[Alexios]

Hi,

I have recently installed a boost gauge on my mini. I have noticed that say in third and half throttle the gauge fluctuates between 2psi and 5psi. Is this normal?

Alex

[MINI-Morgan]

Maybe the bypass value fluctuating but cant say ive ever had that myself.

What mods do you have or standard MINI?

[Alexios]

I have the gtt cai and re-route pipe.

The car is driving smoothly and i can't detect any hesitation. I was thinking about the bypass valve. I am a bit unsure how it works. Can somebody please explain?

I would expect the bypass valve to regulate the boost level and keep it constant and not fluctuating.

Alex

[Alexios]

Hello there

I am surprised by the lack of answers. I guess if you are not putting out big hp numbers you are not getting any answers. No members or tuners want to shed any light on the subject?



How are you supposed to interpret the reading from the boost gauge? Don't you get valuable info from it or for most people it is something cool to look at. What kind of problems can you diagnose with the boost gauge? (ex boost leak, faulty bypass valve?

Thank you Mini-Morgan for taking the time to answer my thread.

[BigShow]

Its probably because more people spend money on making their car go faster before spending money measuring what's making it go faster, I wouldn't take it personally mate its just not everyone has one.

I've just bought a scan-gauge but don't really understand how the boost measurement works on that yet although the reading does sometimes flutuate on half throttle so I'd be interested to know myself.

[Aberdeen Al]

Quote: Originally Posted by BigShow (original)

I've just bought a scan-gauge but don't really understand how the boost measurement works on that yet although the reading does sometimes flutuate on half throttle so I'd be interested to know myself.

Snap!

[MINIAC]

Quote: Originally Posted by BigShow (original)

I've just bought a scan-gauge but don't really understand how the boost measurement works on that yet.

I think the Scanguage MAP reading needs to be adjusted for air pressure at altitude. For example, if you're driving at sea level you need to subtract 14.7 psi from the readings.

[Alexios]

Big Show - that is what I was wondering about. Is the fluctiation normal or something is amiss.

Also before spending more money on making the car go faster, one should make sure it is running properly.
I have been delaying the installation of the pulley so I can see how much the boost increases.

I have installed the gtt intercooler snoots and I am a bit nervous that I got a small leak. You need all the boost you can get so you can go fast.

[BigShow]

Quote: Originally Posted by MINIAC (original)

I think the Scanguage MAP reading needs to be adjusted for air pressure at altitude. For example, if you're driving at sea level you need to subtract 14.7 psi from the readings.

Ahhh.. so it won't do that itself then, bit pants.

[BigShow]

Quote: Originally Posted by Alexios (original)

Big Show - that is what I was wondering about. Is the fluctiation normal or something is amiss.

Also before spending more money on making the car go faster, one should make sure it is running properly.
I have been delaying the installation of the pulley so I can see how much the boost increases.

I have installed the gtt intercooler snoots and I am a bit nervous that I got a small leak. You need all the boost you can get so you can go fast.

You don't have to tell me about making sure it runs properly before spending money on making it go faster, I have an empty wallet because my car wasn't its healthiest before modding it. That said BMW did a 'thorough' check on the car before the warranty ran out... so in other words kicked a tyre or two.

If you're unsure about the leak, I'd take it to a local specialist like 1320/GTT/Lohen etc for a proper heatlh check, it'll save you money in the long run

[Alexios]

Big Show

Have been reading your threads "sick mini" and "pressure test". Interesting reading. Makes me wonder what kind of shape my mini is really in....
Unfortunately I am located in Oslo, Norway. Gtt, 1320, lohen are a bit out of the way....

Alex

[BigShow]

Ahhh, just noticed the flag. The problem is there is so much that can go wrong and affect the true performance. Mines out of warranty now so I rely upon people like 1320 to spot when things aren't quite right and have a good idea what it might be without spending hours investigating to no avail and passing the cost on to me. Have you got anyone like this in Oslo as its worth finding out how healthy your car really is.. GT4 Bazs' idea of using coolant that detects head gasket problems sounds like a very good and inexpensive idea.

[Dave Elliott]

Alexios,

I haven't got a boost gauge, but I have what is commonly called the YoYo effect (on the NAM forum). At part throttle the car surges. It's not too bad, but it can be annoying sometimes.

