mx5cartalk.com

I fluked it and found a set of genuine Apexi extractors on the net. It's a 4-1 with a \"twisty\" collector.
Butt-dyno definitely says there's more ooomph, and she revs easier and faster to redline.
4-1 systems are supposed to give better top-end at the expense of bottom-end, and most go for 4-2-1 (as I'm sure you know all this anyways), but I couldn't feel any losses with mine.

One important thing to look out for in a quality header are the actual holes/ports in the manifold flange. Make sure the exhaust tubes and ports match.
In other words, cheap systems will just be round tubes welded onto a flange with oval ports, therefore there will be parts of the round tube sticking out into the flow-path, and other parts hidden causing unwanted ebbing of flow.

Am I explaining this properly?

This is crude, but I think you get the idea:

Black represents the exhaust port on engine and exhaust manifold flange;
Red is the round exhaust tube;
Orange is the part of the tube that sticks out into the exhaust flow;
Purple is the part of the tube that is hidden behind the flange creating ebbs.

You need a header with the tubes \"squashed\" at the top and bottom, thus expanding and flaring the ends, to match the ports.

I had the Genie headers on my NA6 - along with enlarged intake, CAI, hi-flow cat and exhaust. The quality of the headers was fine. The performance was minimal (if any). They were (from memory) one of the more expensive upgrade items of the whole intake/exhaust bit and were easily the least effective.

The factory headers are already fairly good. I'd suggest saving your money.

I have had headers on both an NA and NB mx5.

The type I chose were the Loch Stewart headers.

On both mx5's they were a vast improvement on standard headers.

They also make the car sound more racy.

View http://www.miata.net.au/loch.html

Cheers Novice1 aka Ron

Slugoid wrote:

Novice1 wrote:I have had headers on both an NA and NB mx5.

The type I chose were the Loch Stewart headers.

On both mx5's they were a vast improvement on standard headers.

They also make the car sound more racy.

View http://www.miata.net.au/loch.html

Cheers Novice1 aka Ron

I shall look into the Loch Stewart headers.

Roughly how much were the headers for the NA?

$550 from memory, I know a tad expensive but they are quality and will last a lifetime.
Cheers Novice1 aka Ron

1red5 wrote:This is crude, but I think you get the idea:

Black represents the exhaust port on engine and exhaust manifold flange;
Red is the round exhaust tube;
Orange is the part of the tube that sticks out into the exhaust flow;
Purple is the part of the tube that is hidden behind the flange creating ebbs.

You need a header with the tubes "squashed" at the top and bottom, thus expanding and flaring the ends, to match the ports.

...and my Jackson Racing header and the OEM ones -

Andrew's got my back

In brief Slug:
* 4-1 headers should give you better top end power at the expense of low-end torque
* 4-2-1 headers should improve power across all rev ranges with maybe a negligible drop in low-end torque
* the standard headers are 4-2-1 with very short primary and secondary pipes, check out Andrew's pic, his is a 4-2-1 with much longer primaries and secondaries. This changes where the power is made in the rev range.
* mandrel bends are good if you can afford them, but unnecessary.
* for naturally aspirated cars, do not go bigger than 2.5\" diameter for the rest of the exhaust as this will disrupt proper flow and exhaust scavenging.
* replace your catalytic converter with a true high-flow cat. You will need some research to find genuine high-flow cats. I wouldn't go by the word of your exhaust shop as they don't really care what they sell you. Perhaps buy this separately and bring it with you when you get it done.
* get a straight-through muffler
* stainless steel and mild steel pipes produce different sounds. Stainless produces a higher-pitched/raspy sound, mild steel produces a deeper/droning sound. Choose what you like.
* Genie headers are well-made. Don't let price be a total judge on quality.
I have Genie on my other car and love them. Around $200 fitted.

The two biggest tips I can give you is ask around for a reputable exhaust shop, and good ones will trial-fit different mufflers so you can choose which one you like the sound of, and ring around to get an idea on price.

I also somewhat agree with Mr Q in that the standard headers are well-made items. Maybe do it in stages Slug, get a high-flow cat and the exhaust from that back to the muffler. Then change your headers later.

Happy hunting.

genie headers 200 fitted??

thats really cheap!

For all the talk of which model/type (eg 4:1 vs 4:2:1) of header to get, the reality is that in general, for a road car on mild cams, it makes bugger all difference. A good header vs the OEM one will give you maybe 2kW difference at the most.

The arguments for different tuning lengths or \"top end vs midrange\" type headers are really only effective for engines with long cam duration and large amounts of overlap.

The basic keys for a road car are:
Avoid cross-pollution between the cylinders (eg don't join adjacent cylinders in a 4-cyl).
Allow enough flow rate to not be restrictive.
Don't go any bigger than you need to or it'll only make more noise.
Pick a design that still allows good access around the engine bay (eg to manifold nuts)

Build quality would be a bigger factor for me.

garettb16 wrote:genie headers 200 fitted??

thats really cheap!

I thought so too that's why I got em on the spot!
They were only the mild steel , as I know Genie makes pretty Stainless ones, and the shop charges very good rates for labour.

i am in the market of buying a set of headers.. i would prefer stainless.. and am waiting for something to catch my eye?

i did have a look at the lock stewart page and dont mind those sorts of dollars..

any other good value for money headers available.. im in melb and wouldnt mind doing it befor christmas.

FWIW These are the ones I'm looking at
Definitely not Loch Stewart prices, but I guess I'm not chasing those sorta gains. But just going by eye they look nice!

Follow eBay linky

Anyone have any opinions to shed?

PS they have them for 1.6 too (slightly cheaper)

yes has anyone bought headers from Npower?

any good.?

a tad off topic, but how much power could you expect to gain if you changed your cat? what aftermarket brands are there?

i hear that magnaflow have excellent hi flow ones and i'm thinking of going down the magnaflow track..

ooh just another quick question.. I recently installed a cat back system on the five and on the mid pipe, there's a hole for the oxygen sensor. where do i find the oxygen sensor to plug into the mid pipe? or can i just leave it where it is and plug up the hole?

I think the general concensus is that anything you do to upgrade your exhaust, with everything else being pretty stock, will give you SOME power increase, but probably nothing noticeable by the good ol' butt dyno.
I know that mine definitely revs alot faster.

As with stainless for headers, I would like to hear from a metalurgist/engineer as to the practicality of stainless for headers. From my research I deducted that it may not be as good as mild steel due to thermal expansion. In other words, stainless expands considerably more than mild, therefore more prone to cracking. Someone in the know please comment .....