What does backpressure do to a motor?
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From: Thornton, CO & Pasadena, MD
Ya same one. How do you know what muffler or remember what muffler i have on my car? LOL props to you if you are corect but also kinda of creepy. what else do you know about me?
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So if DB tuned the car to 40lbs as he says he did and then I drop the exhaust at my house, not the dyno and hammer on it is there going to be an issue? Can I go lean, rich = smoked motor? I would assume I could since when the tuning was done there was no change in how much fuel or air was needed since there wasn't an increase in power.
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Yes, it absolutely could. If your muffler is in fact this restrictive, once you remove it the car is going to make a lot more power. Its probably going to make more more power across the map, but especially as boost pressures rise. You could very well discover that the car is lean everywhere, but especially 25psi and higher. I would be very careful or you'll be paying Dave to fix your new engine
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One of my buddies suggested I look into this:
Can someone explain this a bit more? Here is what he said (copy & pasted)
"hey josh are running AEM EMS? just a thought, with my car i was boosting 29lbs and making 0 hp. The turbo was spooling pushing the air the the engine was running but no horsepower was coming out. I had no other issues except this -> "John Doe" went into the ecu, (forgive me here i don't remember what it was) and corrected so small none CEL light problem that was causing an incorrect translation of air flow to power push. i only mention this relatively because i was suppose to be at 350 and i was only at 230. so your 600+ instead of 800+ sounded like that. I hope the exhaust and air filter take off works."
Can someone explain this a bit more? Here is what he said (copy & pasted)
"hey josh are running AEM EMS? just a thought, with my car i was boosting 29lbs and making 0 hp. The turbo was spooling pushing the air the the engine was running but no horsepower was coming out. I had no other issues except this -> "John Doe" went into the ecu, (forgive me here i don't remember what it was) and corrected so small none CEL light problem that was causing an incorrect translation of air flow to power push. i only mention this relatively because i was suppose to be at 350 and i was only at 230. so your 600+ instead of 800+ sounded like that. I hope the exhaust and air filter take off works."
Actually it can. If you have a boost leak, say the compressor is pushing 45 psi of boost and 80 lbs/min of air, but only 40psi and 70lbs/min of air is making it into the engine. So the turbo is doing a lot of extra work which means it has to spin a lot faster. The turbo spinning faster creates more backpressure. On the top end of the operating range, the back pressure goes up faster than the positive compressor pressure. So, with the boost leak, the turbo is doing a lot of extra work creating a lot of extra backpressure due to the turbo spinning much faster having a negative impact on volumetric efficiency. Therefore, no power increase. 
Is there anything else you'd like to comment on?
Is there anything else you'd like to comment on?
Or your saying that multiple shops and tons of different people wouldn't have checked a car for boost leaks?
Good noob suggestion on the boost leak.
And yes josh if you find a restriction and fix it the car will run lean because although it was tuned at 40 psi it was based upon the current VE at that pressure range. So all of a sudden you go from not very efficient and low overall airflow of the engine to much more efficient VE and airflow actually moving through the engine and not just creating a high pressure on the intake side.
Thread like this makes me not want to put more money into the car. I am trying to hit 500 and am 66 whp short. At 28psi but any more boost doesn't not net more power 
I was just about to swap everything out, as my tuner says a bigger turbo isn't likely to make it better.
I was just about to swap everything out, as my tuner says a bigger turbo isn't likely to make it better.
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Thread like this makes me not want to put more money into the car. I am trying to hit 500 and am 66 whp short. At 28psi but any more boost doesn't not net more power
I was just about to swap everything out, as my tuner says a bigger turbo isn't likely to make it better.
I was just about to swap everything out, as my tuner says a bigger turbo isn't likely to make it better.
I wouldn't lose your mind over it like I am. I've literally replaced everything that we thought of. You only running a stock turbo probably haven't or are at the ends of the turbo where as I am not even in the thick of the powerband for this turbo yet its not making power. Slight difference between my car and yours.
It sounds backpressure related. I had a friend with a small section of stock pipe still in their exhaust. Car wouldn't make above 300whp (Civic) and once it was removed it gained 150whp. No joke. I am surprised you never tried unhooking the exhaust.
Did Dave confirm visually that the varex butterfly plate is fully opened? I suggest the 3.5" inlet Varex muffler if you are running larger than a stock turbo. I personally haven't seen a varex exhaust hold back power on the few cars I have tuned with them on pump gas although they weren't with such a large turbo as the OP's.
-Jamie
-Jamie
Last edited by Dynotech Tuning; Jun 19, 2013 at 09:59 PM.
-Jamie
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From: Thornton, CO & Pasadena, MD
After someone on this thread pointed it out I don't have a Varex like originally thought I believe I have the Aeroturbine muffler. Sorry for any confusion, car isn't in my possesion yet so I couldn't run out there and look before posting.
