Badger
Part of things
Posts: 250
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Aug 21, 2021 22:01:44 GMT
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Hi all, got a slightly odd issue. I've got a Jag V6 on my kit car, married to a St200 intake manifold and ST220 throttle body (blended to match the manifold).
On part throttle acceleration the intake lets out a horrendously loud and annoying squeal until the RPMs increase, at which point it goes. Definitely coming from the intake.
I've just finished stripping and rebuilding the throttle body, and that's made no change at all. I squirted a load of carb cleaner on all the joints and there was no variance in RPM, so fairly certain it's not vacuum.
It's some form of weird harmonic airflow thing going on, and just wondering if anyone else has had a similar issue and if so how they fixed it!
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Most of the Vauxhall/Opel stuff has some sort of resonance pipe or chamber on the intake pipe work for noise, this one goes from the air cleaner to throttle body and has that blank stub of pipe hanging of it, you might need to make something like that up?  |
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Badger
Part of things
Posts: 250
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Aug 22, 2021 20:51:05 GMT
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Unfortunately I have no room to fit something like that; there's just about enough room for an air filter to sit on the throttle body before I start hitting the bulkhead.
I'll try to get a video of it tomorrow, it's a fairly odd one.
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Aug 23, 2021 12:20:20 GMT
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I would expect it to be the worst under vacuüm. Your description sounds a lot like my exhaust manifold leak on my donor vehicle. When the manifold is cold there is a small leak due to a sheared off bolt. Screams like a pig until it warms up and straightens itself out.
If your intake makes that high pitch scream i would expect it to be a small leak sucking in air at high velocity. Unless you have a blocked intake system i would expect the sound to dim off with the throttle opening more as the air would be sucked in more the normal way.
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Badger
Part of things
Posts: 250
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Aug 23, 2021 20:40:53 GMT
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Well here's the video showing the noise - it's only a chirp here as the engine doesn't spend much time at the throttle position\rpm range to cause it, whereas it does when driving the car. Definitely seems to be coming more from the bottom of the valve, but even partially blocking it didn't stop the noise completely.
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Looks like it happens when the butterfly is just slightly open so maybe like how you whistle or put a blade of grass between your thumbs to sound like a duck. Can you disturb the airflow at the engine side of the butterfly and see if it still happens?
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Badger
Part of things
Posts: 250
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Aug 24, 2021 10:51:31 GMT
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Looks like it happens when the butterfly is just slightly open so maybe like how you whistle or put a blade of grass between your thumbs to sound like a duck. Can you disturb the airflow at the engine side of the butterfly and see if it still happens? Aye, I think it may be the only remaining option now. I'd hoped putting something on this intake side may alleviate it a bit, but that doesn't seem to be the case. My suspicion is that it's at least partially to do with the blending on the throttle body; it has to diverge quite sharply to match the intake manifold and I reckon that's causing some flow funkiness. It could be that the high velocity air going around the butterfly separates from the walls and the turbulence is causing that noise. |
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Aug 24, 2021 15:13:11 GMT
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I get this on my Sunny - the engine has a Weber carb replacing the original Hitachi. There's two adaptor plates, a bakelite heater element and then 4 gaskets keeping it all together.
While it's usually fine, it can produce this whistle - like 88zxturbo says above - similar to a blade of grass between thumbs. Is there on idle and drops off as the throttle is opened.
I usually find that some of the nuts holding everything together need tightening down. Worst case, just a hour or two resetting things - take carb and plates off, clean everything up, cut new gaskets, grind the plates flat if needed. Then it's always all sorted.
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Nissan N13 owner | Mechanical neonate since 2016 (Give me all the info)
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Aug 24, 2021 16:29:11 GMT
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That sounds exactly like my old ST200 when it had an open cone fitted. It the sound of rapid air movement.
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Badger
Part of things
Posts: 250
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Aug 24, 2021 20:37:18 GMT
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I get this on my Sunny - the engine has a Weber carb replacing the original Hitachi. There's two adaptor plates, a bakelite heater element and then 4 gaskets keeping it all together. While it's usually fine, it can produce this whistle - like 88zxturbo says above - similar to a blade of grass between thumbs. Is there on idle and drops off as the throttle is opened. I usually find that some of the nuts holding everything together need tightening down. Worst case, just a hour or two resetting things - take carb and plates off, clean everything up, cut new gaskets, grind the plates flat if needed. Then it's always all sorted. Air leak around the gaskets was my first thought as well, so I took it all apart, made sure everything was flat, made new gaskets and put it back together again; no change whatsoever unfortunately  It's almost certainly due to the rapid acceleration of the air around the butterfly at part throttle, though whether it's the airflow itself, flow separation or something more odd causing the noise I don't know! Unfortunately it's not really liveable with long term, every time you pull away it sounds like the aux belt is slipping horrendously. Although when you get to open the taps up it sounds AWESOME! |
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mk2cossie
Club Retro Rides Member
Posts: 2,948 
Club RR Member Number: 77
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Intake Squeal/Squeakmk2cossie
@mk2cossie
Club Retro Rides Member 77
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Aug 24, 2021 20:59:25 GMT
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Its not just a variable inlet actuator causing the noise is it?
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Silly thought
On the early carbed V8 land rover engines, there was a restrictor ring fitted between the carb and manifold, think a circular saw blade with the teeth on the inside of the ring.
I'm not suggesting you want to restrict the intake, but would something like that disrupt the airflow enough to stop/reduce the noise?
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Badger
Part of things
Posts: 250
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Aug 25, 2021 21:49:21 GMT
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Its not just a variable inlet actuator causing the noise is it? Unfortunately not, there's no variable inlet stuff on the vehicle! That was accomplished by the Lower Inlet Manifold, and I'm using the original Jag ones (via an adapter plate). I did check the idle air valve, but blocking that up makes zero difference. Silly thought On the early carbed V8 land rover engines, there was a restrictor ring fitted between the carb and manifold, think a circular saw blade with the teeth on the inside of the ring. I'm not suggesting you want to restrict the intake, but would something like that disrupt the airflow enough to stop/reduce the noise? That's really interesting, hadn't realised that such things existed. I think the noise is coming from just behind the butterfly valve, so it could be a good solution (either fitting one or more likely making something akin). I'll have to have a research! |
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I might have one somewhere buried, if I can find it I'll get some pictures, but most people just pulled them out and binned them!
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Badger
Part of things
Posts: 250
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Aug 26, 2021 18:44:42 GMT
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I might have one somewhere buried, if I can find it I'll get some pictures, but most people just pulled them out and binned them! I've had a bit of a google search, and it certainly looks like it would disrupt the flow! I would like to not restrict it so much though. I'm starting to think about vortex generators and similar, though in reality my first port of call will be to try a stock throttle body and see what happens  |
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Badger
Part of things
Posts: 250
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Oct 24, 2021 20:01:17 GMT
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A bit delayed, but I thought I'd update this. I ended up buying an ST220 throttle body, turns out the one I had on originally was not a ST220 one - I've no idea what it was from, couldn't find a match! The new throttle body has pretty much cured the issue - there's a little chirp on occasion, but nothing like before. I did have to rework the throttle cable and chock the bonnet slightly to gain clearance, but it's a fix and I'll take it  |
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