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tunning idle with 750's

Old 12-12-2007, 11:26 PM
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Default tunning idle with 750's

Just got my rc 750s today.. Car will be N/A till this weekend hopefully, well it idles pretty shitty.. just wondering if someone has any tips on tunning the idle so it runs alittle better.. Or is this close to impossible with this big of injectors??

O another question.. Car seems to hesitate for just a split second when i floor it?? Any clues?? Only this i changed was my map and my injectors..

thanks..
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Old 12-13-2007, 07:58 AM
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Default Re: tunning idle with 750's

Big injectors want more fuel beyond the recurve, because they have heavier internals and take longer to open. If you have high-Z RCs then it's just a little bit. If you have low-Z RCs I'm surprised they idle on just a recurve. Shoot for stoich on the wideband.

As for the hesitation... yeah, you haven't tuned anything. What were you expecting, the car sits right up and runs 9's?
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Old 12-13-2007, 07:42 PM
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Default Re: tunning idle with 750's

Originally Posted by Joseph Davis
Big injectors want more fuel beyond the recurve, because they have heavier internals and take longer to open. If you have high-Z RCs then it's just a little bit. If you have low-Z RCs I'm surprised they idle on just a recurve. Shoot for stoich on the wideband.

As for the hesitation... yeah, you haven't tuned anything. What were you expecting, the car sits right up and runs 9's?

sounds good bro. not sure which rc's they are... other then i know there saturated.

I believe these are the specs on them, i cant find 750s on rc's site but here are the specs for 650s

Resistance:
12.5 Ohms @ 68 F

Voltage:
8-15 Volts, nominal 13.5 Volts

Amperage:
1.0 Amps


anyways.. i was just curious because ive never had a basemap i made run this shitty before i fine tuned it.. well... ive never had this big of injectors either so... i guess thats my problem lol..

hey bro quick question.. I think i know what the problem is.. It hesitates for a split second only when i quickly jab the throttle down to wot. I cant remember where in crome i can adjust how much extra fuel initially squirts for that split second when u jab your foot to the floor. Im guessing thats my problem.
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Old 12-13-2007, 09:04 PM
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Default Re: tunning idle with 750's

Those are high-Z injectors. Congrats, they run sweet.

I suggest you latch onto the whole map - not just the idle area - and add fuel until it idles right.

You really need a wideband, it's easy to mess something up tuning blind like that.
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Old 12-13-2007, 10:01 PM
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Default Re: tunning idle with 750's

Originally Posted by Joseph Davis
Those are high-Z injectors. Congrats, they run sweet.

I suggest you latch onto the whole map - not just the idle area - and add fuel until it idles right.

You really need a wideband, it's easy to mess something up tuning blind like that.
i have a wideband. I just dont have the sensor in because i wasnt gonna put it in until the turbo was on. But your right. So im just gonna put it on now to ---- with it alittle while its still n/a
thanks bro.
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Old 12-13-2007, 10:20 PM
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Default Re: tunning idle with 750's



Do so pls, you can tune the NA portion of your maps pretty close before the turbo goes on... that really saves you a lot of time later not trying to dick around in and out of the throttle with a street tune.

You'll find fuel trims under the drop down menu that has boost tools, it's been a hot minute since I used Crome and can't remember the exact tab. There's probably something under the advanced tables, ALT+L, check there too.

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Old 12-19-2007, 10:04 PM
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Default Re: tunning idle with 750's

Originally Posted by Joseph Davis
Those are high-Z injectors. Congrats, they run sweet.

I suggest you latch onto the whole map - not just the idle area - and add fuel until it idles right.

You really need a wideband, it's easy to mess something up tuning blind like that.
What don't you like about low resistance injectors, JD?
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Old 12-20-2007, 12:23 PM
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Default Re: tunning idle with 750's

They are harder for n00bs to tune, especially the bigger ones. Precision aren't so bad, but a n00b + some larger low-Z RCs is a combo that = not believing me when I say to really add in a lot of fuel.
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Old 12-21-2007, 12:44 AM
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Default Re: tunning idle with 750's

First car I did was an NA z6 and used Siemens 780cc's - I recurved it in uberdata, then added something like 10-15% to the whole map (based on wideband readings of ~16:1 in some spots). After a little adjustments to the idle portion of the map, it was idling absolutely perfect.

Like JD said, bigger injectors open slower, so they end up shooting less gas overall. And since each pulse is smaller just due to size, that tiny delay has a big impact on idle.
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Old 12-21-2007, 10:52 AM
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Default Re: tunning idle with 750's

Originally Posted by HiProfile
First car I did was an NA z6 and used Siemens 780cc's - I recurved it in uberdata, then added something like 10-15% to the whole map (based on wideband readings of ~16:1 in some spots). After a little adjustments to the idle portion of the map, it was idling absolutely perfect.

Like JD said, bigger injectors open slower, so they end up shooting less gas overall. And since each pulse is smaller just due to size, that tiny delay has a big impact on idle.
Yeah, I understand that a larger injector will behave differently, especially at low duty cycle, and that there will most likely be a bit of lag as they open and close due to the added mass. I just purchased some bosch 680's low imps, they will be the largest injector size that i've tuned to date, so I want to be prepared for them. I can't find much info on them, but they're sold by FAST, ~3 ohms. Thats the shitty part about buying injectors that aren't widely used, I won't have any known info like injector battery offsets to start with, but i have some ideas on how to determine that. I plan on starting with a basemap VERY generous with fueling. Learning is funn!!
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