15psi after replacing cat with 3" downpipe

[mr299ron]

Just replaced my cat with a 3" downpipe and out of nowhere I'm boosting about 15psi and it will rocket straight to 20 or just short in the lower gears (2nd)!

I have an MBC fitted, however this has been wound all the way out to its lowest setting.

Before I replaced the cat I was hitting 10psi with the mbc, and before the mbc I was hitting 7 max.

The cat was absolutely ruined. Was just a big ball floating around and was actually blocking the flow of the exhaust where it was just sat covering the hole! This might have explained my low boost pressure before!

My guess here is that the mbc's stock pressure is about 15psi(?), but I've seen other people (2mad) with 0.9 bar from the lowest setting on the mbc, so I have to think the boost gauge is incorrect?

I also have fuel cut disconnected and the VSV. Everything is in as it should be.

[2mad]

3" downpipe can do this ... this is why i ported my turbos wastegate .


Can post pics if your going to port it.

[rgb]

you wanted more boost and now you've got it. if you let it boost to 20 psi you'll blow it up. its harder to keep the boost down than to turn it up. I don't recon your mbc will do any thing cause they just turn it up . an ebc might help. if removing the cat made it boost too much there used to be metal plates that reduce the exhaust from 3 inch to whatever you want. they look like a gasket but the hole is smaller. I'm not very good at explaining but I have blown up a mr2 cause of too much boost

[mr299ron]

It won't hold at 20psi it will fly up to probably 18 then just bounce off of 15, before dropping off from 4.5k-5k when the turbo dies off.

I know the mbc won't do anything other than raise it, but I'm wondering if I should try disconnecting it and just re-plumb the vsv and see if it solves it.

This is so shitty - ive gone from underboosting to over boosting.. god dammit.

[masterbateson]

what size drill bit did you use to port the wastegate?

[Nails]

My first rev 2 had a broken cat. It had happened gradually and I thought I was just getting used to the power. When I decatted it I was like YEEEHHAAAAA down the road lol.
you may need to cut some coils off the spring in the mbc to lower the boost to a safer level.

[mr299ron]

Im thinking I should just go back to the stock setup. I'll probably be hitting 10-11 psi from stock now anyway.

I knew it was the cat causing an issue, but people were like noooope.. so if you see this and that was you..

[tiff_lee]

Never saw this coming...

I can see it now, "Too much boost engine blown!!?"

Im thinking I should just go back to the stock setup. I'll probably be hitting 10-11 psi from stock now anyway.

I knew it was the cat causing an issue, but people were like noooope.. so if you see this and that was you..

Not being funny mate but you didn't know that at all hence why you had 4 different threads all asking the same thing and even then you claimed to understand how it all worked you clearly didn't.

3" downpipe can do this ... this is why i ported my turbos wastegate .


Can post pics if your going to port it.

Was you getting boost creep then?

[mr299ron]

tiff_lee, also not being funny mate, but why are you continuing to add salty comments to my threads? I don't care if I'm annoying, I don't care if I'm wrong. It's how you gain a scope on things and how you learn!

Yes I did post in four threads, with almost 4 different things, but that's like speaking to 4 different people in real life to confirm if you're right, and 4 different ways of looking at it so you can gain a real understanding.

And yes I did understand it enough to realise that poor flow could easily be causing this.

In all honestly, you look worse than anyone when you whinge about someone else taking part in a forum thread. Take a hike if you're gonna get emotional.

[tiff_lee]

Salty comments? it's an internet forum and you can't take a little banter? but please feel free to share these salty comments that have clearly upset you.

I never said you was annoying? and as for being wrong of course making mistakes and asking questions is how you learn but why state the obvious to try and validate your argument.

You clearly didn't understand hence your contradictory posts but even that's not a problem, I only bothered to say that because you gave it the big one as to how you knew all along.

I'm not whinging at anyone else taking part in the forum thread? I was making an observation of you but in your own words don't get emotional.

