Would running a V8 with no exhaust cause this? (apart from hearing loss)

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Originally Posted by duff

Using laymans talk and broadly speaking:)

And to add to what you are saying
The gas pulse is not a gas body that reflects, it is a shock wave that will only travel along the solid medium of the pipe containing the gas. when the shockwave reaches the end of the solid medium(open air) it will return back up the pipe. It is exactly the same for using explosives, the blast is one thing the returning shockwave is quite another with equally devastating results.
The "tuned length" of an exhaust(as far as exhaust piping goes) is all you need for Torque.(extractors) the rest of the system is an exercise in making the most efficient means of staying legal. there are gains to be made by carefully reducing the systems diameter and then enlarging the diameter back to the equal some of all the header pipes. This does increase the velocity of the gas thru the restricted area and provides gas purging to allow more mass movement thru a part that is only required for legal reasons. eg better without the restriction.
Ther is a book of about 200 plus pages , written buy a mad scientist at a Scottish university. He spent nearly forty years studying the science of gas flow and all that goes with it. Incredible reading that goes way beyond the stuff most of us learn thru trade or life. He put all his theories into to practice to remove the white mans magic aspect of lab tests.
At the end of the book his summary was carefully tuned individual stacks for all out power at narrow rev range(ala Drag). and tuned length pipes joined progressively, maximising shockwave(gas slug) timing to aid in scavenge,, or more to the point not disrupt gas flow with a poorly timed gas slug that opposed mass flow. There are acknowledgments that a heap of other techniques can be implemented but basically they had weight penalties or economic penalty etc.

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yes, the reflected wave is not a body of gas but a shock wave moving at or near sonic speeds up the tube, however, your assertion that only the primary pipes do anything for 'extraction' and torque production is incorrect. The entire system can and is in race car applications tuned to harness these waves. Each time you have a junction with a corresponding tube a reflected wave results.
By also changing diameters at various points and changing the velocity at these points a primary system that is tuned for top end power, via tube length and diameter/volume can have it's torque curve improved significantly below the point at which torque peaks, improving drivability without penalty to top end power production.

Yes, I've had the mad Scots book for over twenty years, and while the theory is good, much has been learned and improved upon over the last forty years since it was written.

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Originally Posted by rovercare

.. best way would be take your petrol powered vehicle, drop the exhaust/fit something larger and see for yourself......But DON'T mistake the added noise for a feeling of power..

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From my experience this technique is almost certain to mislead or confuse. Seat-of-the-pants doesn't work all that well. It seems to be almost impossible to ignore the extra noise and separate it from other possible changes.
I was told in the mid 70s by the owner of an SL 125 Honda that his expensive new Pacoe pipe had definitely given him heaps more power. My bike was still standard at that stage and I was the same build as him so we lined up side by side and took off at the blistering pace that only SL 125s were capable of. Several runs with the two bikes exactly side by side all the way convinced him that he had no more power than me. The best he could do to justify his expensive new pipe was to say, "well it does make it sound better."
I made a similar mistake myself when Honda brought out their not very successful MT125 two stroke. When I rode one I was absolutely convinced that it had more power than my four stroke SL 125. When we lined up for a few drag races, I quickly realised that the reason the two stroke seemed to have more power was because it actually had less power at lower revs. The sudden change in the amount of power as the revs rose made it seem as if there was more power.
If anyone is curious about two strokes as opposed to mutiple cylinder four strokes, the book to have was written by Gordon Jennings. Using his information I was able to design and build expansion chambers for short circuit motorcycles and for go-karts that performed better than racing pipes the owners were able to import from America.
Not quite on the topic of V8s, but I found exhaust systems for single cylinders a bit easier to understand and build.

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Originally Posted by rick130

yes, the reflected wave is not a body of gas but a shock wave moving at or near sonic speeds up the tube, however, your assertion that only the primary pipes do anything for 'extraction' and torque production is incorrect. The entire system can and is in race car applications tuned to harness these waves. Each time you have a junction with a corresponding tube a reflected wave results.
By also changing diameters at various points and changing the velocity at these points a primary system that is tuned for top end power, via tube length and diameter/volume can have it's torque curve improved significantly below the point at which torque peaks, improving drivability without penalty to top end power production.

Yes, I've had the mad Scots book for over twenty years, and while the theory is good, much has been learned and improved upon over the last forty years since it was written.

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Very much agreed Rick130, I have said that about the remaining system in my post. I agree reduced diameter carefully placed is good. but I was disscussing the prospect of restriction(read the guy took his run of the mill exhaust system out of the equation).
The increased velocity induced by the reduced diameter utilized in an exhaust system is not what I consider a restriction, more an extraction. I took it that the discussion was about the restriction within a normal exhaust system.

(I did open with "in laymans talk")

Again, in broad terms for discussion
My experience has been that mass extraction after the primary system helps of course, but this will be adequately achieved very close to the point that you have achieved your gas slug timeing. And agreed who on earth would build their primary system without addressing mass flow within it, that would be counter productive.

In crude terms you induce velocity at the end of you extractors and jobs done. From there on it is just to persue other secondary concerns at the risk of added weight, surface friction,, And without continual expansion relative to length you might even induce secondary gas slugs that will impede all the good work done within your primary system.

The physics involved have changed none, and the manipulation of these physics have changed some. They where tuning exhaust s in ny granddas day with many of the same tecniques. (Holdens might not have been) but engineers where. Modern manufacturing techniques have improved, with the effect of reducing the negative offsetting factors. Some "difficult to explain" techniques have provided results. A LOT of commercial products have made cool sounding claims that increase the velocity of the cash out of your wallet.

I look at current systems on racing cars and they are still largely tickled versions of the same base theories, Tune your slug, tickle the mass extraction and then get the hot waste away from your aerodynamics in the least restrictive and most aerodynamically efficient way possible.

Just an update:

I put the Y Pipe on today (no muffler) - the pipe stops at about the location of the handbrake drum. Anyway, the difference was incredible - it runs smoother, HEAPS more low end torque and no popping and backfiring. Also a lot quieter, even without any muffler.

Based on these observations, I'd be reluctant to run a straight twin system on a 4WD although I do acknowledge that this may be an incorrect assumption.......

If you are making an exhaust system for a road going vehicle, I suggest you digest Phil Irving's thoughts on the matter. "tuning for speed" and another whose name escapes me. For high end competition engines have a look at Smoky Yunick who was light years ahead of his comtemporaries and particularly of the factory engineers. Smoky's work with flow benches and dynamometers have stood the test of time.

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Originally Posted by duff

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I look at current systems on racing cars and they are still largely tickled versions of the same base theories, Tune your slug, tickle the mass extraction and then get the hot waste away from your aerodynamics in the least restrictive and most aerodynamically efficient way possible.

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Yep.
What I considered 'state of the art' the ten or twelve years ago I was playing with systems on a dyno were merely variations on what had been done back in the fifties or maybe even earlier.
Even the collector design hasn't changed since Cosworth (or maybe someone even earlier, maybe Coventry Climax ??) almost set it in stone, it is that good. I believe that having a proper merge collector helps dissipate any reflected wave in the secondary system which could disrupt the primary systems performance. Is this true ? Obviously they also help the flow out of the primaries (and secondaries if utilised) a hell of a lot better than a road going box style collector.
Anyway, basically all we were doing was reducing the outlet of the collector to below the dump pipe diameter and tapering back up at a nominal 15* angle (any steeper angle and I believe flow separation occurs, creating turbulence) This just increased velocity substantially at this point, so we could then utilise a larger dump pipe, helping and extending top end power while not losing (actually increasing) torque.