Reply With Quotehow long have you owned the turbo to still be making tweeks to it? Does prodigy give a correct torque spec for bolts? or is it just turn it till it stops?Originally Posted by UselessPickles
Some of the numbers you're talking about sound like fuel trims rather than target air:fuel ratio. Fuel trims can jump around quite a bit. It's how the computer adapts to variances in manufacturing of fuel injectors, variances in reality vs calculated model of reality under current local conditions, etc.
The -100% while coasting down just sounds like the computer cutting fuel while decelerating (no need to burn fuel when decelerating, engine will keep turning without it). That's a normal thing for modern vehicles, although I've never seen -100% trims in my data logs.
Yes, I replaced the head flange gasket when I replaced the exhaust pipe. I think I just under-estimated how much I had to tighten the bolts, and I erred on the side of under-tightening because it would totally suck to strip the threads on the head. I re-tightened, and tightened them more than the first time. The obvious loud leak sound is gone now, but I plan to thoroughly check for leaks to confirm proper installation before I focus on forming/sharing thoughts on how it drives with this new turbo compared to the Garrett. I already experienced previously how a small exhaust leak (pre-turbo) can have a noticeable impact on the performance of the turbo: http://jeeplab.com/showthread.php?13...ull=1#post3705
how long have you owned the turbo to still be making tweeks to it? Does prodigy give a correct torque spec for bolts? or is it just turn it till it stops?
Yes, the 1/1 and 2/1 are the short term readings (left and right side) based off of the O2 sensors. The other with the 12k reading is the long term. It's calculated from the short term history. I was throwing those numbers out there since I believe it's related to why my FAR numbers don't make sense.
I got a DTC this morning that said O2 sensor circuit slow response... Which probably has something to do with my right side short term lagging so far behind the left.
Pickles, would you be interested in taking a look at some DataLogs of mine?
You can look at the history of my install thread to see how long I've had the turbo: http://jeeplab.com/showthread.php?13...bo-DIY-Install
First stage 1, then stage 2. Keep in mind that I'm not an experienced installer, so some of the tweaks have simply been corrections to my own mistakes. Other tweaks have just been personal preference.
Sounds like you might possibly have the O2 sensors installed in the incorrect locations? You should have transferred the O2 sensors over to the same exact relative locations from the stock pipes to the turbo pipes. It's a bit confusing because the colors of the sensor's connectors are opposite on one side of the engine (white is upstream on one side, black is upstream on the other side). Need to make sure that the sensors themselves are in the correct locations, and that they are plugged into the correct connectors.
So there was some miscommunication about this new Precision turbo. All the talk of spooling at lower rpms, spooling around 2000-2200 rpm, feeling the turbo kick in around 2200 rpm, etc... I was interpreting that all to be in reference to when boost really ramps up quickly toward max boost during full throttle acceleration. I was wrong.
At full throttle, the boost curve is nearly identical to when/how the Garrett ramps up in boost through the RPMS. In 2nd gear, full throttle starting down near 2000 rpm, I feel the acceleration really ramp up and push me back in my seat right in the 3000-3500 rpm range. Based on my misunderstanding of what Prodigy meant by "feel the turbo kick in", I expected that this shove-you-back-in-your-seat increase in acceleration would happen down around 2500 rpm.
So this is an interesting position to be in. I was initially disappointed and thought something must be wrong with my install causing my turbo to spool up late. I was so focused on it not meeting one specific expectation that I was completely blind to the real benefits. Driving around with my family, my wife and I were in total disagreement. I was saying I didn't really notice a big difference from the Garrett. My wife was saying she could feel a big improvement even from the passenger seat. The big thing she noticed was that it was "much smoother" when we were driving around normally and doing some faster part-throttle acceleration in the mid-rpm range (not flat out full throttle through the entire rpm range). Then I got to a nice straight entrance ramp from a 30 mph road to a 75 mph freeway, dropped to 2nd gear and punched it (probably around 3000 rpm?). My wife let out some PG expletives (kids were in the back seat) then commented on how it took off more quickly than with the old turbo.
Once I got some clarification and stopped focusing on my one incorrect expectation of huge acceleration being available down around 2500 rpm, I started to notice and enjoy the improvements myself. The improvements are actually pretty big, but It's taken me a while to recognize that since my expectations were so different than reality.
Since the full throttle boost curve is not really any different, there's really no data/graphs/charts I can show you to visualize how the Precision turbo is better. It all has to do with how the Precision responds to lower amounts of exhaust flow (part throttle, lower rpms), and how quickly it responds to changes in throttle.
It's really normal daily driving where the improvements are very noticeable. Driving around town and upshifting around/below 3000 rpm, it just feels much better. After upshifting and dropping down to near 2000 rpm in the next gear, the Garrett would feel sluggish/laggy compared to the amount of acceleration you had just before the upshift. The Precision doesn't have that problem. Power delivery just feels more consistent/predictable/linear. This is what my wife was talking about when saying that my driving felt much smoother. With the Garrett, the turbo would just be starting to spool up and increase acceleration just as was about to upshift. The result was often a brief increase in acceleration just before I let off the throttle to upshift, followed by a mismatched (low) amount of acceleration when I got back in the throttle at lower rpms after shifting. It really accentuated the clunkiness of shifting the Jeep's manual transmission during "brisk" part throttle acceleration.
