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Jan 18, 2018 17:37:05 GMT
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Right, fixed 90% of the leaks and although the lag has reduced a few 100 rpms and feels more responsive, I can only get 3 psi ever. I kept opening the bleed valve and nothing was changing, so decided just to disconnect the wastegate completely, to prove that it wasn't creeping early or something, and still 3-3.5psi at 4k in 4th (gained a small amount from fixing leaks I guess). Any ideas or am I looking at a knackered turbo?
thanks
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lebowski
Part of things
Hillman Avenger, Clan Clover
Posts: 483
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Jan 18, 2018 19:09:13 GMT
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What have you done (if anything) with the pop-off valve on the plenum? If your wastegate is closed and you're still only getting low boost then perhaps the pop-off valve is opening early.
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Jan 18, 2018 19:24:13 GMT
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What have you done (if anything) with the pop-off valve on the plenum? If your wastegate is closed and you're still only getting low boost then perhaps the pop-off valve is opening early. Yeah sealed it unfortunately!
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Phil H
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Club RR Member Number: 133
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When you say "disconnected the wastegate completely", I'm assuming you mean you disconnected the hose feeding it and blocked it off at the turbo end?
If so, that doesn't rule out a weak spring in the actuator - lockwiring the wastegate shut is the only way to really confirm BUT beware you've now got nothing to stop it lunching itself if/when the boost rises (especially as you've now sealed the pop-off valve). Maybe jerry rig the wastegate with a spare choke cable so you can hold it shut but release it if needed in a hurry!
I seem to recall the A-series turbo was very much over-turbo'd to limit the torque (hence why it doesn't come in until you'd normally change gear..as it's still spooling up?). As you're using a stronger gearbox than in the Metro I would have looked at using a smaller turbo (T2/T25) but as I'm no turbo expert (just owned an old-school T3-converted car) it might be a case of the turbo specs actually deliberately made this way. This is, after all, early 80's tech and turbos have come a long way since.
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ChasR
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^^WHS. And yes with the wastegate locked up there is a real risk the engine can go bang, so try with caution .
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Phil H
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Jan 19, 2018 10:14:48 GMT
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I did (dodgy, I know ) lockwire my wastegate shut but being a 1st Gen T3, the boost would rise slow enough for me to be able to change gear safely somewhere between 0.8 and 1 bar - basically I looked at the boost gauge rather than the rev counter.
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Jan 19, 2018 13:22:49 GMT
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When you say "disconnected the wastegate completely", I'm assuming you mean you disconnected the hose feeding it and blocked it off at the turbo end? If so, that doesn't rule out a weak spring in the actuator - lockwiring the wastegate shut is the only way to really confirm BUT beware you've now got nothing to stop it lunching itself if/when the boost rises (especially as you've now sealed the pop-off valve). Maybe jerry rig the wastegate with a spare choke cable so you can hold it shut but release it if needed in a hurry! I seem to recall the A-series turbo was very much over-turbo'd to limit the torque (hence why it doesn't come in until you'd normally change gear..as it's still spooling up?). As you're using a stronger gearbox than in the Metro I would have looked at using a smaller turbo (T2/T25) but as I'm no turbo expert (just owned an old-school T3-converted car) it might be a case of the turbo specs actually deliberately made this way. This is, after all, early 80's tech and turbos have come a long way since. Yeah that's all I did take the hose off, thanks for your help that's just what I wanted to hear! I do have a blow off valve fitted if that helps. Yeah I should have looked into the lag of the turbo more before fitting, I did LOTS of research but must have missed that! haha And this is my first turbo conversion Will try and lock the waste gate and very carefully see if it makes a difference...
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Phil H
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Jan 19, 2018 13:44:31 GMT
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Blowoff valves can leak - but your compressor-based leak test would probably have shown that up I would have thought.
Have just found the following (to back up the vestiges of memory I had about the A-series turbo):
"The Achilles heel for the Turbo was the 4 speed gearbox as the engine was in simple terms too powerful for it. To try and compensate for the weakness Austin rover developed a two stage electronic control for boost to try and soften the impact. The problem was that peak torque with even low levels of boost would damage the gearbox so boost was set on the wastegate at a low 4 psi. However, at 4000rpm or higher an electronic module would allow a controlled leak from the sensor hose going to the wastegate and would allow air to ‘leak’, so that the wastegate actuator would see a lower pressure and would not lift the wastegate valve off its seat. That allowed the boost pressure to rise and only when it reached 7psi would the module then close off the ‘leak’ and allow the wastegate to move. It would then modulate the leak to maintain this raised boost pressure until rpms dropped below 4000rpm."
So...base pressure on the wastegate is 4psi with a controlled bleed allowing up to 7psi over 4000rpm (I have a feeling the original pop-off valve might be set not much higher than this - 8 or 9psi?). You have an intercooler (something the Metro didn't) and that WILL have a pressure drop across it, and 1psi sounds about right.
