I can now confirm that my SAI combi-valve is still opening with the N249 and N112 disconnected from the manifold. I have no idea how this is happening, but it is. 
N249 Bypass guide LCR
- Thread starter rsmith
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- bypass guide n249 seat leon cupra r
Cupra Ross wrote
The exhaust note from a full Milltek system under SAI is very different from that produced in the absence of SAI, believe me. I'll check tomorrow morning but what you're saying makes a lot of sense.
and later
I can now confirm that my SAI combi-valve is still opening with the N249 and N112 disconnected from the manifold. I have no idea how this is happening, but it is.
Can you check to see if the combi-valve is stuck open? Pull the hose off the output side of the secondary air pump and blow down it? Everything I can find about this system says that vacuum is needed to open the combi-valve, it isn't just a non-return valve.
Diesels have a vacuum pump for this purpose due to their lack of a conventional throttle. The intake system on a diesel is incapable of creating vacuum in the way that a petrol engine does. The N75 on a diesel is there to control blade pitch as you say but a diesel cannot technically overboost. A diesel engine takes a full charge of air regardless of the position of the accelerator pedal. Petrol engines are completely different in this respect.
Yes, I know that diesels have no throttle and so never produce any depression in the inlet manifold. This is one of the reasons diesels are more efficient, no pumping loss.
Supercharging by any method can be regarded as increasing the compression ratio, so a diesel can overboost, and indeed one of the common failure modes, sticking VNT vanes, causes overboost, triggering limp mode.
I expect that the ubiquity of vacuum brake servos is the original reason for vacuum pumps to be present on diesel car engines, and once a vacuum source is present it makes sense to use it for hot-side engine controls.
The exhaust note from a full Milltek system under SAI is very different from that produced in the absence of SAI, believe me. I'll check tomorrow morning but what you're saying makes a lot of sense.
and later
I can now confirm that my SAI combi-valve is still opening with the N249 and N112 disconnected from the manifold. I have no idea how this is happening, but it is.
Can you check to see if the combi-valve is stuck open? Pull the hose off the output side of the secondary air pump and blow down it? Everything I can find about this system says that vacuum is needed to open the combi-valve, it isn't just a non-return valve.
Diesels have a vacuum pump for this purpose due to their lack of a conventional throttle. The intake system on a diesel is incapable of creating vacuum in the way that a petrol engine does. The N75 on a diesel is there to control blade pitch as you say but a diesel cannot technically overboost. A diesel engine takes a full charge of air regardless of the position of the accelerator pedal. Petrol engines are completely different in this respect.
Yes, I know that diesels have no throttle and so never produce any depression in the inlet manifold. This is one of the reasons diesels are more efficient, no pumping loss.
Supercharging by any method can be regarded as increasing the compression ratio, so a diesel can overboost, and indeed one of the common failure modes, sticking VNT vanes, causes overboost, triggering limp mode.
I expect that the ubiquity of vacuum brake servos is the original reason for vacuum pumps to be present on diesel car engines, and once a vacuum source is present it makes sense to use it for hot-side engine controls.
Hi I am looking at doing this and had a look at my engine 2005 225 LCR, and it only has one pipe straight from the N249 to the DV in the pics I see the pipe has a T pipe and another pipe coming out of it, I dont have this, will it make any difference?
Or can I just join the pipes and job done?
Thanks.
Or can I just join the pipes and job done?
Thanks.
You can ignore the T-peice, this is for my boost guage as stated in Step 3, just join the 2 pipes together
Oh right sorry about that should have thought, least I know where to put a boost gauge in now then
I have just trimmed (reduced its diameter) the smaller pipe slightly and put it into the larger one and taped up for the time being. Will it be ok like that?
Hi guys,
Sorry but i could not help reading your posts and i was just curious to know that if i do this mod on my LC does this mean when i wake up in the morning and start the car my engine it should not make that loud reving noise (pump) ???
Is this the secondary pump coz it does my head in and i will do this mod just to stop it.
Oh right sorry about that should have thought, least I know where to put a boost gauge in now then
I have just trimmed (reduced its diameter) the smaller pipe slightly and put it into the larger one and taped up for the time being. Will it be ok like that?
No way, you need to use a proper hose joiner and cable ties or clips, remember this is part of the vacuum system.
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do you need to get the new hose or can you just use the original. if ive read it correctly you can just connect the 2 leads in the middle or are they not long enough, too big/toosmall. i havent looked at mine yet to find out i have only looked at the thread.
Guys, don't be to hung up on the details, these are flexible pipes, so just get a 4/5mm connecter and force it in and cable tie it.
Alternatively, what i did after was buy some 4mm or 5mm silicon hose from http://www.siliconhoses.com/ and replace the whole hose going from the DV to the inlet manifold.
Yeah good point , only prob is the connector on the manifold is also the same size as the t-piece on top of the valve so would 4mm not be too big, take it you want a nice tight fitment so there is no leak..
i used 4mm, striaght from my DV to manifold and it was a good fit, please see my pic below.
thanks very much what sort of length would I need, would a meter be enough?
I have seen some cheap tubing online, what other piping can I replace round about then engine at the same time, and what sort of diameter and lengths would I need (I'll do a search aswell just thought would ask, any help would be great)
I have seen some cheap tubing online, what other piping can I replace round about then engine at the same time, and what sort of diameter and lengths would I need (I'll do a search aswell
just thought would ask, any help would be great)
paul-murphys
efr 6758 here i come
just done this on mine. Not sure if its me but doesn't feel like boosts holding as well. Might be cause its a hot day but doesn't feel as strong. More responsive but not sure on boost. Before would peak 21 and hold at 20 now boosts to 20 an holding a little below maybe 19. Also it is a hot day but not sure about this. Will see again later.
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