exhaust/header help
 

Hey guys,

I hope everyone had a great new years.

SO... I crawled under my car this weekend to fix one of the exhaust tips and the dealer decided that it looked cool to have it stick out 1/2" further then the other one.

In the process I came to discover what I thought was only axle back indeed is cat back! Boy am I excited!

So my question is since I am not the one that bought it I am trying to figure if anyone know what size the cat-back Flow master exhaust is since it doesn't say on the website. I didn't have a tape with me yesterday it just looks bigger then 2.5.

I am just trying to figure out if I should run 2" or is it safe to run 1 7/8 headers if my exhaust is 3"?

I was going to hold off on headers, but now that I know I have cat-back I am going to order my headers and finish up the exhaust.

Thanks guys
Keith

I would imagine FM makes their exhaust in both sizes so you'd have to measure or compare it to the mid pipe size to be sure. 3in is considerably bigger than 2.5in so it shouldn't be hard to compare the size of the mid pipes to the catback pipes.

You can run any size header you want. The most popular size is the 1 7/8 since it fits perfect and flows extremely well. If you go by Jannetty's header test, each size increase showed a slight increase in peak HP/tq while not suffering down low. Many, of the 1 7/8in headers have a 3in collector and use the off road pipe or HF cat to reduce from 3-2.5 for the OEM size exhaust. 2in headers are typically run by guys that have aspirations of making huge power. From what i've read, they fit but are a bit tight.

Exhaust size doesn't matter to header selection. You do need to be sure of the cat back size so that you get appropriately sized hf cats or connecting pipes. I have seen both 2.5" and 3" cat backs.

That said, take a piece of string and wrap it around your cat back piping in a straight run (not on an elbow). Do not stretch the string, but wrap it around the pipe and mark the string where it meets itself. Measure the length of marked string. This will give you the circumference of the piping. Then it's a simple d=C/pi to figure diameter (7.85" for 2.5" and 9.42" for 3"). I'm not sure if the 2.5" and 3" diameters refer to inside diameter or outside, so the measurement may not be exact due to wall thickness. I would guess that less than 9.42" circumference is 2.5" and greater is 3".

However, make sure to check the sleeve clamp where the exhaust meets the stock manifolds. Many 3" catbacks neck down to 2.5" to be compatible with the stock manifolds.

Thanks guys! I will have to get the car up on ramps again the next dry day and find out for sure. Sounds like 1 7/8 is the way to go, I highly doubt I will get much higher then 500-550HP. I will do some research to determine which headers are best for me. I wish I could get away with out cats but that just is not an option :(

Thanks again guys!
Keith

I'm pretty sure the Flow Master cat-back only comes in a 3" exhaust. Realize that the first part of the cat-back will be 2.5" to match up with the factory mid-pipes or aftermarket HF cats.

Stick with 1 7/8" as it will be the best all around header unless you know you'll be in the 600+ range. In that case 2" might be worth the extra money.

Also know that the size of the primaries has nothing to do with the collectors. The collectors is the part where all the primaries come together and is usually 3". You'll then have a HF cat that will have a 3" inlet but a 2.5" outlet to hook into your cat-back.

Cool so from a little more research it does look like that Flow Master only has a 3" exhaust so I am looking at the SW 1 7/8" 3" catted pipes. A lot of people seam to be happy with these and for $1400 they seam to be middle ground on pricing as well.

CALL AROUND!! Manufacturers often have limits on advertised pricing. What you find listed on the internet may not be the lowest you can find. My exhaust combo was a LOT less than MSRP. I found an awesome deal online and called the company and they gave me an even lower price.

Just to clarify so that you understand how the exhaust will work, those 3" cats will be a 3" inlet and 2.5" outlet. Your Flowmaster cat-back will have a 2.5" inlet and then shortly after the connection point it will jump up to 3".

So, technically you won't have a true 3" exhaust. The only way to do that is either buy a complete system (KOOKS has one as well as LG) or you would have to take your car to a muffler shop to have the front of the cat-back taken off and 3" welded in......which is not woth the money.

You won't have any performance loss with the 2.5" step in the cat-back unless you start going over 600 HP and/or maybe with forced induction.

Agreed. Don't always go by the price on the web. Alot of vendors have to post "Suggested Retail Price" but then have coupon codes and things to bring down the cost significantly.

I don't know what the prices are now but a year or so ago when I was looking at getting headers I could've bought some 1 7/8" KOOKS with HF cats that were Jet Coated for $1,350 to my door. Probably $1,200 without coating. That was not the advertised price but the call in price.

Keep researching the different brands and call the vendors from this forum to get some good prices.

Not a complete list by any means but here are a couple off the top of my head:
JDP Motorsports
Ivan @ Southwest Speed
Apex
Maryland Speed
Jannetty Racing
ADM Performance

Don't forget that you'll probably want to look into having your car tuned once you've added the headers. Best bet will be to find a good local performance shop that can do a dyno tune. If you don't have a shop around you look at doing a remote tune from someone like Jannetty Racing.

Budget $400 for the tune.

Thanks guys! I plan to order them this weekend hopefully. I have been emailing Ted back and worth and I think I figured out what I am going to go with. I am leaning towards the DynaTech headers with 3" cats

Caverman I actually picked up a tuner last week and LOVING IT! Ordered through Ted he sends a free MAP with anything you buy from him so it makes it easy :)

Thanks
Keith