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  Topic Review (Newest First)
11-21-2019 03:01 PM
Jjorgis5569 A straight pipe will lose some torque on the lower end of your power band, but on a diesel that isnít an issue. I work with turbines on a daily basis-basically a turbo but with 6 axial stages and one centrifugal stage on the compressor for an Allison c20. The ďexhaustsĒ are literally a few inches long, so letís call that a straight pipe. If we were to decrease the pipe diameter, the result would be higher TOT (EGT as itís known here), which would cause a compressor stall (interruption of airflow over compressor blades when the supplied airflow cannot meet the airflow needed). Thatís the semi scientific explanation. Basically the air becomes turbulent, and can even reverse direction.
More restriction=more stress

Itís my long winded way of saying the tech is full of it, but I can back up my explanation with physics and real world experience.
11-21-2019 03:51 AM
alaskan155 will say after running a straight pipe/6637 for 80k miles, my turbo finally gave out at 233k....

the mechanic is partially right, with the 6637 and 4" straight pipe the stock turbo issue is surge when towing and running a tune. the turbo will start cha cha cha going up steep hills unless you drop a gear and that will kill it in short order so i would recommend changing to a wicked wheel/better housing.

what finally killed mine i think is the combination of stage 1 single shots and the bellowed up-pipes not leaking compared to the stock.
11-19-2013 09:42 PM
JSchuricht The only way the exhaust can cause turbo damage is if the exhaust isn't properly secured to the chassis and is hanging off the turbo. The weight and vibration could break something over time. As for the back pressure, it's a non issue. You can take a 90 and run it from the turbo right out of your hood without causing any damage.
11-19-2013 07:23 PM
Arctic Driver Thanks to both. I was 99.84% sure that there was no risk, especially considering all the 7.3s running straight piped with no problems (myself included on the original engine). Even looking at the design of the exhaust side turbine, it seems that if the turbo is compressing more than it should, that is what the wastegate is there for. I'm not worried about the engine/valves pre-turbo since the turbine creates it's own backpressure. Once I'm done with this move and have a better job again I will free the engine once again.

Has anyone other than myself heard someone claim that lack of backpressure damage the turbo? (Just trying to be extra extra sure. A major break down would break me.)

11-19-2013 06:57 PM
'01SilverBullet That straightpipe has no effect on the turbo whatsoever. It was more likely than not, a defective unit from the factory, that does happen on occasion.

Think about all the straightpiped diesel pickups and semi tractors on the road. If not having a muffler hurt anything, they wouldn't be doing it.

So, in short, the dealer was feeding you a line of BS, plain and simple.
11-19-2013 06:46 PM
blue99stroker straight piping it will have no bad side effects.

that guy is full of baloney.

it is actually easier on the motor, the stock muffler is restrictive and just puts more load on the engine.

putting the turbo out of its efficiency range will definately damage it over time. but it takes lots of miles to do this.
11-19-2013 06:41 PM
Arctic Driver
Straight piping damaging turbo?

Hello, I have searched long and hard, but perhaps not in the right places, or not long enough, or hard enough... Whatever the case may be, if the answer is already either on this site or out on the internet somewhere, then I apologize for wasting your time.

So here's the story, I'll keep it as short as I can. I bought my truck, being a '99 F-350 7.3. I drove him, worked him, and loved him for quite a while. Shortly after I bought it I straight piped it. I left the original downpipe on, made a bracket to support the end, and added a cheap 45 degree elbow to direct a little exhaust out, for whatever good it did. LOVED IT! Between the DIY 6637 and straight piping it, the turbo spooled faster, at less RPMs, felt like more boost (no gauges or scan tool at the time sadly), more power, less fuel consumption, beautiful sound like angels and gods singing together, blah blah blah. Never a problem (aside from starting the engine in a sleeping neighborhood...).

Took a job hauling horses across the country. Ran well, but the construction company that owned the truck before me ran the engine out of oil several times. The engine finally gave out, and I replaced it with a brand new from-Ford engine. Did the swap myself. Made a few trips, put several thousand miles on the engine with no problems until I was coming home on the last load for that group and I started blowing smoke, not much at first, then more.

Anyway, the turbo came apart on the exhaust side THANKFULLY, and sprayed oil in the exhaust. Took it to Ford for the warranty and they got it replaced at no cost to me. Then the tech pulled me aside and said "We weren't supposed to warranty the turbo because part of the exhaust system is removed."

His explanation almost made sense, enough to scare me from straight piping it again even after the warranty ended because IF he's right, I can't afford a new turbo. According to him, straight piping it increases flow but puts too much pressure on the turbo straight out, wearing/damaging the bearings due to increased load... in other words too much force perpendicular to the shaft instead of flowing around it. Without conducting an in-lab test on a dissected 7.3, it almost makes sense except for one glaring fact: My previous stock turbo with almost 200,000 miles on it never gave me a problem no matter how high, hot, or fast the exhaust was pouring out. Also, tons of 7.3 owners straight pipe their engines from stock DP to 5 inch high-flow hoopy-do mirror finish DPs.

I think the dealerships are full of... baloney, but again I can't take a chance on ruining my turbo at least until I have a spare sitting in a box in case they speak the truth.

Your thoughts? Expert opinions and scientific explanations are preferred, I don't care if you prove or disprove the stated concept, I just want to know. Also if you know of a place where Ford ACTUALLY STATES it as a fact rather than a tech and a former tech that I trust, that would be great.

I want to free up the engine load by straight piping not only to get more power in reserve and better MPG, but less wear and tear overall performing the same task. Not at the expense of a turbo though.

I'm open to all of your thoughts and humbly appreciate all advice you can offer.

Thanks in advance!

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