Is there an issue with my external wastegate?

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pvan
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Is there an issue with my external wastegate?

Post by pvan » Thu Dec 06, 2018 4:00 pm

Hi all,

I've made some updates to my '85 XR4Ti (5-speed), but it isn't performing as I believe it should be.

Here's what I've done so far:

Rebuilt head with new valve springs, bronze guides, used Ranger roller cam and roller rockers, and new followers.

PE Computer, Bob's log header with external wastegate (17 PSI, 38mm), 3" down pipe, Cosworth intercooler, ported upper and lower intake, Thunderbird large VAM, and adjustable boost control.

The car starts and idles just fine. In first gear the car winds up and goes as I would expect. It pulls hard and boost stops right at 15 PSI. When I shift into second it pulls hard until 3,800 RPM. Boost hits about 10 PSI and I can feel the wastegate start to open. It feels like a stumble. Then the boost shoots up to 15 PSI and about 4,200 RPM it's like hitting a wall. The boost gauge still reads 15 PSI, but pulls like it is naturally aspirated.

Shift again and repeat. I'm not sure how/where the boost is measured, but it feels like the wastegate is allowing too much pressure to escape. Is this possible?

I'm also getting what I at first thought was an exhaust leak when accelerating, but now believe that it is the wastegate valve jiggling. I've read that I could open the wastegate to add a washer or two above the spring to give it a little more initial pressure.

I'm not a turbo expert by any means, so before I do anything further, if anyone has some insight they could provide, it would be greatly appreciated.

Thanks!

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andyofcolumbusmerkur
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Re: Is there an issue with my external wastegate?

Post by andyofcolumbusmerkur » Thu Dec 06, 2018 7:05 pm

Post up some pictures of this setup. Also can you run ok from idle to redline with no boost? Like if you unhook the actuator and are basically non turbo? If you can do that fine then I guess it's that wastegate.
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cmouta
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Re: Is there an issue with my external wastegate?

Post by cmouta » Fri Dec 07, 2018 2:26 pm

Try to get a hand pump with a gauge hooked up to your WGA directly. Pump it up to 17PSI and see that it is operating as expected, if so you can look elsewhere.
Chris
2013 Nero Fiat 500C Abarth
1988 Mono Rosso Red Merkur XR4Ti
1974 VW Thing
2006 Bajaj Chetak 4T w/ sidecar

pvan
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Re: Is there an issue with my external wastegate?

Post by pvan » Fri Dec 07, 2018 3:49 pm

I have no doubt that the wastegate is working. My concern is, is it working too effectively? Is it possible to be dumping too much? My gauge still reads 15 PSI, but it feels like the turbo was turned off.

Has anyone else had similar issues and found a problem?

cmouta
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Re: Is there an issue with my external wastegate?

Post by cmouta » Sat Dec 08, 2018 11:33 am

If your wastegate is opening at 15psi consistently, then it is doing it's job, boost is building and being properly bled. Is it just lack of power but runs ok or is it stumbling? I'd check all the intercooler hose clamps for a boost leak that's a quickly checked culprit to rule out.
Chris
2013 Nero Fiat 500C Abarth
1988 Mono Rosso Red Merkur XR4Ti
1974 VW Thing
2006 Bajaj Chetak 4T w/ sidecar

pvan
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Re: Is there an issue with my external wastegate?

Post by pvan » Mon Dec 10, 2018 5:06 pm

I'll look over the hoses again, but last check, everything was tight. It seems to run fine except that it feels like the boost is gone. I posted to another site which suggests getting a wideband O2 sensor and to close the gap on my plugs as the spark may be blowing out. I'm still running stock boost, so I'm not sure how that could be the culprit, but I will give it a try. I will also get the wideband O2 sensor as it probably is a good idea either way, but not sure it will solve my current issue.

One other thing mentioned was upgrading the fuel pump. I will have to circle back to see if that isa possible issue, but the pumps I have are both new installed by me and were making good pressure.

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