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SRT Prowler Project: Plymouth with 6.1 Hemi V8 Engine

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by Trey Byrum

I have been a proud Plymouth Prowler owner for over ten years. I absolutely love the car's style, the thumbs-up, and overall design. To this day there isn't another car that I see that looks so good and is so unique. Being just a weekend car, I have always wanted to keep the thrill of good looks with the power to match and its the only thing that has fell short to me over time.

Every article says it should have had a V8, but it's still the best.

I added gears, intake, headers and still always wanted a bit more. After that started drag racing for fun; everyone loved the ride but always fell short on third and fourth gear - but still fun. The biggest moment was a dyno day in Florida, everyone was excited about the Prowler, but even with all my mods, it only scored 196 hp to the wheels; I felt a bit down vs the other cars, everyday cars, pushing closer to 300hp.

Since this time started exploring all options to put power into the Kat, from twin turbos to superchargers to 4.2 strokers to the 5.0. After many years of review, I decided to go with the big boy Hemi 6.1 SRT V8 conversion, with Performance Innovations. The SRT-8 engine packs 425 horsepower and 420 ft-lb torque, in a car that will be over 1,400 lbs lighter than its brother Challenger or Charger.

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Just after a few weeks of talking to Brendan from Performance Innovations (out of North Carolina) and hearing his passion for the project, I got on and scheduled a private hauler to take the Kat from NJ to NC for a long winter nap.

There a thing about trust and taking risk is always there especially when you love your car, and it's a low production vehicle. But after talking with so many different people (fellow owners, shops, mechanics, etc) and hearing his personal experience with custom projects, it was a done deal. The goal is to equalize the delivery across the power band, while still being able to enjoy everyday driving since this motor is a stock high performance engine.

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A number of parts went up for sale, headed to fellow owners in Texas, the UK, and Australia.

We had to make a custom bell-housing engine adapter to adapt the 6.1 Hemi engine to accept the Prowler style drive shaft; the rear engine mount is integrated into the bell-housing. The team had to shave a part of the railing to clear the frame and tweak the oil pan as needed to insure a good clearance underneath.

NHRA that limits convertibles without a roll bar to about a speed of 13.5 on the 1/4 mile. With the 6.1, we plan on smoking that, so we started looking for options and to also change the looks up a bit. We found a great deal on a nice used black TGF hardtop in California on Craigslist. It will support our new red on black theme and should buy some more time for track days. We also picked up a nice used modified grill from a fellow owner.

To help with braking, we decided to upgrade the front rotors and brake pads all around, with EBC 3GD sport series rotors (dimpled, vented, and slotted). There are few options for back rotors, but you can drill holes in the stock ones for better cooling.

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We tried it with a hood scoop (for clearance) but I wasn't sure of the look and wanted it to be functional, and Brendan suggested an old style Mopar shaker hood. We ordered the Autoform design; they build the only fully functional and integrated shaker, with a built in K&N, full water drainage system, and a cover that is moveable inside for more protection on rainy days. It's designed for a Challenger. It was relatively easy to modify the shaker, but cutting the Prowler's aluminum hood was no picnic.

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The Prowler was a low production car, so not many high performance bolt in options exist; when you look to do something radical like putting a SRT-8 Hemi engine in a car that had a V6, pretty much everything ends up being a custom one off job. This is what makes the project complex, a ton of work, and it requires skilled builders to make it all come together. Take the headers and exhaust system . Most cars you can go online and order a high performance set. But where do you find headers for a 6.1 hemi engine that will work and fit in a Prowler? They don't exist, so with 30 hours or more of hand work and welding, the team at Performance Innovations converted a lot of metal to high performance headers.

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So anyone can buy a crate 6.1 engine, but how do you properly secure it to the frame in the perfect position, insure safety, the proper height, location and fit? Motor mounts where handmade by Brendan and the team to get this engine to sit perfectly. The oil pan sat a little low, but Brendan worked his magic again, fabricated a new pan, still insuring plenty of space for the oil and pump, with depth to recirculate. Great custom work, while still maximizing the core components and no worries for clearance. It's been pressure tested.

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We decided to get the headers coated by Jethot. They coat inside and out, it looks nice and can reduce surface temperatures up to 50% to keep things cooler in the engine bay. I also started thinking about is badging; I'm not looking for a sleeper car but want to keep it classy, so ordered these 370 Hemi custom ones for the side of the shaker. On the back, I went with the SRT8 tail badge. I also have a set of 6.1 Hemi side badges, and a small SRT badge grill.

