Piggyback ECU (or other) system advice - Toyota Nation Forum : Toyota Car and Truck Forums
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post #1 of 5 Old 02-06-2018, 09:15 AM Thread Starter
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Piggyback ECU (or other) system advice

I am looking for input regarding which piggyback or other control system to choose. I have added an HKS (Rotrex) centrifugal supercharger to my 07 V6 Rav4, and I want to put in larger injectors.

The factory ECU handles everything (timing, fuel) pretty well with stock injectors. However, injectors are maxed out as it is, and I am considering upping boost slightly, within the specs of the supercharger (stock is 5.5 PSI, and it looks like it can do up to 6.88), and I'd also like to open the exhaust a little bit. So, the main consideration is larger injectors, and as such, that will be the primary (possibly only, at the start) duty of the piggyback or other system. Depending on the injector size I choose, it might only be modulating the stock ECU during open-loop running for fuel; In any case, it needs to be able to handle fuel control (and preferably modulation of a primary injector signal) well.

Cost is a factor; I will be trying to find the lowest price on whichever unit I choose, and if I find a particularly good deal on something, that might be the deciding factor. However, my preference when investing in a thing like this is such that I could use it later on, possibly even in another vehicle, for functions exceeding those which it will be serving now. So, price, performance, and functionality are all considerations.

I have been looking at the AEM F/IC 6, the Greddy E-Manage Ultimate, and eyeing the Apexi PFC and bigger AEM systems simply because prices have been almost comparable in some cases. I'd be happy paying a bit more for added capabilities later, but I want to avoid serious issues which might be known to plague a system, especially if those issues might lead to engine/transmission damage. I am definitely open to suggestions for models other than the ones I mentioned. I have tuned a full EMS before, so I'm not worried about complexity.

Last edited by biyanpian; 02-06-2018 at 06:40 PM.
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post #2 of 5 Old 02-06-2018, 11:55 AM
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I'm surprised you're asking, with the knowledge/ability you have.

Obviously a stand alone will be by far the most versatile unit you could buy, but I'm going to assume you want to retain the stock ECU largely in part for OBDII purposes. I'm not a huge fan of piggyback myself, but then again, I haven't really done extensive ECU work on anything newer than ~1990 (megasquirted several MR2's, have my 350 in the FJ40 on MS2 with a WB, modified the ecu of a 1990 corolla).

One small step you could consider would be to simply up the size of the injectors and see how the stock ECU handles it. Older ECU's really didn't have an issue with this (the stock 4afe ecu was meant to run something like ~200 cc/min, batch fire, and I had it pushing I believe 312 cc/min.... for years it ran 250 cc/min on a 4age no problem, but the last iteration of a high compression 7age just needed more than a stock ecu). Either way, my point is consider just upping the injectors - you aren't exactly throwing 2-3x the boost at it and hoping it holds together.

If you don't already, throw an independent WB into the car to monitor

1) Frame-off "Rusto-Mod" FJ40/350/350 2) 2001 Lexus LX470 3) 2017 Prius V4

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post #3 of 5 Old 02-06-2018, 12:31 PM Thread Starter
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I'm asking mainly because I have no experience with other systems. I know that the principles are the same, but how well they have been designed, how well they function in practice, and how much they offer for the $ is what I'm asking about. Things like "This system was fine for older cars but it's hard to get it to work with modern ECUs" or "I've tuned 5 (or even 1) modern cars with this system and there weren't any huge hurdles."

Other generous and intrepid souls have experimented and shared findings as far as what the stock ECU can handle, which is quite a lot. I have confidence in their findings, so I have the numbers I need, but I'd like opinions about what to use to trim the fuel. Mostly I'm concerned about open-loop fueling and avoiding a scenario where the stock ECU thinks the injectors are at 100% duty, like pushing it hard at high RPMs. My understanding is that the stock ECU can trim for considerably larger injectors in closed-loop. If not, I don't mind modulating the signal with a controller so it can...as long as said controller is capable and reliable. I may or may not play with timing later, but for now, I will not.

Edit: Wow, you've built a 7age? That's pretty cool. My friend and I swapped a 7afe and manual transmission into his Corolla AllTrac, and he was eyeing 20-valve heads for a long time, but he decided to turbo it instead, I think mainly because of parts rarity with 'age' and flexibility with boost. It's a neat car.

Last edited by biyanpian; 02-06-2018 at 12:39 PM.
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post #4 of 5 Old 02-07-2018, 12:16 PM
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The downside of asking a forum, or multiple forums, what their opinion is on something like a piggyback - is that unless they themselves are proficient at that piggyback in the same type of car with similar modifications, it's all up in the air. For instance - there's a local shop that HATES Megasquirt - they claim it takes too much time to figure out. They suggest other options (primarily because that's what their dyno techs use) - but then you get a DIY'er like me in the discussion and Megasquirt is a great option (not for OBD2 cars - well, maybe with MS3 but I don't have experience with that).

As far as the stock ECU goes - it's not like you're going to reprogram it what injectors it has. It's programmed with a certain expectation of what the AFR's, fuel req, and the volumetric efficiency is - with algorithms that change the supplied fuel based on sensor input. If you throw more air/boost at it one of the sensors will most likely pick that up (map, air flow) and the O2 will sense a lean condition - but if throw larger injectors in, the O2 sensor won't really notice a huge issue. The static values in the ECU don't change when larger injectors are thrown in.

Yes - I built a 7age using a 7a block, oil pans, crank, rods - with late smallport (10.3:1) pistons, a smallport head, early bigport cams, AEM adjustable gears. It was like having a strong smallport 4age. Noticably slower than the 5sfe/s54 swapped first gen MR2 I built which was also just a hair slower than the smallport 4agze/C52/Megasquirt swapped MR2 I built. I had a high mileage stock, manual, AE95 (corolla alltrac) and it was dirt slow.... my wifes old Prius C could walk away from it without trying getting on the freeway.

1) Frame-off "Rusto-Mod" FJ40/350/350 2) 2001 Lexus LX470 3) 2017 Prius V4
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post #5 of 5 Old 02-09-2018, 05:10 PM
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For best value in bang-for-buck, I'd suggest a Megasquirt in T or interceptor configuration. You get a fully programmable standalone EFI system for $300.

1. disconnect injector & ignition outputs from stock ECU and install dummy-loads in their place (ballast resistors). For all intents and purposes, factory ECU still thinks it's controlling everything.

2. split sensor-inputs with Megasquirt and use it as standalone EFI system with fully-programmable fuel & ignition-maps. Use closed-loop under partial-throttle modes and stock ECU will be happy. WOT is open-loop, so program in whatever you want for best performance.

Now I've only done this up to an OBD-1 car (Porsche 968), but it worked perfectly. This car used a fairly standard 60-2 crank trigger wheel that MS supported right out of box.
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