not to sound ignorant BUT I am fairly new to the 951 and turbo cars in genereal:

1) what does a manuel boost control (MBC) do?
2) where does it go?

And, are there other modifications you should do if you are installing a MBC?

thanks
tom

 

The MBC is like a check valve in that it is plumbed into the wastegate line from the Banjo bolt. (this is the 90 degree elbow on that IC pipe on the left side of the intercooler) It's purpose to to hold to a certain psi of boost before opening and thus allowing the wastegate to open.

If you install it and run more than what ever boost you are set up to run, you would need new chips (to add more fuel to the aditional boost/air you just put into the motor) and an aftermarket boost guage, as the stock guage has been found to be fairly inaccurate, and at least, hard to read in specific psi.

 

You WOULD need a boost gauge to prevent you from over boosting, which leads to blowing a head gasket.

Second, You can't just add a boost comtroller, since the factory computer has a boost limit of 12psi or something.

Over that, you NEED chips that are tuned for say 15psi or more.

If you get 18psi chips, and run say 15 psi of boost, then you are going rich, since more fuel is added and you are not using the boost.

If you have 15psi chips and go for 18psi of boost, then your running lean, where too little fuel is burning.

 

Thanks for the good info. When I purchased the car the PO indicated that the car had been chipped and the WG was shimmed - how do I the findout what the boost (psi) range is for the car (or installed chip)?

 

Best Bet, unless you have the recipts is to take apart the DME and KLR, which are located under a wooden panel in the passenger footwell. Most chips are set up for running 15psi boost. But it is better to be safe than sorry. When you take apart the computers, make sure to disconnect the battery and if you have one where a leash to ground yourself to the computer. Good luck and welcome to the boards.

 

OK - so if i have a chip that allows 15psi boost - this means I can adjust the MBC to achieve a MAX of 15psi at WOT - correct! Therefere, it is good to have a more accurate boost gauge. In addition, what about the air/fuel ratio - I suposse this gauge would be nice to have also? how do I change the air/fuel mixture on these cars if she is running lean or rich?

tom

 

"In addition, what about the air/fuel ratio - I suposse this gauge would be nice to have also? "

Make sure you get one that's actually accurate. The only one that works with the standard O2-sensor is the digital unit from Link (analog needle round display). Otherwise go straight to a wideband O2 setup.

"how do I change the air/fuel mixture on these cars if she is running lean or rich?"

My GURU chip-upgrade is spot-on for stock cars. No need to adjust air-fuel ratios. Some minor adjustments of air-fuel ratio can be done by increasing or decreasing boost. Same with fuel-pressure. This changes the entire fuel curve up and down.

To make changes in only a single spot on the fuel-curves, or to make adjustments in opposite directions close to each other, you'd want a signal-interceptor massager. Something like the SMT6 or Apexi S-AFC would work.

 

You need to find out what chips you have first to see if you can run 15 psi. Then get a boost gauge to see what you are running. My guess is that you have a jetted banjo bolt. Which is the bolt off the intercooler pipe from the turbo to the intercooler. If you want to know your a/f don't bother with anything but a wideband. You are throwing your money away, I know from experience, because I have one. When I dynoed my car and it said I was running rich I was actually running lean. Also after all this is found out, it is a good idea to get the car to a dyno and get the a/f checked under load.

 

Guru chips are nice but you need to dyno to make sure your afm is working properly, so I would suggest sticking with what you have and getting it dynoed.

 

Danno: What about other a/f ratio analog gauges out there that are similar to the link? they read 20:1 to 9:0. Arn't these as reliable as the link analog ones? and use the stock o2 , plug and play basically?

 

Well said, I recently made some changes and tried to adj my fuel pressure based on my ARM1 was telling me..hahahaha, went to a dyno and it was so far off it wasnt funny. Ive got my car in the shop right now getting the wideband sensor mounted in my testpipe. A narrowband makes a neat light show...thats about it. Heres a good link:

http://951forums.com/forums/index.php?showtopic=48

 

Wideband O2 setup?

have you had any luck with Autometer gauges? please further explain your GURU - upgrade? is this something that I add to my computer OR do I swap out the chip I have and use the GURU chip you speak of?

I'm looking for insight - this is the first TURBO car I have even owned. I understand the concept of a TURBO, but I am completely in the dark on how all the pieces work together - looking for some education!

thanks to all for your knowledge and guidance - I've been an air cooled Porsche guy for to long!

tom

 

where do I find a wideband O2 set-up?

 

you can do a search on google for one, or right here on this board (951 forum). Just this forum I know we have alot of people using the Zeitronix Wideband, Innovate, PLX, Tech Edge, they all have websites and are universal.

 

The problem with those a/f ratios using leds is that between each mark you cannot tell weither if it's 12.7:1 or a 13.1:1

Our cars run on a 12.5:1 ratio, on LED gauges that would read rich (blue LEDS?)

Save the money, get an analog or wide band