Because the Precision spools up more easily at lower rpms at part throttle, I can often get the daily driving acceleration I want without downshifting, or by downshifting fewer gears than I would with the Garrett. This is a bigger deal for the manual transmission, because it takes effort to downshift. I'm sometimes lazy and don't feel like going through the effort of downshifting just to accelerate a bit faster
Another example is cruising on the freeway at 75 mph in 6th gear. I'm at about 2200 rpm. If I press the throttle a bit, I hear the turbo spool up, and acceleration is a bit stronger than I got with the Garrett in the same situation. It's just enough extra that I can adjust speed with traffic on the freeway more easily without downshifting, maintain speed up gentle inclines more easily without downshifting, etc.
The noises from the Precision are much different. There's a faint turbo whistle sound that I can hear occasionally during normal driving. At full throttle above 3000 rpm, I can definitely hear the turbo whistle. More interesting is that there's a lot more air "whooshing" sounds. I believe this is that anti-surge ports doing their job. It's most noticeable at part throttle. Give it just enough throttle to create some engine load and spin up the turbo, but the throttle is still closed enough that air flow rate is still relatively low. When the turbo is making some boost at low flow rates, that's when pressure backs up into the compressor blades and starts recirculating through the anti-surge ports. This also happens whenever you lift off the throttle a bit after the turbo was making some boost. Under heavier acceleration when lifting off the throttle enough for the BOV to open, the sounds of the anti-surge ports comes just before the BOV sound and they blend together.
Since the turbo spools up more easily at low rpms, and the turbo makes more noise due to its anti-surge ports, I actually get turbo noises much more often during gentler normal driving. I have mixed feelings on this. I like the crisp sound of the BOV, but I don't get to hear that clearly anymore because it's always accompanied by the whoosh of the anti-surge ports.
I still need to figure out why I only get 7.5 psi boost now. I haven't had time to thoroughly check for exhaust leaks yet. I'd also like to compare to MatthewLee - do you happen to know how much boost you are actually getting?
The Precision has a slightly smaller turbine housing with a smaller A/R ratio. It's possible that this turbo creates more exhaust back pressure than the Garrett. Since we're simply using wastegate spring pressure to control boost, it's actually a balancing act between the spring, boost pressure, and exhaust pressure that determines when the wastegate actually opens. It's possible that the Precision just makes less boost than the Garret with the same wastegate spring due to higher exhaust back-pressure (increased exhaust back-pressure would also be part of why it spools up more easily at low rpms). I'll try to get some info from Prodigy about this.
I forgot to mention that when you are at higher rpms where the turbo is capable of producing larger amounts of boost, cruising at a steady speed, then punch the throttle, the Precision reacts more quickly than the Garrett. Less lag in that sense.
As a $495 upgrade option at the time of the initial purchase of the turbo kit, it is definitely worth the money.
As a $1350 stand-alone purchase for the new turbo to replace an existing Garrett... it really depends. If you can easily afford it and the part-throttle low-to-mid rpm driving with the Garrett annoys due to the way it lags at low rpms, I think you'll be happy with the purchase. If you're expecting to be blown away with big acceleration when you step on the throttle below 3000 rpm, you will be disappointed. If you are operating on a tight budget and have other things you want to do with the money, and you are satisfied with how the Garret is working for you, then spend your money elsewhere.
If I discover that I'm low on boost due to an install problem (exhaust leak, etc), and I find away to regain that 1 psi of boost I think I may be missing, some of my analysis may change.
Just looked at a couple of Matthew's data logs. Boost looks pretty similar to mine, so that's a good sign that the Precision just makes less boost than the Garrett on wastegate spring pressure (probably due to increased exhaust backpressure). I'll still double check for exhaust leaks to be sure, but I'm feeling better now.
Prodigy agrees with my assessment that lower boost with the Precision turbo compared to the Garrett is normal due to increased exhaust pressure from the design of the Precision that gives it faster spooling at lower rpms.
Now I'm waiting on a response as to whether it would be safe to bump the boost levels back up into the mid 8 psi range using a manual boost controller. I'm thinking of maybe even returning to the stage 1 wastegate spring and using a boost controller to set boost to the mid 8 psi range. This should theoretically give me better response/spooling. The boost controller combined with a lighter wastegate spring should hold the wastegate closed longer than a heavier wastegate spring alone.
BTW - The more I drive the Jeep without focusing on trying to notice improvements over the Garret, the more that I'm actually noticing/enjoying improvements. I've even noticed improvements in part-throttle acceleration in the 1000-2000 rpm range. When I stop thinking about trying to compare, I just find myself smoothly driving around, sometimes at lower rpms than I usually would, downshifting less, upshifting sooner, etc.
At this point, it's been so long since my Jeep was stock that I have absolutely no idea how this low rpm acceleration compares to the stock engine. I need to find someone with a manual transmission base model 2-door sport to do some back-to-back comparisons.
Here's some eye candy:
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Side-by-side Garrett (left) vs Precision (right):
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Precision has a slightly larger compressor wheel inducer (the visible part): 58 mm vs 56 mm
Precision has a slightly smaller turbine wheel exducer (the visible part): 62 mm vs 64 mm
The biggest difference is the shape of the turbine housing. The Precision very clearly has a smaller, more "tightly wound" shape that causes the exhaust gasses to more squarely hit the turbine blades. I can't find any A/R markings on the Garrett's turbine housing, but the Precision is marked as 0.58 A/R. The Garrett's A/R is almost certainly larger. Read about A/R here: http://www.turbobygarrett.com/turbob...housing_sizing
Very nice! SO Pickles... if you could have the money back and start over, would you stick with prodigy? Or roll the dice with a different power mod?
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