N75J/N75C/MBC Comparison - with graphs

[badger5]

Tuffty's is AMK dude....

doh!

[Welly]

doh!

[DJ_Troopa]

One of my friends on his Mk3 Ibiza Cupra has disconnected his N75 valve also. Hes taken the vacuum pipe off it and kept it electronically connected. He's done this because he says the actuator on his turbo is shagged. He's tried turning the actuator up for more boost but it doesn't do anything! Is it safe to run the N75 like that? He holds boost through the rev range big time, only seems to tail off just before the red line!

[Welly]

One of my friends on his Mk3 Ibiza Cupra has disconnected his N75 valve also. Hes taken the vacuum pipe off it and kept it electronically connected. He's done this because he says the actuator on his turbo is shagged. He's tried turning the actuator up for more boost but it doesn't do anything! Is it safe to run the N75 like that? He holds boost through the rev range big time, only seems to tail off just before the red line!

As long as the engine is strong enough to take it - and going crazy with it isn't the best idea.

I've set mine to 22 initially but it kept going into limp mode under very heavy load (in 6th on the motorway for example) so will drop down to 21 psi which is around the requested boost level anyway.

Safe boost is OK - going mad will cause serious problems.

[DJ_Troopa]

I hit 22.3 psi peak on my liquid gauge, is that all good? I have a few mods though but i don't know what psi i should be getting? Is there any point of me getting an MBC or should i just keep the N75F i have?

[Welly]

I hit 22.3 psi peak on my liquid gauge, is that all good? I have a few mods though but i don't know what psi i should be getting? Is there any point of me getting an MBC or should i just keep the N75F i have?

I'd stick with what you've got mate, the reason I'm using an MBC is that the turbo wasn't making the requested pressure. It's old and tired... and I think the wastegate is creeping...

So it needed a little help.

[Madeley]

Ok guys whats egt, these codes are doin my head in.

[badger5]

Exhaust Gas Temperature=EGT
AFR=Air Fuel Ratio
AIT=Air Inlet Temp
MAF=Mass Air Flow meter

to name but a few abbreviations you see

[s3_kev]

here are my results from fitting my mbc

std N75=
259.02 BHP
233.58 LB/FT

MBC + N75=
261.63 BHP
250.99 LB/FT

MBC only=
262.4 BHP
260.43 LB/FT

note all these figures are taken from vagcom the calculated after so gs. was divided by 0.8 and nm was divided by 1.35582
boost was @ 20psi on std which would drop to 18psi then hold 17psi to red line, n75 and mbc set @22psi peak hold 20psi to redline MBC only set @20-21psi hold 19-20 to redline.

[dannycawsey]

im running stage 2 map at 267hp but want to try and find a few more horses before going hybrid or bt,
is it worth me getting an mbc? p.s how comes everybody uses mbcs and not ebcs on here?

[s3_kev]

im running stage 2 map at 267hp but want to try and find a few more horses before going hybrid or bt,
is it worth me getting an mbc? p.s how comes everybody uses mbcs and not ebcs on here?

who's stage2 mapp is it?? mine was rr at 269bhp with amd mapp and 312lb/ft so mapping figures should be ignored imo as there not true figures they make them look good!
no need to waste money on an ebc reallly mbc works and no lights if the n75 is left plugged in

for the cost of the mbc its not too bad as you do get a slight gain and boost is held higher through out the revs @ the risk of bending rods though..it wont make such a difference that you will decide not to continue wanting a hybrid though if thats what your already wanting

[dannycawsey]

mines got an AMD map also, so i take it there isnt really anything els i can do before turbo except fit my fmic?
how much psi can u actually run through the ko4 turbo could you reach 280-290 hp with out hybridizing it?

[s3_kev]

mines got an AMD map also, so i take it there isnt really anything els i can do before turbo except fit my fmic?
how much psi can u actually run through the ko4 turbo could you reach 280-290 hp with out hybridizing it?

i think there is a guy on seatcupra.net who runs those sort of figures he's using water methanol so thats whats needed to really help. but really a k04 would be doing well to reach those figures

[Matt82]

so just going on the raw figures (without seeing the plots) it seems the mbc makes it more diesel like with the higher torque spike.

really tempted to fit one to mine and experiment with moving the boost up and down to see hwo it effects the output. i recon if you brought the boost down it would reduce that spike without killing the top end too much

[Welly]

so just going on the raw figures (without seeing the plots) it seems the mbc makes it more diesel like with the higher torque spike.

really tempted to fit one to mine and experiment with moving the boost up and down to see hwo it effects the output. i recon if you brought the boost down it would reduce that spike without killing the top end too much

I'm battling with issue at the moment.

