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Leaning out?? 

 

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 Post subject: Leaning out??
Posted: Sat Jun 24, 2006 4:16 pm 
Stock as a Rock
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Age: 32

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Joined: 27th Jun 2005

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Ride: EF XR8 5spd

Location: Newcastle
NSW, Australia

Had my car back together for a while know (heads, inlet, cam change etc)
still running 19lb injectors, i have 24lb injectors but waiting on new clips to arrive from USA. Anyway car is running great no dramas at all, have not fitted adjustable fuel pressure reg yet , should i be limiting my revs to avoid lean out up high??

 

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EF XR8 5spd: 302ci /178rwkw

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Posted: Tue Jun 27, 2006 3:41 pm 
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Age: 43

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Joined: 19th Mar 2005

Ride: xlsv8ute

Location: mundulla
SA, Australia

Did you have your eec remapped or changed?I have the same set up on au111 (most parts standard except cam rr etc). The car sounded nice and lumpy but really ran like s**t, too rich and timing all over place. I really think its a waste of money & time for bigger injectors for that set up unless you have twin turbo or supercharger. How do you know it is leaning out? The info i got off this site and what ive read about standard eec handling modified engines with larger cams on this site is somewhat way off the mark! Mate do your homework and speek to performance specailist before ending up with a s**t running car and more money to spend to correct it. Sorry to sound a bit sceptical, too many people on this site cranking there own handle without much idea.

 

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Posted: Tue Jun 27, 2006 5:57 pm 
Getting Side Ways
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Location: Noble Park
VIC, Australia

hey mate, i have a very similar setup to urs, except edelbrock manifold and 2020 cam. just make sure ur timing is right and maybe get it on a dyno to check air-fuel ratio. u can put the 24's in as long as u have a matchin MAF calibrated to the 24's.
i still have the 19's & stock maf and it pulls well, best of 186rwkw, so it shows the 19's have a bit in em. but 24's would be a worthwill idea as u have em.
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Posted: Tue Jun 27, 2006 9:17 pm 
Stock as a Rock
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Age: 32

Posts: 169

Joined: 27th Jun 2005

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Ride: EF XR8 5spd

Location: Newcastle
NSW, Australia

Thanks for the replies, the car is running fine and pulling hard , ecu is standard and i have not had it dynoed yet to check air fuel ratio, as i was waiting till i change the injectors and maf for a final hp reading, no reason to suspect leaning out just thought i would ask for your opinions.

 

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EF XR8 5spd: 302ci /178rwkw

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Posted: Wed Jun 28, 2006 12:27 am 
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Ride: 351 Vogue,XH 5.0,'17 5.0 Stang

Location: Perth
WA, Australia

Kato,

You can work it out yourself with the following formula;

HP=(Cyls x Inj size x Duty Cycle)/ BSFC

Where Cyls = number of them
Inj size = lb/hr
Duty cycle = % (eg .8 = 80%)
BSFC = Brake Specific Fuel Consumption (Default NA = 0.5)

Example; (8 x 19lb/hr x .85)/ 0.5 = 258.4hp
Hence a good safety margin by the factory rating of 225hp for the 5.0L

You can rearrange this formula to achieve this;

Inj Size = [(HP x BSFC)/ Cyls]/Duty Cycle

Example; [(350 x 0.5)/8]/.85 = 25.73lb/hr

Now you may think that these figures are low but, the reasoning is sound.
Operating injectors at over 85% duty cycle shortens their life dramatically. Which is why the factory specifies 24lb injectors much earlier in the piece than what you can get away with.
The next problem occurs when pushing your engine past it's maximum power level. This may occur when trying to achieve a certain speed. Generally at max power an engines BSFC is about as good as it's going to get, after this your power will drop off and the BSFC will go up. This means more fuel will be required and for this reason your injectors should be sized at around 80 to 85% so they have a bit up their sleeve.
Fuel pressure is another way around the problem but only to a certain degree. Injectors don't really like running at higher than their rated pressure and this can also lead to failure....dribbling injectors can result if the pressure is too high and the ECU can have difficulty controlling them properly. This has obvious engine life consequences due to washing down cylinder bores with excess fuel.
Your current mods shouldn't warrant a change to 24's unless you spend all your time in the upper end of the rev range. Still, you should get on the dyno and have the operator check injector duty cycle so you can make an educated guess at the very least.

Pete.
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Posted: Thu Jun 29, 2006 11:37 pm 
Getting Side Ways
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Location: Sydney
NSW, Australia

Fuel pump may be getting a bit lazy !

 

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