Pentastar in action

[Nick R]

So, it's time. The new Chrysler 3.6L DOHC Pentastar in action. Chrysler has a lot riding on this engine. They've replaced every other V6 in their lineup with this single engine. Let's see what it can do, and what it sounds like?

First off, the new, and much improved Grand Caravan, and it's 6 speed FWD Auto. I love the shift into 3rd here.


Next, the Jeep grand cherokee, with it's outdated 5 speed, RWD Autobox.


I would say, looks good to me. Now, to drive one and find it's powerband.

 

[chad8]

Like all Chrysler's (ahem,Fiat's) , it quit running after 26 seconds. Same junk , new owner.

 

[demarpaint]

Give it two years in the Liberty, and them not ruining it with DI [fingers crossed], and I'll buy another Liberty.

 

[sciphi]

Good exhaust tuning. I like the note, at least from those videos. It sounds muscular and refined. It also doesn't sound like it's working that hard to pull two fairly heavy vehicles to speed quickly.

 

[Hokiefyd]

Boy, that Grand Cherokee needs different gearing, and bad (if that was WOT). The van sounds good. The 2-3 gear spacing in my car is also very tight; it's fun.

 

[UNC017]

Originally Posted By: Hokiefyd
Boy, that Grand Cherokee needs different gearing, and bad (if that was WOT). The van sounds good. The 2-3 gear spacing in my car is also very tight; it's fun.


IMO, the Pentastar is going to be a great engine.... but NOT for the Grand Cherokee. Its much more of a passenger car engine, with a high specific output at relatively high RPM, and a peakier powerband than what a Jeep needs. Which is why they're still building the venerable 3.8 for the Wrangler. Wrangler buyers know that they don't need 260 horsepower, they need torque that the old 3.8 delivers in spades- it was chosen for the Wrangler because its specs were the most similar to the 4.0L straight six that they were replacing. I guess the thinking is that Grand Cherokee buyers like the big HP numbers and more modern specs on the Pentastar, and its probably true. If they can work on the tune of the Pentastar for more low-RPM grunt, then fine- I don't think its necessarily anything fundamental to the engine's architecture that is making it behave this way. Until then, if I consider a JGC it will have to have the 5.7 (and why the heck don't they offer the 310-horse 4.7 in the JGC???)

 

[rjundi]

Seems like a really noisy engine.

And I drive a raucous for a vehicle (2004 Subaru WRX).

I wish Chrysler luck, engines do not seem to be the key to a vehicle's success.

 

[demarpaint]

Originally Posted By: 440Magnum
Originally Posted By: Hokiefyd
Boy, that Grand Cherokee needs different gearing, and bad (if that was WOT). The van sounds good. The 2-3 gear spacing in my car is also very tight; it's fun.


IMO, the Pentastar is going to be a great engine.... but NOT for the Grand Cherokee. Its much more of a passenger car engine, with a high specific output at relatively high RPM, and a peakier powerband than what a Jeep needs. Which is why they're still building the venerable 3.8 for the Wrangler. Wrangler buyers know that they don't need 260 horsepower, they need torque that the old 3.8 delivers in spades- it was chosen for the Wrangler because its specs were the most similar to the 4.0L straight six that they were replacing. I guess the thinking is that Grand Cherokee buyers like the big HP numbers and more modern specs on the Pentastar, and its probably true. If they can work on the tune of the Pentastar for more low-RPM grunt, then fine- I don't think its necessarily anything fundamental to the engine's architecture that is making it behave this way. Until then, if I consider a JGC it will have to have the 5.7 (and why the heck don't they offer the 310-horse 4.7 in the JGC???)



Good explaination. I haven't owned a Chrysler product since my 72 318 Satellite, so I never paid much attention to them. Now I have the 08 Liberty and really like it. I never understood why they had the 3.7L and 3.8L now I think I got it, thanks. The 3.8L has more torque I guess. I'm hoping to see some version of the Pentastar in the Liberty, and they stay clear of DI.

