AR Racing Step Headers with GG Heads and Cam

[Robert Dyck]

Has anyone had any experience or knowledge about the AR 1 5/8 to 1 3/4 step headers? Supposed to provide more torque at low to mid range.

This will be for an 02 rt that will have Greg Good heads and cam, Also, Nick from AR said that he has seen that with this configuration, a 3" cat back does little or nothing over the stock 2 1/2" exhaust. So I'm wondering if I should include a 3" cat back with this build. Next time I talk to Greg I will also ask him.

Thanks, Robert.

 

[345s-bspinnin]

My Gen III GG heads/cam car loses over 50hp between 3" exhaust and OEM 2.5". There are equations for determining volumetric flow capacity for a straight pipe. Dual 2.5" pipes start becoming a restriction at about 550+whp. You can certainly make more power, but the head losses climb quickly and thus creating a restriction.

I am not sure how different the OEM headers are between Gen II and III, but Gen III OEM primary is 1.75". I cannot fathom why anyone would want to downsize to something smaller than OEM. Before the heads and cam, my headers only (1.75 ARH) would make more torque at all rpm when compared to stock.

My $.02

 

[Dom426h]

Prob not much benefit using a 3" system after a stock 2.5" cat, but if your going heads & cam & headers(with a 3" outlet) then you should def ditch the stock cats and run a 3" component wether it be a hi-flow cat or simply replacing it with some type of muffler. And then continue with 3" to the exit.

Let us know what you end up with.

 

[Robert Dyck]

Right now I'm using a high flow 2 1/2"cat with the stock pipes.

345, are you saying you "gained" 50 hp by using a 3" pipe?

 

[Camfab]

Here is an amazing oddity. My headers which I believed to be way undersized proved me wrong. I've got the original SVS headers 1 1/2" stepped to 1 5/8" with Burns merge collectors. My car puts down 585 to the wheels. Do I think it would make more HP with larger tube headers, probably, however I'd venture to say that mid and lowrange torque would suffer. I'd love to try some bigger tube headers to find out.

 

[345s-bspinnin]

I have a catless setup, so my comparison may not be apples to oranges.

But yes, going from my catless ARH with OEM 2.5" exhaust to the same catless ARH but with ACRX 3" exhaust gains me 50hp (both have 3" test pipe, j-pipe, or whatever its called that replaces the cats). I still alternate between both exhausts setups. ACRX is only racing since it unGodly loud and accompanied by drone. I switch to the OEM exhaust with cross-over for the daily grind and the weekend out with the Ms (its so quiet at cruising speed its amazing)

My losses are so big that I have to change my tune too. My "racing" tune is built around the 3" exhaust. If I keep the same tune after an exhaust change to OEM, my A/F goes from a nice flat 13:1 to a progressively richer mix as the rpm climbs and ending in high 11s:1 by redline.

 

[1997GTS]

I put on AR 1 5/8 to 1 3/4 Step Headers with a Single Hi Flow Cat into the Corsa Cat Back Exhaust. I have not dyno'd the setup since this last upgrade but it seems like the loss of back pressure at the low end seemed to bring the range up some for power. I did the cat back at the same time as ignition and custom tune so got a lot more overall performance in line with what others are claiming they measured. The engine feels great, revs up quick and definitely the best power upgrade so far.

Headers were also pretty easy to install (once I figured out broken engine mount sagging on one side and bought the right saw blade to cut 304 to fit length). My only complaint is the exhaust noise level went through the roof. I got hit for 104 db at Laguna and 107 at Thunder Hill.