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Old 02-12-2010, 09:29 PM   #1
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Default Whats wrong with the Link piggy back?

I recently bought a car that has the FMII link piggy back system on it, and I am wondering why does everyone say not to run more than 9 psi with it? I did search but only really found threads with people selling them. It seems to me that it has the capablity to fuel more boost than just nine pounds.
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Old 02-13-2010, 03:04 AM   #2
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I ran my car at 12psi with one for 5 or 6 years, making 220ish at the wheels. Someone else ran a 10AE at 15-18 psi with one making a lot more than that. The 9 psi recommendation from FM came primarily from the fact that lots of people were breaking rods on NBs, so they were recommending 9 psi on stock rods with any/all fueling solutions.

The main drawbacks to the piggyback are that it has no wideband autotuning capability and that it's working in conjunction with a stock ECU. The stock ECU is MAF-based, the piggy is MAP-based, so it's difficult to synchronize them. This means that you need to leave wide safety margins to prevent engine damage, which costs you potential power. I tuned mine on a dyno with a wideband, and ran it on 94 octane.

It's a lot better than a fuel pressure regulator, and allows higher power numbers (due to more fuel) than a fuel injector pulse lengthener like a PowerCard, but it cost as much as a full ECU and is inferior in tunability (although drivability can be better out of boost because you're just running off the stock computer). No datalogging, no autotuning, no wideband, all it did was retard timing, run a boost control solenoid, and inject fuel through the aux injectors.

The 4-injector manifolds worked better than the earlier 2-injector-in-the-throttle-body setups, although there were some cases of the aux fuel rail mounting tabs breaking. The O2 sensor clamp was a must-have. If the power went over about 250 at the wheels, you'd get a fuel cut from the stock ECU and a CEL due to an overvoltage on the MAF. Since the piggy wouldn't cut fuel at the same time, it could go dangerously lean in that situation.

If you want a plug-in-and-forget-it solution for up to low-200s rwhp, it can work pretty well. If you want to do a lot of tweaking and tuning, it's fairly easy to outgrow it, and that's why I ultimately switched to a full ECU.

--Ian
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Old 02-13-2010, 11:49 AM   #3
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Thanks alot for the reply, that is exactly the answer I was looking for. I was hoping the nine pound limit wasn't due to it being unreliable. It seems to do it's job pretty well, but I haven't tried anything higher than ten pounds. I do have a wideband and am hoping to get in on the electronic det cans that another member is making soon. Then maybe I will try 13 or 14 psi. I do plan on getting a full ecu but I am having trouble deciding which to go with. From the point of view of never using one, they all seem a little over my head.
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Old 02-13-2010, 02:27 PM   #4
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it's old, slow, hard to use/tune, and just plain sucks.
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Old 02-14-2010, 12:51 AM   #5
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I do wish I didn't have to select each cell one at the time to change it. It does suck. lol.
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Old 02-14-2010, 02:54 AM   #6
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Quote:
Originally Posted by K20 Mini View Post
I do wish I didn't have to select each cell one at the time to change it. It does suck. lol.
Yeah, the UI is less convenient to tune. What I used to do at the dyno was to keep a notebook, write down the entire map before I started, and then keeps notes on what changes I made. Burn it when I was done, and write down the new map in the notebook too.

Consider this, though: since you can really only tune the piggyback on the dyno, you're not doing this hand copying thing very often. It's also pretty convenient to have the keypad in the glovebox so that you can tweak simple parameters (boost control settings, say) any time you like, without having to dig out a laptop.

--Ian
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Old 02-14-2010, 02:41 PM   #7
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I blanked out all the fields on a copy of the chart that flyin miata has on there site, so i can write the map down in a grid. It is definitly time consuming, but like you said you aren't going to have to do it alot. At least I hope not.
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Old 02-14-2010, 04:54 PM   #8
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ha. i can compare my offline tune to my loaded tune.
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Old 03-05-2010, 05:04 PM   #9
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Recommendation: If you've pulled the manifold support brace, put it back on. I've gone trhough so many sets of fuel rail tabs I cannot explain it in mere words.

Eventually, you'll want to control everything from one place.

