X51 and all that - in search of power
01-07-2019, 12:37 AM
#31
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Thread Starter
My 14 Cayman S PDK had a new factory 3.8L 991 GTS X51 engine installed in 2015 and the dyno curves match up with yours until somewhere around 6000 RPM, where I peak at 372 HP at the wheels, BGB posted my car's dyno chart at the link below. About two years later, after melting two sets of catalytic headers and plugging the muffler, costing 50HP loss, I went to race headers and race exhaust and redid the dyno locally and it matched the original BGB dyno HP exactly. The BGB Dyno run was made with Fabspeed Sport headers and a Cargraphic sport exhaust. GT4s still outrun me on the track due to the Final Drive Ratio difference between PDK (3.25:1) vs MT (3.87:1(.
Dyno Chart
I suspect the first set of headers died due to leaded fuel (wrong marked pumps at the track) contamnation of the Oxygen Sensors. They were not changed out when the second headers were installed and later, found that the packing in the Cargraphics sport mufflers dissolved and created a blockage that measured at 8 lbs backpressure. Once a good exhaust was installed and new oxygen sensors installed, the problem has not recurred in two years. Since then I have avoided getting fuel at the track, instead bringing my own race gas that I get from a trusted fuel vendor or just running on pump gas purchased off-track.
V6
Dyno Chart
I suspect the first set of headers died due to leaded fuel (wrong marked pumps at the track) contamnation of the Oxygen Sensors. They were not changed out when the second headers were installed and later, found that the packing in the Cargraphics sport mufflers dissolved and created a blockage that measured at 8 lbs backpressure. Once a good exhaust was installed and new oxygen sensors installed, the problem has not recurred in two years. Since then I have avoided getting fuel at the track, instead bringing my own race gas that I get from a trusted fuel vendor or just running on pump gas purchased off-track.
V6
01-07-2019, 02:17 AM
#32
Great effort with the GT4, thats a lot of love - also it looks like you got a good outcome through perseverance. The ECU seems to be a real "watch it" area - its the same with the series II 991s - the ECU has to be sent away to be "opened".
I have money down on the new GT4 and I'm following the developments very closely (e.g. BGB and GT4CS ~ I am prepared to pick a used 991 Series II GT3, but as something that will be a pure track car it has to start with the clubsport package, and given its very much a buyers market, come at the right price.
Well done with the GT RS - and with Oz pricing you are doing the right thing in using it wisely and keeping the GT4 for the track
How do you find the Trofeo Rs relative to Cup 2 N1 spec on the GT4?
01-07-2019, 02:54 AM
#33
Pro
Thread Starter
991.2 GT3 is the way to go and hopefully pricing will ease. With all the mods I've done my car is now competitive with 997.2 and maybe a 991.1. A 991.2 walks away from it. Having said, that my old 1999 build 996.1 GT3 is still the fastest road-registered car I've competed in but that has the benfit of running 18" wheels and Yoko AO50's.....it's secret is that is weighs one hell of a lot less than any modern Porsche GT car (GT4's included).
As for tyres, I have found Trofeo R to be better than Cup 2. I am going to try 255/35 19 and 305/30 19 Bridgestone RE 71R next as the Pirellis are very expensive.
As for tyres, I have found Trofeo R to be better than Cup 2. I am going to try 255/35 19 and 305/30 19 Bridgestone RE 71R next as the Pirellis are very expensive.
01-07-2019, 03:52 AM
#34
996.1 GT3 and 996.2 are quite possibly the best (from a driving POV) and most under rated GT cars. On soft O50s they are really glued down and very quick too Hope the RE71Rs work out well for you . Happy hunting.
Hope the RE71Rs work out well for you . Happy hunting.
01-07-2019, 07:03 AM
#35
991.2 GT3 is the way to go and hopefully pricing will ease. With all the mods I've done my car is now competitive with 997.2 and maybe a 991.1. A 991.2 walks away from it. Having said, that my old 1999 build 996.1 GT3 is still the fastest road-registered car I've competed in but that has the benfit of running 18" wheels and Yoko AO50's.....it's secret is that is weighs one hell of a lot less than any modern Porsche GT car (GT4's included).
As for tyres, I have found Trofeo R to be better than Cup 2. I am going to try 255/35 19 and 305/30 19 Bridgestone RE 71R next as the Pirellis are very expensive.
As for tyres, I have found Trofeo R to be better than Cup 2. I am going to try 255/35 19 and 305/30 19 Bridgestone RE 71R next as the Pirellis are very expensive.
I like the Trofeos for the first track day...after that I have found they loose a lot of grip and don't last a lot. The RE71R is a just a little bit less sticky out of the box but very consistent and last a long time, way over MPSC2 and Trofeos,
I have been testing the Pirelli DH slick but buying scrubs......with a little bit of Keysers Hot Lap treatment they seam to grip way above any of R tires and are lasting enough to warrant the cost.
I may take the plunge this year and buy a sticker (new) set of DHs and see really how long they last...as you mentioned, new ones are not cheap but once you try them it's like a drug!!!!!
01-07-2019, 08:05 PM
#36
I am confused on the IPD plenum with GT3 TB results. There have been multiple posts on the forums that said there was only negligible or no gains with those. Even Dundon Motorsports said the plenum and throttle body were not a restriction until high 400HP output for the GT4. So what is the true story on these items ???♂
01-07-2019, 08:08 PM
#37
Do you know can it be installed on a bare ECU? I doubt you are motivated much by the prospect, but perhaps you can get back some of your investment by having your tuner do the install on an ECU shipped to them.