Full throttle is fine with the MBC as I have set the boost to about 21.5 PSI which is requested boost level of the map.

The issue is when on part throttle, especially on the motorway for example, the MBC is always trying to achieve 21.5 PSI boost.

Map at this point is requesting about 3-4 psi and getting WAAAAAAAAAAY more, goes spakko and throws limp mode buy cutting one of the coils.

A pain. A big big pain.

[s3_kev]

took mine off today, went into limp mode with out even putting my foot down just starts boosting so easy with the MBC its hard to drive but at the same time its very smooth to drive..
also doing vagcom logs the torque is peaking at very low revs in very quick plots then filters out to quick im scared for my rods so took it off.

[s3_kev]

since refitting the std n75 my boost has dropped again to 17 18psi if im really lucky and im proper annoyed as prior to fitting the mbc i had just fixed my long term boost issue and boost was at 20psi easily 21 sometimes.

can fitting the n75 pipes the wrong way around damage the n75?? as i made a mistake and got them the wrong way for a bit... also i think i may have a slight tear around the n75 where it goes into the TIP im going to silicone that tomoz to eliminate that but could that cause boost loss too???

[harty190486]

I'm battling with issue at the moment.

Full throttle is fine with the MBC as I have set the boost to about 21.5 PSI which is requested boost level of the map.

The issue is when on part throttle, especially on the motorway for example, the MBC is always trying to achieve 21.5 PSI boost.

Map at this point is requesting about 3-4 psi and getting WAAAAAAAAAAY more, goes spakko and throws limp mode buy cutting one of the coils.

A pain. A big big pain.

i have a Lcr with cc stage 1 remap, fmic, decat, filter, descreened maff and have been playing with my unos and found i had the same problem on part throttle also getting maff signal to high due to part throttle boost deviation so fitted it in parrelel with my standard n75 f valve which is tweeked to give alittlke bit more initial boost, set the unos with stronger spring it comes on at 1.54 bar now and hold 1.2 at the red this is running 3 deg advance timing and slight fueling adjustment with a bit more pre load on the wastegate, the boost this way feels so strong compared to just running an n75 and has made the car even more responsive, i did the varios logs boost timing pull fueling egts etc and all looks good fueling is 0.830 troughout timing pull is no more than 5 egts no more than 910 on wot and boost is bang on heres a boost log to show you this is on a 25 degree day also when cooler boost timing and gs are better have seen 220gs with logs to prove

[Matt82]

good reading in this thread, not getting a lot of time to spend on the board lately though :S

[Welly]

i have a Lcr with cc stage 1 remap, fmic, decat, filter, descreened maff and have been playing with my unos and found i had the same problem on part throttle also getting maff signal to high due to part throttle boost deviation so fitted it in parrelel with my standard n75 f valve which is tweeked to give alittlke bit more initial boost, set the unos with stronger spring it comes on at 1.54 bar now and hold 1.2 at the red this is running 3 deg advance timing and slight fueling adjustment with a bit more pre load on the wastegate, the boost this way feels so strong compared to just running an n75 and has made the car even more responsive, i did the varios logs boost timing pull fueling egts etc and all looks good fueling is 0.830 troughout timing pull is no more than 5 egts no more than 910 on wot and boost is bang on heres a boost log to show you this is on a 25 degree day also when cooler boost timing and gs are better have seen 220gs with logs to prove

I get the same issue with lower logs in higher ambient temps.

This liquid gauge I have now has proven to be a most useful tool for this....

Car is broken at the moment and receiving a new prop and downpipe, but once done I shall take some photos.

The interesting thing being my requested vs actual live graph. With it being a live display of actual boost with a smaller white line to show ECU request, it makes it easy to see what's happening there.

On the N75 valve - of any type - my actual boost never meets the requested level. Requested on full throttle is ~21.5 PSI. Actual gets to around 19 PSI tops.

