foo

Exhaust manifolds vs headers on a 455.
what is going to give better performance in general?
Im wondering if I should find a pair of Z,W exhaust manifolds or just use headers.

s i 442

Depends on your intention with the car?
For just a show car manifold and 2 inch exhaust would work.
But for a romp down the track you need at least 2.5 inch exhaust and free flowing mufflers such as Flowmasters.
I have Hooker headers and love them but my car isn't stock and they let you hear the cam pulses alot better than manifolds.

foo

answered my own question, you also helped confirm it

oldcutlass

For a 455 you would want to run a 2.5 inch exhaust, and for performance headers are better than the manifolds. Flowmaster mufflers don't flow well, just read the comparisons. I like Walker Dynomax Turbo's they flow great.

s i 442

An "S" configuration muffler is restrictive. Take a look.


A Flowmaster style muffler is as least restrictive as it gets, take a look and make your own decision.

joe_padavano

Because the sharp bends and direction reversals are LESS restrictive? Sorry, but I suggest you take a course in subsonic aerodynamics THEN make that statement. Bottom line is that you can't "eyeball" subsonic aerodynamic flow. Gentle curves will ALWAYS be less restrictive than sharp ones. More to the point, I believe published test data, not someone's eyeball "engineering".

442Chris

Take a look at this: http://www.boyleworks.com/ta400/psp/exhaust.html

It's a test with Pontiacs, but the result should certainly still apply to our A-bodies, at least. Looks like the Flowmaster works, not surprisingly better with the center in and center out. The other p/n Flowmaster is a center in/offset out.

I put the Dynomax ones to replace some 30-series Flowmasters on my car based on the test. Can't tell really what the performance difference is, but I can hear myself think on the highway now. I just put on some electric cutouts for when I want it really loud, so it's the best of both worlds.

For the OP, I'd say that the headers will be much better for performance, especially if you've modified the engine. However, headers can be a pain with starter issues if you don't properly insulate it. The brake proportioning valve is also not in a good spot with headers, at least on my 442. Generally they are just a pain over the manifolds, but they sure look cool.

s i 442

Like I said make your own decision, do you want your car to sound like a truck with turbos or do you want it to sound like a hotrod like everybody else?

allyolds68

If you want your car to sound like every foxbody mustang out there put on flowmasters

Like you say, to each his own

joe_padavano

I want the car to PERFORM first. Using mufflers that simultaneously obnoxiously loud AND more restrictive (that's a real engineering feat, by the way) is not my idea of improved performance. Posers can worry about APPEARING (or SOUNDING) fast.

Jimmy_B

I have to agree with Joe here.

Has anyone considered the Factory Headers from Ram Air Restoration?

http://www.ramairrestoration.com/old...e-headers.html

joe_padavano

Uh, those ARE just factory W/Z manifolds. The "oversize" ones simply have a larger outlet port. There's no internal difference.

TripDeuces

Beat me to it 442Chris. I was just going to post that same link. I've personally never liked the sound of Flowmasters and the data proves they are some of the worst for performance. My friend had some on his 70 Cutlass and the noise was just plain obnoxious inside and out. I didn't even like being in the car.

joe_padavano

Gotta love those (no)Flowmaster 42551s.

Let's see if I got this right. The LOUDEST mufflers in the test, yet the highest backpressure by a bunch (again, THAT'S not easy). The slowest trap speed in the quarter mile, and second to longest elapsed time.

Yup. I want THOSE on my car...

s i 442

Kind of strange that every show and magazine that dynos an engine hooks them to Flowmasters and gets great numbers, not once have I saw a set of turbo mufflers used.
But I guess your all logic passes on to other parts like smaller tires get better traction and smaller hammers make bigger dents than bigger hammers?
Thats OK because some cars just can't handle a Flowmaster so they blame the muffler. Im surprised Magnaslows haven't been brought up yet, they are strait though but somehow that promotes reverse strait flow back pressure and slows the car down.

rjohnson442

Paid advertising vs Real world use...... To each is own.... My .02 some cars will preform better with more back pressure so "Technically" some restrictive mufflers could have HP gains on some motors. but you're also asking the guy who runs flowmaster with electric cut outs directly after the headers. And I can tell you I have more power off the line with them closed. Too much to be exact

s i 442

With Flowmasters!



Without!

joe_padavano

Wow, talk about a poser. I'll bet the truck has a Thumpr cam also (motto: all the crappy idle of a radical cam without the pesky extra horsepower).

If crap like that impresses you, Google Rick Dobbertin.

s i 442

Oh Im sure your right at home with a 14X6 Olds rally rim and a 235/60 tire.
National attention and magazine coverage is just not your cup of tea because you are the king in your garage as long as the doors are closed and the neighbor doesn't come over and say the words "aftermarket" or "performance" . LOL

joe_padavano

You probably missed the feature on one of my cars in the Oct 1985 issue of Car Craft because you weren't born yet...

Back to that truck - certainly if I were building a performance vehicle, my very first thought would be, "what's the heaviest, least aerodynamic vehicle I can find?". Of course, that would only matter if that truck ever actually ran down a quarter mile, as opposed to just idling around a fairgrounds. Pro Street at it's finest...

oldcutlass

You know...for a guy who can't put a manifold gasket on his own car, you sure are knowledgeable. Another legend in his own mind. You have no clout my friend.

foo

boy is it funny how my little question turned into this long debate on exhaust haha

joe_padavano

Yeah, a long and EXHAUSTIVE (perhaps even exhausting) debate...

(Sorry, SOMEBODY had to say it... )

oldcutlass

So many have pipe'd in and I'm exhausted.

s i 442

Its no big deal at least I can help people without needing 4 pages of info and 50 pics.