Boost pressure drop down

[lmfidalgo]

Hello people...i'm new on this forum.
I'm experiencing an intake boost pressure drop down.
I have a boost pressure meter from Greddy. When I'm running 6000RPM 6th gear after 2 or 3 minutes WOT, the pressure drops abruptly from 16PSI to 10 PSI.
Do you have any experience like this?
Is it possible that the pulley is spinning on the belt?
I have a 15%pulley installed and a shorter belt.
Thanks friends!

[Richard Crofts]

6000rpm in 6th is massive speeds, and so hot charger esp with a 15% pulley. Your boost drop is probably due to the engine retarding because of exceptional high tempretures.

[lmfidalgo]

Quote: Originally Posted by Richard Crofts (original)

6000rpm in 6th is massive speeds, and so hot charger esp with a 15% pulley. Your boost drop is probably due to the engine retarding because of exceptional high tempretures.

Thanks!
What do you mean with "...hot charger esp..."?
So the boost drop due to a engine protection system wright!?
All the best!!!

[Keano]

Quote: Originally Posted by lmfidalgo (original)

Thanks!
What do you mean with "...hot charger esp..."?
So the boost drop due to a engine protection system wright!?
All the best!!!

The super charger will be spinning fast at engine speeds of 6K+ rpm and with a 15% pulley it will be going even quicker - possibly faster than the manufacturers reccommended limit - so will be generating alot of heat and increase air intake temps. The drop in boost will probably be there, as you point out, to protect the engine.

[brainycheddar]

on my car when the inlet air temperatures go above about 100 F I get a drop in boost and the timing gets pulled at WOT.

So why does the charger get hot?

You've got to thank a man named Boyle for figuring this on out.
Boyle's law states that if a certain volume of air is compressed, the temperature will increase.
so, if stoichiometric pressure is 14.7psi at sea level, and you are running 16 psi of boost, you are more than doubling the density of the incoming air. The temperature will increase plenty because the desity is 2 fold what it was a second ago. That, plus heat soak of the components of the engine (remember: heat rises) and you've got a hot charger.

So that should account for some of the boost drop. When the engine's IAT's are so hot, also the intercooler can't keep up, with the demand, so it starts to heat up as well. (if you don't have an oil catch can, cleaning out your intercooler now and then can make your car much happier)

So we have established this drop in boost, but what about the pulled timing?

well, we already have deduced that the temperature is higher than normal for the air going into the engine. This air is hot, so the fuel coming into the engine is heated. as this warmer gas hits the even hotter cylinder walls and the scalding hot spark plug, and there becomes that distinct possibility that the fuel air mix reaches the flashpoint. the temperature where the fuel air mix spontaneously combusts. good for a diesel, not for you. instead of having a smooth flame from traveling from the spark plug, you get a mini- explosion that goes off before the piston is ready for it. this is called knock, and sounds like someones taking a hammer to your beloved engine.

In order to prevent this, the mini retards the timing and enriches the fuel mixture to cool off the cylinder. in a dyno you'd see this as a scary dip in torque all of a sudden.

So now we know why this is caused, how can we prevent it.

Cool down that incoming air:
by installing a larger intercooler and an oil catch can.

Cool down the engine to prevent it from causing engine knock:
not much you can do here except install a colder range of spark plug, I recently installed some iridium plugs and they work fine.

Warning: side effects include a happier engine, a grin across your face, and some more power....

[k-huevo]

The law which is attempted to be used as an explanation is the Combined Gas Law, of which Boyles’s law is one component. The bottom line is a pressure increase, not a drop in pressure, when a given volume of air is heated.

Pulled timing is being used indiscriminately here.

A cool, low pressure charge has a greater density of important Oxygen; some misplacement of the density explanation being used here also.

High speeds will create outstanding flow across the intercooler if the hood duct and foam diverter are in place and there are no air dams on the front in the form of giant running lights or humongous license plates to divert flow.

Loss of power or speed has not been mentioned so I would look for a pressure leak at the gauge fittings.

If there a decline in performance, look for a leak in the charge air path. If the tensioner stop strap does not have at least a half hole showing, the belt is too short or has stretched beyond usefulness for your application. Look for oil on the tensioner strut; oil leaking from a ruptured seal can contaminate the belt causing slipping also.

[lmfidalgo]

In fact no loss of power or speed occurs.
The intercooler is the original one and it is ok (foam duct and no lights or trims!). I have an ALTA oil catch can installed.
I do not see any belt debris and I can see almost a complete hole on the stop strap.
I think that most probably I'm experiencing a "protection system" activated to protect the engine, in Portugal we are in summer it was 33ºC - 91F when it occurs.
Question: Do my Mini have a "protection system" like we are talking about here?
Thanks for All!

[k-huevo]

The MINI has a fail safe mode or “limp mode”, which will keep rpm under 2k; it will feel like running on 3 cylinders and have no power, not a behavior like you’ve mentioned.

[MINI-Morgan]

More than likely your intake temps are hitting 60degrees and your timing is being pulled right back. the Temps are effected largely by the temp of the intake manifold too and not just the intercooler. Doesnt explain the loss in boost pressure though....

[k-huevo]

I’ve seen timing retard at lower and higher IAT than 60C; that claimed 60C threshold can not be universally applied.

The SC does not create boost at all times, when there is throttle lift off the by-pass valve opens and pressure drops, the change is in moments not minutes. Perhaps Imfidalgo is letting off the gas a bit when he reaches a cruising state?

[MINI-Morgan]

there are many reasons for the timing to be pulled but as yet we cant confirm thqt it is even happening.

I dont think anyone has really come up with a reason why there is a boost loss yet. Its a very simple system and to loose 6psi doesnt sound like a hot charger to me. All I can think of is a boost leak that forms at high temp or more than likely the ECU is trying to protect the engine and is closing the throttle body slightly to cause a vacuum. that will then cause the bypass valve to open also.

[k-huevo]

A leak perhaps as a result of high pressure, not high temp; monitor IAT during a variety of road usage and you will discover transient temperature peaks greater than your fears can handle.

The ECU doesn’t “slightly” close the throttle body without input from the driver which includes cruise control settings.

[lmfidalgo]

Quote: Originally Posted by MINI-Morgan (original)

there are many reasons for the timing to be pulled but as yet we cant confirm thqt it is even happening.

I dont think anyone has really come up with a reason why there is a boost loss yet. Its a very simple system and to loose 6psi doesnt sound like a hot charger to me. All I can think of is a boost leak that forms at high temp or more than likely the ECU is trying to protect the engine and is closing the throttle body slightly to cause a vacuum. that will then cause the bypass valve to open also.

I agree with you "Morgan"!
In my opinion I think that with the conditions verified:
>30ºC outside
>WOT 3 minutes at least!
>235Km/h claimbing!
>JCW air filter box + Mini Madness high flow filter
>JCW 380 injectors
>Iridium NGK spark plugs
>15% ALTA pulley + shorter belt

The ECU is trying to protect the engine slightly opening the by-passe valve...but I'm not sure!
Anyway tomorrom I'll check every hose conections to the pressure gauge and discard a possibel leak on the hoses.
I'll give you guys the result!
Thanks for all!

[MINI-Morgan]

Thats the only way I could think of that the ECU could do it. Unless it doesnt injector and ignite on one cylinder and uses it as a cooling chamber.