01-08-2019, 03:16 AM
#38
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Thanks heaps for posting that. Apart from the 40 bhp power differnce (just the way the different dynos report), the shape of your X51 plot is a match for the green trace on my Plot 2 right through to redline, which is the X51 heads and plenum and the special Cobb tune. I would argue, that if you remove the X51 plenum/intake runners and replace with IPD/TB plus GT4 runners your car will make a lot more power right through the range. My Fabspeed cats also failed. Just removed all the ceramic and now straight through.
https://rennlist.com/forums/gt4/1118...whp-gt4-3.html
it's suggested that the X51 intake is responsible for most of the gains. As the comments are the opinions of Rennlist members who own/operate racing companies, I'm not sure what think anymore??
What I will comment on is an intake should be mated with a complementary exhaust system + tuning, to realize the optimum benefits of "charging" & "scavenging" airflow/exhaust.
What design of headers/exhaust are you using on your car. Perhaps your exhaust system is optimized with the IPD/GT3 intake combination, giving your car the best realized gains?
Further comments on your part would be greatly appreciated!
01-08-2019, 03:25 AM
#39
Pro
Thread Starter
Thank you for posting your independent modifications & results. I'm also somewhat confused with the results & some of the comments. In posts #40 & 41 on this other current thread
https://rennlist.com/forums/gt4/1118...whp-gt4-3.html
it's suggested that the X51 intake is responsible for most of the gains. As the comments are the opinions of Rennlist members who own/operate racing companies, I'm not sure what think anymore??
What I will comment on is an intake should be mated with a complementary exhaust system + tuning, to realize the optimum benefits of "charging" & "scavenging" airflow/exhaust.
What design of headers/exhaust are you using on your car. Perhaps your exhaust system is optimized with the IPD/GT3 intake combination, giving your car the best realized gains?
Further comments on your part would be greatly appreciated!
https://rennlist.com/forums/gt4/1118...whp-gt4-3.html
it's suggested that the X51 intake is responsible for most of the gains. As the comments are the opinions of Rennlist members who own/operate racing companies, I'm not sure what think anymore??
What I will comment on is an intake should be mated with a complementary exhaust system + tuning, to realize the optimum benefits of "charging" & "scavenging" airflow/exhaust.
What design of headers/exhaust are you using on your car. Perhaps your exhaust system is optimized with the IPD/GT3 intake combination, giving your car the best realized gains?
Further comments on your part would be greatly appreciated!
01-08-2019, 03:33 AM
#40
it's all actually in the first post. The car runs Fabspeed sports headers with the ceramic knocked out of the cats (thus straight through with small (cat volume) expansion chambers. one of the cats collapsed which is why I did this. Others have reported the same experience with Fabspeeds.
01-08-2019, 05:16 PM
#41
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it's all actually in the first post. The car runs Fabspeed sports headers with the ceramic knocked out of the cats (thus straight through with small (cat volume) expansion chambers. one of the cats collapsed which is why I did this. Others have reported the same experience with Fabspeeds.
01-08-2019, 06:11 PM
#42
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Thread Starter
01-15-2019, 12:50 AM
#43
Three Wheelin'
Thank you for posting your independent modifications & results. I'm also somewhat confused with the results & some of the comments. In posts #40 & 41 on this other current thread
https://rennlist.com/forums/gt4/1118...whp-gt4-3.html
it's suggested that the X51 intake is responsible for most of the gains. As the comments are the opinions of Rennlist members who own/operate racing companies, I'm not sure what think anymore??
What I will comment on is an intake should be mated with a complementary exhaust system + tuning, to realize the optimum benefits of "charging" & "scavenging" airflow/exhaust.
What design of headers/exhaust are you using on your car. Perhaps your exhaust system is optimized with the IPD/GT3 intake combination, giving your car the best realized gains?
Further comments on your part would be greatly appreciated!
https://rennlist.com/forums/gt4/1118...whp-gt4-3.html
it's suggested that the X51 intake is responsible for most of the gains. As the comments are the opinions of Rennlist members who own/operate racing companies, I'm not sure what think anymore??
What I will comment on is an intake should be mated with a complementary exhaust system + tuning, to realize the optimum benefits of "charging" & "scavenging" airflow/exhaust.
What design of headers/exhaust are you using on your car. Perhaps your exhaust system is optimized with the IPD/GT3 intake combination, giving your car the best realized gains?
Further comments on your part would be greatly appreciated!
That said, I'm not sure how many folks have actually gone through the testing of separate components of the x51 to really break it down. FWIW, Deman installed the full x51 kit, 4L stroker, and Dundon race headers on my car and I picked up about 70 rwhp. My experience was great since they've done a number of these before so all I did was drop the car off, wait a couple weeks, and pick it up again. Most of the gains were in the top end but it still made more torque than stock across the entire rev range though it's not an apples to apples comparison with the extra displacement. Are you positive the tune is controlling both sets of flaps in the X51 manifold? I know you said you checked them but from the loss in mid-range in the dynos looks like maybe the flaps aren't opening/closing to maintain the mid-range torque.....
01-16-2019, 04:26 AM
#44
Pro
Thread Starter
Thanks for contributing ajw45. We are sure that both sets of flaps were operating correctly. If you have before and after dyno plots of your car (even though after is 4 litre) that would be helpful. I did read the Porsche spiel as per your post, but that is not what we found in practice. It is interesting that the new GT4 CS has a plenum that looks a lot like an IPD job in terms of shape and there are no obvious individual flaps in each tract.
01-16-2019, 11:35 AM
#45
FYI, It maybe obvious to some, but just to mention that each flap should open and close multiple times across the rev range. Older design concepts just opened some and closed some at high or low RPM, this is not ideal and does not exploit proper resonance tuning.