For the techies...
Discussion
Why you would want to 'pull' exhaust gasses out i will never know.
But if so, what you need is some venturi system.
basicly assuming the vehicle will be moving, some sort of cone shaped duct to catch clean air as its moving forward, this gets chanelled or ducted down to a point or jet, this fires the air into a larger cavity and out to air again. on the side of this cavity will be an inlet, inside you will get a depresion where the point or jet fires the air forward into a larger space causing a vacuum at this inlet, to this attach the exhaust.
I hope you get the jist of that, i would draw a silly piccy but i'm tired and off to bed soon
But if so, what you need is some venturi system.
basicly assuming the vehicle will be moving, some sort of cone shaped duct to catch clean air as its moving forward, this gets chanelled or ducted down to a point or jet, this fires the air into a larger cavity and out to air again. on the side of this cavity will be an inlet, inside you will get a depresion where the point or jet fires the air forward into a larger space causing a vacuum at this inlet, to this attach the exhaust.
I hope you get the jist of that, i would draw a silly piccy but i'm tired and off to bed soon
You arrange a diverging cone in the exhaust system at a suitable distance down from the engine, so that when the pressure wave from one exhaust pulse hits it, an expansion wave is reflected back up the pipe to the exhaust port in time to help suck out the gases on the latter part of the exhaust stroke. Or a bit later, to do the same thing but for the next cylinder. Basically, make half a two-stroke exhaust; a megaphone.
Ok, lots of ideas here - but which one will work...
spinning parts in there doesnt seem ideal unless I spend MASSIVE bucks to get things done rock solid... but me simple mechanical shapes like the cones is not an issue...
Can someone bang up a drawing of one...
I'm using a 4-1 collector... from the collector to the back we're in total control, there wont be any bends or twists... can someone draw one up to show me what this cone concept looks like... ????
would there be a restriction if I was to say drop a 3.5" pipe into a 5" pipe out - no baffling of course... will this have an advantage?
spinning parts in there doesnt seem ideal unless I spend MASSIVE bucks to get things done rock solid... but me simple mechanical shapes like the cones is not an issue...
Can someone bang up a drawing of one...
I'm using a 4-1 collector... from the collector to the back we're in total control, there wont be any bends or twists... can someone draw one up to show me what this cone concept looks like... ????
would there be a restriction if I was to say drop a 3.5" pipe into a 5" pipe out - no baffling of course... will this have an advantage?
[quote=SXS ]
Can someone bang up a drawing of one...
I'm using a 4-1 collector... from the collector to the back we're in total control, there wont be any bends or twists... can someone draw one up to show me what this cone concept looks like... ????
would there be a restriction if I was to say drop a 3.5" pipe into a 5" pipe out - no baffling of course... will this have an advantage?[/quote]
The best way is with an extractor exhaust, but you need to decide where in the rev range you want your max power to be, this will always be a bit hit and miss as you won't know until you build and test the complete engine, by then you'll already have an exhaust on it. An extractor exhaust makes use of pulses that travel up the exhaust to extract the gases, the length and diameter of the primaries, secondaries (if you want them) and main exhaust pipe all need to be carefully calculated and manufactured, bends in the pipes affect the performance as does poorly made collector boxes where the 4 go into 2 or 1 etc as they can upset the travel of the pulse. Also if you need to put in a silencer this will affect the exhaust performance.
This is a very complicated, hit and miss subject, the best bet is to settle for a race manifold if there is one for your engine/car and then finish it off with as straight an exhaust system as possible, then spend more time tuning it in other ways.
hope this helps.
Paul
Can someone bang up a drawing of one...
I'm using a 4-1 collector... from the collector to the back we're in total control, there wont be any bends or twists... can someone draw one up to show me what this cone concept looks like... ????
would there be a restriction if I was to say drop a 3.5" pipe into a 5" pipe out - no baffling of course... will this have an advantage?[/quote]
The best way is with an extractor exhaust, but you need to decide where in the rev range you want your max power to be, this will always be a bit hit and miss as you won't know until you build and test the complete engine, by then you'll already have an exhaust on it. An extractor exhaust makes use of pulses that travel up the exhaust to extract the gases, the length and diameter of the primaries, secondaries (if you want them) and main exhaust pipe all need to be carefully calculated and manufactured, bends in the pipes affect the performance as does poorly made collector boxes where the 4 go into 2 or 1 etc as they can upset the travel of the pulse. Also if you need to put in a silencer this will affect the exhaust performance.
This is a very complicated, hit and miss subject, the best bet is to settle for a race manifold if there is one for your engine/car and then finish it off with as straight an exhaust system as possible, then spend more time tuning it in other ways.
hope this helps.
Paul
Stevie, I can only suck one exhaust - you'll have to do the other side bud... 
But I dont know about 3.5" - might have problems there...
I was going to use the vortex back boxes bud decided against them... as they'll reduce the grunty noise which I want to keep... plus they're pretty heavy...
But I dont know about 3.5" - might have problems there...
I was going to use the vortex back boxes bud decided against them... as they'll reduce the grunty noise which I want to keep... plus they're pretty heavy...
Anything that uses exhaust gas pulses is only going to be effective over a small RPM range. If you figure out where you want that range to be, it will make a difference. Then it's down to good ol' math. Primary pipe size, length, secondaries, collectors, etc, etc.
Any place you have an increase in volume of the exhaust (ie. 1 primary into collector), you will get an inverse pressure (low) wave travelling back up all the primary tubes connected to that collector. If everything is set up right, one of those low pressure waves will get to the exhaust valve just as it is opening, which will increase the pressure differential between the cylinder and the exhaust, helping to 'suck' out the gases.
It's all good fun to figure out, if you're into that sort of thing.
Gary
Any place you have an increase in volume of the exhaust (ie. 1 primary into collector), you will get an inverse pressure (low) wave travelling back up all the primary tubes connected to that collector. If everything is set up right, one of those low pressure waves will get to the exhaust valve just as it is opening, which will increase the pressure differential between the cylinder and the exhaust, helping to 'suck' out the gases.
It's all good fun to figure out, if you're into that sort of thing.
Gary
If your increase in volume is gradual rather than sudden, you can convert a high-amplitude short-duration pulse into a lower-amplitude longer-duration reflection, so it has less effect, but over a wider rev range. Hence tuned two-stroke exhausts use cones rather than step changes in diameter.
sonic tunning will cost you an arm and a leg, if only in dyno time, and you wont see much benerfit on the road. a siplier idea is to duct air into the exhaust. if you took something like a brake ducked from the front air damb and connected that into the exhaust then you may see some gains, but only at speed. you would need a lager duct though as even at high speed the air would still be moving relativly slowly. take a look at some turbo info and see how they incease the speed of the exhaust gasses as they enter the turbo. you could use a similar idea to help increase the speed of the air, thus increasing the "pull" the air would have on the exhaust.
hope that helps som, and keep us poste, this could be a good idea for cheap power!
thanks Chris.
hope that helps som, and keep us poste, this could be a good idea for cheap power!
thanks Chris.
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