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  #1  
Old 10-22-2015, 05:08 AM
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5.7 hemi questions

regarding the WK model with the VVT and MDS system.

How many "cats" are there in th exhaust setup that can be removed?
Is it easy to fool the lambda sensors? On my 3.7 it was quite easy, if you know how.
Does a free flow exhaust negatively affect the MDS working?

thanks in advance

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Old 10-23-2015, 08:37 PM
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Re: 5.7 hemi questions

I don't Believe the WK's had VVT. As far as cats I have mine set up that share one. I would like to know how to improve the MDS
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Old 10-24-2015, 04:44 AM
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Re: 5.7 hemi questions

from 2008/2009 the 5.7 engine of all Jeeps was fitted with VVT and MDS
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Old 10-24-2015, 07:01 AM
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Re: 5.7 hemi questions

I don't know what you mean by "improving MDS", but here is all the info for the engines that were available for the WK.
Jeep Grand Cherokee WK - Engines
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Old 10-24-2015, 12:29 PM
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Re: 5.7 hemi questions

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Originally Posted by skala View Post
regarding the WK model with the VVT and MDS system.

How many "cats" are there in th exhaust setup that can be removed?
Is it easy to fool the lambda sensors? On my 3.7 it was quite easy, if you know how.
Does a free flow exhaust negatively affect the MDS working?

thanks in advance
Variable Valve Timing (VVT) for the 5.7's became available in late 2008 and all subsequent 5.7's have it. VVT comes in the 5.7 WK's of the same years.

There are 4 O2 Sensors and 2 catalytic converters in the U.S. built 5.7's, two 02's for each cylinder bank....one before the converters (main function is to control fuel mixture) and one after the converters (main function is to check converter efficiency). The rear O2's can be removed, but you would need to have a custom tune to shut them off or you'll forever get a Diagnostic Trouble Code (DTC) reflecting converter inefficiency. The converters are high flow, low restriction "wire spun" units, and are quite efficient.

If anything, a more free flowing exhaust will enhance the operation of the MDS, as will either a Diablosport or Superchips Tuner. With either tuner, you'll get much more MDS active time, but the switchovers (on and off) are generally a little more harsh than the factory settings.....which, IMO is complete garbage. With my mods. (see signatuve) on relatively level highway driving, driving in 4th gear, I'll get in excess of 90% MDS active time.

If you're just going to try and improve the exhaust system, you need to start with the crappy exhaust manifolds (logs), because this is the biggest choke point in the exhaust....not the cats. The stock muffler/resonator are the next weak points, and finally, the pipe size. Also, if your main goal is fuel economy, the best things you can do is a good header back exhaust system, a longer duration, higher lift camshaft, and a good tuner that will allow you to fully adjust the transmission shift schedules and torque management. With my setup, I normally get 22-23 mpg, with a high of 24.1 mpg over about a 250 mile stretch of highway at around 5000 feet elevation, running 85 octane fuel. And, mine doesn't have VVT, just an aftermarket cam advanced a total of 6 degrees.....4 ground into the cam by the manufacturer and 2 degrees at the timing set.
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Old 10-24-2015, 12:49 PM
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Quote:
Originally Posted by "jeepgcoman View Post
There are 4 catalytic converters in the U.S. built 5.7's, two for each cylinder bank....one before the converters (main function is to control fuel mixture) and one after the converters (main function is to check converter efficiency). The rears can be removed, but you would need to have a custom tune to shut them off or you'll forever get a Diagnostic Trouble Code (DTC) reflecting converter inefficiency. Why would you want to do this, without removing the converters?? Converters are high flow, low restriction "wire spun" units.
Bro, I think you ment 4 o2 sensors. There is only 2 cats on all WK's
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Old 10-24-2015, 06:48 PM
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Re: 5.7 hemi questions

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Originally Posted by Strongjeff View Post
Bro, I think you ment 4 o2 sensors. There is only 2 cats on all WK's
Can't believe I did that, LOL. You're sure right, Jeff. Guess I hadn't turned the brain on yet when I wrote that. I went back and fixed it. Thanks for the heads up too.
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Old 10-24-2015, 07:13 PM
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Originally Posted by jeepgcoman View Post

Can't believe I did that, LOL. You're sure right, Jeff. Guess I hadn't turned the brain on yet when I wrote that. I went back and fixed it. Thanks for the heads up too.
Its alright bro. I've made errors like that before
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Old 10-25-2015, 05:55 AM
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Re: 5.7 hemi questions

wow seems I hit the information jackpot!!!

