MCX 240 Lean AFR Under Boost

[zx4ever]

Correct me if I’m wrong but I think most mcx240 kits are running at 12 lbs of boost depending on elevation, and it compensates up from there. With the head shim you would not need any race fuel at all it might be in your best interest if you use the boost calculator on this site so you can see what octane you really need. I used to run av gas mixed with premium but a few years ago put in a head shim and run only premium now. Change out your sensor and I bet you are good to go.

 

[zx4ever]

Also it is really good practice to boost test your turbo system every summer. You would be amazed what can change from year to year

 

[MatthewW14]

I am using the AEM Wideband

You are correct- the headshim is supposed to be good for 91 pump fuel. I mix a marginal amount of C14 because 1) I have lots left from my race sled which will be no good by next year and 2) I don't trust the fuel around here to be true 91 anymore as I've seen it vary so much from tank to tank and station to station.

Thank you for the good advice though- I will try a new sensor, redo that zip tie, and keep the C14 out for a bit to see if it solves the problem. I will let everyone know if that solves the problem and I wasn't aware race fuel was so hard on sensors.

What do you mean boost test your system? Isolate each component and test it with regulated tested air?

 

[zx4ever]

I’m sure there is a proper procedure on the site somewhere but, I just made a cap to pressurize the turbo intake. Turn the shop air compressor down to 15-20 lbs. clamp a few hoses and pressurize the blow off valve with 20 lb as well and listen for air leaks. And then spray soapy water and find leaks. Mine is a front mount so it might be a bit different than rear mount. But the theory is the same. I also hear the rear mount headers crack quite often.

 

[ClutchMaster]

He’s talking about a boost leak test. You put your motor at TDC and pressurize the intake. A leaky BOV or hose will be found easily. With your problem that’s the first thing I would have done, but I wasn’t sure if you had a tester. If you have a leak in a certain area, it can cause your map sensor to read low and you’ll get a similar condition too what your getting.

If it’s your O2 sensor causing the problem it’s usually not boost related. You said it seems normal off boost so I was thinking not a sensor issue.

this is what I use, basically a regulator and some way to connect it too your intake system, post turbo. Shop air can be regulated to whatever pressure you run in your intake system. I check my evo @ 50 psi because normal turbo boost is around 45 psi. Go 5 pounds over what your system requires for peace of mind.

 

[MatthewW14]

Ah ok- Similar idea that I used to do for leak testing my 2 stroke motors. I will gear something up. Unfortunately the snow is depleting fast and with the covid pandemic we may not get up again to try it. I did run it on the stand with feather the brake to simulate resistance after I re-ziptied the lines and put a new sensor in. I was only able to get it up to about 3-4lbs boost but the AFR numbers stayed consistent around 12-12.5 so one of those may have solved my problem.

I examined my header and its all cracked. Collector is cracked, along with weld for the MCX pipe adapter. I guess with 5000km on it it was about due time. Debating on options now. Get the shop that build me my stainless tunnel dump to fab a new one, buy a new one, or aftermarket, weld up mine.

Has anyone converted a rear mount to front mount or are the heat issues not worth it?

 

[kinger]

If you convert go to a mid mount turbo set up with a XP gas tank and seat. No one has ever said the heat trade off wasn't worth it, just be smart with thermal management and you will be fine. Mid mounts on a apex completely change the sled for the better. Both balance, response, and handling. I happen to have both a tank and impulse mid mount header that may even fit your turbo, I would have to confirm. Good luck!