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How far to I crank the spring tension up - AFM question

Discussion pertaining to positive pressure E28s.
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photo500
Posts: 86
Joined: May 16, 2007 12:25 AM
Location: Perth, Western Australia

How far to I crank the spring tension up - AFM question

Post by photo500 »

Hi,
I will be using the standard AFM in my turbo build and
I was wondering how much to (or if I need to) increase the spring tension to compensate for bigger injectors (32lb)and the extra air flow requirements of the turbo. I currently run a piggyback fuel computer on which I can adjust the fuelling at 128 points across the rev range, because of that I will not be running a RRFPR to increase fuel delivery. Do you guys think
i will need to adjust the spring tension if I have the ability to alter my fuel map?

Please - I wont be changing my mind on using the standard AFM. :argue:

I only want to know what has actually been done and that actually works from people who have done it in regards to spring tension changes. ;)

Thanks heaps guys!
Jeremy
Beamter
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Post by Jeremy »

Well, I never used a piggyback, but I seem to remember 15-20 clicks tighter being the starting point and then moving on from there. That was just so the car would start and idle without stalling, I know I went tighter from there as I was tuning. If you don't have WBO2, getting this right will difficult to impossible for you.

Jeremy
photo500
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Joined: May 16, 2007 12:25 AM
Location: Perth, Western Australia

Post by photo500 »

Ok so 15-20 clicks tighter? I have found that even 1 or 2 clicks can make a huge difference. I'm pretty sure that tightening it that much would make mine undrivable. I could understand it being 15-20 clicks from a slack spring though? I have a WB O2 unit on order so i should be able to sort it out rough enough to get it to a proper dyno tuner.
Jeremy
Beamter
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Post by Jeremy »

Going from 19lbs injectors to 32lb injectors is a huge difference in required injector PW for the same result. I can pretty much guarantee that the car will not start and run if you swap the injectors and leave the AFM spring tension where it is right now. It may catch and try to run, but it'll flood and stall. It was 15 clicks from the starting point.

YMMV.

Jeremy
Bill in MN
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Post by Bill in MN »

I went at least 20 before it would run properly.
Jays535is
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Post by Jays535is »

24lb injectors
3-4 clicks with the stock O2 unplugged & using a wideband.
turbodan
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Post by turbodan »

I just change my required fuel value for bigger injectors. Sure beats the days of jacking up spring tenson and drilling holes in my AFM flapper to run larger injectors.

Just another way standalone is far superior to motronic...

With a piggyback I have no idea if you can take as much fuel out as you'll need to at low loads with 32lb injectors. Thats a lot of extra fuel. I guess you'll find out.
photo500
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Location: Perth, Western Australia

Post by photo500 »

I see, ok I think I understand now. I didnt realise that it was THAT much extra fuel. With the 1-2 clicks I was referring to the motor as it is now - unturboed. I should have been more clear on that. The piggyback will adjust at 128 points over the range and at each of those points its possible to alter the voltage from 0-5v so in theory I should be able to adjust it enough. But thats only in theory. I have picked up a fully ported and polished b35 head which is currently being machined so once thats back I can make a start on the engine. - I'm getting excited already!
///ARINUTS...
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Post by ///ARINUTS... »

When you install larger injectors, you need to trick the ECU to thinking their is less air , so that it pulses the injectors to deliver less fuel, because the new injectors flow more, at that point the injectors will be delivering the same amount of fuel as it was at the original AFM setting with the stock injectors.

make sense?

this doesn't matter if the engine has been turbocharged or not. even if you use a piggy back, it essentially does the same thing, maybe a little better because it's a little easier.
Jeremy
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Re: How far to I crank the spring tension up - AFM question

Post by Jeremy »

photo500 wrote:because of that I will not be running a RRFPR to increase fuel delivery.
I just noticed this . . . how much boost do you plan to run and what are your power goals? Without a rising rate FPR, you may find yourself at duty cycle limits very quickly.

Jeremy
///ARINUTS...
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Re: How far to I crank the spring tension up - AFM question

Post by ///ARINUTS... »

Jeremy wrote:
photo500 wrote:because of that I will not be running a RRFPR to increase fuel delivery.
I just noticed this . . . how much boost do you plan to run and what are your power goals? Without a rising rate FPR, you may find yourself at duty cycle limits very quickly.

Jeremy

you almost have to run a RRFPR aka FMU with the factory ECU
Jeremy
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Post by Jeremy »

Well, if he runs light boost (say, 6 psi non-intercooled), he could probably get by with the piggyback. However, I notice that he says the piggyback adjusts fuel delivery based on rpm only. 4k rpm and 10psi has very different requirements than 4k and 3 psi or vacuum. Even it connects to the WOT and only works under that situation, you still have part throttle to worry about.

The more I think about this, the more I'd advise you to dump the piggyback and get a RRFPR or just get a full standalone to start with.

Jeremy
photo500
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Location: Perth, Western Australia

Post by photo500 »

I'm hoping to run about 10psi. No more than that for a good while anyway. I understand what you guys are saying about the piggyback going on rpm. Its actually altering the voltage based on the position of the AFM flap. Its true that if its 75% open at 3000rpm its gong to give the same voltage if its 75% open at 5000rpm. I think I just answered my own question - I need a RRFPR don't I ?!
M. Holtmeier
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Post by M. Holtmeier »

The only way a piggy back could work for you with a boosted application is if it deleted the afm and converted your engine management to speed density, where the piggyback used a manifold pressure input.
Save yourself the headache and use a RRFPR.
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