Exhaust back pressure pushing open internal wastegate

T

ttribejr

Member
Joined
Dec 1, 2015
my hole isn’t ported beyond my large rjc puck. But I can’t get boost above around 15psi

Stock actuator on car. I have never read of people having back pressure push it open on a stock longblock car like mine. Any tips or fixes?

I tested it completely disconnected from vacuum and I get about 18psi. All hooked up to stock wastegate solenoid I get about 14psi even though I have xfi telling it to go higher

I installed a plate between turbin and downpipe for a test run and sure enough hit 30psi in about 1 second.

Only thing I can think of is exhaust pressure pushing it open?
 
I ran across a few threads about back pressure pushing the puck away from an enlarged wastegate hole when trying to run higher boost.
I don't recall the combo but the wastegate hole size that worked was .95 in.
I'm sure it's different with every combo, but that maybe a good place to start.
I've seen threads where guys add tension springs from the puck actuator arm to the mounting bracket to increase pressure on the puck like an HD actuator.

I have basically a stock engine running a TA49.
Back in the '90's it was said running more than 23 psi boost would result in blown head gaskets (probably stock chip??), so I never ran more than 20 psi (with race gas). I opened up my wastegate hole to 1.312 in. to prevent boost creep.
I've converted to E85 and would like to run 28 psi. boost so I will be experimenting with a block off plate and a smaller hole.

Just sharing some info I've run across.
George
 
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Sounds like your wastegate doesn't have enough preload to stay sealed, -OR- it doesn't seal that well to start with.

The way to check is to put grease on the puck, install the pipe/elbow and swing the wastegate so it leaves and imprint on the exhaust housing. If you have an alignment problem (or from overporting) it'll be plain as day.


If it's not an alignment issue it sounds like you need to increase the spring preload so it will overboost then install a MBC to set the desired boost level and get the spoolup time sped up.
 
@dvernst had this issue. We lengthened the swing arm, giving the actuator more leverage. That took care of it
 
Remove the clip that holds the actuator rod on the wastegate crank. Use one end of an external spring in place of the clip. Drill a small hole in the actuator bracket to fasten the other end of the spring to. This will create extra force to hold the wastegate shut.
Pressure is measured in pounds per square inches. If we increase the pressure of a gas or fluid pushing on something,we create more force pushing on that something. In this case,the puck. Another way to increase the force pushing on the puck is to expose more square inches of the puck to the same gas or fluid pressure. This is what we are doing when we enlarge the wastegate hole. We are creating a problem while trying to solve another problem,boost creep. More square inches of the puck are being pushed on causing it to open sooner than we would like it to open causing lower than desired boost pressure. To increase boost we need to create more force to hold the puck shut.
 
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I looked into a tester and it was north of $200. don't want to spend it right now. Know of a cheaper option?

I disconnected the vacuum source on my car just to see what max boost it would make. 18psi. with vacuum hooked up, about 13psi.

Do the adjustable precision wastegates cure this issue? I see one adjustable from 18psi and up.

I also ordered a new MAC valve to replace my stock one. I really want to keep controlling boost with XFI if I can get it to work. I want it tied into my flex fuel so boost drops If I am away from an E85 pump and have to put 93 in the tank. Its one of the main reasons I bought XFI.
 
Also, I have GN1 aluminum heads and a roller cam waiting to be installed. Is this going to increase or decrease back pressure. I have been told it will decrease it, but my uneducated opinion is that it will increase it do to a higher flowing motor and the same turbine housing.
 
ttribejr said:
I looked into a tester and it was north of $200. don't want to spend it right now. Know of a cheaper option?
Click to expand...

W/ the XFI, you can plumb in a 0-100psi pressure transducer, [Not a lot of $], a ft of 1/8" copper tube/fittings, and a little time to drill/tap/wire it. Maybe, $50, not 200+. You can get them on the bag, for cheap. Either 0-5vdc, or 0-12vdc. Not sure how he XFI is set up w/ I/o's.
I have one plumbed into my turbo LS set up/Holley Dominator system. Mine is plumbed w/ 3/16 ss brake line/AN fittings, and is permanent.
Take your pick....
https://www.ebay.com/sch/i.html?_od...-5vdc+0-100psi++pressure+transducers&_sacat=0
 
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