[rev3turbo]

wastegate is probably hitting the downpipe, not opening fully, meaning the exhaust gasses cant escape and so overboosting.

fitting a 3" downpipe should still be boost controllable via a MBC

[tiff_lee]

wastegate is probably hitting the downpipe, not opening fully, meaning the exhaust gasses cant escape and so overboosting.

fitting a 3" downpipe should still be boost controllable via a MBC

Yeah Bob Hatton mentions in this thread at the end
http://www.imoc.co.uk/forums/viewtopic.php?t=187535

Even with his mbc set though if the wastegate can't fully open then he will basically see massive boost creep/overboost/<insert term here>.


2mad is that what you meant by porting your wastegate? Just to clarify, not sure if you ported because of wastegate not being able to fully open as per what Bob said or because it was fully open but not flowing enough exhaust hence boost creep.

[mr299ron]

Okay so I disconnected the boost controller, connected the wastegate backup to the turbo as normal, and left the vsv disconnected. So I should be seeing only wastegate pressure.

Nope, was seeing 15psi as I was out, however it was 5psi less than what I was seeing yesterday. (which is about the difference of having the vsv working)

However, the car was obviously being throttled by something as the boost gauge wouldn't go above 15psi at all and the car felt exactly like it did before I replaced the DP when cold, but now I just have more power.

I reckon the boost gauge is mis-reading, as there's no way I should be reading 15 pounds on wastegate alone with a 3" downpipe.

The guy who replaced the downpipe isn't a complete moron though, so I know he would have picked it up if the dp was blocking the wastegate.

Is it easy enough to see if the wastegate is being blocked? Can I just take off the heatshield on the turbo?

[tiff_lee]

So just to clarify with the mbc it would peak at 18 and hold at 15? and is it now peaking at 15 and holding there?

I've not seen the clearance issues with these pipes but if it is as Bob says then you will never fully control your boost no matter how early the wastegate opens because you wont be diverting enough exhaust to prevent making making more.

[mr299ron]

Yeah it would spike to about 18-20, hold for a bit and then just drop off as normal as the ct26 would start to run out of puff anyway.

Now it climbs up to 15psi and holds there until 5.5-6k as it should.

Anyway I can easily check if the dp is blocking the wastegate?

[tiff_lee]

Depends how easily you consider removing it, the chinese/ebay ones are all the same so if one does it no doubt they all suffer from it. If it were me disconnect actuator arm from the wastegate and move it by hand to see/feel how much it moves, ideally the downpipe would be off so you can compare with and without to see if there is any restriction.

Hopefully 2mad can chime in later with those pics he mentioned.

Even though you have only the actuator controlling the wastegate the reason boost is so high (assuming wastegate is partially blocked) is because the turbo is constantly trying to make boost.

[mr299ron]

Depends how easily you consider removing it, the chinese/ebay ones are all the same so if one does it no doubt they all suffer from it. If it were me disconnect actuator arm from the wastegate and move it by hand to see/feel how much it moves, ideally the downpipe would be off so you can compare with and without to see if there is any restriction.

Hopefully 2mad can chime in later with those pics he mentioned.

Even though you have only the actuator controlling the wastegate the reason boost is so high (assuming wastegate is partially blocked) is because the turbo is constantly trying to make boost.

I'd probably be able to hear something if it's hitting it. It is a Japspeed dp, but you're right they all look the same as the eBay ones, so maybe I am having this issue.

Can I easily do this? A little Googling suggests I might need some "e-clips"? and thats its a poo job to do

[C35Rob]

If you look at the cheap DP compared to a berk DP you'll see the section behind the wastegate flapper is tiny, which can stop them opening fully, mr2's are prone to boost creep anyway with a decat/free flow exhaust, people try to port the wastegate with varying levels of success but in reality the exhaust housing on the turbo is too small, which is great for fast spool but makes turbo speed control at high revs a pain. Realistically the only way around it is to fit a large external wastegate that's capable of diverting enough exhaust gas away from the turbine, or ditch the stock turbo and fit something with a bigger hot side

[mr299ron]

That seems like a right god damn pain.

I think the best way to sort this would be to install the correct supporting mods. IC and a metal headgasket.. although the headgasket looks like a sh1te job too..

[rev3turbo]

welcome to the world of modifying mr2's.

But the best way isnt to fit a metal HG and intercooler. The correct way is to sort out the reasons as to why you cant hold lower boost pressures.

Its a game that gets expensive, even more expensive when you have to buy twice due to buying the cheaper parts the first time around.