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When the transaxle went back in, it was measured and calibrated to the millimeter. The tolerance was even better than factory, but if it's not tight all around, it can spell trouble. We used the existing transmission, but with an upgraded torque convertor, shortened drive shaft, custom engine mounts, and connecting it to the shaft differently. A stock V6 prowler V6 is rated at 253 hp @ 6400 rpm and 255 lb-ft of torque @ 3950 rpm. I'm putting in a 6.1 srt hemi with 425hp at 6000rpm and 420 ft lb torque at 4800, as well as intake mods. A stock Prowler may do 170 hp to wheels; I got 196 hp on the dyno with headers, intake, etc.

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I also ordered a set of "Lambo" doors from Vertical Doors, but the shop said they should stay stock for the overall quality, safety, and looks of the car; it would not be ideal for racing, either.

For electronics, we need a custom wiring harness; there are three computers that must communicate, one for the Hemi, one for the Prowler itself, one for the transmission.

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Building a custom Prowler hood: The team spent over a week doing custom fiberglass work to try to build up the hood using the custom trim ring to shape the hood. Overall, it was not bad, but required a lot of material and build up to make it to the lip of the shaker. They wanted to ensure the highest long term quality for the car, so Brendan and the team decided to take another route and start over.

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The prowler hood is made out of aluminum to save weight. The goal is to create a custom hood that integrates the shaker into the curves and design, so they decided to create a custom aluminum panel to raise the over hood to line up to the shaker so it will look more like a stock piece. Aluminum can be formed and welded, and then directly integrated into the current Prowler hood. This can insure for a permanently sealed solution as well as provide a rear nice look to the car.

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The first step was a custom trim ring to set the positioning and build up area. Then, using tape, the team laid out the build up outline design from the custom aluminum piece to be built, formed, and attached to the hood. It slopes, only leaving the top of the shaker sticking through - very creative. Brendan wrote:

There is plenty of clearance between the shaker and engine. About 1/2" all the way around. The same clearance that the shakers have in stock Chargers and Challengers. Also keep in mind the Hemi engine in a Prowler doesn't torque or shake as much like it would in the Charger or Challenger because the trans is not connected to the engine; the trans is what transfers the torque and with it being mounted in the rear, it won't torque like a Charger or Challenger, bolted to the back of the engine.
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With the custom shaker work and limited amount of space / visibility in the engine bay, we decided to keep the Hemi block as is (still orange) and ordered the OEM 6.1 coil covers instead of painting them red. Nothing fancy, just a coated plastic piece but seeing 6.1 Hemi (in white and red) under the hood and 370 hemi on shaker (like below) coming through feels pretty good to me.

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Performance Innovations is also making a hand-built custom radiator; the first 6.1 Prowler they built did not have air conditioning, but mine will. It has the condenser on the front with mounting bosses; they used the stock prowler condenser (black) and mounted it to the much larger custom Hemi radiator. It was pressure checked, submerged in a tub of water, to check for leaks. A Hemi compressor was added, with custom hoses.

In April 2012, with all of the buzz around the SRT Prowler project, I was invited by the SRT team to see the new Viper reveal in NYC. I had a press pass, and had a chance to meet most of the SRT engineers that worked on the Viper, some who had worked on the Prowler, and best of all, SRT CEO Ralph Gilles.

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We learned a few things on this project...

  • The Prowler uses an analog (mechanical) gas pedal, but the 6.1 Hemi requires an electronic pedal that sends a signal to the computer to control fuel injection. Since the last build that part number changed so a new pedal was ordered.
  • Oxygen sensors that pick up signals to control the engine also changed.
  • We also needed some new header spacers and custom radiator parts.
  • We needed a catch can (from Billet Tech in this case) for blowby, to slow down and filter oil that may otherwise end up in the intake.

The first official reveal of the car will be at the Chrysler Nationals on July 6, 2012.

Overall, the conversion is not a piece of cake, it takes time. If you are serious and interested in this build, I would give Brendan a call early on. You have to love the car a lot, plan to keep it a long time, and plan financially. You have to have a true passion for the project, be patient, take risks, and love the potiential outcome to make it worthwhile for you and the builder.

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If you talk with any Prowler owner or builder that has done a major build, there is passion you hear, it's a universal and priceless decision. I must have talked to at least a dozen people before I pulled the trigger with Performance Innovations. Now I'm one of them and why I decided not to keep it a secret, but to share the project with other fellow owners that may have a simular passion.

As for the cost, it's less than what I'd have to spend to get similar peformance from a new Corvette, Porsche, Camaro, Mustang, or SRT8; none look better or turn heads like a Prowler. I plan to keep it forever.

Is it worth it? Yes, I love the car and rather than trade it in, why not keep it forever with the power to match most modern cars on the street?

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