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Boost Gone Wild

SwedishKnievel

New member
Joined
Sep 16, 2013
Location
Los Angeles
The essence of the problem is that I'm unable to control boost.

The motor is a 94 b230ft. It's been converted to microsquirt. It has LS2 truck coils, Red fuel injectors, 3 in custom downpipe, Open 3in Exhaust, oversize Pistons, new valve job, Red fuel injectors, walbro in tank pump.

My ambition was to raise boost to approximately 12 PSI. My first attempt included an electronic boost controller. I never was able to get that to work and boost levels remained at factory settings. Roughly 7.5 PSI. I then introduced a manual boost controller. Immediately it became clear that the Boost was increasing unchecked. I double-checked the plumbing for the manual boost controller and determined that it was plumbed properly but even with the manual boost controller essentially open presenting no restriction or resistance to the Boost signal the wastegate was not effective in limiting the amount of boost. I suspected a bad wastegate but it seems to test okay on the bench. I replaced it anyway with an aftermarket type from Kinugawa. I started with a 0.8 bar Spring yet still the Boost climbed 2 in excess of 14 PSI 4500 RPM. I switched out the spring to a 0.6 bar and while boost was equally uncontrollable the Boost curve did change in that at any given RPM the Boost was lower with the 0.6 spring than it was with the 0.8 spring although with both Springs the Boost was headed to catastrophic levels.

At this point I suspected some mechanical issue so why tested the wastegate with a hand pump while fitted to the turbocharger on the motor in the car. The external actuation observed seemed appropriate. I've then suspected that perhaps there was some mechanical problem with the wastegate itself inside the turbo housing. But after removing the downpipe and again observing the wastegate Actuator, it seems to be consistent with normal operation.

The wastegate actuator is connected to the turbo housing nipple with a short piece of new silicone hose. I've checked to be sure that the turbo housing Port is not clogged or blocked in any way.

If anyone has any ideas as to what's going on here, I would sincerely appreciate hearing them. I'm really at a loss for what's happening. Complicating matters is that this is a track only car without registration so my only opportunity to identify these issues is at the dyno and that is a bit of a hassle never mind the expense.
 
that turbo is way too small for a open dp in 3inch.. what you have is a perfect example of boostspiking / creeping

get a proper 15g with at least a straight flange.. that conical housing ist scheisse :)
 
Thanks for the reply.

So you believe that's my only/best option?

Can you help me understand what is happening that the 15g will solve?



that turbo is way too small for a open dp in 3inch.. what you have is a perfect example of boostspiking / creeping

get a proper 15g with at least a straight flange.. that conical housing ist scheisse :)
 
the backpressure will push through the wastegate so for the flow it seems like the gate is closed. test it!

unhook the wastegate lever.. you will have max bosst at around 4500rpm even the wg is set to fully open all the time...
 
Have you done a compression and leak down test? I had similar issues on my lemons car and it turned out to be a burnt exhaust valve. Unburnt fuel was burning in the exhaust manifold producing lots of boost. I was at 20 PSI at 4500 rpm with the wastegate wired open.

As far as 12 pounds of boost, why not just get a 12# actuator.
 
did you take the boost controller off? some of the cheap boost controllers... well, don't.
 
did you take the boost controller off? some of the cheap boost controllers... well, don't.

I did. MBC is off the car. It really does seem that MadDog_945's assessment is correct. I've had the same issue with both the factory and aftermarket WG actuator.

I don't believe we have a burnt valve, yet. I just refreshed the head.

What is interesting is that this condition did not occur when the motor was tired but it did after I rebuilt the motor. Makes sense that with a fresh motor it's a more efficient airpump and therefore more likely to cause the issues I am experiencing.

Assuming my problem is boost creep, how does the 15G solve the problem? Are there any other solutions that retain the 13C? The dyno tuner suggested a sandwich adapter with a proper wastegate.
 
