When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
As far as Matt's dyno, Matt's stock runs were a bit lower, but the intake temps there were quite a bit higher for both the stock and with header runs as well so we would expect the car to produce lower than optimal numbers. He's in florida...
The GT4 and Matt's GT3 dyno's aren't really comparable different dyno's ,different intake temps, different continents... All dynos have to be taken in context and are not absolute measures. If you guys are interested we can overlay some GT4 and 991 GT3/RS stock and modified dynos for you,
When Matt ran his car stock, the dyno reported what the cars output was, if you're interested in the why's well that takes science and an understanding of what the car is doing, happy to help explain...
Here's the dyno's we generated almost 18months ago, on a dyno jet. Our dynapack is very close to these numbers as well.
991 GT3 Stock vs Dundon Race Headers, (no tune)
Here's the GT3RS dyno as well.
991 GT3RS Stock vs Dundon Race Headers on 991 GT3RS
We chose to do these dynos without tunes as 95% of owners under warranty don't want a tune. We also have tunes available, they add about 15-20whp on the GT3 and about the same on the RS...
No CEL on the 991 GT3, RS or 981 GT4 Headers
Also we have the 991 GT3/RS Street system (200 CPSI cats) available as well, same 321SS, fully back purged, jigged construction as our Race headers.
We have shipped many many race headers world wide, all customers feel the power, reduce lap times on track, improved ET's and trap speeds and love the sound and 100% fitment. We honestly can't make them fast enough is our only issue!
And a link to our blog with many reviews from happy customers all over the world, and some interesting studies we've done on the sensitives of the 991 GT3RS on the dyno. We're finishing a similar study on the GT4 that will hopefully help the community to understand that dynoing these cars is non trivial and extra precautions need to be taken to get reliable repeatable data.
We choose to use 321SS for its superior properties and how long it's proven to last (we have 996 GT3 PCA club race car with Dundon Race headers out of 321, welded by Charles that have well over 300 hours of track time on them, 3 engine rebuilds and the headers and exhaust are still going strong, no cracks, issues etc.).
We've used slip fit 321SS merge collectors on all of our systems going back to the 996 GT3, it's the right way to build a header, and honestly we wouldn't build them another way.
At the end of the day, there's a product out there for every buyer. We don't expect everyone to purchase from us, but we are proud of what we design and build and stand behind our products and our results.
Any questions feel free to get in contact with me!
jamie@dundonmotorsports dot com
So there is only one thing that still keeps me off from getting headers, I have heard that the CEL will be part of your dashboard after you install headers and honestly even if it doesnt mean anything i still dont want to have that on.
Not necessarily true. It all has to do with the positioning of the O2 sensors. Each cat has an O2 sensor before and after for the ECU to monitor them. If you eliminate the cats, the ECU will typically pick up on this is short order and throw a CEL for catalyst inefficiency. However, some cars are not so sensitive. I've had some GT4/GT3 owners run catless for hundreds of miles until the CEL was triggered, then they clear it with a handheld scanner (around $100 on Amazon) until it comes back on again. Most decide to use our O2 spacers on the rear O2 sensors, which helps to simulate readings to the ECU within the parameters of having a cat in the system. Most of the time this hits the nail on the head and the CEL stays off, if your ECU is particularly sensitive you may have the CEL still come on every now and then. The only foolproof way to eliminate a CEL is to tune the ECU, but its really no bother to hook up your handy dandy scan tool and clear the code if it comes on once in a while. Very small inconvenience compared to the transformation of performance and sound, which maximizes the driving experience to say the least
So there is only one thing that still keeps me off from getting headers, I have heard that the CEL will be part of your dashboard after you install headers and honestly even if it doesnt mean anything i still dont want to have that on.
Have Dundon race headers no cell since day one even after 800 km and one track day
I think dyno results are very hard to compare unless it's all done same day, time.
So many variables like ambient temps, barometric pressure, different SAE smoothing, race gas or mixed gas or pump gas. The numbers can be affected by all these variables.
I think it's safe to say gains between 20-30whp should be expected from race headers. If someone thinks they can pick up 50-60whp on a NA motor they are foolish.
I think dyno results are very hard to compare unless it's all done same day, time.
So many variables like ambient temps, barometric pressure, different SAE smoothing, race gas or mixed gas or pump gas. The numbers can be affected by all these variables.
I think it's safe to say gains between 20-30whp should be expected from race headers. If someone thinks they can pick up 50-60whp on a NA motor they are foolish.
So true. I have personally spoken to some vendors here that just shake their head in disbelief that anyone here would believe gains over ~30whp.
Personally, even 30whp gains are stretching it. I would expect 20-25whp gains and be very happy with that.
However, some cars are not so sensitive... if your ECU is particularly sensitive
Oh come on, the ECUs and the cars are exactly the same... The difference is the road/driving conditions pushing the engine through the drive cycle for catalyst monitoring. You guys are using DIMSport for tuning? You should post the drive cycle conditions.
