Originally Posted by ExcursionDiesel
Most manufacturers match drive line components in ratings. The larger ZF 8 speed used for the Hemi, Diesel, and SRT is beefier but not "over engineered" any more than the v6's drive line...its matched.
What I said would hold true for the Hemi as well if supercharged. Supercharging, depending on the method, can turn the v6 Pentastar into a torque monster! That's great...but I fear the lighter duty ZF won't hold it any more than the larger ZF would survive behind a supercharged Hemi.
Sorry if I sounded like the v6 isn't well built...it is. I think the motor can take more than the tranny....time will tell.
You know, I agree with you. It makes sense in theory and it makes sense in practice. But then again, in practice hings are different from theory and my experience with Subaru dictates otherwise.
The 2005 Subaru Legacy GT (5 speed manual or 5 speed auto) came rated 250 hp / 250 lb-ft at the crank which translated into about 190-200 whp and 210-220 wlb-ft at the wheels. The vast majority of enthusiasts go Stage II which means stock turbo, exhaust mods (up-pipe, down-pipe), custom tune. That in itself is a massive power gain.
My own numbers when I went Stage II were 250 whp and 300 lb-ft. And that was in 2008. It is the dyno graph from P&L Motorsports. I will admit, within a year I needed a new clutch but that is because I went to the racetrack; gas was cheap and I enjoyed AWD starts. I know plenty of people on stock clucthes. That was the weak link in the drivetrain.
But over the years I added a better turbo, Mitsubishi EVO 16G, a fuel pump, an electronic boost controller, an intercooler. I went once more on the dyno, just before I sold my Cobb Accessport (the tuning programmer) as Open Source (RomRaider/OpenECU) tuning was becoming more evolved and I still needed some adjustments. My last known numbers were 278 whp and 323 lb-ft at the wheels and the dyno graph was probably in the folder with the Cobb Accessport which I deleted years ago. I still have those mods on the car and I still drive it, aggressively at times. It's been in this state of power for 36,000 s
miles. I went Stage 2 a 21,000 miles. I went Stage 3 (the turbo upgrade) at 69,000 miles. I have 106,000 miles on the car now.
I attached a graph with identical mods: BNR 16G (for Legacy, there are just a handful of popular turbos Mitsubishi EVO16G, Subaru Impreza's VF-52, 18G) TMIC (Top Mounted Inter Cooler, the choice is either a Perrin unit or an AVO unit, same size, most people in USA have a Perrin) Pump (Walbro 255 no exceptions, later Deutshwerks and STI pumps become popular) up-pipe; down-pipe. There's still power left for me to get (replace injectors, new tune) but I am done with modifying the Legacy, I am in long term support mode. And in case you are wondering why my numbers are lower, well I am running peak boost 19 psi; most people on this setup go 21 psi. I wanted reliability, not squeezing every "torque
" out of the engine.
For all the calculations back to engine values, use 0.25% for drivetrain losses.
So...at my current power levels I would be destroying the light duty 8 Speed ZF. And I should have grenaded
my transmission with the nearly 50% power improvement long ago. So, while I agree with the fact that something might give up following the addition of a supercharger to the Jeep, I think the drivetrain will take it. By the way, 5 speed auto Subaru gearboxes take the abuse much better than the 5 speed manual, and are known to last up to about 400 lb-ft at the wheels when a valve body is needed.
The last point I want to make is that the supercharger might not necessarily add that much top power, though it will, no doubt. But if you look at the dyno graphs (the colored one) which shows the difference between two turbos, for most people it will be enough if the supercharger can shift the power/torque curves to the left ensuring availability of stock power of 290 hp/260 lb-ft from 2500-5500 and tapering at the high end. It is the area under the curve that makes most difference, not the outright values. Even looking at my obsolete dyno, look at how much wheel torque I had available from 3000 rpm to 6000 rpm. You know that was fun to drive.
According to the ZF brochure
, the lighter duty ZF 8HP45 is good for about 450 N-m torque. Assuming 85-90% efficiency (10-15% drivetrain losses), the V6 Jeep should have around 220 - 235 lb/ft at the wheels. On the other hand, 260 lb-ft of torque is about 350 N-m so, on paper there is about 100 N-m or 70 lb-ft of torque to be reclaimed by the Supercharger and still keep it within the scope of the light duty transmission. I think it is not only possible to add 70 lb-ft to the truck using a supercharger, but it is possible to make this power increase available over much of the power band.
I am looking forward to this product.