1.5" Primaries? Interesting. Im trying to decide on design for my bridgeport's header and every time I think i've figured it out I see something new. Im thinking of making the primaries short (around 18"). I was planning on having 2" inner diameter primaries, is this too big? The exhaust port sleeves have been ported. Also, should the primaries collect straight into 3" or should they collect at something like 2.5" and then go into the 3" exhaust. Any advice would be appreciated whether it regards primary length, primary diameter, collecter etc etc.

I can post some pictures of the porting (intake and exhaust) if you like.

Thanks

 

The smallest that I had figured out should be used on completely stock sized exhaust ports was 1-5/8" and that was pretty tight. I settled on 1-3/4".

 

Hrrm, how did you figure that, and for what housings? Or was that not with your insert dealies?

My reasoning is that, measuring the S5 NT ones I have, the inside port area ended up at a bit less than 10 square centimeters; this gibes with Mazda published values for MFR housings (9.2 to 12.5cm^2 depending on variant) They also mention it opening to a pipe diameter of 43mm, which is a touch over your 1-5/8" ID number and a great deal over my planned 1-1/2" ID... but then, they weren't trying to operate with any restriction in the exhaust, I'm running a bit milder on the intake ports, and in that paper, I don't see any signs that the exhaust diverged from their baseline design either.

I figure I want to see what happens with really minimal expansion of the port area; 1-1/2" ID is some expansion from the 10cm^2 opening, but not much. I've a friend with an engine dyno setup for rotaries; may have to get some mild steel mandrel bends and see what happens prior to doing a "real" header out of 304. Possibly play with stepped diameter headers too; what the heck, I love TIGing stuff now that I've got a real setup.

I full well acknowledge it might just not work very well, but what's the fun of an experiment where you know the outcome?

 

You guys arent making this easy . I have no idea what primary diameter to use now. I dont want to choke my bridgeport but I dont want my primaries to be too large and give me poor scavenging.

 

I figured it based on S5 T-II housings. While the total port area itself may work out to around a 1-1/2" pipe, my figure came from crushing down a 1-5/8" pipe into the necessary oval to match up. You lose a bit of open area this way but it wasn't much. This was with my exhaust sleeves. I settled on the 1-3/4" pipes just to have a slight step for reversion reasons.

 

Mm. I think I figured out the perimeter worked out with the 1-1/2" pipe... it was all a bunch of back of the envelope calculations, but after crushing and cutting the angle it does seem to have worked out to a near enough approximation for my purposes. Will take photos when it's a bit more finished.

 

Collect the pipes early with a rb header, add a qtec, then slap a couple presilencers and a nice aero muffler on to keep things quiet. When you wanna race just open the qtec. Crank up the volume then click the link http://s222.photobucket.com/albums/d...ortexhaust.flv

 

I had a q-tec for a VERY short time! Insanely loud and no appreciable benefit. An exhaust doesn't have to be restrictive to be quiet. In fact a properly designed one can be very quiet and rob no horsepower in the process.

 

I rarely see internally rusted headers but they *are* usually filled with so much carbon you can pour it out.

 

Actually broke down and took pics of the little insert I made. This is for an S5 NA housing. 304 stainless, 1/8in wall tube. Figure it should work.