CT20B's and overboost

[Malcolm]

Well crikey dick, I fixed a problem I was having with the mr2 missing today, disconnected the map sensor to get rid of fuel cut and took it for a spin. It's f*cking fast as hell now, but that's probably because it was hitting like 17 or 18psi, and that's with no form of boost control on, not even the factory VSV. This is something I will need to fix if I want my engine to last more than a few weeks.

Brad (Mmm Boost) - did you manage to fix your overboosting problem? You didn't give me your busted actuator did you?

[Al]

Odd. When I turn my boost controller off (actuator controlled boost) I get 7-8psi throughout the rev range and trys to creep up to nearly 9psi above 5000rpm.

MR2SIK has put on his ct20b and Aussie downpipe now too and AFAIK has no boost creeping issues.

[Malcolm]

I think I'll check to make sure the downpipe allows the wastegate to open properly sometime. I don't see why it wouldn't, and I'm fairly sure I checked before install.

[Dell'Orto]

Brad (Mmm Boost) - did you manage to fix your overboosting problem? You didn't give me your busted actuator did you?

I have indeed, will PM you with some ideas.


Nope, car behaved exactly the same with your actuator as it did with mine, so that wouldnt cause it anyway.

Odd. When I turn my boost controller off (actuator controlled boost) I get 7-8psi throughout the rev range and trys to creep up to nearly 9psi above 5000rpm.

Maybe its because I have no VSV and a GT Four actuator, but mine sits at 13psi...

[BBBrad]

That dreaded boost prob again.
Mmm B, I see now your car is all going good now, you "still" trying to sell it!!! I think you better keep it, put some nice wheels on it and get in pc mag.

[Dell'Orto]

Might have to come see you about doing a 3" exhaust first

Think I may have found a buyer for the old one, so it will cost me nada

[Wildcard]

FYI I ended up taking off my turbo and porting the wastegate housing to fix my boost problems. Can now run ~0.65bar min.

[Malcolm]

Well it looks like I'll have the old extremely wicked+harcoredownpipe from my gt4 that I sold to my mate back to borrow for the drags (yay), and whilst that pipe is on my car I'll see if I can improve on the XS power one. I'm thinking I might cut a section off a bend and attach it over the top of the current wastegate route to provide a path for the air to go through.

[Malcolm]

oh btw,
Ben, did you have the housing ported professionally or did you just attack it with a die grinder? and did you have to change the wastegate flap or was it still large enough? Also that's on an aftermarket turbo, isn't it? I haven't heard of many having problems with the CT20B overboosting in cases that weren't just related to downpipe design, so I would probably be better off just trying to sort the downpipe first. Interestingly I haven't heard any complaints in the past of overboost with the xs power pipe.

[fivebob]

Could be that the actuator rod is too short. Before modifying the pipe I'd try removing the actuator from it's mounts and wiring the wastgate fully open.

If you still have high boost then start looking at the flow path through the wastegate. If the boost is low enough when the wastegate is open then try making a bracket to move the actuator closer to the wastegate.

[anthonym]

I think your 1m long 3" exhaust probably has something to do with it. Extremely free flow exhausts are known to cause overboost in the manner you describe. I don't think the XS pipe is the culprit, other than adding further flow. FWIW I have one on my car and I have severe underboost problems .

[BBBrad]

As above, mmm, boosts car had the same prob. Here is the pipe I built for it...
http://photobucket.com/albums/y248/BBBrad/?start=20
Had to take it back off and do some minor mods to the wastgate section, kind of made it slightly more aero-dynamic, and all is good now. The wastegate flap was checked for full movement and to make sure it wasnt hitting anywhere in side the wastegate chamber.
It seems to me even with its quite large flap and outlet holes the ct20b seems to be quite vonerable to this unable to flow at the top end. Just about all of the pipes on the market seem to be of the shared main outlet/wastegate area type, similar to the factory setup. I can see why though, its a tight squeeze in there, with the oil filter in the factory position and aircon still on. But in the end its all good with a proper divorced wasgate system.
Without aircon or a remote filter Im sure a very simple effective downpipe could be made.
Is there much info on this overboost problem, the americans never seem to talk much about it??

[Malcolm]

fivebob - how would an actuator become too short? It is completely unmodified since I bought the turbo off anthony, so there should be no logical reason why it would be too short unless dodgy anthony while playing around with his turbos decided to customise the actuator for more boost Failing that, have you ever looked at enlarging the wastegate ports on the ct20b?
anthony - I have actually heard of similar problems on Evo's now that you mention it, where a good downpipe can cause overboosting, but the wastegate port of a TD05 is quite a bit smaller than the combined ones on a ct20b I'd think. It's a little reassuring to hear that your XS power pipe isn't causing overboost, although that could just be because your turbo is so crap and you need to by mine back

I'm wondering if for all the hassle it might be easier to run an external, admittedly that's kind of a last resort, although I would rather just do that than spend ages stuffing about trying to find a solution. Arg problems are annoying!

[Al]

Is there much info on this overboost problem, the americans never seem to talk much about it??

I haven't seen much talk at all of the ct20b overboosting from the yanks.

Now my exhaust is pretty free flowing, Aussie 3" dp, then a 3" exhaust with 5 mandrel bends then 3" inlet N1 muffler...yet I suffer no overboosting, merely a spike when the TVIS opens up.

[Malcolm]

Is there much info on this overboost problem, the americans never seem to talk much about it??

ha! americans! too busy faffing about with their 8" chrome twin outlet exhausts to care about doing any real mods

look at all the useful help I got from the mr2oc people:
http://www.mr2oc.com/showthread.php?t=139223
and that moron is a moderator. God, I don't know why I ever bother asking help from that bunch.

Anyway, I could probably modify the xspower pipe to having a separate wastegate pipe, I have no aircon but I have the alternator in the celica position, and oil filter is in the stock gen 2 position. Still don't know if it's going to solve the problem and it could be a lot of stuffing about for nothing if it doesn't.

[Malcolm]

Now my exhaust is pretty free flowing, Aussie 3" dp, then a 3" exhaust with 5 mandrel bends then 3" inlet N1 muffler...yet I suffer no overboosting, merely a spike when the TVIS opens up.

5 bends?

that's what I'm talkin' about


here's the old downpipe me and a friend made that was on my gt4 (the one I am going to borrow off my mate to see if it'll work)

[Al]

Crikey

Mine comes off the downpipe, up over the crossmember then down to the left of the car then into the muffler.

[Malcolm]

ah there's your problem, it's an sw20 and there's a crossmember in the way of exhaust perfection

[fivebob]

fivebob - how would an actuator become too short?

Sorry, I assumed from your posting, and Mmm, Boost's comments, that this was not the actuator that was supplied with the turbo, or at the very least had been removed from the turbo at some stage.

That said however, my comments still stand. IMO the easiest way to determine if your problem is with inadequate flow through the wastegate, or a problem with the actuation of the wastegate, is to wire the wastegate open and see if it limits boost the around 7-10psi.

Of course you could spend far more time and replace or modify the downpipe, but that's just another example of what's wrong with most peoples approach to fixing problems, they don't determine what the problem is, and instead rush in trying to fix the symptoms, or in some case just guess at a possible fix.

I've always found it easier to find the cause of the problem first before attempting to fix it. Experience shows that it's usually cheaper and less frustrating that way.

[Malcolm]

well at the moment I'm trying to find all possible causes of the problems, and possible solutions. When I have time I will obviously do some troubleshooting checks to try to decide the most likely cause of the problem, and then start making necessary repairs. Generally speaking, I'm also not overly keen on fixing things if I don't even know if they're broken