Hawk Yama

Cool!! Some products seem very interesting especially for the shorter final gear I might fly there to try out (if you have a demo car) to decide I really want to do it one day. That thing makes GT4 going to 6th gear at COTA back stretch . So the racing header doesn't make exhaust too loud, does it? How much improvement can I expect just intake/tune?

AutoQuest Motorsports

You have an open invite to come on over here, we'll typically have at least one with the shorter final drive at the shop. Just let me know before you head over so we can arrange something, it truly is a very transformational upgrade...it's what the GT4 has needed from Day 1.

I'm not going to tell you the Race Headers won't make it too loud, only because sound can be quite subjective and I don't know your point of reference. I would personally never consider a race header/pse GT4 to be too loud, it's pretty much perfect and it is the same exhaust combination we run on all GT4's we build here at AQ.

Plenum/TB and a Tune I'd say about 15-20hp/tq max gains, but it'll vary a bit less throughout the powercurve. The headers are the weakest link, if you put those race headers on that alone is about a solid 25-30hp/tq across most of the curve. That is what will make the biggest difference. Plus headers take like 1.5-2hrs to switch out. Throw them on and take them for spin, no harm done and you'll know for sure.

Yargk

The independent dyno runs seem to indicate that some popular brands of headers provide only 5 hp. Which ones do you find that add more power?

AutoQuest Motorsports

We don't yet have an in house dyno to do independent testing supporting or denying any claimed dyno results from any manufacturer. What we do have is Sebring about 1.5hrs away from us that we visit on average 30 times a year for testing and running the Suncoast PCA DE events. We know what is making power on these cars (as well as many other factors), and currently our GT4 "Powerkit" that we put on the GT4s coming through our shop consists of Race Headers, Plenum/TB, and a Tune. That being said, there are a number of good headers out there and the aftermarket is always striving to improve and provide the best performing product for the community. We have great relationships with all these manufacturers, and we use the best products at our disposal that we have tested thoroughly on the track. Over time the manufacturer of those products may change as we do our testing and determine the best solution for the goals we have for our cars and our clients. Therefore, I will not publicly state which we are using at this time, as I would not want an assumption made for those reading this post in the future or for different products on different cars. If you would like to chat a bit more in depth about this particular upgrade, please feel free to give me a call on my cell at 484 883 6197 and I'd be happy to privately give you the information you need to make an educated decision moving forward.

Yargk

I was just curious if you were going to recommend any catted headers that made good power. Race headers do seem to do something substantial.

Agreed that racetracks can make okay dynos. I'm within 1 mph on any given day at thunderhill at the end of the main straight and 30 hp would give me another 3-4 mph I think.

AutoQuest Motorsports

For majority street use absolutely. Now I'm not going to say I'm a professional exhaust manufacturer, but from what I understand cats will typically limit optimal primary tube/merge collector design and exhaust flow/pressure, which prevents it from making the most power where you want it on the track. Most of the gains end up being in the lower/mid range of the powercurve than the higher end where you're living on track, but is actually rather enjoyable on the street. This is why you don't see much "peak" HP gains on Sport Headers and it's not the best ROI for a track car, in addition to cat cores being a wearable item under consistent track abuse. I'd always recommend a catless setup for us track junkies, and they're easy enough to swap out if necessary. Sport Headers are a nice upgrade for street use though, next time you look at a dyno graph of them take a look at the delta of performance gains between around 2k-5k rpm where you'd typically be enjoying the car on the street. You'll find good gains there that are a noticeable improvement on the street manners of the car.

ShakeNBake

I would strongly recommend against running cat'd headers if the car is a track toy. It's not a matter of if, it's a matter of when a cat melts or disintegrates. The results of that can range from meh to a new motor. I've tried all the mods, and catless long tube headers on 101 octane and stock tune make the most noticeable and consistent power on the track. Everything else I tried caused trouble on the track or when hot the car pulls back a ton of timing. A dyno run is very different than heavy, continuous use on the track in 80-90F weather. The 101 octane is more to help the car deal with the heat, it does not produce any extra power when the ambient temps are low. I got this advice 2 years ago when I got my GT4 from a very knowledgable vendor on this forum, but I didn't listen and proceeded to try everything. After two years and a world of headaches, I am back to his advice. Also happens to be what the clubsport folks do...and how many of those car are beaten to hell on a race track?

Mech33

+1.

Yargk

Agreed on not wanting to spend my time buying cat after cat. I was just curious academically because it seemed that some dyno plots from sport header end users didn't show much of a benefit.

MarcD147

Cat is a warranty item....
Speaking from experience.....

EVOMS

We didn't find any gains worth writing home about with sport headers. The stock headers and cats are well designed and constructed with hydroformed tubes and I'm sure a ton of R&D. An aftermarket 'sport cat' header likely isn't constructed or optimized as well as stock, and the cat doesn't make that much of a difference in flow. It's possible to get a real, substantial change in performance with long tube headers because by eliminating the cat you open up the packaging options to go to a substantially different (and higher performing) design than stock. Adding the cat back in gets pretty difficult on the GT4 as you're limited again by packaging. The 'ideal' spot ends up in the wheel well where a proper sized cat won't fit, or will give off a bunch of heat in an area of the car not built for it. If you move it too far down the exhaust, it won't warm up and you'll have to mess with the O2 sensors to get them to reach...at that point you're messing with a bunch of knock-on complications that aren't worth it.

AutoQuest Motorsports

+2

Hawk Yama

Thanks for the invitation John!! I put that on my ToDo list in the future Also, thanks for the tips. I absolutely want to try the racing header, Plenum, TB and ECU tune combo first!

Yargk

Cool, thanks for the explanation!

(And thanks to autoquest as well)

AutoQuest Motorsports

No problem, give me a call sometime I'd love to catch up and hear what you've been up to : ) Sebring is incredible, every petrolhead deserves to run that track so get over here ASAP! Here is a little video of me running it for the first time the other week as a little teaser, best of a 2:28.7 in my Cayman R...car needs tires and camber haha.


My pleasure Yargk. If you want to get a set of Race Headers I typically have a set or two sitting on the shelf, just give me a shout : )