Assuming my problem is boost creep, how does the 15G solve the problem? Are there any other solutions that retain the 13C? The dyno tuner suggested a sandwich adapter with a proper wastegate.

The 13c and 15g are hilariously undersized turbos if you're using the car for anything other than daily driving it. Adding an external WG sandwhich plate could work (if there's room), as will porting the wg opening on the 13c hotside. I have a good ported 13c hotside that I would sell for cheap.

If you're using the car for crap can racing (guessing from your avatar), grab a t3/t4 60 trim or TO4E turbo from ebay. Slap the ATP ultimate wastegate on it. Have more fun and more reliability.
 
Thanks for the reply.

So you believe that's my only/best option?

Can you help me understand what is happening that the 15g will solve?

What happens is your free flowing downpipe becomes the path of least resistance for the exhaust gasses. That is to say, even with the wastegate puck fully open, the exhaust gasses will spin the turbine, increasing boost pressure, rather than flowing through the wastegate hole under the puck and regulating boost pressure effectively.

Your downpipe is more efficient than the tiny wastegate hole. A fun experiment to further support this idea is to fully remove the actuator arm from the wastegate. This will allow the flapper/puck to move freely. Now go for a drive like this and I bet the vehicle will still make boost. In a proper sized wastegate capable of regulating turbine speed, and thus boost pressure, you would expect to see little to no boost pressure with the puck wide open, because the exhaust gasses would ideally bypass the turbine and exit through the wastegate hole.

A bandaid solution (though I don't even think I'd call it that, as it has proven to be long term effective) is to port the area underneath the wastegate puck. You will notice that on the 13c, the hole is extremely small. Now compare that size hole to a 15g. I ported a healthy 13c and it helped with a few psi at least, but I was conservative with my porting as I did not want to do any irreversible damage.
 
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unfortunately it is not only the size of the wg port, it is also the arrangement in the conical housing.. i believe the two flows interact somehow..

believe me.. you wont get rid of this as long as you use the conical housing
 
conical housing is hot garbage.

Atleast the straight or angled setup gives it a chance to breath a little bit.
 
Seems like we are missing something, Many of us have run a 13c with a 3" downpipe/exhaust with a cam upgrade and had zero issues holding 8psi of boost to redline.

Are you using the stock 13c WG actuator? Threaded or unthreaed?
 
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unfortunately it is not only the size of the wg port, it is also the arrangement in the conical housing.. i believe the two flows interact somehow..

believe me.. you wont get rid of this as long as you use the conical housing

Yeah it is tiny and flows like crap. Though I had good luck porting mine.

At the end of the day it makes more sense to upgrade to something that flows better.
 
Whats the smallest inner diameter of the 3inch downpipe at the connection to the conical housing? Stock downpipe is 56mm.

I measured the smallest diameter of conical turbine housing outlet is 54.5mm. Maybe its possible to open it up slightly to get less flow interference?
 
Whats the smallest inner diameter of the 3inch downpipe at the connection to the conical housing? Stock downpipe is 56mm.

I measured the smallest diameter of conical turbine housing outlet is 54.5mm. Maybe its possible to open it up slightly to get less flow interference?

Perhaps, but I think the actual flow section of the hot side itself is tiny tiny. Places where we can not reach easily.
 
Whats the smallest inner diameter of the 3inch downpipe at the connection to the conical housing? Stock downpipe is 56mm.

I measured the smallest diameter of conical turbine housing outlet is 54.5mm. Maybe its possible to open it up slightly to get less flow interference?

but you can get a shot 16t for 50 bucks to use the hotside??
 
Seems like we are missing something, Many of us have run a 13c with a 3" downpipe/exhaust with a cam upgrade and had zero issues holding 8psi of boost to redline.

Are you using the stock 13c WG actuator? Threaded or unthreaed?

I have the boost creep issue with the stock unthreaded WG actuator. Two different actuators in fact, both bench tested.
 
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