996 Turbo / GT2Turbo discussion on previous model 2000-2004 Porsche 911 Twin Turbo and 911 GT2. Sponsored By Vivid Racing
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John have you got any dyno tests for comparison? It would be very nice to know at what power level the 2.5 becomes a restriction. 2x 2.5 ought to flow about as well as say a single 4inch. In my past experience a 4inch pipe vs a 3.5 gained NOTHING other than noise on a 700+RWHP car. Obviously mufflers make a difference and these cars have short pipes too so it's not apples to apples. If one of the guys with say about 700-800RWHP could do some back to back test or maybe one of the vendors, it would be VERY helpful! The Supra guys used to do this, gather up like 8 exhausts and test them all for sound and power - super helpful to say the least.
I've got a fairly cheap exhaust myself. Drones! Not super bad but bad enough I would love to change it. However I ain't paying multiple $K for an exhaust that still drones <sigh> A crossover piped exhaust would be my ideal replacement, I understand that having the two sets of pulses merged SHOULD cut down on the drone, it sure did with Mustangs when you moved the crossover around. But with the cost of the systems out there no way am I going to start trial and erroring to find a solution that makes me happy!
Right now I'm waiting to hear what Mikelly says about the next exhaust HE tries as he's already been through like FOUR looking for one that's tolerable, I think a crossover system is next on his list but his trans is down right now so it could be awhile.....
P.s. Al, I disagree - bigger is not always better. On my supra I went from a 3.5 to a 4inch exhaust. Gained NO spool, no added power, just lots of noise. It was kewl as hell to hear the turbo spool up AND down as I drove but other than noise at my power level it made no sense. I do not know at what level various exhausts are good enough on these cars but I'd like to. A backpressure test or simply a dyno test - perhaps both - would sure be helpful. Just going bigger is a great way to spend more money and lose your hearing while maybe not making any more power...
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We did test a 2.5" cross-flow vs. a 3" cross-flow and found that the 3" made an additional 30AWHP more power from about 3500 RPM's to 4700 RRM's with K24/18G turbos. From 0 to 3500 RPM's (initial spool up) and from 4,700 to 6,800 RPM's, the power was absolutley identical. So, from a strict dyno power standpoint, the tendancy would be to go with the 3" system for the brief performance advantage at the 24/18G level. In the real world, however, one can not feel this brief 30 AWHP increase on the road. When I spoke to Tony at EPL about this he said "John, your at 700 HP, 30 HP at that level, in a tiny window, is not detectable, you need at least another 100 to really begin to feel it". I have driven these systems back to back several times, trying to detect the difference and I can not feel any difference. Perhaps a timed event would show a slight difference, but I would switch to the 3" bypass pipes for a timed event, anyhow.
At the end of the day, the way I use my car, I have choosen the 2.5 because it sounds almost identical to the 3.0, which is a great sounding system (it's just a hair quieter) and lacks the cabin noise and drone of the 3". IMO, this is really what most people desire. It is just not worth it to me to have the drone in order to know I have a 30 HP advantage for a few RPM's that I can not feel, anyhow. If the car is a purpose built racer and you want to street race, 1/4 mile or track with the exhaust in place and you do it daily or frequently, then the 3" is probably the best choice, so that you have the most you can at all times. Or if you just prefer a loud exhaust, then go 3", too. Personally, I would rather enjoy the car daily, without a lot of intrusion, then slap on a set of bypass pipes for a track day. I think this fits a lot of 996TT owners. These exhausts are not unlike other performance components, you can improve handling with stiffer springs, steel monoball suspension, solid motor mounts, etc., but it begins to detract from the comfort and enjoyment of these cars when used on a daily basis. Again, in my opinion, the 2.5 offers a perfect blend of sound, performance and cabin comfort that most would be extremely pleased with...and the ability to switch to full 3" performance in minutes. I am all about performance and have gone to great lengths to make my car fast. It is currently perfectly dialed in, running stronger than ever, sounding great and a true pleasure to drive on a daily basis...with our 2.5 exhaust.
I think you are on the right track, talk to Mike Kelly once he installs his exhaust.
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If you are looking for a 70mm 996TT exhaust, we offer a twin cannister, full 70mm exhaust. Not all exhausts that are advertised as 70mm are full 70mm. If the exhaust re-uses the OEM tips, that means it is necked down at the outlet and you will lose the advantage that 70mm piping usually provides. We have specially made tips that look like the OEM twin tips, but flow a full 70mm. We also have a 6speed member discount. PM me if I can answer any questions.
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John D (also post as John D, member since 2003)
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Thanks and I appreciate your help. I am just trying to gain more knowledge on several exhausts before I purchase.
