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Performance Exhaust Modifications Part 1 |
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For any vehicle, and diesels especially, moving air out of the system is at least as critical as getting it in. When you have upgraded the engine with a chip or tuner and an intake, the next step is the exhaust. Actually, if you are running the truck hard with a big chip, it needs to be done at the same time, or even beforehand. Often, there is a synergy between those three, and the best performance comes when all the systems have been upgraded.
For a Diesel, a four inch exhaust is the minimum improvement. Crazy levels of performance may need a five inch, or dual four inch system. Newer Fords and Chevys run a stock three and a half inch system, while the 600 series Dodges have a stock four inch system. However, the Dodge system is not mandrel bent and the muffler is very restrictive. If you do the math, a four inch system yields a 30% improvement in flow over a three and a half inch one. This can result in a 100 to 200 degree F drop in Exhaust Gas Temperatures (EGTs). With many of the performance improvements to a diesel, fuel is added, resulting in higher EGTs. If these become excessive, the cylinder heads and turbo are at risk of being damaged. A set of gauges or at least a pyrometer keep you alert to this. That is where the four or even five inch exhausts come in.
Good Exhaust systems are full four inches in diameter for the length of the system, as well as mandrel bent, which prevents those flow robbing wrinkles. The muffler is also a critical component. It should also be a full four inch pass through. Any restrictions here can undo most of the other improvements that were just made. Sometimes, allowances have to be made for vehicle geometry. A Ford 6.0L requires the firewall pinch weld to be folded over in one spot to allow clearance for a full four inch turbo back exhaust. A Chevy or GMC Duramax can only be done from the Downpipe back, due to the exhaust manifold geometry.
Four inch systems do help some with power and economy, as backpressure is reduced to the engine making it more efficient. However, it does not yield nearly as much as a good performance chip. It will help the turbo spool up a little faster, but the primary point is to allow for increased exhaust flow. It's all about the EGTs.
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