Guest Posted February 5, 2004 Share Posted February 5, 2004 just making sure theres only one ext. manifold heat riser on the ext. manifolds on a 454. no adaptors or spacers on the left side, just front pipe bolted to the ext. manifold.for some crazy reason i thought i spotted two when i took it apart, but i only found one in the garage. thanks gene Link to comment Share on other sites More sharing options...
Bob Hansen Posted February 5, 2004 Share Posted February 5, 2004 only one required, unless you have a dual snorkel air cleaner assembly. (I think) Link to comment Share on other sites More sharing options...
ejw71 Posted February 5, 2004 Share Posted February 5, 2004 Have wondered why only one was used on all the motors I've ever work on. Anyone know the answer? Ed Link to comment Share on other sites More sharing options...
Guest Posted February 5, 2004 Share Posted February 5, 2004 When the engine is cold, the heat riser is also cold forcing exhaust gases up through the intake crossover passage heating up the manifold and helping the carb to get warm sooner and also heating up the choke spring. If you had one on both sides, it would prevent this from happening. As the manifold heats up and opens the spring/butterfly on the heat riser it would allow the gasses to exit normally through the mufflers. Link to comment Share on other sites More sharing options...
Guest Posted February 10, 2004 Share Posted February 10, 2004 Good description George.Dual snorkel setups used a common vac source controled by some type of thermo switch to open the flapper door once the engine reaches temp(again with only 1 heat riser to usually passenger side snorkel).If youv'e ever worked on a mid '70's to late '80's Jeep/AMC there a variety of thermo switches to control/route engine vac.Can be a nightmare.Also on the AMC V8 they used a flaper valve on the passenger exhaust manifold that was temp controlled. Link to comment Share on other sites More sharing options...
ejw71 Posted February 11, 2004 Share Posted February 11, 2004 Thanks, George. If I only stopped and thought a while I would have realized/remembered about the exhaust crossover warm up feature. Many makes used it. Although, some carbs were coolant heated water. Some block off the intake crossover ports for better ets. Biggoh mistakeoh when winter cold temps come around. Ed Link to comment Share on other sites More sharing options...
Rob Peters Posted February 11, 2004 Share Posted February 11, 2004 George gave an excellent description of what is occuring, right down to the choke assembly thermal spring. Just a point on this, it would seem to me that if there were one in both sides of the engine it would create too much back pressure and stall the engine.... but I don't know this for a fact, I am just taking a guess at that Rob Link to comment Share on other sites More sharing options...
montefrazer Posted February 12, 2004 Share Posted February 12, 2004 Since the heat riser blocks some of the exhaust flow on the right side of the engine when cold and sends it under the carb and out throught the left side, having another heat riser blocking the left exhaust flow would definitly cause problems. Link to comment Share on other sites More sharing options...
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