[jim_howard_pdx]

First of all, I am really sorry for my comment about UGLY Novas.

(They really are UGLY, but I have never found a mother that didn't love her UGLY baby either.)

I guess I need sensativity training.

Now to the power / header leak issue.

First of all, any exhaust leak will effect cylinder filling during the intake stroke. WHY? Because the Intake and the Exhaust valves are both open for a short period of time. On my street cars that event is about 36 to 42 degrees. On a racing cam it might be 110-120 degrees of overlap. The leak means that the cylinder will not purge during the exhaust stroke, and that means more burnt fuel in the intake charge. Since it is fuel density, not fuel mixture that creates horsepower, a slight decrease in fuel charge density can make big swings in torque and power production.

Your torque curve will reduce, and sometimes we see exhaust leaks in reduced ET times before we hear it from the engine.

To find an exhaust leak. Have a buddy fire the engine when it is cold, and run it up to 2200 RPM immediately, just as you would if you were breaking in a new flat tappet camshaft.

Take your hand and feel around each port. You are looking for puffing. You might have some initial leaks that go away immediately as the gasket expands due to the heat. This is normal. I usually check the exhaust bolt torque first to minimize this.

You will feel a leak before you hear it. By the time you hear a header leaking, the seal is completely gone and exhaust is now rushing past the gasket.

Many times a repeatedly leaky exhaust is the sign of exhaust system problems. If you are running a CAT it may be too restrictive. If you have small tubes and high power, you might need to go up in tube size to reduce the pressure on these gaskets.

I think this is one reason Kevin Price has such problems with his gaskets on his Yeats Head. At 800 HP he really needs a dragster type exhaust system. What I mean by this is that to develop full power, an engine needs the first 6 to 10 inches of exhaust flow to be a straight tube exiting the exhaust port. So on my Mustang with the first primary bend about a 1/2 inch off the exhaust port I am immediately giving up about 4-8 HP. That is what my shock towers contribute to my engine. NEGATIVE 4-8 HP!

I think Kevin is already running 4" primary tubes and large collectors.

Something that people don't know is why exhaust header leaks form in the first place. Actually the exhaust flow is like an explosion. The power rings back and forth against the sides of the pipe as it slowly moves its way down the length of the pipe.

Take some time to think about what I just said. The exhaust pulse beats side to side against the tube. It actually moves quite slowly down the length of the pipe. One reason that X tube exhaust systems are effective is that the X tube itself subjects this ringing pulse energy to a 45 degree angle that reduces its back pressure. That is the only reason why an X system exhaust makes more power than an H system exhaust. It reduces the side to side ringing.

What we did in the 60's and 70's to improve cylinder scavanging was to run a product called swirl tech mufflers and pipes. In fact our 427 AC cobra engines and GT 350 R cars were all fitted with swirl flow tubes. The had NO provision for muffling the sound, all they did is convert the horizontal energy of the exhaust pulse to a rotational energy created by the fins that created the swirl. We often picked up close to 20-25 HP on a big block, but we also picked up total MPH capability as well.

We ran this swirl tech system on a GT 350 R and got 370 HP from a car that was getting 338 HP on mufflers. It improved from a top speed of 148 mph to 157 mph. THIS IS HUGE!

The exhaust was so loud we were pulled over once driving 55 mph with a 98db reading. We did not tell the CHP officer that the reading would be 106 db at 80 mph and above. That was one loud Mustang!!! Just starting the car was an event all its own! That 289 in a 65 Mustang was almost as loud as the 427. The 427 AC Cobra swirl tech exhaust side pipes could set off earthquake alarms. I kid you NOT.

Hope this helps. I make all my friends fix exhaust leaks BEFORE I do any type of engine tuning. Fix the exhaust, and often your problems will go away. Then you super tune to get ET consistency and to equalize cylinder to cylinder power production to maximize your bearings life expectancy. I wonder what Kevin's bearings look like after 25 passes!!!!!

800 HP on a small block can make for some pretty hammered out looking rod bearings on a NOS car. His is naturally aspirated. Man is his engine "cooking."



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