I've set my MBC to 21.5 PSI now and it achieves it with now problems. If achievable with the MBC connected - this means that it's not the fact that the turbo is tired causing this problem.

The main difference between the MBC and N75 is the simple fact that the actuator doesn't see ANY air at all untill set boost level is achieved - this is not true with the N75 valve.

What I think is happening here is that the actuator has gone soft on the turbo, and is being blown open long before requested boost is achieved.

I am planning to add more preload to the actuator and then retest to prove or disprove this theory. I also have a spare K04 actuator at home which I can fit if required for testing purposes.

I shall post results when done.

[Welly]

since refitting the std n75 my boost has dropped again to 17 18psi if im really lucky and im proper annoyed as prior to fitting the mbc i had just fixed my long term boost issue and boost was at 20psi easily 21 sometimes.

can fitting the n75 pipes the wrong way around damage the n75?? as i made a mistake and got them the wrong way for a bit... also i think i may have a slight tear around the n75 where it goes into the TIP im going to silicone that tomoz to eliminate that but could that cause boost loss too???

Fiting it the wrong way round won't do it any damage -it will just give you actuator pressure at all times basically....

[s3_kev]

Fiting it the wrong way round won't do it any damage -it will just give you actuator pressure at all times basically....

yeah i noticed i was only getting actuator pressure was only about 6psi peak... just woundered if it was posible to have damaged the n75 as that is all that has been messed with between using the mbc. iam going to pick up my old n75j i sold a mate this eve to see if this helps. if not all i can put it down to is tesco's momentum99 being cack and i will go fill up with sheel again.. thought id try the momentum after your recent thread and could'nt be arsed to drive 20 odd miles to get shell at the time

[s3_kev]

changed n75 over and problem solved again lol, so my n75 must be intermitantly faulty too. so i won't be blaming tesco fuel haha however i have got a full tank of sheel in her now

[s3dave]

kev.. running my j valve makes mine run sweet and strong boost

[s3_kev]

kev.. running my j valve makes mine run sweet and strong boost

yeah i had it on when i had mine stage2'd but swapped back to std after and made no real difference at the time so i sold it on but got to buy it back now hahaha

[Madeley]

I got a n75c and the nipple that goes into tip has been opened up(looks like its been done with a hot pin) ,makes a big differance, pulls like a train.

[Welly]

I got a n75c and the nipple that goes into tip has been opened up(looks like its been done with a hot pin) ,makes a big differance, pulls like a train.

?? Pics!

[Madeley]

Theres no chance of a pic, it's tiny. l think it just gives the actuator more vacuum pressure, the hole is only about a mill bigger.
If you look inside the nipple you will see the restriction.

[dannycawsey]

ive just ordered a forge unos mbc last night can somebody please give me some quick instructions on how and where is the best place to fit it?
cheers

[Madeley]

Anyone had a try of one of these Awesome > ECS Race N75 Frequency Valve 1.8T
I bet its just got a bigger hole like mine.

[Welly]

Anyone had a try of one of these Awesome > ECS Race N75 Frequency Valve 1.8T
I bet its just got a bigger hole like mine.

Hmmmm, I've heard various rumours. I believe these are the N75H valve from the S4 relabelled with Awesome's logo. It's much the same as te J valve and encompasses many of the same problems. I.e limp mode caused by overboost on a standard map.

[Madeley]

Hmmmm, I've heard various rumours. I believe these are the N75H valve from the S4 relabelled with Awesome's logo. It's much the same as te J valve and encompasses many of the same problems. I.e limp mode caused by overboost on a standard map.

What about a J valve with a mbc fitted between the tip and n75 to tweak the boost up abit before it over boosts. only a idea..

[Welly]

What about a J valve with a mbc fitted between the tip and n75 to tweak the boost up abit before it over boosts. only a idea..

Tried that in the past - will bring on limp mode. It will over boost. End of.

[Madeley]

Can you compare the n75c and J reducer sizes?

[S3 Nattie]

Ive been running a J valve for ages on a standard map and its not once put me in limp mood.

