Map Limit 3D Table

[LeeE]

I want to control turbo boost by MGP rather than MAP. I set up a 3D MAP Limit table as per the attached image.

I was expecting the MAP limit to vary according to BAP. So if BAP is 102kpa the MAP limit would be set to 202kpa which would limit boost to my required limit of 1Bar / 100kpa MGP.

However it appears that the MAP limit only increments in 5kpa steps i.e 200kpa -> 205kpa -> 210kpa.

Can anyone confirm this please?

Thanks

[Adamw]

Yeah that table only has 5kpa resolution in 3D mode.  You will notice you can only adjust the cell values in 5kpa increments also.  

[LeeE]

That's a shame.

Is there any other way of limiting boost to allow for BAP otherwise won't I have to configure the limit artificially low to allow for cold weather temperatures?

 

[Adamw]

Does limiting to the nearest 2.5kpa matter?  You wouldnt normally be touching the limiter in normal use, this is generally just to stop engine parts coming out when something goes wrong.  

MAP is what breaks engines, not MGP.  

[LeeE]

13 minutes ago, Adamw said:

MAP is what breaks engines, not MGP.

That's interesting because I'd read that MGP was a better measure of how hard a turbo is working - are you saying that's not true because if so I need to re-think my strategy anyway?

 

 

[Adamw]

MAP has a direct influence on cylinder pressure.  Excessive cylinder pressure is what breaks pistons/rods/head gaskets/and initiates knock or pre-ignition.  

The engine has the same cylinder pressure and hence same load on it at 110kpa BAP and 90kpa MGP (200kpa MAP) and is does at 80kpa BAP and 120Kpa MGP (still 200kpa MAP).  

Yes, at low BAP the turbo will be working harder to achieve the same MAP so IAT and EMAP will increase, but these do not affect the load on the engine components.  These factors can become a big consideration if running large pressure ratios at high altitudes such as Pikes Peak, but generally these are taken care of with other safeties, not the MAP limit (usually turbo speed monitoring).  

[LeeE]

Great info - thanks

My situation is that until I upgrade next year my turbos are limited to 1 Bar boost (i.e MGP) as above this the ceramic wheels have a tendency to disintegrate. The engine components will take more than 1 Bar MGP comfortably.

So I want to run as close to 1 Bar as possible and have the wastegate table configured with MGP as the y-axis. However I have to configure the MAP limit for cold weather which results in under boost in warm weather.

I might be being overly cautious / greedy re boost but a MGP RPM limit would have been ideal.

What are these other "safeties" used at Pikes Peak?

 

[Adamw]

How much does your BAP vary where you live?  Note a MAP limit is going to start adding cuts when you approach it so it is probably more dangerous to your ceramic wheels than boost, im not sure that is a wise strategy.  I would be avoiding any limiters at all with those.  

[LeeE]

BAP can vary by around 9kpa which is 4kpa weather and 5kpa elevation so a significant amount when only boosting to 1 Bar.

16 hours ago, Adamw said:

Note a MAP limit is going to start adding cuts when you approach it

You can see from the MAP Limit table that I specify the cut 10kpa above the 1 Bar limit and have a control range of 10kpa so the cut will start just after the 1bar limit. I have specified a very soft cut (which feels like the OEM limiter) with a hard cut at the end of the control range as per the attached image.

17 hours ago, Adamw said:

I would be avoiding any limiters at all with those.

My logic was that if the rev limiter is no worse than OEM it should be ok on the ceramic wheels providing I'm not constantly hitting it.

Would be interested in your thoughts

[Vaughan]

you could put BAP on an axis of your MAP Limit table so that you can have different MAP limit values for different BAP values.

[LeeE]

It's on the y-axis as per my first post above:

22 hours ago, LeeE said:

I set up a 3D MAP Limit table as per the attached image.

 

 

[Vaughan]

26 minutes ago, LeeE said:

It's on the y-axis as per my first post above:

sorry, skimmed through

[Adamw]

When I used to play with GTR's a lot 20 years ago, the ceramic wheels would fly off at the slightest hint of stress if you had a free flow exhaust and touched any limiter at all.  I dont remember many of them running much boost or having boost spike issues.  

I cant imagine 20 years of fatigue has helped them, so I would definitely try to avoid any limiter at all and nurse those as best you can.  

[LeeE]

Thanks Adam