Hello all..

currently running a eurocharged stage 2 and modalworks downpipes. Ever since the tune I’ve noticed that above about 5k rpm the power seems to fall off pretty hard when under full throttle. The strange thing is that if I take my foot off the gas to maybe 3/4 and roll back on above 5k it actually pulls much harder than just flooring it.

I’ve read about “soft codes” that may cause power loss like low voltage or an exhaust flap not opening fully but I don’t have a way to test for that at home. The car is not throwing any actual codes.

prior to tuning the car I did brand new plugs and coils, gapped the plugs to .022 like I’ve read about here.

just wondering if any of you have experienced anything similar and what you did to fix it. Also anyone with similar tuning and mods does your car pull harder all the way to redline or does it drop off a bit at the top?

really appreciate any help guys

 

*****If your car has stock turbos, the turbos are out of oomph by about 5k with downpipes, assuming adequate fueling and a proper tune for the mods you have on the car, etc.. My car with stock turbos, stock tune, stock downpipes, etc.. had peak HP between 5.8-5.9k or so, and peak torque around 4.2-4.3k or so. With the downpipes, the stock turbos started running out of steam at a lower rpm due to not being able to flow enough air to keep up with the greater exhaust flow out of the engine - so more total power and torque from the downpipe install, but the power band shifted somewhat down in terms of peak and above 5.5k or so rpm there was a very marked decrease in power with a lot of heat increase due to compressor on the turbos not being in their sweet spot anymore and out of their efficiency band.

Bigger turbos with a proper tune and downpipes will flow a *LOT* more air to a higher power band and depending upon how big the turbos are pull very hard at higher rpm, and if you have more boost and adequate octane and fueling, pull a *heck* of a lot harder at higher rpm as well. A lot of thinking goes in to sizing turbos for a motor and on a street or passenger type car stock turbos are generally sized for snappy response with low lag as most driving is done at street speeds. Bigger turbos feel laggy down low and seem slower on the street unless other things are done to mitigate this, but they flow a lot more air up top and shift the torque and power curve to the right, sometimes significantly.

Below are a couple of dyno pulls on one of my cars. Stock everything except an intake on the *earlier* pull (higher numbers first pull..second pull was stock air cleaners and housings,etc..Verifying how much restriction we could get away with, and doing fuel trim adjustments, blah blah), both on pretty hot and humid days but still within specs for the car (C63s). These were baseline pulls to make sure the car was ok before throwing on parts. I have lots of other pulls, including with downpipes, intakes, exhausts, and turbos, etc... Experimenting with different tunes and fuel/air trim ratios, etc.. for optimization of the car with the parts I've been messing with.

The modified graphs look a lot different in terms of power band movement due to increased flow, etc.. Power curve shifted down with the stock turbos and opened up exhaust (DP, secondary cat delete, 200cell cats). More power and torque down low with the stock turbo setup and a more marked drop in power above 5k, again with the stock turbos. Again, higher peak power in terms of HP and torque but the band shifted left a bit due to less exhaust restriction. The stock turbos are nice street turbos and a good balance for most people, but are limited in terms of higher numbers just due to mechanical limitations of the inducers/exducers size.

Anyway, dunno if it answers anything, but it is what I have observed with actual dyno testing on my car versus a butt dyno, or because the car sounds seems more powerful after leg day at the gym, or whatever..



Neato torpedo Non-butt Dyno Testing..

 

Same mods same problem no solution.
​​​​ my car gave 330 hp on dyno and feels like no boost after 5k rpm and no leaking boost
I ordered handheld and i’ll try to re tune