4L X51 is IN!
06-19-2017, 12:12 AM
#1
Three Wheelin'
Thread Starter
4L X51 is IN!
Dropped the GT4 off with Deman Motorsports a month ago with DMS headers and tune already installed and picked it up this week stroked to 4L with the oem X51 kit and a ltw flywheel. I immediately called in sick and put a few hundred miles on the car 
Holy crap, the 4L X51 combo makes the flat 6 feel like a different engine! There is more power everywhere but the top end is the big change with the engine pulling hard from 5k rpm all the way to the new 8k rpm redline. Revving out the engine is such a rush now having both more power and a broader rpm range to enjoy it. It was probably 20-30 degrees hotter during the tuning runs than the baseline but the dyno still showed a 70+ rwhp peak gain and that's on top of the already installed headers and tune. Low and mid range are improved too though not as dramatically as the top end. It's not like having a big honking V8, you still need to rev the engine but the run up the rpm range feels smoother and meatier than the stock engine. The change in the low/mid range is most noticeable to me in the upper gears where I find myself downshifting less often to pass. Rolling into the throttle in 6th while cruising is totally fine for passing now.
FWIW, I never really felt like I needed more power or speed. The GT4 is already more than powerful enough for our roads and has more performance than I have driving ability on the track. I really just wanted the engine to chase redline harder and be angry about it. Will report back as I get more miles on the car but so far all signs are this is an awesome upgrade so if you've been on the fence about a 4L and/or X51, go for it!
Holy crap, the 4L X51 combo makes the flat 6 feel like a different engine! There is more power everywhere but the top end is the big change with the engine pulling hard from 5k rpm all the way to the new 8k rpm redline. Revving out the engine is such a rush now having both more power and a broader rpm range to enjoy it. It was probably 20-30 degrees hotter during the tuning runs than the baseline but the dyno still showed a 70+ rwhp peak gain and that's on top of the already installed headers and tune. Low and mid range are improved too though not as dramatically as the top end. It's not like having a big honking V8, you still need to rev the engine but the run up the rpm range feels smoother and meatier than the stock engine. The change in the low/mid range is most noticeable to me in the upper gears where I find myself downshifting less often to pass. Rolling into the throttle in 6th while cruising is totally fine for passing now.
FWIW, I never really felt like I needed more power or speed. The GT4 is already more than powerful enough for our roads and has more performance than I have driving ability on the track. I really just wanted the engine to chase redline harder and be angry about it. Will report back as I get more miles on the car but so far all signs are this is an awesome upgrade so if you've been on the fence about a 4L and/or X51, go for it!
06-19-2017, 01:15 AM
#4
Nice review 
My friend is on the fence of doing the 4.0L + X51 or wait for the Dundon 4.5L + X51, it's a good problem to have 
My friend is on the fence of doing the 4.0L + X51 or wait for the Dundon 4.5L + X51, it's a good problem to have
06-19-2017, 02:39 AM
#5
06-19-2017, 03:29 PM
#6
Drifting
I can only imagine. Just came off the X51 3.8 911 GTS in my avatar and the acceleration difference between that and my new GT4 was very, very noticeable. And on the track, my one GT4-owning friend who is at least as good as I am (probably a little better) could keep me in sight for a whole session but I'd always win in the GTS, running OEM Pirellis and OEM suspension setup.
Sounds like you have the best of both worlds! (well, assuming the 500hp 4L RS motor isn't an option.)
Sounds like you have the best of both worlds! (well, assuming the 500hp 4L RS motor isn't an option.)
06-19-2017, 03:38 PM
#7
Rennlist Member
Dropped the GT4 off with Deman Motorsports a month ago with DMS headers and tune already installed and picked it up this week stroked to 4L with the oem X51 kit and a ltw flywheel. I immediately called in sick and put a few hundred miles on the car
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06-19-2017, 03:39 PM
#8
06-19-2017, 03:54 PM
#9
06-19-2017, 04:03 PM
#10
Three Wheelin'
Thread Starter
There's a little more mechanical noise in the cabin and it does seem a touch louder at the exhaust but it was already loud with the headers so the difference is pretty small.
Cost vs power ratio? Well, kinda terrible compared to say mods for an American car or a turbo. For a Porsche, it's reasonable I guess compared to trading into a 991.2 GT3. I'm a mid-engine manual fanboy so I would be illogical enough to try to shoehorn the GT3 engine in there if there was a gearing solution for 9k rpm. Then the cost/power ratio would really be total crap....
Cost vs power ratio? Well, kinda terrible compared to say mods for an American car or a turbo. For a Porsche, it's reasonable I guess compared to trading into a 991.2 GT3. I'm a mid-engine manual fanboy so I would be illogical enough to try to shoehorn the GT3 engine in there if there was a gearing solution for 9k rpm. Then the cost/power ratio would really be total crap....
Last edited by ajw45; 06-19-2017 at 08:06 PM.
06-19-2017, 05:58 PM
#12
Addict
Rennlist Member
Rennlist Member
Congrats! Interesting impressions, as I would have expected a stroked engine to shine at the low and mid ranges more than at the high revs. Must be the contributions of some of the other hardware and tuning as well...
06-19-2017, 09:23 PM
#14
Three Wheelin'
Thread Starter
I can only imagine. Just came off the X51 3.8 911 GTS in my avatar and the acceleration difference between that and my new GT4 was very, very noticeable. And on the track, my one GT4-owning friend who is at least as good as I am (probably a little better) could keep me in sight for a whole session but I'd always win in the GTS, running OEM Pirellis and OEM suspension setup.
Sounds like you have the best of both worlds! (well, assuming the 500hp 4L RS motor isn't an option.)
Sounds like you have the best of both worlds! (well, assuming the 500hp 4L RS motor isn't an option.)
I thought the difference between the 991 S and GTS was huge after driving them back to back but that might be a minority opinion since I think most reviews seem to say the X51 feels like a minor upgrade on the 991. On the GT4, I'm guessing it not only adds the claimed 30hp but you get the extra 15hp from the 991S that Porsche left at the factory when it shipped the 3.8 with standard cayman throttle body and intake plenum.
06-19-2017, 09:27 PM
#15
Race Director
I would assume you may need to re-tune the car but who would have a tune for this type of upgrade???
Would not the "brains" of the car not be able to adapt to what is now going on with the motor??
Would not the "brains" of the car not be able to adapt to what is now going on with the motor??