Thanks jeepgcoman and strongjeff for your info sharing. Much appreciated.

I studied the extensive inputs from strongjeff before I went ahead and bought my 3.7 V6, because by then I knew exactly what I was letting myself in for.
I enjoy the 3.7, but am looking for more power, hence the investigation into the hemi, but must be the uprated engine.

The high fuel consumption is a factor, but I also realise the way you drive, plus other changes made can bring it down to an acceptable level.

In South Africa we do not have the support you guys have on your doorstep, although there are plenty hemis running around here.

So, if I go ahead a buy a hemi, I will certainly come knocking for assistance with you guys, if you dont mind.
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Old 10-27-2015, 08:22 PM
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Re: 5.7 hemi questions

With some well chosen mods. for the Hemi's you can improve both fuel economy and performance so it is better than most 3.7's and 4.7's. Mine gets a normal of 12-14 mpg in town (about like other Hemi's), but my mixed and highway mileage is somewhat better than any I've heard of. On the highway (hilly at around 3000 ft. elevation) mine gets a normal of 22-23 mpg. and I've gotten as high as 24.1 mpg over about a 250 mile run at about 5000 feet elevation.
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Old 10-27-2015, 08:34 PM
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Quote:
Originally Posted by jeepgcoman View Post
With some well chosen mods. for the Hemi's you can improve both fuel economy and performance so it is better than most 3.7's and 4.7's. Mine gets a normal of 12-14 mpg in town (about like other Hemi's), but my mixed and highway mileage is somewhat better than any I've heard of. On the highway (hilly at around 3000 ft. elevation) mine gets a normal of 22-23 mpg. and I've gotten as high as 24.1 mpg over about a 250 mile run at about 5000 feet elevation.
That's good numbers. Should be even better down closer to sea level
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Old 10-27-2015, 08:57 PM
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Re: 5.7 hemi questions

Funny about that, Jeff, I've never been able to give it a "real good" test at or near sea level. I've driven it on trips at or near sea level (the Oregon Coast), but there are too many small towns all down the coast, and the speed limit in Oregon is only 55 mph on most highways. The best I've done on one of those trips was around 21 mpg. I've also done a couple trips to Vegas, but that is over more mountainous terrain (a few over 7000 ft.) before you start dropping down into Vegas. I have gotten around 22 on one of those though. The best economy for me is around home (~3000 ft.) where I can run non ethanol fuel and the terrain is more hilly than mountainous. One other thing I've noticed is that the economy falls off a little with the 20 in. wheels and huge tires on it. Still, since all the mods., I've only gotten less than 20 mpg. about 3 times in about 3 years.

Haven't done any mod. in nearly two years now and I am getting the "itch" again. I am actually thinking of putting a low boost (~5 PSI) supercharger on it, but I am having trouble getting past the price. When I started all this, my main goal was better fuel economy with slightly better performance without any real invasive engine work. So far it's all worked out well, but a blower is a whole different game. For sure I'd never be able to keep my foot out of it then, LOL. So far, my research has found that, if you can keep your foot out of it, it will improve the fuel economy to some degree, but the break even point would be more than several years down the road. I do tend to keep my vehicles for a long time (longest was my classic Mercedes....29 years), so it may be OK in the long run.

If I get one, it'll probably be a Vortech unit, as most of it is also bolt on without requiring any engine teardown. At about 8 PSI they're suppose to be worth about 100-120 rwhp. but I'd be happay with about 80-100 more. I am sure I could deal with that though.
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