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Old 03-06-2005, 01:40 PM
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small tubes added to headers for more power?....

i once read where ole' smokey yunick inserted small tubes near the exhaust ports on headers ,so that some fresh air coming in would help the exhaust scavenge better, for more power. anyone read about this also?

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Old 03-06-2005, 03:19 PM
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Only works really well with rich mixtures and high temps like that coming from a rotary engine, basically you react the unburnt fuel after it leaves the chamber again with fresh air. Rotary engines run very rich under racing conditions so there is lots of unburned fuel in the exhaust, literally throws 3 ft flames out the tailpipes.Heh.

It's not used much because the heat load under the hood is bad enough already without glowing orange inconel headers to make things worse. I wouldn't try it with plain steel headers, they wouldn't last long.
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Old 03-06-2005, 03:20 PM
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No man. The fresh air will cool the gases and slow em down. I think "the Smoke" might of been referring to cross over tubes after the collectors. I would do everything possible to keep the heat in the primaries and collectors.
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Old 03-06-2005, 04:29 PM
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welding one 2" tube to the sides of each header, horizontally. leaving both ends open,to flow cool air,and act as a heat sink. if you cool the headers they should flow better . is that what your describing?

or actually having cutouts venting to freshair?
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Old 03-06-2005, 04:43 PM
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I have been looking into those PCV fittings that you weld into the exhausts. You know the ones that you can use to help ring seal and lower crank case pressures? Does these do anything similar to what you are talking about?
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Old 03-06-2005, 05:00 PM
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I have seen antireversion headers, with a small cone inserted into the header at the head to prevent the exhaust gasses from being sucked back into the engine diluting the charge for the next cycle. ???????????
I read about a Pontiac engine build where they welded a piece of pipe into the collector with a check valve from a mid 70's style smog pump. It would open by the exhaust flow to allow fresh air into the exhaust system to dilute the exhaust, replacing the smog pump that had to be belt driven. ????????
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Old 03-06-2005, 06:54 PM
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Quote:
Originally Posted by 4 Jaw Chuck
It's not used much because the heat load under the hood is bad enough already without glowing orange inconel headers to make things worse. I wouldn't try it with plain steel headers, they wouldn't last long.

They glow bright orange anyway. I ran the motor home once with the cover removed to adjust the cruise control. At 55 mph the exhaust manifolds and about a foot of the pipes were bright orange at night. It would light up the whole cab. As soon as you let off the gas it would go dark. I thought at first there was something wrong. After checking with a few motor heads they said it was normal. I put 101,000 miles on it with no engine problems so I guess they were right. It was a 77 gmc coachman with a 400 small block.
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Old 03-06-2005, 10:49 PM
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spinn, if you cool the headers, the exhaust WILL slow down,not spped up. i am referring to something like a smog pump manifold setup,where the small tubes are in the headers to feed it some O2,so that whatever unburned gas there is, will get burned so hopefully faster exhaust
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Old 03-07-2005, 10:43 AM
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Air injection

