stock pipe off turbo was told better than 3inch round? - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 3 (permalink) Old 05-30-2011, 05:08 AM Thread Starter
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stock pipe off turbo was told better than 3inch round?

Hey Guys new to forum and always ran my 95 powerstroke stock...I'm just able to do a few upgrades. My mechanic I've used since its been new has always told me that the stock pipe off the turbo is the Equivalent to a 4 inch round pipe and has no restriction for mild chips/reprogram. We get into it every time this comes up as everyone is replaceing it, He's A GREAT Ford trained powerstroke MECHANIC owns and operates a powerstroke only shop & LOVES THE 7.3. He's has talked me into leaving it (Squish pipe) doing a cat delete & 4' stainless all the way back with a no restrick muffler & a tymar type air system & reprograming the computer & steping up fuel psi......I've lurked forms and never seen this arguement...any input greatly appreciated
thanks Dave
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post #2 of 3 (permalink) Old 05-31-2011, 03:39 AM
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In the case of volume, the stocker may win. The issue is not how much air it could hold, but how much it can flow. Air tumbles and rolls through the exhaust, so a smooth round pipe can and will out flow a larger (volume wise) down pipe. Think of the exhaust exiting the turbo as a tornado. It needs to be round to work right. Take a 3in soft foam ball and shove it through a 3in down pipe, now try that with the stock pipe. See how the ball deforms? That is what the stock pipe does to the exhaust. Invest in a good DP and you'll never regret it.
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post #3 of 3 (permalink) Old 06-04-2011, 09:32 PM
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I agree with your mechanic and not....

The exhaust gasses are hottest right AT the turbo, therefore they occupy the most volume there as well, the further up the system the larger it should be. BUT, for mild to medium mods, Ford has more than enough pipe for you stock - he's 100% right.

Now, adding size or "low restriction" exhaust down-stream is a joke unless you are building a pulling rig, then it has value. I don't mean that if you EVER pull anything it has value, but if you pull on a track (compete) or pull EVERY DAY for a living, then it has value.

Why and am I on [email protected]? LoL, no. Exhaust cools RAPIDLY as it leaves the turbo and flows thru the down-pipe, that is unless you are PULLING HARD, then it carries the heat further back. The exhaust and muffler are more than big enough for even mildly modded engines because the exhaust VOLUME has decreased significantly due to it being cooler than at the turbo.

The only way to KNOW if your mods require a less restrictive exhaust is to weld a bung just after the turbo and monitor EBP. If you lock the warm-up device open, you can simply move the EBP sensor to bung on a length of tube to keep it from getting too hot and watch EBP with a scan tool. You will be supprised at how little restriction the factory exhaust has.

Now that I said all of that I need to clarify one thing. That ASSUMES the mods don't increase RPM more than a couple hundred. This is because exhaust restriction is a cube function of flow velocity (RPM if you will), adding RPM (a WRONG but favorite trick of Tooners) to get more HP on the dyno can cause the exhaust system to be a restriction on one truck where another equally powerful truck might have the stock system; due to better programming and not using RPM as a HP crutch.

'93 F-250 HD, 7.3L IDI, 5spd - FARM TRUCK
I Support: Trailer brakes an every axle over the towing vehicle's GVW; CDLs for RVers; Safety inspections for ALL vehicles and 6 axle trucks (97K GVW proposal).

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