.....asking for a friend with a prelude (h22 turbo). His old turbo housing cracked, and the new housing looks bigger (swapped in his internals??). Now, according to datalog, his MAP sensor detects 10psi, so it is cutting his fuel. This appears to make sense to us anyway.

Is the bigger housing increasing the boost level? His new turbo housing is on top in the picture.

 

No. it is not increasing the boost pressure level. What's happening is that the turbine is allowing more exhaust energy (if its a larger volute than your original) and more power is being made in the higher rpm range. It "shifts" the power curve to the higher portion of the rpm band. ON THE SAME BOOST PRESSURE LEVEL.

But, no, if they are the same size A/R without a change in exhaust wheel, it will not make a turbo go from 10psi -11psi, unless your gate is not bleeding the excess exhaust energy properly.

Just because the outer casting is larger, doesn't mean the volute inside is larger, UNLESS they are different A/Rs. Check your buddy to see if he upgraded.

 

Your answer is very informative. I will check with him as soon as I can. He said he "swapped the internals" from the old cracked housing to the new housing.

So it is possible to create more boost you use a turbo housing "that is a different A/R"? Like I said, hondata datalogs show that when he floors it, it accelerates until the MAP sensor reaches 10psi. At that point, Hondata is programmed for fuel cut.

We are just trying to confirm why the MAP sensor is maxxing out after: new headgasket and new turbo housing.

 

If its an OEM MAP sensor, it's going to do that anyway. If you are using an aftermarket one, make sure the hondata sees the correct voltage calibration for your specific map sensor. Either way its not turbine housing related.. It won't change actual boost pressure

 

It's a turbonetics turbo build with sleeved block and all. He traded for it, but it hauled #*() and ran great for the first year he had it. It always held 7 or 8psi of boost (on the gauge) with no problem. It is an OEM MAP sensor on a Skunk2 IM. He has already swapped in another OEM MAP sensor with the exact same part number printed on it....it made no difference.

If it's set for 8psi boost, then the MAP sensor should never get readings of 10psi, right?

He did cap off an open vacuum leak on the intake arm before these problems started. During street datalogging today, the cap on that vac port blew off, and then it ran GREAT without reaching 10psi on the MAP sensor. We have no idea how long that cap may have been off.

Is it possible that the boost controller (manual??) is set too high? It's hard to believe that this awesome build was tuned/build/designed/whatever with a vac leak on the intake arm. It seems alot more logical that it has been capped off and something else is causing this new issue???

 

You answered your own question. The mbc was set artificially high to overcome the boost leak. Your friend capped the boost leak and now it over boosts. Then you said the cap blew off (so now its leaking again) and its back to 10psi. There ya go.

So either run it with the leak OR cap the leak and turn down the boost controller.

 

I'm surprised to hear that it could have really been mistuned (due to an obvious open vac leak). This car seems like it was built by a PRO. But I guess we will find the boost controller and try to turn it down.

So my final question is: Does the MAP sensor reading (on hondata) measure the EXACT boost pressure?

 

only if it detects the right voltage from the Hondata.

 

Or it's just as simple as boost creep compounded by a vacuum leak

 

^^ + possible boost leak from cracked housing?

 

It ran great before fixing the two issues: replaced headgasket and turbo housing. Then during reassembly, he saw the open port on the intake arm so he capped it. Then during test drives it was overboosting. We have no idea if it has been uncapped the whole time he owned it (for a year, but rarely drove it).

But for now, he said he is probably going to invest in a 2.5bar MAP sensor, and try to find a "different spring" for his turbonetics wastegate.

 

what are the housing AR on them

 

Yeah, it sounds like there was a vacuum leak that was unchecked during the original tune (or shortly thereafter). You found where those were, repaired them and now its boosting past its original set. You won't even need a full retune, just some adjustments for the higher boost level, regardless of A/R of the housing, which doesn't cause an actual overboost phenomenon

 

AR housing size does not cause overboost?

that is not true.

lets say swap a 82 housing with something tiny, like 32-38 AR housing, and youre chances to spike boost is a greater.

Although since he upgraded to larger that does'nt really matter with this.