I have been wondering how the performance of the SLP/Roush/Hillbank Thunderbolt dual exhaust compares to the factory muffler/tailpipe. When SLP offered this exhaust as part of a performance option on the Thunderbolt Rangers, they claimed a 15 HP increase when used along with their cone filter. It doesn't feel that much stronger to me but sometimes it's hard to make an objective evaluation when the sound is different.

Lacking a dyno, I decided to run a simple acceleration test. This is not very scientific, just a back-to-back comparison. I scouted the local roads and found a deserted piece of country road with good visibility and no driveways or cross roads. A line of telephone poles provided convenient start and finish markers.

In an attempt to eliminate as much variability as possible, only one gear was used along with a rolling start. That way there would be no clutch launch or shifting involved. For each run, I rolled up to the starting point at 40 MPH on the cruise in third gear and did a WOT stomp until I had completed three telephone pole intervals. At the last pole, I noted the indicated speed on the speedometer.

This should be a good real world test with the initial RPM at about 2500 on the tach and the final approaching 5000.

After three repetitions, I returned home and swapped the exhaust. This is actually much easier than it sounds - just jack up the truck to let the axle drop, remove the spare, pop off the 3~4 isolation biscuits, remove two bolts and slide the whole system out over the rear axle. On my 4x4, this works for both the factory system and the fully assembled duals.

Doing the swap and running the two sets of trials on the same day minimized any possible effects due to differences in temperature, humidity or barometric pressure. The wind was calm throughout the day and the skies were overcast. My overhead console was reading 45F during the first tests and 45F in the second group as well.

All tests were run at WOT in third gear from a 40 MPH rolling start with the same start and finish points. The truck weighed the same except for the added weight of the duals which weigh more than twice as much as the stocker. Here are the results (indicated finish line speeds in MPH):

Factory Exhaust:
78
78
78

Thunderbolt Exhaust:
80
79
79

I should also mention that my engine is nearly stock. I have the intake silencer removed from the airbox, a set of JBA headers and synthetic 5W30 in the crankcase - that's it. Another truck with significant breathing mods might possibly make better use of this exhaust.

So, obviously, if you are looking for a big performance gain with a stock Ranger, this is not the answer. It is a good looking and good sounding exhaust system at a great price. I'm still glad I bought it.

 

awsome write up bob... good info!

 

Bravo, Bob!

 

Isn't this pretty common with most exhausts on an engine with the stock intake?