Nathan

[dannycawsey]

my mbc turned up today, could somebody please post up some instructions on where and how to fit it ?
cheers danny

[s3dave]

my mbc turned up today, could somebody please post up some instructions on where and how to fit it ?
cheers danny

Not been funny or anything, but as you dont know where to put it,, do you actually no the risk of fitting this?
most that fit them on here know a thing or two of how it works....just dont want it to end in disaster for you danny....

[s3_kev]

Have to agree here, seen all to many cars over my time where people who dont no what there doing make a hash of it leaving it to myself and my work mates to fix..
i took mine off as it was no good caused over boost and limp mode anyway so unless your patient enough to set it up or can have it setup/mapped accordigly it may not be suitable anyway.
just dont go silly with boost as you may end up bending rods

[Speedy Steve]

Can i use my G/S to claim my BHP? hehe

[Welly]

Can i use my G/S to claim my BHP? hehe

Yep, do you know the conversion equation?

[dannycawsey]

alright guys i fitted it today after work on its own and the n75 electronically connected, before i had fitted it i was getting 1.5 bar in 5th gear and droping to 1.25

i wound it right out and went up 2 clicks at a time till i got to 41 clicks which went into limp mode was reading 1.3 bar in 5th gear and dropping to 1.1

so ive now wound it back 2 clicks and it is reading 1.2 bar and droping to 1 bar but it holds all the way to redline and feels just as strong as the n75 running 1.5

Any explanations to why it feels better running less boost?
And what triggers limp mode?
cheers Danny

[s3dave]

did you plug the ends of the n75?
overboost will have caused the limp, if it deviates to far from requested boost you will hit limp.....
you say it feels just as strong, it is better in what way ....smoother?

[Welly]

Firstly, what N75 valve are we talking?

Normally the N75 will give you a good spike, and then fade away quite quickly. The reason being that the map that's on the car controls it. You can see what's going on by looking at the N75 duty cycle on a log.

You need to understand how the N75 actually works for openers. Boost controller - Wikipedia, the free encyclopedia & What the N75 valve does... - SEAT Cupra.net - SEAT Forum.

When trying achieve max boost the duty cycle will be at 95% - this means the N75 is effectively closed. As the boost gets close to requested, this will drop down to the 70s and then down further. This means that the valve is opening and is allowing the boost to fade away as it opens the wastegate on the turbo via the actuator.

An MBC doesn't suffer from this. The ball and spring mechanism on the MBC will not open untill the pre set boost level is reached, and will keep this boost level for as long as the turbo can produce it. As the pressure drops because the MBC is open, the ball & spring will close the valve again, allowing boost to come back to the preset level. Good info here: Intro to Boost Control

Limp mode, as you know is a self protective safe mode effectively. Brought on by many things, boost being one of them. The engines have a MAP (Manifold Absolute Pressure) sensor - so the ECU knows what the boost pressure in the charge system is. The ECU therefore can compare what boost it asked for, and what boost it has. If there is a difference between the two of more than 250 millibars, it will assume there is a problem and hit limp mode.

Also - if fitting a manual boost controller, it is usually worth doing the N249 bypass. This is another way that the ECU is able to vent boost from the charge system - it opens the DV at the ECU's request.

Even with the N249 disconnected, the ECU can still have you though. I have no N75 and no N249. This means that boost is completely beyond the ECU's control. However, being the clever little sod it is, when (and I do occasionally on the MBC) hit limp mode, it cuts the spark to the coil on cylinder 1 to stop it being driven...

Little git.

[dannycawsey]

Cheers for all of that juicy info its a great help, its the standard n75 that i was running.
right ive been out for a long drive today testing.
On the n75 as i stated on the last post it was boosting at 1.4 in 5th gear,
now im running the MBC and can only get 1.2 untill it goes into limp mode but the dv is a lot louder and the the turbo sounds loads lauder then it did running 1.4 on the n75. which doesn't make sense, so the only thing i can come up with is
that the turbo is actually producing 1.4+ and i have a boost leek in the inter-cooler pipe as i have relocated my dv to the cold side and my boost gauge is plumbed in to the dv vac pipe, so the pressure on the gauge would be the boost im achieving at the inlet mani hope that all made sense to you.

Im going to change the MBC back to the n75 tomorrow and see if i still get 1.4 in 5th that should tell me if i have a leek.

if anyone has anymore theory's please share them.

danny