[jim_howard_pdx]

Kevin,

You know for a guy like me that knows a little bit about a bunch of stuff, I really must tell you that I know nothing about the Moroso spin muffler.

We built an exhaust system for the cobra jet alot along the lines of your exhaust. Similar but different.

The exhaust port on a 428 SS class must remain the same dimensions as stock, so to get 9's we reshaped the bowl to be 80% the valve dimension, smoothed the runner and made sure the rectangle had a 3% twist effect. We had to go through alot of castings to find ones we could modify to hit this mark. Then we shot peened it so that it appeared "as cast".

Some will say we cheated, but the dimension to the stock port was exactly the same, the ports pocket and bowl smoothing and widening was really to prevent the flow from bumping and bruising. In other words, CFM increases were not the goal, just smooth, regular, flow.

EVERY CHEVY AND CHRYSER HEMI I FACED WAS DOING THE SAME THING.

So to get more swirl, and better scavanging we needed to increase the velocity of the exhaust. We ran 1 7/8 inch primary tubes off the head, the pipe was neither round nor rectangular, we shaped it to create swirl. I will not describe it further, because I do not want the Chevy crowd to know how to do this.

Then after a few inches we ran it into 2 1/4 inch primaries, and then stepped it to the 2 1/2 inch primaries, then it dumped to the collectors. The idea was to get each section of the exhaust to "SEE" low pressure in front of it, so it would be tugged along to move faster. The reshaping of the tube was to generate some areas of the tube that would impede the exhaust speed, and some that would allow the exhaust to scoot right along. The impeded area would get suctioned by the faster moving exhaust.

We tried a second design that started out with Primaries that were rectangular to match the port and continue the twist to encourage spin, then bumped the primary up by 1/4 inch steps to the collectors and maintained the rectangular shape all the way to the collector. This design showed NOTHING on the dyno, and showed NOTHING on the track, but the seat of the pants feel was very torquey.

So we ran the first design all during season one. Then I saw my first Chaparrel car, and Smokey Yunich had built this snaky exhaust system that took the out of phase cylinder exhaust from one bank and added it to the correct in phase ports of the other bank. It was like any regular header but with one of the four primarys welded to the other banks collectors.

What a mess of tubing. He aluminized the header so it also looked like Medussa's head of snakes.......

I cannot remember who I spoke to, but he told me the mess was good for almost 20% better scavanging, almost twice what you get from an H pipe system.

So we decided to build a third header. My muffler champ, Chuck, ran the three in phase primaries as we had with header number one. But the out of phase primary was made LONGER and we ran the tube inside the collector about 6 inches, but cut on a 45 degree angle.

The out of phase pulse was then dumped into an area of very fast exhaust flow to get equal scavanging form the cylinder bank. This worked well, so we ran it the next two years. It showed big horsepower gains with no loss or shift of the torque range. We liked this!

This is so similar in principle and function to Flow Tech's muffler that I wish we had applied for patents...... They dump the out of phase exhaust pulse past the collector to do the exact same thing, but without the extra welding and fabrication.

Now for the spin insert....We had to make a larger and longer collector than normal.

What I will tell you about the inserts is this. We tried one with vanes similar to the impellers of a centrifugal super charger. Wide space on the outside, thinner and tighter on the inside, with additional shaping to enhance fluid movement of the gas so it would not create a dam of exaust that slowed everything else down.

We tried a second design with spiralled tubes of different lengths and 45 degree entrance and exits. This was like putting a hundred straws into a big hole, and twisting them so the exhaust had to spin through them.

The third design was to take a wide mouth split it into two pipes and then back into one wide mouth. So the exhaust would have to split, and generally speed up then dump back together which created swirl.

To understand the physics here, watch TOP GUN the movie. When Tom Cruise is gunning for JESTER in the first training session, he puts the TomCat into afterburn (extra fuel is dumped into the jets exhaust to provide momentary thrust increases). You will see two plumes of dark exhaust that counter spiral away from the air craft. Taking a wide pipe to two narrow pipes and back to one wide pipe creates this same effect inside the exhaust tube.

Chuck was running just your standard Hooker Competition headers on his 400 ci smallblock. He ran the collectors to 4" side dumps just past his front wheels. He had a bypass switch to 3" exhaust and hemi mufflers for driving around. This was also a 9.2 bracket car, but he ran downdraft webbers and direct port NOS injection. He found that with NOS, an insert wasted top end torque and slowed his ET's.

This seems to be the effect of those MOROSO mufflers on your car. So be carefull not to waste 20 hours of time trying a trick that works on a super stock class engine, when you are headed to the 8's.

There is a universe of difference between these engines, and you need unrestricted flow even more than you need exhaust spin. I would like to see a Yates head again. I cannot remember the exhaust port shape. But I think it is rectangular. Try making the port roof round. So rectangular on the bottom and sides, and round on the roof edge. This should generate some extra swirl in those big primaries you are running.