Air injection is what the manufacturers used in the late 60's up through the late 80's to fool smog sniffers. All they did was to inject fresh air into the exhaust to make the sniffer readings show smaller ppm of polutants going into the atmosphere. Using air injection into the exhaust system as a performance item will have no effect and as was previously mentioned, it cools down the exhaust and there fore slows exhaust gas velocities. The best way to improve headers, other than an efficient exhaust system behind it, is to wrap them with the current exhaust system insulation wraps. This not only keeps the heat in the exhaust, but also keeps it cooler in the engine bay. The trick with the exhaust is to get proper scavenging, which cleans out the cylinder of burnt and partially burnt fuel air mixture before the next charge comes in. Some exhaust systems are so efficient that they can actually create a vacuum in the cylinder, and in effect, create a supercharging effect with the incoming intake charge. The added vacuum of the scavenging will actually make the intake system think its feeding a larger cylinder than it actually is.
So many times people get lost in the idea that they have to build an engine for peak HP and lose sight of whats being sacreficed on bottom end.
The most efficient exhaust has always been and will always be a single exhaust system. The riddle to this is getting the proper tubing sizes to do the job. In my opinion, Flowmaster has probably done more in this area than many of the other exhaust specialists, particularly in recent years.
The major limitations to running a good single exhaust system are practicality and cost. For some cost is not an issue, however practicality can be. For example, a vehicle with a properly set up single exhaust with 4 1/2 tube finals will deliver more power over a broader range than will a duel exhaust of 2 1/4 inch tubing with H or X pipe connectors.
Going to the analogy of stock cars on a super speedway, having several cars drafting and even two rows running side by side will run faster than any single vehicle out there, due to drafting, one of the principles of tuned exhaust. The first pulse out creates a vacuum behind it, allowing subsequent pulses to travel at higher and more efficient velocities, and in addition, create more vacuum behind them. Potentially if you had all 30 some cars at the Daytona 500 running in single file on a straight track, while drafting, they could run at speeds far exceeding that of any one vehicle on the track.
In the late 80's, if I remember correctly, Bill Elliott showed up with a single exhaust on his car with a 4 1/2 inch final tube size. During time trials he ran off from everyone, NASCAR made him take the system off and go back to the conventional dual exhaust system. Subsequent rule changes have made running a single exhaust illegal on the now Nextel and Bush cars, as well as the super trucks. As for running them in lower classes, I think its all a matter of practicality. It has been proven, particularly in classes that have to run stock manifolds, that going from a factory 2 inch header pipe into a single 3 1/2 inch exhaust does enhance performance quite a bit, particularly in the lower and mid range power areas and with absolutely no losses on the upper end. In referance to the anti reversion cones in the primary tubes or even at the collector, have been proven to work quite well. Again, the gains at this point can be described as somewhat minimal on most setups, making the added expense of production, not worth it in light of gains. A simple way to do this to your car and it does work, having found out from personal experience, is for instance if you are running a 2 1/2 inch exhaust system, to put an additional set of reducer cones between your collector and your exhaust system, cutting the cones so thay they have an outlet diameter of 1/4 to 1/2 inch smaller than your exhaust system. This is something you will have to play with. On a 302 Ford, I once ran a 2 1/2 inch exhaust system, and it seeemed to hurt my bottom end. I added another set of cones, behind the collectors. I ran out through the stock 2 inch opening of the cones, and my lower end did indeed pick up considerably, with no noticeable effect on the top end. Just my $2.98 on the issue, thank you for your patience.

Last edited by Max Keith; 03-07-2005 at 10:53 AM.
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Old 03-07-2005, 12:41 PM
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i need to work on thermodynamics

expansion of gases ,do to heat, would take up more space. if cooler gas is less dense , then couldnt the same passage flow more gases?

i know i wrong here. velocity and performance go hand in hand.
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Old 03-07-2005, 06:35 PM
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Nope you guys aren't getting it.

The method Smokey used was akin to an afterburner in the exhaust stream to gain a scavenging effect at the exhaust valve. There are a number of ways this can be accomplished but on a standard 4 stroke it usually is done with a rocket nozzle shape in the exhaust header right at the exhaust port with an annular hole discharge of fresh air at the throat of the nozzle. With lots of raw unburnt fuel in the exhaust stream and long overlap camshaft it will light off at rpm and burn creating a low pressure zone behind the nozzle which exerts a scavenging effect on the chamber while the valve is open.

Temps exceed 2000 F typically requiring Inconel tubing or at the very least, thick stainless tubing. You need lots of raw fuel in the exhaust stream for it to work or you have to inject fuel into the exhaust stream, not real good for mileage as you can imagine.

Stock RX7 rotaries used to have a simliar system but reacted the fuel in a high nickel content cast iron "reactor" log to burn the excess fuel to lower emissions and to create a scavenge effect at certain RPM's. Most people thought of the system as only a emission control device but anyone who has ever owned one will tell you if you disconnect the smog pump injection air supply you lose 10-15HP particularily at higher RPM.

Since 4 strokes have so little raw fuel in the exhaust stream (compared to a rotary) it doesn't work unless you richen the mixture a lot or inject the fuel in the exhaust stream. For all of the reasons listed above it is not very practical to accomplish and a horrendous waste of fuel not to mention insulating the manifold to prevent heat soak in the engine compartment is not easily done either. It's not illegal in any racing classes I know of but because you can't (legally) inject fuel into the exhaust stream you have to richen the induction system up so much that the power gain offsets the power loss from running such a rich mixture.

You can't have your cake and eat it too, unless you like rotary engines.

Hoi, epitrochodial clavin!
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