Quote:
Originally Posted by John@SpeedTech
Project911,
If you are looking for a 70mm 996TT exhaust, we offer a twin cannister, full 70mm exhaust. Not all exhausts that are advertised as 70mm are full 70mm. If the exhaust re-uses the OEM tips, that means it is necked down at the outlet and you will lose the advantage that 70mm piping usually provides. We have specially made tips that look like the OEM twin tips, but flow a full 70mm. We also have a 6speed member discount. PM me if I can answer any questions.
We did test a 2.5" cross-flow vs. a 3" cross-flow and found that the 3" made an additional 30AWHP more power from about 3500 RPM's to 4700 RRM's with K24/18G turbos. From 0 to 3500 RPM's (initial spool up) and from 4,700 to 6,800 RPM's, the power was absolutley identical. So, from a strict dyno power standpoint, the tendancy would be to go with the 3" system for the brief performance advantage at the 24/18G level. In the real world, however, one can not feel this brief 30 AWHP increase on the road. When I spoke to Tony at EPL about this he said "John, your at 700 HP, 30 HP at that level, in a tiny window, is not detectable, you need at least another 100 to really begin to feel it". I have driven these systems back to back several times, trying to detect the difference and I can not feel any difference. Perhaps a timed event would show a slight difference, but I would switch to the 3" bypass pipes for a timed event, anyhow.
At the end of the day, the way I use my car, I have choosen the 2.5 because it sounds almost identical to the 3.0, which is a great sounding system (it's just a hair quieter) and lacks the cabin noise and drone of the 3". IMO, this is really what most people desire. It is just not worth it to me to have the drone in order to know I have a 30 HP advantage for a few RPM's that I can not feel, anyhow. If the car is a purpose built racer and you want to street race, 1/4 mile or track with the exhaust in place and you do it daily or frequently, then the 3" is probably the best choice, so that you have the most you can at all times. Or if you just prefer a loud exhaust, then go 3", too. Personally, I would rather enjoy the car daily, without a lot of intrusion, then slap on a set of bypass pipes for a track day. I think this fits a lot of 996TT owners. These exhausts are not unlike other performance components, you can improve handling with stiffer springs, steel monoball suspension, solid motor mounts, etc., but it begins to detract from the comfort and enjoyment of these cars when used on a daily basis. Again, in my opinion, the 2.5 offers a perfect blend of sound, performance and cabin comfort that most would be extremely pleased with...and the ability to switch to full 3" performance in minutes. I am all about performance and have gone to great lengths to make my car fast. It is currently perfectly dialed in, running stronger than ever, sounding great and a true pleasure to drive on a daily basis...with our 2.5 exhaust.
I think you are on the right track, talk to Mike Kelly once he installs his exhaust.
John, most rollons happen between 3500-4500 so that extra power may help there. However, what was the power curve below 3500. I ask because when I went to fabspeed straight pipes I lost low end power, and it was noticeable. I then went to my custom crossover system and definitely gained low end and did not seem to loose on the top end. But this is all seat of the pants, no dyno.
Also, to OP, john was at 700 bhp, when he dynoed. With a less hp setup there may be no difference and you sacrifice drivability and low end torque.
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If you are concerned with winning roll-ons and want maximum power at all times, then 3" would probably be the way to go, especially if you have a higher HP car. If you are concerned with retaining a comfortable sound level in the cabin for daily use, but still wish to considerably upgrade the sound and performance, then 2.5 is the better choice, IMO.
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John D (also post as John D, member since 2003)
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Check out our Fabspeed Maxflo Exhaust with Sport Cats. We have it available in both 2.50" and 70mm for ultimate power. The 2.50 system can easily handle 600+ HP and torque and it sounds great. If you are looking to increase some HP and make the car sound sportier, the 2.50" will be fine. If you are looking for maximum power and will be doing the ECU tune, intercoolers, bigger turbos or so on, then I recommend doing our 70mm system along with the EVOMSit tune to maximize power and boost with least turbo lag. The 70mm will sound more aggressive and deeper and we have everything in stock and ready to go. Let me know if you have any questions or if you need more details on the muffler upgrade.
Thanks,
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215-646-4945 Ultimate quality T304 Stainless Steel exhaust systems, Carbon fiber airboxes and ECU Tuning for all exotic cars.
The 30HP spike sounds to me like the turbo spooled up, bumped a bit past set boost, and then settled down. This would make most sense on a freer flowing system to over shoot. Is it possible that this occured?
. However, what was the power curve below 3500. I ask because when I went to fabspeed straight pipes I lost low end power, and it was noticeable. I then went to my custom crossover system and definitely gained low end and did not seem to loose on the top end. But this is all seat of the pants, no dyno.
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