Not necessarily true. It all has to do with the positioning of the O2 sensors. Each cat has an O2 sensor before and after for the ECU to monitor them. If you eliminate the cats, the ECU will typically pick up on this is short order and throw a CEL for catalyst inefficiency. However, some cars are not so sensitive. I've had some GT4/GT3 owners run catless for hundreds of miles until the CEL was triggered, then they clear it with a handheld scanner (around $100 on Amazon) until it comes back on again. Most decide to use our O2 spacers on the rear O2 sensors, which helps to simulate readings to the ECU within the parameters of having a cat in the system. Most of the time this hits the nail on the head and the CEL stays off, if your ECU is particularly sensitive you may have the CEL still come on every now and then. The only foolproof way to eliminate a CEL is to tune the ECU, but its really no bother to hook up your handy dandy scan tool and clear the code if it comes on once in a while. Very small inconvenience compared to the transformation of performance and sound, which maximizes the driving experience to say the least
Fabspeed's 02 sensor spacer appears to be a "universal" fitment. It does not fit well on the 991 GT3, and it does not work as advertised.
I bought mine from Evan Fiorentino, who's no longer with the company (Fabspeed has tremendous employee turnover, so not a surprise).
I'm happy with the price I paid for my headers (the original short tube catless design), but it's ludicrous to me to compare Fabspeed with a higher end provider like GMG, BBI, Dundon, etc. Fabspeed is a low cost provider.
Matts numbers were done on our dyno, personally I will be the first to admit that had I not personally witnessed the numbers and power gains myself I would have called BS. Matt paid for the dyno time, we did not provide the parts so I have no horse in this race but was quite impressed with what I saw with the Dundon headers on the 991 GT3 platform.
In terms of dynos, we run a Dynojet 424 lc2 with link system, as far as Dynojets go its all the bells and whistles, however because the front is linked it's been known to be a heartbreaker for those only looking at numbers. I should also note that in Florida it's typically 90+ degrees and 70-100% humidity in the summers, not the most ideal conditions for making huge numbers but nothing we can change.
and estimating the cars weight at 3350lbs (car at 3200 and driver at 150lbs)
Center Delete: 121.4mph = 467.8bhp
Dundon Race: 126.8mph = 533.0bhp
If the car and driver is 3200lbs
Center Delete: 121.4mph = 446.8
Dundon Race: 126.8mph = 509.2
If the car and driver is 3100lbs
Center Delete: 121.4mph = 432.9
Dundon Race: 126.8mph = 493.3
Estimating the weight at 3350 gets us pretty good alignment with stock numbers at the crank... (car is advertised at 469 SAE HP)
This was the same driver, same launch, same tire pressures, same track, same rear wing removed...
This also would include the effect of ram air which we know adds power, but is hard to reproduce on the dyno. Also changing the weight of the car has an obvious effect on the numbers, but the delta stays about the same.
This is just basic physics, accelerating a known weight over a known distance and using the ending velocity calculating the power it takes to achieve that velocity...
You're all free to go run the numbers or play with the calculator yourselves...
The increase was enough that the race tech guys pulled him out of line and searched the car for NOS...
IMNSHO, I wanted to increase sound and didn't want to lose any torque in the process. I knew less cat would add to sound so for me i decided to do center section replacement and add headers and cats for extra volume. I liked the idea of having left and right pipes of center section connect so all six cylinder pulses would combine. This ruled out Sharkwerks. Several others though.
I liked quality of GMG and past experience so I did both headers and center section from GMG.
Very happy with the outcome. Car seems much smother though the power curve as the headers brought up toque where most of the stock system drops. Since I don't track total power was not and issue as it is very rare where I find more power up top useful.
Fairly quiet at cruise and seemed insanely loud at first when the values opened. All good after I got use to it.
IMNSHO, I wanted to increase sound and didn't want to lose any torque in the process. I knew less cat would add to sound so for me i decided to do center section replacement and add headers and cats for extra volume. I liked the idea of having left and right pipes of center section connect so all six cylinder pulses would combine. This ruled out Sharkwerks. Several others though.
I liked quality of GMG and past experience so I did both headers and center section from GMG.
Very happy with the outcome. Car seems much smother though the power curve as the headers brought up toque where most of the stock system drops. Since I don't track total power was not and issue as it is very rare where I find more power up top useful.
Fairly quiet at cruise and seemed insanely loud at first when the values opened. All good after I got use to it.
No doubt that their products are top notch. James does not need to post ridiculous #s. One thing I've noticed is the less that a vendor beats his chest on a forum the more established they are as a company.
No doubt that their products are top notch. James does not need to post ridiculous #s. One thing I've noticed is the less that a vendor beats his chest on a forum the more established they are as a company.
Funny you say this. On the AMG forums that I belong to, you never(very rarely) hear from the big Vendors(Renntech, Weistech, AMS, etc.), seems like they just let their costumers speak and show results, and their products do the job intended/advertised. Very different on Rennlist, but then again, the AMG's have turbo's which is easy to make additional power and A LOT of it. NA engines can only muster up so much additional HP/TQ before going internal, some of the gains I see here advertised on a NA engine with only headers/exhaust just makes me shake my head and smile.
01-23-2017, 04:10 PM
(in US units)
