As many of you already know I am the one who went remote mount twincharged. Im starting this separate thread to get more attention to this unknown problem as its been well over a year now without having my car. All together this set-up has been a disaster and should never have been done but a new issue has occurred.

Previously after the build was complete the car put down about 408hp with the 2.5” exhaust. There was extreme back pressure which caused a resonator to explode so SMG wanted to go larger on the exhaust and eliminate the resonator to relieve restriction. This was done and when put back on the dyno the car lost several horsepower. Went down to about 350 and lost about 4psi or so. Boost was expected to drop as more flow was now present. However after tuning the most we would get out of the car at the new boost level was in the 360’s. He turned the boost up to 28psi (where it was when the 2.5” exhaust was installed) The best he could get out of it was 384hp. The tune was rich at this time so he tried leaning it out a tad bit. Next pull on the dyno horsepower was lost! Back into the 360-370’s. This made no sense. On the dyno graph (also on twincharged thread) power was improved down low but after about 4500 rpm we started loosing power. Several tuning hours were spent with no luck.

Next he started searching for boost leaks. Was able to find one on the intake on this rubber nipple. He replace it and we gained about 8hp. He at that point replaced all couplers, t-bolt clamps, o-rings and gaskets. No leaks were found other than that one i mentioned.

He checked to see if there was a boost difference from the rear mont turbo and the intake manifold. At the turbo we saw it spike to 36psi and slowly drop down and at the turbo it spiked close to 30 and stayed around 27-28ish. We eventually eliminated the turbo and took the waste gate out and ran the car with just the supercharger. While under full acceleration boost maxed to about 12psi then slowly started to drop to about 8 where he let off. This proved that it had nothing to do with the turbo or the charge pipe.

Everything was rechecked at this point. The supercharger was even swapped to test that, we tried not using the phenolic spacer and he checked every connection and seal. A compression test was even performed and passed fine with about 150ish in each cylinder. Everything connected to the bypass valve has been eliminated and still no luck.

So we have no idea what is going on. My IATs are perfect averaging in the 90’s. I have every cooling mod available pretty much. More information can be found on the twincharged thread... https://www.cobaltss.net/forums/2-0l...6/index12.html ...Most on this subject is on page 12 but other info is on previous pages.

This boost drop has been verified by the MAP and we have used both electronic and digital boost gauges to test with. If anyone has any ideas or suggestions on what we could try or could be the problem it would be much appreciated. All my modification are on page 1 of the twincharged thread. Thanks in advance

 

bump

 

did he check the injector o-rings?

Try replacing the bypass check valve next to the evap canister?

belt slip?

 

He said the check valve next to the evap is completely disconnected at the moment so there is no control of the bypass on the blower. He said he did that on purpose. He said the o-rings on the injectors are fine. Belt slip was what seemed to be a possibility though there was no sign of wear or belt wear. All the lettering was still on the belt and looked good as new. He even tried swapping belts as well as different pulley sizes. They are trying something with the pulleys tomorrow to make the belts grab better if that was an issue however we don’t think it will be.

 

leak down test? Smoke test? You don't magically lose 50whp by going from 2.5 to 3" exhaust

 

Check the boost bypass actuator for sticking(inspect the link for corrosion and move it up and down)
Also if the boost control selinoid is not working properly it could have the same affect?
I'm no expert but you seem at a loss so I thought I would throw a idea in.

 

Thanks for the ideas, I passed that info along and that all checked out ok. He brought my car to another shop to give it a smoke test and no leaks were found. Belt slip seems to be the only other resort however there is 0 signs of wear or slip. We modified the pulley to grab better and he is now in the process of making something to give the belt even more tension. Its just weird that this problem never occurred until immediately after swapping exhausts