OOOOOOOooohh - yea

RIPPTECH

 

pentastar has 90% of torque at 1,800 rpm.

Well, they state: 270 lb.-ft. of torque at 4,800 rpm; 90% of torque is available from 1,800 to 6,350 rpm. I read that as 90% of torgue at 1,800 but I think I may be reading that wrong.

edit: quote: "The Pentastar V-6 engine has more torque than any 2010 Chrysler V6, and has a broad, flat torque curve with 90% of peak torque available between 1800 and 6350 rpm."

 

Yep and 90% of 270 lb-ft is ~240 lb-ft (almost exactly what the completely stock 3.8 puts out at the flywheel). So there will be no significant torque gain over the 3.8 for the pentastar. Like I said before the only way they get that extra 80 horsepower is by revving it an extra 1000 RPMs.

So as far as usable power a RIPP supercharged 3.8 will start putting out HIGHER torque by about 2200 RPMs than the peak torque of the pentastar that happens at 4800 RPMs (due to the boost hitting ~2 PSI which gives an approximate 14% boost in power).

RIPP on that note about how much boost is generated in the 1800 - 2000 RPM range? I am curious because of this discussion plus this is the general range that my RPMs sit on the highway. I am trying to get a good feel as to whether I will lose or gain MPG if I leave it in 6th gear sitting at about 2000 RPMs on the highway with a gen 2 SC. You said that it delivers more air in these low RPMs but I know you also said that the JK runs rich at WOT at lower RPMs so I was wondering whether any extra fuel is added at these low RPMs for the SC tune or whether you allowed the extra air delivered by the SC lean out the rich tune that came stock.

 

the gas mileage between 3.8L SC and stock pentastar ends this argument..

 

I currently get 23 mpg highway, exactly what the stock grand cherokee (that is much more aerodynamic than the JK) gets with the pentastar. So if I had to guess the rating for the JK with the pentastar would be rated at around 21-22 mpg on the highway. Therefore if the SC only generated 1 - 1.5 PSI at 2000 RPMs it should roughly only use 7-10% more fuel since atmospheric air pressure at sea level is 14.7 psi, resulting in the same 21-21.5 mpg on the highway. HOWEVER that is the reason I asked RIPP about their fuel mapping at that point, because if they richen the air/fuel mixture more than 10% at 2000 RPM (due to dealing with knocking, etc) then the fuel economy change on the highway would be more significant.

Not surprisingly when you do the math the energy use of the JK on the highway (aerodynamic drag and various other parasitic losses) does not change in spite of what engine is under the hood which makes perfect sense! Additionally since the pentastar is not significantly more thermodynamically efficient at 10.2:1 compression ratio compared to the 3.8 at 9.6:1 then your conversion of potential energy in the fuel to energy used to overcome the forces acting on the JK does not change, so once again, you use the same amount of fuel.

 

The cherokee pentastar gets 26mpg highway every place it is mentioned. and no one buys the S/C to baby it everywhere. Real world driving, the S/C gas mileage wont compete, and most people know it. Its a great option for people that are stuck with the 3.8L, but thats about it.

 

And on and on, after all this I think I will keep my 07' and save up for the Ripp... Future Ripp customer

 

Cite your sources. According to EPA fuel economy the 4x4 grand cherokee actually only gets 22 mpg (I stand corrected compared to the 23 I originally said when I looked for these elusive reviews saying they got 26 mpg out of the pentastar). Most reviews I found during a quick google search said they they averaged between 19 and 20 mpg with the pentastar with those averages more biased toward the highway. Not to mention in those reviews they said that they disliked the lack of off the line low-end torque (exactly what I once again said I would expect from the pentastar).

 

I think I'll swap a HEMI and supercharge it

 

What are you averaging now with the SC?