 

[Hokiefyd]

Frankly, I don't know why they ever used the 3.7L in the Liberty to begin with. My parents used to own a Liberty, and frankly, it was a raucous and un-tamed beast in that vehicle (an '05 model as I recall). It's a 90-degree V-6, which is inherently unbalanced, because it's essentially a 4.7L V-8 with two fewer cylinders. The 3.8L is a 60-degree V-6 and is a much smoother engine. Neither set records for refinement, but with both options available, the 3.8L would have been the better choice in my opinion.

For the Rams, I understand the financial decision to use the 3.7L. It probably shares mounting points and transmission bellhousings with its 4.7L cousin, so it was likely quite interchangeable. But in vehicles like the Liberty and Nitro, where there is no V-8 option, I don't see the purpose of the 3.7L.

 

[meep]

I have wondered if the 3.7 had a stouter block, better suited for the heavier vehicles. as you said, it's a lopped-off 4.7. The 3.8 is just a bored 3.3, which was in itself a good engine, but a limitation. Chrysler experimented with a forced induction version of the 3.3 and the bottom end was not up to the task... so the 3.8 prolly has the same weakness. As it is, the 3.3 and 3.8 have a webbed series of joined crank bearings in a single plate to stiffen the bottom of the block. So-- the wrangler sees easier gearing and a lighter vehicle than a GC at least and may be easily handled by the 3.3/8, which was home to many 3800lb minivans. The liberty-- lighter weight-- yea... the 3.3 or 3.8 would have been a great choice. But in the bloated (I drive one) WK, it has a lot of weight to move (and tow).

I'm not very impressed with the 3.7, even if it is sturdy. I've had valve noise since 3,000 miles which is really bad after highway drives. 5-20.... needs a qt of 10-30 in there to control it. It drives fine.... but I miss the 4.0. 3.7 probably needed for that tow capacity.

M

 

[kkreit01]

All the tests in the new GCs/Durangos have placed 0-60 in the mid 8s -- which is also last compared to most all the competition. They need a diet.

 

[UNC017]

Originally Posted By: rjundi

I wish Chrysler luck, engines do not seem to be the key to a vehicle's success.


True, because Chrysler would have been the #1 carmaker for the past 80 years if that's all that mattered. Seriously, they've always built superb engines (the only real stinker I can think of between 1930 and today is the 2.7L v6, which was ordered to be designed by Daimler anyway).

They've managed to screw everything else up from time to time, but never the engine.

 

[UNC017]

Originally Posted By: demarpaint

Good explaination. I haven't owned a Chrysler product since my 72 318 Satellite, so I never paid much attention to them. Now I have the 08 Liberty and really like it. I never understood why they had the 3.7L and 3.8L now I think I got it, thanks. The 3.8L has more torque I guess. I'm hoping to see some version of the Pentastar in the Liberty, and they stay clear of DI.


Well, the 3.8 doesn't have much (if any- too lazy to look it up) more torque than the 3.7. The 3.8 was built on the 3.3 block, which was the first 60-degree v6 block Chrysler made. Their only previous v6 was the 3.9, a 90-degree block based on the 318, and it only existed because it was very easy to build on the same line as the 318 and 360, and they had neglected the slant-6 to the point of irrelevance and needed a more modern replacement.

When the 318 was axed in favor of the 4.7, they did the same thing- sawed two cylinders off and made a 90-degree v6 that could be built on the same assembly line as the 4.7, and the 3.7 was born. It only went in RWD Jeeps and pickups because its too wide for a transverse front-drive layout, so the 3.8 stayed. And stayed. And stayed. Powering almost nothing but minivans for years, and the finally the end of the line came for the Jeep 4.0 straight six (pause and place hat over heart for a moment of silence...). And it turned out that the 3.8 was the best v6 replacement for the 4.0 that they had. The 3.7 would probably have been fine too, but with it going into so many Libertys, Nitros, Dakotas, etc., the choice probably came down to balancing production capacity.

