Turbo Caravan exhaust backpressure study

The reason I purchased my Caravan was to have a vehicle that could be used for towing but would not clean me of house and home when it came time to pull up to the pump. It's primary use was to be for towing, it had to have a/c and it had to be fairly quiet because several of my racing excursions involved 6-20 hour spans behind the wheel! I had a Dodge truck that I used before, it was ok but got single digit gas mileage, was moderately loud and a 110 degree day at the track convinced that a/c really was needed necessity. 

pressure tap installed pre-catalyst

On selection of the exhaust system components I knew mandrel bent tubing was a must, 2.5 inch was chosen because the van was going to spend the majority of it's life at 3000-3300 rpm. Muffler selection was my old favorite the Hooker "max flow" (PN 21602) and for catalytic converter replacement a Edelbrock RPM series unit (PN EDL-5500) was chosen. This seemed to be a good time to do some information gathering while I was doing a system install. A pressure tap was located before the converter and a boost & backpressure gauge was mounted in the passenger compartment. 

For an engine the van has a 89 2.5 with no balance shafts, the swirl head has been ported with backcut valves, it has a ported exhaust manifold and a Garrett Turbo II turbocharger. Boost was regulated by hooking the actuator line directly to the intake, observed boost was 8 psi. Pressure readings were all taken at 6000 rpm, WOT in second gear.

Old vs. New system

The results.

Exhaust system PSI vs. engine RPM

The testing was completed as follows- 

Test 1- baseline with stock system
Test 2- stock cat, mandrel system with Hooker muffler
Test 3- stock cat removed, Edelbrock RPM unit in it's place.

WOW. I observed a peak pressure of 9 psi with the stock system in place! Which is odd considering how well the van ran. Replacement of the rest of the system only provided a modest reduction of backpressure compared to replacement of the factory catalytic converter. ZERO backpressure at any RPM or engine load. I was very pleased with the results, the van had more zip, better gas mileage and was very quiet. At idle you would be hard pressed to tell that the van had such a low restriction exhaust on it! Sounded just like a stocker. Under full load (when towing) it has a little noise to it, nothing nearly as loud as my Daytona though. More testing will be done when the van is fitted with a proper intercooler and the boost is raised to 20 psi.

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