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I'm a little unclear of the real world advantage of adding X51 to a stage1 mod. on 981 GT4/Spyders given both improve higher end performance and not much low end tq. Same with the 4.0 outside of cost. Can you
clarify?
I'm a little unclear of the real world advantage of adding X73 to a stage1 mod. on 981 GT4/Spyders given both improve higher end performance and not much low end tq. Same with the 4.0 outside of cost. Can you
clarify?
I think you meant to type the X51, right? I think it's mostly that people want the top end power from the X51 bits (5K - 8K) and the low end grunt around town (4.0L) and typically, stroking a motor adds a disproportionate amount of torque vs. power whereas boring the motor and increasing the bore affects top end horsepower more than bottom end grunt (torque). I think the combination is the big favorite because one produces a lot of torque and a bit of horsepower while the other produces a massive amount of horsepower instead of torque.
John, can you talk about the change in sound with the stage I, II, and III upgrades?
I honestly think they all sound the same when the exhaust and intake are held constant. Maybe someone else can chime in but I think the same intake and exhaust bolted to a 3.4L, 3.8L, X51 or 4.0L all sound the same.
I think you meant to type the X51, right? I think it's mostly that people want the top end power from the X51 bits (5K - 8K) and the low end grunt around town (4.0L) and typically, stroking a motor adds a disproportionate amount of torque vs. power whereas boring the motor and increasing the bore affects top end horsepower more than bottom end grunt (torque). I think the combination is the big favorite because one produces a lot of torque and a bit of horsepower while the other produces a massive amount of horsepower instead of torque.
Yes, meant X51. Any idea what that difference means in terms of 0-60, segment times 60-80/120mph or 1/4 miles times and trap speed so we have a relative measure? I appreciate the feedback.
As you can see, the X51 upgrade is very much a horsepower producer with very little changing on the torque between 4500 and 5500; what it does to the flatness of the torque curve up top however is awesome and the slope of the power curve is what you want in a car like this. It's for this reason that the shortness of the gearing never bothered me because my car was making more and more power all the way to red line. Add in the shorter ratio gears and now you're really going to be matched in the powerband and pulling like a champ up top!
I included both baseline dyno runs because i didn't realize that my 360hp baseline had a spike where we the tach signal must have hopped for a brief second just over 7K. The issue that i fought was that the air quality was better when i did the original dyno baseline. It's been getting hotter and hotter here and more humid and at one point the intake air temps were 120F so i had to go back again earlier in the day to try and get the intake air temps that were close to the original runs, which i never was able to do successfully. It never ceases to amaze me how hot the engine bays get on these Caymans and Boxsters. The little midengine car really does struggle to be able to get hot engine bay heat out which is easier for a 911 and way easier for a front engine car. After a few pulls on the dyno, the car settles in at the same number as originally produced but it becomes near impossible to create any gains from tuning after the 3rd and 4th runs because of the heat soak.
The effect of the better breathing top end bits from the X51/GTS package make for a flat torque curve all the way to the red line and north of 6660 RPM, the power curve looks like a staircase relative to the stock curve. We could have easily run the car up to over 8K RPM and it would have kept climbing but i didn't do it on the Stage I curve because with the small intake bits, at those levels you're not gaining anything so i'm lifting off just at about 7700 RPM on the dyno, all in 5th gear in both runs. We learned a fair amount with this build and yet i feel like i found even more tricks hidden up the sleeve of the Cobb software, all of which will be given to my X51 customers as updates on the tuning front. For example, after returning from the dyno and studying the logs and runs I realized that we could fix the deficit of the red curve to the blue and black curves at 5500. I made a final update to the file and at that point the customer had just showed up from the airport, i gave him the updated file along with several others for the track and away he went. Thank you Cobb tuning for your awesome software.
I can tell you that it feels noticeably stronger from about 5000 rpm on in a very linear way. I am anxious to see how much the extra horsepower effects my lap times. First up will be Road Atlanta where there is room to take advantage of the top end gain. John, and the whole team at BGB, are absolutely at the top off the list when it comes to getting the most out of the mid-engine Porsches. Not only are they extremely knowledgable, but they are also a pleasure to work with.
02-16-2018, 12:39 PM
