70NPORT
Old Man with a Hat
Ross sez its important:
http://www.imperialclub.com/Repair/Exhaust/riser.htm
From Ross:
The exhaust heat riser valve is, like the PCV and leaner choke settings of the late 60's era of early emissions devices an ironically good thing for motor longevity. Ironically, because those of us who bemoaned the 1970's crude technology came to hate emissions devices due to the lack of appropriate technology to keep them serviceable over the long run.
Yet this is not true with the above-mentioned: A properly operating riser makes a significant contribution to motor longevity -- and this is important -- in conjunction with a well-calibrated carburetor whose intake air is ALSO regulated. You'll notice that vehicles with "heat stoves" on the exhaust manifold which lead pre-warmed air to the carb, or a BLEND of air heated and not heated, finally only "cold" air as the motor warms up and under-hood temperatures rise above about 85-115 degrees F have a demonstrably shorter warm-up period than those cars not so equipped. The heat riser passage which leads from one end of the passenger-side exhaust manifold (valve closed) through the underside of the intake manifold and on out the driver's side is, when kept clean and operating properly, making a noticeably significant difference in keeping the fuel/air mixture IN SUSPENSION. Once those fuel droplets "fall out" the differences in mixture cylinder-by-cylinder are aggravated, thus making a fair running car lose efficiency. The valve is on the passenger-side on most American cars (trivia time) because Cylinders 5 & 7 always fire one after the other: too strong an exhaust pulse for a valve, yet it aids in "pulling" the charge thru the intake area. It also (heat riser valve) has the benefit of warming the underhood air a bit faster as all that cast iron is being cooked thus enabling the valve to close faster and the carburetor come out of cold operating parameters. Chrysler was ahead of the game in emissions also in the late 60's as GM's needed the dreaded smog pump (A.I.R.; "Air Injection Reaction") to pass the minimal guidelines of the day.
Yes, the heat on the intake underside reduces what is called charge density, but that is really only significant to full-throttle acceleration, and then it is a gain of perhaps 5%. Our kind of ultra-low rpm driving (off-idle thru about 3500 around town) benefits from the "constancy" of temperature regulation, and the attending leaner carburetor calibration. In short, better BSFC numbers on the dyno, (fuel usage versus work performed; most especially in numerous part-throttle transitions), and a LONGER-LIVED MOTOR!
With all that said, no, probably none of us bother to keep the valve operable, it needs a shot of "Heat Riser Valve Lubricant" on the pins about once a month; 90-days without fail (GM used to market the best version of this). Obviously it is also a significant exhaust restriction and eliminating it (not just pinning it open) probably saves more gasoline than it ever did operating. Yet it is fundamental that to have the longest-lived motor, one must shorten the interval from dead-cold to @ F 180 as much as possible as this is where the really nasty **** (sorry, it's the only correct word) gets in the lube oil, very corrosive acid compounds which it takes at least 10 miles/20 minutes of driving @ 35-40 mph before they BEGIN to burn off.
So disabling the valve has a price, albeit over a period of time. Some of us know this and forget it, yet we're the one's who also know that ol' granddaddy who kept that Imp in ideal condition for us to buy also understood it. If it'll work, free it up and let it do its intended job. A low performance Imperial motor needs whatever Ma Mopar gave it. (At least up through 1970). And pull that intake manifold once in a while to clean out the accumulated carbon buildup in the passage. This can solve more than a few mysterious "lowered gas mileage" woes.
http://www.imperialclub.com/Repair/Exhaust/riser.htm
From Ross:
The exhaust heat riser valve is, like the PCV and leaner choke settings of the late 60's era of early emissions devices an ironically good thing for motor longevity. Ironically, because those of us who bemoaned the 1970's crude technology came to hate emissions devices due to the lack of appropriate technology to keep them serviceable over the long run.
Yet this is not true with the above-mentioned: A properly operating riser makes a significant contribution to motor longevity -- and this is important -- in conjunction with a well-calibrated carburetor whose intake air is ALSO regulated. You'll notice that vehicles with "heat stoves" on the exhaust manifold which lead pre-warmed air to the carb, or a BLEND of air heated and not heated, finally only "cold" air as the motor warms up and under-hood temperatures rise above about 85-115 degrees F have a demonstrably shorter warm-up period than those cars not so equipped. The heat riser passage which leads from one end of the passenger-side exhaust manifold (valve closed) through the underside of the intake manifold and on out the driver's side is, when kept clean and operating properly, making a noticeably significant difference in keeping the fuel/air mixture IN SUSPENSION. Once those fuel droplets "fall out" the differences in mixture cylinder-by-cylinder are aggravated, thus making a fair running car lose efficiency. The valve is on the passenger-side on most American cars (trivia time) because Cylinders 5 & 7 always fire one after the other: too strong an exhaust pulse for a valve, yet it aids in "pulling" the charge thru the intake area. It also (heat riser valve) has the benefit of warming the underhood air a bit faster as all that cast iron is being cooked thus enabling the valve to close faster and the carburetor come out of cold operating parameters. Chrysler was ahead of the game in emissions also in the late 60's as GM's needed the dreaded smog pump (A.I.R.; "Air Injection Reaction") to pass the minimal guidelines of the day.
Yes, the heat on the intake underside reduces what is called charge density, but that is really only significant to full-throttle acceleration, and then it is a gain of perhaps 5%. Our kind of ultra-low rpm driving (off-idle thru about 3500 around town) benefits from the "constancy" of temperature regulation, and the attending leaner carburetor calibration. In short, better BSFC numbers on the dyno, (fuel usage versus work performed; most especially in numerous part-throttle transitions), and a LONGER-LIVED MOTOR!
With all that said, no, probably none of us bother to keep the valve operable, it needs a shot of "Heat Riser Valve Lubricant" on the pins about once a month; 90-days without fail (GM used to market the best version of this). Obviously it is also a significant exhaust restriction and eliminating it (not just pinning it open) probably saves more gasoline than it ever did operating. Yet it is fundamental that to have the longest-lived motor, one must shorten the interval from dead-cold to @ F 180 as much as possible as this is where the really nasty **** (sorry, it's the only correct word) gets in the lube oil, very corrosive acid compounds which it takes at least 10 miles/20 minutes of driving @ 35-40 mph before they BEGIN to burn off.
So disabling the valve has a price, albeit over a period of time. Some of us know this and forget it, yet we're the one's who also know that ol' granddaddy who kept that Imp in ideal condition for us to buy also understood it. If it'll work, free it up and let it do its intended job. A low performance Imperial motor needs whatever Ma Mopar gave it. (At least up through 1970). And pull that intake manifold once in a while to clean out the accumulated carbon buildup in the passage. This can solve more than a few mysterious "lowered gas mileage" woes.
ccasion14:
