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Old 11-15-2007, 08:59 PM   #21
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How about at the push of a button?
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Old 11-16-2007, 08:42 AM   #22
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Older dodges used to have a throttle in the exhaust right after the manifold. They had an actuator on them that opened the valve as the manifold temp got high.

I think you were also running under the impression that back-pressure causes better fuel economy or that just having extra exhaust in the chamber upon intake stroke will increase economy. Lets explain both of these.

Back-pressure helping fuel economy. Gross myth that needs rid from the internet and old people's heads. Back-pressure is ALWAYS the enemy of people trying to get fuel economy or power. Exhaust Gas Velocity or EGV is what causes good economy and low-end grunt from engines using a small exhaust diameter, not back-pressure. A high exhaust gas velocity increases an exhaust system's scavenging effect and pulls more waste from the chambers.

I think the idea you got 'exhaust in the chamber causing increased economy' from is the idea of EGR. EGR doesn't get it's benefit from just having exhaust gas in the chamber. It gets it's benefit from putting the exhaust gasses back into the intake and lowering manifold vacuum levels and reducing pumping losses.(I'm currently working on an engine that has no real manifold or chamber vacuum at part throttle)
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Old 05-20-2008, 10:38 AM   #23
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But... someone trying to get fuel economy or power out of a production engine with stock valve timings would not benefit from a removal of all back pressure.
And it's possible to see that an increase in back pressure might help fuel economy.
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Old 05-20-2008, 12:54 PM   #24
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Well, it looks like someone else has tried this already. Not sure if you can still buy them, looks kinda like they don't carry them anymore:
Turbolator
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Old 05-20-2008, 01:33 PM   #25
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Quote:
Originally Posted by dkjones96 View Post
Older dodges used to have a throttle in the exhaust right after the manifold. They had an actuator on them that opened the valve as the manifold temp got high.
I remember those. It was a bi-metal coil spring similar to the one in automatic chokes that operated a butterfly valve in the exhaust. My memory is a little foggy... They may have had a counterweight as well. On Dodges they were always getting stuck, but not too hard to get free again.

Never really understood the purpose unless it was for faster warm up in winter.
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Old 05-20-2008, 02:35 PM   #26
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The flap in the old slant sixes was to help warm up the engine quickly. As the spring heated up the restriction was eliminated.

They also used another heat sensitive bimetallic spring to actuate the automatic choke.

My 37 Ford had an exhaust passage under the carb that helped with fuel atomization by reducing or eliminating carb icing.

Later they used the theromstatic elements in the intake snorkel to warm up the incoming air for the carb to reduce icing.

the early Nissan NAPZ twin plug 4 cylinder engines had a heated screen at the base of the carb to create turbulence and help with atimozation.

240Z Datsun had a summer and winter flap on the air cleaner for the same reason.

When they worked right you could feel the air cleaner get hot, probably in the 120 -140 temp range.

carb icing was especially bad in the SU type carbs which used a variable venturi to maintain velocity past the needle valve. If you let it get cold on those Z cars and didn't switch to winter the hesitation was terrible. It was also a way to test your mixture depending on how bad it ran with the flap on cold at low temps you knew the mixture was close to the ideal.

Lots of people didn't understand this and tried to make up for the icing with enrichment. Talking about unburned hydrocarbons!

With fuel injection the problem basically was overcome by forced atomization in the injectors.

Its like a warm air intake just different stages of evolution, from the 37 Ford to the last carburetors in the Nissan NAPZ motor.

Air density at 200F is only about 80% of what it is at freezing, so WAI when it actually warms the air up significantly reduces density which reduces power for the same volume (but less dense) air.

I use it on my VX and I probably will keep it on when its hot outside, as long as it doesnt make the cooling fan run too much. Less dense air reduces pumping losses and reduces the amount of fuel per cylinder filling event.

It also promotes better atomization of the injected fuel, due to the higher temperature of the incoming air whcih can transfer more heat to the injected fuel which tends to cool when it is atomized.

Much the same principle of the evaporator in air conditioning. The feon will not atomize as well when the ambient temperature is already low.

regards
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Old 05-20-2008, 03:55 PM   #27
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IF ya realllllly wanna do something right at the tailpipe...
i)bend it so it points into your low pressure area.
ii)make a ram scoop venturi for ram extraction.
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Old 05-22-2008, 05:50 PM   #28
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The reason you saw your engine temp rise under engine load was because you were restricting airflow. An internal combustion engine is basically a big air pump. The more air you can move, the more free flowing the engine, and the more free flowing the engine, the more efficient it will be. Picture a garden hose: you retsricting the exhaust was like putting your thumb over the nozzle. The water (air) couldn't escape quickly enough and pressure built up inside the hose (the intake, engine, and exhaust). Air pressure inside an engine generates heat, and in some cases enough to overlaod the cooling system. The effect is more pronounced in diesel vehicles. The best thing to do from my experience is allow your engine to take in and exhaust as much air as possble, but don't take advantage of it. The day I cut holes in my grill and fender to allow more cool air into the new intakes feeding my new twin turbo set up, I noticed a remarkable improvement in FE. I shortly after installed dual 6" exhaust pipes from the turbos back, and saw even more improvement. These days, if I manage to keep my foot out of the firewall and leave my block heater plugged in, I can see alsmost 30 MPG from a V-8 almost times the size of my mom's Elantra that averages 25 MPG. Something to think about...
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Old 05-22-2008, 05:53 PM   #29
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Quote:
Originally Posted by ZugyNA View Post
Remember:

...a 60 HP engine only needs ~ a 1.1" ID exhaust...believe it or not.

60HP (at the crank) per square inch of (cross-sectional) flow area needed

PI*r2

Got 90 HP? Need 1.5 square inch flow area or 1.4" ID?

.........

A dime is only 3/4" ID. At 76 HP you might need around 1.25"? Or somewhere between 3/4" and 1.25"?

If it was overheating and the fan was running in cool weather...that isn't a good thing. Fan uses fuel to run. Try 1" to 1.1"?

Seeing as how I lost my scientific calculator years ago, how much exhaust diamter do i need for 650hp at the wheels?
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Old 05-22-2008, 06:35 PM   #30
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Originally Posted by Powerstroke IN View Post
Seeing as how I lost my scientific calculator years ago, how much exhaust diamter do i need for 650hp at the wheels?
Handy table...
http://performanceunlimited.com/docu...austguide.html
bookmark this page..
http://performanceunlimited.com/documents/
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