.1bar is equivalent to oversizing your injectors by 20cc or something?

I will obviously get Rod to sort the map out properly when he fits the cams...
 

·
Registered
Joined
·
2,201 Posts
Kismekapitan...

I'm sure one day you will turn out to be the legend in GTR tuning but will you quit telling people that they are ok to do things when you dont know what you are doing!!

Fuel pressure 2.5bar at idle, please explain how you come to this conclusion and why it would only be at idle?

'Your fuel map should be fine once you have dialled in the correct settings'

Erm no!

Please listen to a small bit of advice before jumping on everyones thread telling what they should be doing when you dont know 100% yourself.

Get some proffesional tuition or something, try and learn a bit more before telling people what they can and cant do.

Rob :)
 

·
Registered
Joined
·
818 Posts
Discussion Starter · #9 ·
ER.... I thought i had itr sorted there tweenierob.. Am confused now!

Can I not just swap the inectors and adjust their rating to around 80% set the advance right and leave my fuel pressure reg as it is. Rod Bell set my fuel pressure a bit higher so as not to max out the standard injectors to be on safe side (running around 400bhp on std injectors). Surley Im just gonna end up running a bit rich but thats ok isnt it for a few weeks or so? till rod puts cams in and does a remap?

Dont want to **** things up! what should i do?!
 

·
Registered
Joined
·
8,804 Posts
Kismekapitan...

I'm sure one day you will turn out to be the legend in GTR tuning but will you quit telling people that they are ok to do things when you dont know what you are doing!!

Fuel pressure 2.5bar at idle, please explain how you come to this conclusion and why it would only be at idle?

'Your fuel map should be fine once you have dialled in the correct settings'

Erm no!

Please listen to a small bit of advice before jumping on everyones thread telling what they should be doing when you dont know 100% yourself.

Get some proffesional tuition or something, try and learn a bit more before telling people what they can and cant do.

Rob :)
2.5 bar seems to be a consensus number for fuel pressure at idle, and rises as manifold pressure rises. injectors are rated at 3 bar at 0 bar, which an engine isn't at, at idle. I appreciate your concern, but wouldn't you sound more convincing if you explained exactly why and where a fuel curve would have to be adjusted, instead of just saying "erm, no". I really wish you'd share your knowledge, instead of just saying (implying) that you know something we all don't.

And before you go into my broke engine, it is the consensus of every professional who has actually inspected the disassembled parts, that preignition due to a fuel pump failure cause my engine damage, and the map itself is reasonably spot on, save for running rich high up on the map.

Anyways, if I'm wrong, for the love of God please say EXACTLY why!
 

·
Registered
Joined
·
2,201 Posts
I'm glad you havent taken it the wrong way...

I dont mind sharing some knowlege.

Fuel pressure must be checked with the vacumn off of the reg for starters, Factory pressure is 2.8bar not 2.5.
If you change the injector percentage and lag time it will get you to your tuner, it is most definately not Good to Go! which may read to some people that they can now drive there car as they did before on the old injector map.
Although 80% will get the fuelling close to drive off boost somewhere, 20% decrease in injector setting does NOT mean 20% decrease at 50% IDC in terms of flow.
Take some time with an injector flow bench and you will see that injector flow rates arent linear with injector duty cycle, 550cc injectors @ 3bar @ 50%dc doesnt equal 275cc of fuel flow.
My point is that at 0-10%IDC with 20% change and correct lag time you will probably be within 4-5% of where you need to be fuelling (should be ok to drive), but change that to 'a bit of boost' and 50%IDC you may be 15% out.

Have you been tuning your car with the injector percentage table?

I havent mentioned your broken engine again, but as you mention it... do you still not understand why your pump failed?

I'm happy to suggest some points to you, even more so if you end up tuning your car and keeping it in one peice.

Rob
 

·
Registered
Joined
·
2,201 Posts
Hi Chaz,

If Rod has upped the pressure as well can you not get the car to him a bit sooner?
Personally i wouldnt drive the car on boost, in fact i would have left it to Rod to change them for the ammount of time it takes (without trying to sound like an arsehole :D )
My concern would be that you ahve perhaps changed them so that you can up the boost a little and maybe not get to Rods as soon as you say..