I've done a lot of reading on this and some say it is due to a week bypass valve spring. The bypass valve is supposedly opening and closing in response to those vacuum fluctuations that many, including you, you have observed on their boost gauges.

I have no idea why the vacuum should fluctuate as it does, but one method to cure the YoYo effect is to fit a modified bypass valve with a stronger spring.

To me this is addressing the symptom rather than the cause.

I would be very interested to find out how the fluctuations can be eliminated, or at least what causes them.

BTW, I also have the "cold start" problem where two turns of the key are required to start the car in the morning. I'm not sure if the two problems are related.


Cheers,

Dave

[Alexios]

another thing I have noticed is that the gauge moves smootly on the vaccum side but a bit notchy on the boost side. At full throttle it goes to 10 psi. (stock pulley). The fluctuations and notchyness happens at part throttle. Also I cannot say I notice the yo-yo effect so much. The car drives smoothly.

>Does GTT sell a modified bypass valve? How easy is to replace it. Have the Bentley manual but it doesn't really talk that much about the bypass valve.

No cold start problems here. It starts on the first try even down to -20C

[Lohen]

Quote: Originally Posted by Alexios (original)

Hi,

I have recently installed a boost gauge on my mini. I have noticed that say in third and half throttle the gauge fluctuates between 2psi and 5psi. Is this normal?

Alex

Hi Alex,

The fluctuation that you are noticing at low throttle is normal. At that king of driving condition the car will be producing very low boost as the throttle body is barely open. (As you may know yourself at idle the boost will sit in the minus) and any small changes to the throttle pedal position will create changes in boost pressure....

Such light change in throttle will most likely go unnoticed by you... (as it is quite difficult to maintain a throttle position when there is very little load on the car) and therefore you will see a change in boost which seems unrelated to anything and hence "problematic".

I am of course making plenty of assumption here, but most importantly you mention that the car drives very smoothly. If your bypass valve was truly faulty then at full throttle you will notice bad power and the car will feel pretty slow and unresponsive.

I hope this helps.

Andrey

[Alexios]

thanks andey

so let me see if I understood this right. A faulty bypass valve will only show symptoms at full throttle? loss of power and unresponsive but be ok at "normal" or city driving? Are these the only symptoms? How does this show on the gauge? Does it show up as loss of boost or eratic needle movement when the throttle is steady?

How much power can you get from an optimized bypass valve compared to a 4 year old valve? Is the newfound power low down or high in the rev range?

Alex

[Snowie]

A boost gauge whilst being a useful tool can also cause some confusion.

I have a boost gauge on my GP and now also have a scan gauge - my numbers will be significantly diffferent than yours as my car is far from stock set up.

Boost gauge reads inlet pressure above atmosphere - in my case circa 17 psi WOT in 3rd or circa 19 PSI WOT in 4th / 5th. Traction control switches off at 18 PSI and warning light comes up.

Scan gauge reads inlet Absolute pressure = boost pressure plus ambient pressure - so is always circa 14.5 PSI above boost gauge depending on altitude above sea level.

Inlet pressure is dependent on many things, SC performance & pulley Size, IC set up, Throttle position, By Pass valve, restrictions in air intake and do not forget Cylider head / valves, etc.

It is very normal to have the boost gauge fluctuating at partial throttle - minor fluctuations and not hunting by say 2 to 3 PSI . You will see this on the boost gauge needle but will probably not see it on the scan gauge read out.

What is key is that on WOT you are getting the same boost reading and the same revs - if not then you probably have a boost leak somewhere. The same applies if you are not getting full negative reading on lift off.

A modified bypass valve is a benefit as you will be sure that it is fully closed when it is supposed to be as sometimes there is leakage past the valve and boost is slow to build and is lower at WOT tahn it should be.


Alan

[Alexios]

19 psi - what size pulley are you running snowie?

how would a slipping belt show on the boost gauge? Lower boost levels at max throttle?

Alex

[Snowie]

Quote: Originally Posted by Alexios (original)

19 psi - what size pulley are you running snowie?

how would a slipping belt show on the boost gauge? Lower boost levels at max throttle?

Alex

+ 3% lightened crank and - 15% SC pulley from GTT

Belt slip shows as low boost build up but on WOT 6000RPM it will probably not be slipping unless belt / tensioner is completely US


Alan