Also, if you lose power to the piggy, everthing seems to go to pass through - half fuel, advanced spark, bent rods.
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Old 03-24-2010, 03:25 PM   #10
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One additional note on the "9 psi" limit - in Maximum Boost, Corky recommends a max of 9 psi for any setup utilizing auxiliary injectors in the intake manifold for fueling. I'm not sure of the theory, math, or experience that led to that conclusion, but I trust his opinion.

I picked up a Link Piggy for $400 and sold the keypad for $200, so I have $200 invested in a low budget engine management/injector/o2 clamp setup for my low budget NB setup. The Link Piggy won't get you a lot of high 5s from the Miata community, but if you can get one cheap enough it is a decent platform that is better than band aids for a <9psi setup.
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Old 03-24-2010, 04:27 PM   #11
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Depending on the use, it can be alright. I ran one for years (and have the whole set up if someone wants to buy it). What got to me was not having full control over everything, or running several different computers for different tasks.

That said, it was more simple, kinda always just worked. I had more mechanical issues with the piggy injectors than anything else. If there was a timing retard on knock, I'd probably still be using it. However that alone made it worth while going to a megasquirt. I do miss the OEM idle though.
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Old 03-28-2010, 12:37 AM   #12
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Well, I do like the link, the megasquirt is such a deal I went ahead and got one. So my piggy back setup will be for sale as soon as I get room in my shop to swap out intake manifolds. I did have the bolts (it's bolted?!) fall out of the fuel rail tabs. I am fortunate to have not had a fire, as I was doing a little freeway "tuning" along side a friend of mine when it let go. I will say that with four open holes POURING fuel out a Walboro 255lpr pump will still run the motor just fine, it will also purge about six gallons of gas at the same time. Needless to say I went ahead and welded the tabs on. Why would they have not already been welded? Seems kinda silly.
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Old 03-30-2010, 03:18 PM   #13
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ONE

TWO

THREE

FOUR

FIVE


The solution that worked.


_____________
Edit:
I'm pretty positive the issue is removal of the intake manifold brace. There's been some evidence of a correlation here, and people have hinted at it, but those who know... won't talk. :-) I feel that with the brace on - which just HAPPENS to be incompatible with a certain company's oil cooler solution - you won't see this, or won't see it as often. I'd weld on the tabs as I did in the final attempt, and call it good.

What was interesting was the better tabs just caused the next link in the chain to break.

Last edited by AbeFM; 03-30-2010 at 09:26 PM.
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Old 03-30-2010, 03:29 PM   #14
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Abe, you live a charmed life. I don't know of anybody who has completely bathed their entire engine compartment in gasoline as many times as you have and hasn't had a fire.
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Old 03-30-2010, 09:04 PM   #15
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Sorry, but after reading all that I had to laugh. I do have to admire your ambition to stick to it. Its only going to happen to me the once. I do not believe that I have your luck. Although based on what I've seen and your experiences there is definitely stunning lack of burned to a crisp Miatas. If that would have happened in any one of my VW's I would have had a video and condolences. LOL.
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Old 03-30-2010, 09:26 PM   #16
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See my edit in earlier post.
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Old 03-30-2010, 10:17 PM   #17
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In contrast, mine only cracked once, after 6 years and 50K miles. Even after that, it wasn't leaking, and I didn't figure out it was cracked until I took it off.

I suspect that a fuel leak on a Miata (while obviously something to be avoided) is a whole lot less likely to burst into flames
than one on a VW, because the aux rail is a long way from anything really hot.

--Ian
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Old 03-31-2010, 01:53 PM   #18
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I've had the car stall for want of fuel, and had the people at the finish line of the autocross get VERY nervous (three of my tires were getting wet) and MAKE me shut it off. :-P And I think I burned a set of pistons once from that, but it could have been poor altitude correction (10,000').

You had it on an NB? You had it with or without the brace?
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Old 03-31-2010, 02:30 PM   #19
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Best I can tell, my car has always had the manifold brace on. Nothing actually broke on mine, the little screws that held the tabs on backed out. I just welded them back on. I haven't had any problems since, but the car doesn't get driven much.
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Old 03-31-2010, 02:47 PM   #20
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I've had my tabs break once about 2 years ago. I made to plates out of steel and haven't had any other issues with it yet. But after reading Abes adventures and what not, I think I am going to reinspect and or change that part of my setup. Especially since I don't even use it.
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