Cheers

Rob
 

·
Registered
Joined
·
8,804 Posts
thanks Rob, I indeed take my ignorance as only a need to learn more. I'm not satisfied with handing my car off to someone - for me, the hobby of tuning, is exactly that - tuning. Putting in parts is really not the interesting part of the game for me - any punter with a fat wallet can order up parts and stick them in.

I do have a good understanding to my pump failure, and it's clearly understood by my builder. A concatenation of things really, but mostly it boils down to running 700cc injectors on an old, stock fuel pump, pushed even further to the limit by maladjustment of the fuel pressure regulator (I saw someone turn the screw with a fuel pressure gauge nowhere in sight when I got my car, but language barriers kept me from stopping the situation, and I wasn't aware of the seriousness of mucking about with the fuel pressure at the time), having the base idle fuel pressure at unacceptably high levels, which only got worse as I increased boost. In addition, as pressure goes up, maximum flow capacity goes down. I wasn't aware of that. I tuned the maps directly, one cell at a time, using map tracer to pinpoint which cell needed adjustment. But I did have to make adjustments to the injector table which were far off the calculated values, and those adjustments compensated for the overly high fuel pressure at idle (Denso 700cc should be 62.5% but my table had them at 50.0%, otherwise the car wouldn't idle stably). None of that could have possibly helped my fuel pump.

I didn't know that the curve wouldn't shift upwards linearly. I would have caught it with the wideband when the engine is complete and tuning starts in 2-3 weeks, but you just saved me a lot of time, if not lessening the risk of going pop on the dynojet. There's a fair amount of experience that will be on the initial map, guys who have a lot of tuning experience, particularly with tweaking and tuning twin-turbo 911s as well as FD rotaries, but this is their first Skyline completely entrusted to them without Japanese tuner involvement. So any info I can input to them can only help, and even if they already know all the answers, I want to know down to the last detail what is going on, what every parameter is, why it was set that way, and how they interact with each other.

sheesh, I'm rambling. well, it's new years, it's past midnight, and I'm tanked. a toast to the R32 and good lord I hope it stays in one piece this year!
 

·
Registered
Joined
·
8,804 Posts
ER.... I thought i had itr sorted there tweenierob.. Am confused now!

Can I not just swap the inectors and adjust their rating to around 80% set the advance right and leave my fuel pressure reg as it is. Rod Bell set my fuel pressure a bit higher so as not to max out the standard injectors to be on safe side (running around 400bhp on std injectors). Surley Im just gonna end up running a bit rich but thats ok isnt it for a few weeks or so? till rod puts cams in and does a remap?

Dont want to **** things up! what should i do?!
just do everything all at once - cams, remap, and injectors. much better that way. and if you haven't changed your fuel pump, I can personally say that you would want to do that as well.
 

·
Registered
Joined
·
818 Posts
Discussion Starter · #19 ·
I know what you guys are saying its just that Rod doens't like using second hand parts on cars and mapping them in case they go bang, and rightly so he has a reputation to think of and if he started fitting any old tom dick or harrys possibly dodgy 2nd hand stuff and the car goes bang hes bound to get the odd person who will say its his fault/blame him/diss him on forums or something like that and its not worth it for his rep.

For Example, the issue i had with my STR clutch which, as it turned out in the end, was due to a slightly malformed gearbox casting. It was in and out of Rods a few times as the release bearing squeaked and the clutch pedal felt like a linear ratchet. Rod sorted it out and eventually realised it was the gearbox casting affecting the travel of the release bearing actuator one of those really weird intermittent problems thats arkward to see whats going on straight away. All fixed free of charge cos it was new part and either it was OS Gikens fault (unlikley) or it was something to do with how it was fitted or as it turned out a weird quirk.

Now imagine if It was a second hand clutch and I was (and maybe am LOL!) a bit of a t**t and started blaming Rod saying he hadnt fitted the clutch right where would we stand? Rod may suggest its the clutch at fault and charge me each time he had a look, I may insist the clutch is ok, I might go back to the guy i got the clutch off and say its dodgy, he wont care cos he sold as seen, it all gets into a right mess and im left with a dodgy clutch and me getting anyoned at Rod and everyone else. I could then bad mouth him and thats how bad reps start

Hence I would like to know how to do it myself! Anyways, I shall bear all the info in mind and get the right equipment to check fueling and fuel pressure and talk to you good people on here and sort it out!

Cheers!
 
1 - 19 of 19 Posts
Top