Big turbo and CX-7 automatic transmission

[dlheman]

Hello,

I am a new member here, but a long time CX-7 owner. Seeing so many here are tuning their CX-7, I wonder if someone can help me understand CX-7 a little better.

So my question is; is there some kind of torque limiter from the CX-7 automatic transmission governing the engine from making power?

About a year or two ago a friend of mine decided to upgrade his FWD automatic CX-7's turbo to Corksport turbo. I think it is CST4 or something, and it has all the necessary parts by Corksport to run this turbo. The car is tuned using Ecutek through remote tuning.

But when I looked at his datalog and I drove his car, I cannot say I am blown away by it. For sure it is nowhere near what I would imagine it to be if I compare it to Corksport CST4 dyno is suggesting. Oh, and also there is this really strange wavy boost behavior and I can feel it during log pull. Looking at the log it looks like an oscillation and I guess this is what made me think is as if something is not allowing it to make the boost properly.

Assuming the tuner did everything he could, I wonder if the automatic transmission is holding it back? Is there some kind of transmission torque limiter which is not allowing the engine to be free to make power?


I truly appreciate any inputs about this matter.


Thanks in advance!

[mituc]

We have an US Spec automatic transmission CX7 in the Romanian community, I suggested the owner to get a BNR S3 and then I tuned it. It's still on factory intake and factory exhaust (including factory cats), but it makes decent power eating up like 270-280g/s of air peak. I did not want to push his as much as mine (320-330g/s or air, also with factory cats) but it's still awesome to drive with about 80-90bhp more compared to stock.

Most probably the EcuTek guys put him some sort of w standard map, probably that one which they also put on 100% stock 2.3DISI-T engines and the cars blow in a pretty large percent after that.

[dlheman]

Thank you for your reply mituc!

Just for my information is there any particular reason why BNR S3? I am not too familiar with turbo options is good for stock block.

And if you don’t mind can you tell me some reasons of why is his turbo curve is wavy? We could not solve it at all and its rather strange and a big let down.

Sorry for the many questions !

[mituc]

The reason i usability. CX7 is a big boat. Almost 2 metric tons. That's the reason why with automatic transmission it came with a tiny turbo that makes peak torque at 2500rpm and peak power at only 5000, because with a larger turbo on that automatic transmission such a large car would be a nightmare to drive.

The version 4 of the S3 is a baby GTX2867R gen2, so it will spool decently low and can make towards or more 450bhp (flywheel) with the right mods. Therefore going big turbo with the right turbo is the key to not make the CX7 worse at low engine rpms or in daily traffic.
I did not have the occasion to drive that AT CX7 I tuned remotely even though looking at the logs it seems to be as it should, but on my CX7 the gen2 GTX spools faster and responds better than the stock turbo (on the manual transmission we have same turbo as the 3/6 speed3, the K04-882).

I also tuned (and drove) a CST5 CX7 and that was BAD! I suggested the owner to get a GTX2867 gen2 and he got back to me very proud of himself that he's got a CST5 for a lot cheaper and capable to produce more peak power.
With that turbo boost came in at 3600rpm the earliest. Peak power was decent (the car had other problems so we never hit 500), we also tuned that car with WMI, but the normal driving got a lot worse with that turbo and let's be honest, you don't really track a CX7, so usability is still key.

If any ATP kits with a gen2 GTX2867R are will available (or if the G25-550 became available) I would get one of those and slap it on to a CX7. The version 4 of the BNR S3 is a good contender.

[dlheman]

Thank you for the feedback!

Yes, and I couldn’t agree more regarding the kind of powerband to suit this automatic SUV. In fact that nice low-mid responses out of the std turbo is desirable.

Well then, to recap:
1. There should be no problem in running a bigger turbo with the automatic transmission - within reason of course.

2. BNR S3 is a good budget turbo for AT CX-7.

3. GTX2867R gen 2 is a good premium turbo for AT CX-7.

One last question please. Do you have any thoughts about the corksport intake manifold? What interest me is their claim of maximum 2% imbalance flow across all cylinders, while oem intake manifold can get up to 21% imbalance. I think that is a good part even if its on standard turbo just to make the engine cylinder head to breathe more efficiently, what do you think?

[mituc]

The intake manifold imbalance is not a problem. The exhaust manifold imbalance is the greatest enemy of these engines in addition to the heat radiating from the turbo to the engine block right where cylinder 3 is. Get the exhaust manifold first, keep the intake manifold for now, you will be fine. I'm making well past 500 with the factory IM (with the VTCS deleted, ofc, with VTCS on I could not go past like 460-470 crank HP).

[mituc]

Also just to clarify a few things: everybody talks about the intake manifold imbalance and then merges this information together with the cylinder 3 ZZBs. Actually the imbalance comes from the fact that cylinder 4 receives the least amount of air, and cylinder 2 (not 3!!!) the largest amount, by just a bit compared to #3. Cylinder 1 is about in the middle of #3 and #4 in terms of flow, #4 receiving the smallest amount because of the air flow direction in the manifold.

The biggest problem with these engines when pushed with stock manifolds (I blew an engine at 36PSI/525 bhp - which is what I call "pushing", and that same engine was making 510bhp at 32PSI, so 4PSI of boost for only 15bhp instead of like 40-50) is the intersection of exhaust pulses of cylinder 2 and 3. the firing order is 1 3 4 2, and the exhaust pulses or #2 and #3 come into conflict and then #3 also meets that harmonic damper thing in the exhaust manifold which is right after a tight corner of the #3 runner.

Then cylinder 3 gets a ton of radiant heat from the hot side of the turbo making things even worse. A lot worse actually. That's why #3 and #2 are the first cylinders to either crack ringlands or seize in the bore and bend or throw rods.

So... yeah, a lot of talking. Long story short - get the exhaust manifold first if you really feel like spending the money, and also install a piece of heatshield (metal + foam) on the block between the turbo and engine.

[dlheman]

Thank you very much for your input, and I have to say I never heard about turbo manifold being the worse of the two, but I knew the turbo manifold is actually unequal. Sounds like the problem is similar to Subaru WRX STI 2.5L.

Having said that, my car does have CP-E turbo manifold since 2012. And I did fabricated a heat shield for it because not having it is incredibly suicidal for BAT when using TMIC. And when having FMIC, the heat travels to the front of the engine and that absolutely ruins the coolant tempt. It also basically grilled the o-ring of the valve cover facing the turbo manifold.

2AF5C31B-1FE2-414A-8F3F-BDC3560584D8.jpeg (95.14 KiB) Viewed 3762 times

By just covering the turbo manifold the coolant tempt improved dramatically. I still use the engine cover too. But now you made me want to think about shielding below the turbo manifold.

My car is basically tuned with Ecutek for stage 2, with FMIC+ducting, CP-E turbo manifold and Aquamist HFS4 v3 (cooling purpose, not tune for it). I just thought well if the CS IM does bring down the imbalance to just 2%, then surely that can’t be a bad thing to my engine.

And that’s why I figured if I do CS manifold then why not upgrade the turbo (as you know one thing always lead to another).