And speaking of "balancing," that's the biggest problem with the 3.7. Its a 90-degree block and therefore has a slight odd-fire even with a splayed crank, plus the usual uncorrectable 90-degree v6 higher order imbalance (well, you CAN correct it, but only by hanging balance shafts on there.) I prefer the 3.8 all-around to the 3.7, personally. Yes, the 3.7 shares the 4.7 feature of having all the main bearing caps joined into an enormous bed-plate/girdle, which is god-awful strong... but they've never dialed up the power on the 3.7 anywhere NEAR the point that it needs all that. When they squeezed 80 more horsepower out of the 4.7 in 2008, I'm sure that bed-plate is a key reason they knew they could do it without a drop in reliability.

 

[demarpaint]

Thanks 440, so far no complaints with my 3.7L, I hope it stays that way!

 

[UNC017]

Some images of how the main caps of the 4.7/3.7 are carried in the bedplate. Its extremely strong- probably stronger than the old big-block (383/440/413/426) Y-block, even when the caps were cross-bolted as in the 426 Hemi. Ford does something similar with the modulars where the bearings being carried in a deep block extension.

Links copied from the DodgeTalk forum:

Assembled to block (no crank)

Bedplate that carries lower main bearing caps:

 

[meep]

Originally Posted By: 440Magnum


And speaking of "balancing," that's the biggest problem with the 3.7. Its a 90-degree block and therefore has a slight odd-fire even with a splayed crank, plus the usual uncorrectable 90-degree v6 higher order imbalance (well, you CAN correct it, but only by hanging balance shafts on there.)


Question: Explain the splayed crank-- I knew that early 90° V6's had a rough idle because the firing timing was not 100% rhythmic, as each pair of conrods sat immediately next to each other, which the 60° V6's corrected. When you say "splayed," does that mean that there is a main bearing between each conrod so each cylinder actually gets to fire in a simple, even rhythm?

The 3.7 I have does have a full-length balance shaft where an OHV camshaft would have been, but it still has a weird vibration to it.

I had a 3.3 and it was s-m-o-o-t-h.

M

 

[OVERKILL]

Originally Posted By: 440Magnum
Some images of how the main caps of the 4.7/3.7 are carried in the bedplate. Its extremely strong- probably stronger than the old big-block (383/440/413/426) Y-block, even when the caps were cross-bolted as in the 426 Hemi. Ford does something similar with the modulars where the bearings being carried in a deep block extension.

Links copied from the DodgeTalk forum:

Assembled to block (no crank)

Bedplate that carries lower main bearing caps:

Correct. Seems to be the new thing. Bullet-proof bottom ends.

Modular for comparison:

Truck 5.4L:

Ford GT 5.4L:

 

[meep]

actually, what I recall seeing was a mesh of metal, a rectangle, that would have interconnected the bearing braces together and to the walls of the block, sandwiched below the block and above the pan. IIRC correctly on the chrysler 3.3.

That said, those pics above are def more stout than the old GM 283 and 350 I knew so well...

M

 

[rslifkin]

The new GCs are relatively slow, even with a HEMI (7.7 0-60, IIRC). They're just heavy pigs. Fully optinoed, they're over 5000 lbs. For comparison, mine is as heavy as the 1st gen ever came, and weighs about 4250. The 2nd gen topped out at 4350, 3rd gen at around 4800 - 4900. 6 cylinder GCs have always been slow, however, usually around 9.3 - 9.7 0-60, depending on the generation.

The Pentastar looks like a good engine though. The GC just really needs a V8. I think they pulled the 4.7 option for the 2011s because the Pentastar, 4.7 and 5.7 Hemi would have left too-small gaps in power output between the choices.

 

[caravanmike]

Originally Posted By: meep
Originally Posted By: 440Magnum


And speaking of "balancing," that's the biggest problem with the 3.7. Its a 90-degree block and therefore has a slight odd-fire even with a splayed crank, plus the usual uncorrectable 90-degree v6 higher order imbalance (well, you CAN correct it, but only by hanging balance shafts on there.)


The 3.7 I have does have a full-length balance shaft where an OHV camshaft would have been, but it still has a weird vibration to it.



M
it is considered and odd fire v-6. the firing is not exactly at 90 degrees like in the 4.7L. i am assuming that splayed crank refers to the split pin set up, that is required to smooth the idle on a 90 degree v-6. mike