Today’s vehicles seem to be in a perpetual horsepower war. Stock Jeep Wranglers put out almost 285 HP and 260 lb-ft of torque right of the dealer lot. The problem is those numbers are all wrong for the vehicle.
The Horsepower Problem
Horsepower makes you go fast, the more you have the faster you can go. An oversimplification but the concept is what is important.
Torque makes things move. The more torque you have the more you can pull, push, and rotate. The boys from Top Gear and now The Grand Tour have said it best. Horsepower is how hard you hit the wall, torque is how far you take the wall with you.
The issue with the current configuration Wrangler motor options is where that power is located in the rev range. For the 3.6L V6 peak HP is just shy of 6000RPM and peak TQ is around 3750 RPM. What you really want when crawling off-road or trying to tow, haul, or use a square SUV for anything but racing is more torque and much lower in the RPM range. The curve barely rises from idle until 2500 RPM. Where you want torque is from idle until redline in a nice flat line but the 3.6L large bore short stroke motors don’t work that way. These are called oversquare because the piston bore is larger than the stroke.
Oversquare versus undersquare.
Oversquare engines (a.k.a. “short stroke engines”) are very common, as they allow higher RPM (and thus more power), without excessive piston speed.
An under square or long-stroke engine has a smaller bore (width, diameter) than its stroke (length of piston travel) – giving a ratio value of less than 1:1.
Under square motors deliver peak torque at a much lower RPM and are common to inline motors. For perspective, however, the much-loved Jeep 4.0 was an oversquare design, albeit more displacement and with a longer stroke than the current V6.
Back to our original question.
So is a V8 swap better than a supercharged V6? For our comparison, we will look at the most common swaps. A 5.7L truck motor versus the RIPP supercharged 3.6.
Price – Depending on how you acquire the V8 and other options, the V8 swap can run anywhere from 10k to 30 thousand dollars installed. The typical supercharger setup runs around 10K installed. The price factor goes to the supercharger. Both can be installed by a skilled mechanic at home if you so choose.
Ease of Install – The supercharger setup is bolt on with normal hand tools and can be done over the weekend in your garage. The V8 swap can be done in your garage as well but is a 40-hour job for an experienced shop much less the nome garage. Once again the edge goes to the supercharger.
Power – This one is a little tricker. You could go big with the V8 and it definitely will win the HP war. That would also up the price several thousand. We did say we would stick to the 5.7 truck Hemi so the max power numbers are very close.
The key difference is everything we discussed above. Where is that power? The 3.6 still makes peak power at 6000 RPM and peak torque moves up to 5300 RPM or higher. You do develop more torque lower in the RPM than naturally aspirated but that peak is way up there.
The V8 Hemi hits peak HP at 5400 RPM and peak TQ at 4500 RPM. The main difference is the Hemi has a flatter torque curve from idle to peak power, never dropping more than 20ft-lbs. The supercharger has a 60ft-lb difference across the curve. Useable power and certainly torque goes to the V8 swap.
What to choose?
As much as the V8 is definitely our favorite the supercharger is more cost effective, easier to install, and doesn’t give up much in the torque department. If you have the coin the Hemi is the better all-around choice for both driveability and that bottom end grunt.
