[jim_howard_pdx]

Old guy with an 87,

I don't care what people think of me from what I write. Anyone who has raced with me knows I do this because I love engines. I love everything about making power. It is my addiction.

My friends do not all go as slow as I do, and some go WAY faster. I took 15 years off racing to raise my two kids, and now they beg to go to the race track and drive the car. It is great family time for me.

Now my 17 year old daughters teachers know she has drag raced! My wife doesn't know what to do with me? She wouldn't drag race if her life depended on it......

So thanks for the kind words. And I hope those that want to know who I am, get to know who I am, cause they will become friends too. I will never mislead them in the quest for power and trophies.

So exhaust is the cornerstone that every other piece of the engine survives on. One guy wrote in a thread one time that backpressure was a bad thing and you should do everything you can to eliminate it all together.

Well run the engine without a header or any tubes. Just let it fire into the air.

The engine will have no torque, or little torque over any rpm range. Then it might create ok horsepower readings at wide open throttle, but I doubt that too.

What I can tell that guy, is that exhaust back pressure, and exhaust flow are his friends. They allow him to build a long and wide torque curve to keep the car clipping right along.

That is why tuning an exhaust system is so frustratingly painful for me. My street rod engine was making 350 hp, and I knew it could make 375 even with the old street cam (since changed) so I went from 2 1/4 inch exhaust to 2 1/2 inch exhaust. Well my horsepower jumped right up to 383 hp, but my torque from 2,000 to 4,000 rpm went down. So my low end throttle response went down. So I am faster, and more powerful, but I really MISSED the low torque I was making with the smaller pipe.

My hope is that someone comes up with a variable backpressure exhaust system where a computer could tune the backpressure to the throttle position, vacume level, and rpm of the engine to maximize both horsepower and torque.

It could be done. the fact no one has done it is more a factor of putting profit over performance.

One friend I respect alot, just put a MAC 3 inch exhaust system on his 4.6 twin overhead cam Cobra. He hates it. He misses the low torque much more than he enjoys the extra 5-8 hp at top rpm where he rarely drives.

So perhaps exhaust system factors can be the subject of speed secret number 10 or so. We have more to cover before we should talk about that......

By the way, my current thinking is to use the flow tech headers with the off-pulse cylinder primary dumping past the three on pulse cylinder's collector point. The idea is to use the excellent flow pattern of the three on pulse cylinders to scavange off the off pulse cylinder and getting more even horsepower from the entire cylinder bank.

This is awesome thinking. I would use this and an X pipe system with Edelbrock or Spin Tech mufflers and Hi Flow Cats. Just delete the cats with by pass tubes until you go for smog testing.

This should give you great exhaust velocity as long as you do not go HOG wild with the size of the X pipe. It should be only as large it takes to provide the maximum horsepower you intend to build. So without a CAT a 400-500 hp engine runs best on 2.5 inch tubes, but the 2.25 tubes would improve low torque. A 500+ Hp engine needs 3 inch tubes. Why not 2.75? I do not know all the physics, but the 3 inch produce dramatically higher torque bands than the 2.75 tubes. So there is a hint of what is to come later.....

Thanks for the encouragement. I am really happy there are some people out there that want to learn some stuff.

Again, I am not purporting these secrets to be the only ones, or the best ones, or the ones to follow. NO. I am just after getting you guys thinking and commenting and looking at a bunch of options that allow you to build the best platform you can to run consistent times. Because in bracket racing the fastest car NEVER wins. The car most CONSISTENT TO THE DIAL IN WINS!

Have fun this weekend. I am still recurving my street rod's distributor. It is getting closer and closer to excellent. AND THANK YOU Denny Aldridge for helping me with that project.