Which header for 13B?

[Chris Wire]

I recently noticed that Mazdaspeed is now selling the SDJ header for the 13B engine. Does anyone have some back-to-back data as to how that header compares with the standard header that has served us so well in the past?

For those that don't know the standard header ends in a flange with two 2" pipes. Many users continue with the dual exhaust to the back of the car, while others will merge the exhaust into a single 3" pipe. What the SDJ header does is to merge the two tubes from the engine before they even get to the flange. Thus the flange has a single 3" opening to mount the rest of the exhaust to.

I am a current owner of an early-style header and would like some input on the newer SDJ style if someone is willing to share.

Thanks.

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Chris Wire
Team Wire Racing
ITS Mazda RX7 #35
[email protected]

[lateapex911]

I saw the header at the ARRCs. They, of course swear up and down it makes more power, but I don't have the numbers to prove or disprove that. Maybe a call to them is in order.

I will say however that it looked great. Very tasty, and well made.

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Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]

[ddewhurst]

Chris, IIRC the new SDJ header also has a slip fit (tube within a tube & not welded) of one of the header tubes so that stress between the two header tubes is not an issue.

Being the header subject is at hand what is the recomended header for the 1st gen non-ported ITA/7 12A ? In the process of converting my Spec-7 to ITA/7.

Comparison numbers would be appreciated.

[email protected]

Thanks
David

[This message has been edited by ddewhurst (edited May 06, 2004).]

[Mike Guenther]

I'll bet that Mike Van Steenburg could give you a good comparison of the two styles for 1st and 2nd gen engines. Mike has done a lot of dyno work on various exhaust configurations. 863 324-4539

[Banzai240]

For those interested... Here is a link to the SDJ headers page:

http://www.sdjmotorsports.com/Headers.htm

[moto62]

Here you go.
http://www.iscracing.net/exhaust.htm

Ray

[ddewhurst]

The picture Darin posted does not show the latest slip tube fit by SDJ. Maybe the slip tube is expermental???????????

Duh, edit....

I like the expansion chamber by ISC Racing. Sort of the same theory as the expansion section of a 2 cycle Kart header I would presume.

Have Fun
David



[This message has been edited by ddewhurst (edited May 07, 2004).]

[Chris Wire]

I find it interesting that SDJ has both a street version and an EProd/ITS version of their header, and yet it is the supposed "street" header that Mazdaspeed is selling.

Things that make you go hmmmm.......

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Chris Wire
Team Wire Racing
ITS Mazda RX7 #35
[email protected]

[C. Ludwig]

The expansion chamber puzzles me. The purpose of it on a 2-stroke is to induce revision. The wave travelling back up the head pipe stuffs the fuel/air mixture back into the exhaust port as the piston is moving up to keep the compression from blowing it all out the exhaust port. What's the purpose of the expansion chamber in this instance?

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Chris Ludwig
08 ITS RX7 CenDiv

[Banzai240]

Originally posted by C. Ludwig:
The expansion chamber puzzles me. The purpose of it on a 2-stroke is to induce revision. ... What's the purpose of the expansion chamber in this instance?

It's because the Rotary is, for all intensive purposes, a piston-port 2-stroke... The timing of the wave helps to "close" the exhaust port once the overlapping intake charge has made it's way into the chamber... Otherwise, the gas has an opportunity to pass right through the chamber into the exhaust port and never gets burned...

That's how I understand it, anyhow...




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Darin E. Jordan
SCCA #273080, OR/NW Regions
Renton, WA
ITS '97 240SX

[C. Ludwig]

True there is overlap. Never occured to me.

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Chris Ludwig
08 ITS RX7 CenDiv

[Banzai240]

Originally posted by C. Ludwig:
True there is overlap. Never occured to me.

I believe that's the reason why an IT header might be different than one for EP... In EP, when you port the sideplates, you increase the overlap and would have some different parameters to work with.

[C. Ludwig]

The RPM capability of an EP motor would be potentially greater than an IT motor as well. Thus creating the need to move the collector. That makes me wonder how the SDJ header works for both the IT and EP applications. Unless they're pulling very similar RPM with each configuration.

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Chris Ludwig
08 ITS RX7 CenDiv

[BrianB]

I believe the expansion chamber is essentially a megaphone with a reducing cone at the end. it's purpose in 2 cycle engines is to create a tuned neg. wave with the expansion of the megaphone.This negative wave helps to pull exhaust gases out of the chamber. In engines with intake/exhaust overlap,this neg wave will help pull intake charge into the chamber and into the exhaust as well. The reducing cone on the end of the expansion chamber creates a tuned pos.wave that returns to push that intake charge back into the chamber. The net result is an increase in air/fuel charge which can produce more power.
On a rotary engine,I don't believe there is overlap(unless i'm missing something). I think the apex seal, the shape of the housing and port timing prevent any overlap.I think a well designed header/ exhaust with a tuned neg.wave to extract as much exhaust as possible to minimize the effect on the intake charge by remaing gases is the best you can do for a rotary.

B