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99 RSK single turbo engine management


RobMinhas

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Hey everyone,

I've got a 99 B4 RSK and I'm wanting to do a single turbo swap using a V6 or V7 STi turbo setup but I'm at a bit of a loss with my engine management setup. My goal is 275-300whp.

EcuTek is almost completely out of the question, no local tuning(I'm in western Canada) and I don't care for mailing my ecu everytime I want a different or modified map.

From my reading I noticed that for most swaps guys use V5/v6 wrx ecus when doing single turbo conversions, seems like most guys have rev C cars and can use the WRX ecus since they both have 9:1 compression ratios. Unfortunately I have an 8.5:1 so it seems like that's not gonna work for me.

Has anyone successfully used a WRX or STi(CR 8:1) ecu on a single turbo conversion? I've looked in to standalones and piggy backs but nothing beats a factory ECU in my opinion.

If anyone has any advice or guidance please share, very new to Subarus so all info is appreciated.

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For our JDM models, the version 5/6 WRX is 8.5:1CR, same as the rev A/B legacy. Rev C legacy steps up to 9.0:1 which matches the JDM forester CR.

To use the version 5/6 STI ECU at 8.0:1, you need to fit thicker head gaskets to lower compression or use an STI engine.

Either turbo setup will work fine on either ECU, but you may need aftermarket boost control as the ECU WGDC will be off.

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Thanks for the response Rosssub, I was under the impression JDM 5/6 WRXs were 9:1, that saves me quite a bit of hassle as I can find one of those easily. Do you know if all version 5/6WRXs are 8.5:1?

My backup option was to use an STi engine but it was hard to justify when my motor was healthy, nice to know I can fit a thicker head gasket to lower it, will keep that in mind in the future.

Aftermarket boost controlling I was expecting as well, any recommendations on ways to do that? Any other mods you'd recommend doing while I'm converting? VF39 is the turbo I'm going for right now.

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All JDM V5/6 WRX are 8.5:1. A decent EBC is the best way to go, but MBC's work just fine. I'm currently using a cheapo MBC with my V6 STI/VF36 in my GTB:

MBC_install_004.jpg

Maybe an aftermarket under manifold silicone intake pipe, while everything is apart.

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I've got a GFB MBC laying around from an old project that would be great for that.

Sorry to keep picking your brain but I've got some more questions about the EMS situation. I'm very new to Subarus so I'm still learning some of the basics.

The V5/v6 WRX ecu is set up for the factory turbo, if the boost is increased can the ecu adjust for it? Is there a certain amount it can adjust for? With my power goals, I would need 18lbs or 1.25 bar of boost on a VF34/Vf39 and that is quite a bit of air. I'd like to stay away from piggy backs and standalones(I really like the reliability of a factory ecu) but if I have to I will.

I found a local selling a Link G4 plug n play but I don't know if I have a tuner I trust to tune it for me.

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The ECU will adjust to suit, but not that much. I think you'll find V5/6 non STI limits somewhere around 14.7psi. I'm running a semi closed deck with version 6 STI ECU at 16psi (1.1bar). To go any higher long term safely without tuning I'd be going on a dyno to check AFR, IAT and knock.

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I think that's not what I'm looking for. Checking afr and knock is something I'd check anyway but the ecu can't adjust for the power I want to make up to my standards.

I did recently reach out to a tuning shop and convinced them to buy an ECUTEK license so I think I will go down that road and copy your build ffor turbo choice while keeping my goal of 300whp.

Anything you would do differently in your build knowing what you know now?

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I wouldn't change a thing as yet, but my build is a long way from finished.

I've never looked into the ECUTEK tunes, but would guess the limiting factors will be the V5/6 MAF, MAP and 440cc injectors. Then your current engines mechanical capabilities with an open deck block, cast alloy pistons and weaker connecting rods.

I would suggest talking to your tuner regarding all of the above. Also check out the dyno leader board threads on here, showing others results with links to garage threads so you can see their set ups.

http://clubsub.org.nz/forum/showthread.php?25354-Dyno-Leaderboard-Version-III&highlight=dyno+leaderboard

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All you really need is an sti vf, 2.5"- tb exhaust, fuel pump, tuneable ecu or ecutek and a tune to get your 300hp. A fmic helps a lot also. 20psi thro any vf will net you 200-230wkw but basically once your injectors tap out youre making as much as you should be from the tiny vf, the weak rods and block as per above. Stick to the factory airbox even if you dont need the maf.

Any tuner worth their salt can tune that g4 if its affordable grab it theyre an awesome piece of kit. Some of the best on board boost control and so much functionality/flexibility. Better chance of a tuner achieving a good tune with the g4 over ecutek.

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@Rossub I believe you're correct with the limiting factors. I'm talking to to tuner right now.

@evowrx The G4 is $1700 plus tuning vs $1050 for the ecutek license and a protune. The G4 will be double the cost at least after tuning which is why I'm leaning over to the EcuTek.

What I'm considering right now is a VF34 setup and see where I'll sit with the factory injectors, if I can hit 300whp that's awesome, if not I'll get as close as I can get safely. I don't mind building another motor(similar to what you've done Rossub) since thats something I'm more familiar with. There's a v6 long block sitting in a shop not far from me I've been eyeballing.

Will do more research and see what I'll need to do. Fuel pump sounds necessary, injectors probably too. Would prefer to keep a TMIC though but that's not something I"m super attached to.

Thanks for the help guys.

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