Volvo Penta 41b boost pressure help

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gery w

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Taking advantage of the poor weather that we are experiencing UP north at the moment I decided to strip and clean the aftercoolers and check the boost pressures on my 41 b's.
On dismantling i was pleased to find very little in the way of oily deposits so after cleaning and rebuilding I moved on to checking the boost pressures.
The pressures on both engines were pretty consistent with each other however as I could find no info online I'm unsure if they are correct but they do seem a little on the low side to me.

Port 3000rpm-7 psi.
3500rpm-12 psi
Wot 3800rpm-14 psi

Star 3000rpm-7 psi
3500rpm- 11 psi
Wot 3900rpm- 15 psi

Any input regarding the above would be greatly appreciated
Gerry
 
Gerry,

Boost pressure at anything other than rated speed is characteristic of your propeller law curve and very few manufacturers publish actual rated speed numbers.

Volvo guys who look in may comment but 14/15 psi at rated sounds reasonable to me.
 
I just checked the manual for this motor and the rated boost is 1 bar at 3000 rpm, and 1.2 bar at 3500rpm, and 1.25 bar at 3800rpm, so both are at half rated boost at 3000rpm and a bit low at 3800 rpm. Have you checked for play in the turbo spindle? They could be approaching overhaul time if you have high engine hours.
 
Thanks for your input guys I've checked for play in the turbo shaft and there is a little there as one would expect definitely not excessive, I've also checked the hot side and taken some pics I'll post these up when I figure out how to.

I had a problem last year when I bought the boat where it would only pull 3300rpm on both engines. After having the local Volvo agents in they said both engines were overloaded and the props should be re pitched to obtain 3900 rpm however I'm now wondering if this was related to boost pressure?

Once again thanks for the input guys.
 
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gery w said:
Thanks for your input guys I've checked for play in the turbo shaft and there is a little there as one would expect definitely not excessive, I've also checked the hot side and taken some pics I'll post these up when I figure out how to.

I had a problem last year when I bought the boat where it would only pull 3300rpm on both engines. After having the local Volvo agents in they said both engines were overloaded and the props should be re pitched to obtain 3900 rpm however I'm now wondering if this was related to boost pressure?

Once again thanks for the input guys.
Click to expand...

Gerry quite simply no.

Volvo agents were absolutely correct, here we go again, 'propellers move boats' the engines merely respond to load placed upon them. No revs no boost as simple as that.

Spannerman, very interested in VP document quoting boost at anything other than rated speed, never seen it on any other manufacturers documentation, do they quote propeller exponent used?
 
No they don't quote a propeller type/size as they don't know what application it will used for, i.e. shaft, drive, waterjet. but the graph gives the boost from low rpm to max, it just states that the measurement is done at 100% load and 20C air temp. I would email you the entire manual but its in Swedish!
 
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Well went to the boat today to try a diagnose the cause of the low boost pressure on both engines. After a lot of digging about in the engine bay I found that both o rings on the pipe work between the turbo and aftercoolers were leaking badly. So I thought I had cracked it and replaced both o rings but it made no difference whatsoever to boost pressure but at least I've fixed the leak.
 
Jumping on this as it’s the closest I can find to ask this question but I’ve never need a turbo with burnt tips could someone shine some light on if this gap is to big, I recon yes but would like a second opinion.
Volvo KAD 300
Floating at 2100 and not getting off of the super chargers
 

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Spudspanners said:
Jumping on this as it’s the closest I can find to ask this question but I’ve never need a turbo with burnt tips could someone shine some light on if this gap is to big, I recon yes but would like a second opinion.
Volvo KAD 300
Floating at 2100 and not getting off of the super chargers
Click to expand...
I would say that turbo is knackered. Gap looks pretty big. New ones have a tiny tiny gap.
 
kashurst said:
I would say that turbo is knackered. Gap looks pretty big. New ones have a tiny tiny gap.
Click to expand...
Yeah this was my thoughts also, I will try a boost gauge on the engine but will be hard to get a reading as I can’t get it off of the super charger.
But this being said I think the gap from factory is 0.4mm between housing and vains so I recon it’s safe to say it’s needing changed
 
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