If you tee'd off the actuator feed line and put your gauge there, you'd likely see your 4psi base boost, I'd wager. The fact it's "only" 3psi at the inlet manifold isn't so much of an issue, as 3psi of cooler air is much better than 4psi of rather well heated air. At the end of the day, it's about the actual mass of the air that goes in (which rises with increasing pressure, and drops with increasing temperature).
You're probably safe trying to get it to run a 7psi base boost - I think that's close to what the Escort RST T3 actuator runs at...as I said, I'm not a turbo guru but the boost on those comes in about 2800rpm (that's what I fitted to mine when the Turbo Technics original started causing issues by cracking the housing, mainly because it was based on a diesel turbo and couldn't take the heat).
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lebowski
Part of things
Hillman Avenger, Clan Clover
Posts: 483
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Jan 19, 2018 14:31:57 GMT
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I would start doing some basic checks I think.
Does the wastegate flap move freely with the actuator disconnected from the arm? It's possible it could have seized in a slightly open position, allowing you to make boost but not much.
If it moves freely, you can move onto the actuator. You've already tested it so presumably that's ok.
If you're confident that the boost control in the plenum is sealed and there are no other leaks, then it's possible that the dump valve could be leaking, so you could try running without it.
As someone said above, the actuators on these are only 4psi. With the intercooler you've added, 3psi sounds about right at the manifold. However, if you have disconnected the wastegate actuator signal line (and plugged the hole on the turbo) you should be getting a lot more boost, so something seems amiss.
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ChasR
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Jan 19, 2018 16:30:30 GMT
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It may be worth checking the actuator arm preload on the wastegate. On Escort RS Turbos it is said to be about half a hole ; i.e you slip the actuator arm over the wastegate with a little bit of preload. As for the actuator, it shouldn't see vacuum pressure; it should only see atmospheric pressure or boost. Basically, it can't be teed into the vacuum side of the throttle plate. But I doubt this is what is causing your problem .
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Last Edit: Jan 19, 2018 23:58:41 GMT by ChasR
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Jan 19, 2018 19:39:34 GMT
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Thanks for the replies everyone!
Went out to see how I could wire the flap shut and noticed it has a bit of play in the same plane which it opens/shuts. It feels like its not under enough tension from the rod to hold it tight, I checked with a different turbo and it was solid so I think I need to adjust the rod.
Havent taken the rod off the flap yet to check the movement but I cant open the flap by hand with it attached. Hopefully the rod is too long causing the flap to be slack and letting exhaust fumes out, thus having a slow spool and low boost...
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Jan 19, 2018 21:52:16 GMT
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Thanks for the replies everyone! Went out to see how I could wire the flap shut and noticed it has a bit of play in the same plane which it opens/shuts. It feels like its not under enough tension from the rod to hold it tight, I checked with a different turbo and it was solid so I think I need to adjust the rod. Havent taken the rod off the flap yet to check the movement but I cant open the flap by hand with it attached. Hopefully the rod is too long causing the flap to be slack and letting exhaust fumes out, thus having a slow spool and low boost... That sounds like you've found the problem, a non sealing wastegate. Fixing that will help a faster spool time but at some point you may want to try a smaller turbo, a t3 sounds like overkill for an engine that size.
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1988 Mercedes w124 superturbo diesel 508hp 1996 Mercedes s124 e300 diesel wagon 1990 BMW E30 V8 M60 powered! 1999 BMW E46 323ci project car
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ChasR
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Last Edit: Jan 20, 2018 10:47:57 GMT by ChasR
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Phil H
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Jan 20, 2018 10:01:53 GMT
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I did spot that the Metro turbo actually hits peak torque (not boost, by the way) at 2800rpm which suggests it’s on boost by then on a 4th gear pull although that’s likely to appear at 3500rpm on the road as you aren’t going to sit at 2800rpm waiting for the turbo.. The lack of preload on the actuator sounds like the main problem though
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ChasR
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Jan 20, 2018 11:34:43 GMT
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TBH most cars back then had epic lag issues.
Look at the 944 Turbo. As standard the 220s picked up boost albeit at 3kRPM. With a bigger hotside that was made worse a little but it gained a nice chunk of power at the top end. The Cossies were no different.
That and not all T3s are the same. The turbine and compressor wheels on a Sierra Cosworth T3 will be different to those on a RS Turbo and also the Metro Turbo.
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Jan 23, 2018 21:20:37 GMT
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Adjusted the rod today and it was way out. Almost a holes width but in the wrong direction! Adjusted it as per the link above and it's a transformation...
Used to spool at 3k full boost at 4k+. Now it spools at 2k and get full boost between 2.5 and 3k depending on the gear. It's a totally different animal!
Thanks for all the help guys! If your coming to the Goodwood Weekender find me and my van and I'll buy you a beer or something!
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Phil H
Posted a lot
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Wonderful news!
Now to wind it up...
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ChasR
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Jan 24, 2018 10:20:05 GMT
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Good to see it got solved.
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