Post by oldschool on Mar 6, 2007 23:09:12 GMT
Unlike the exhausts of Rotary engines and 2-stroke reciprocating piston engines the exhausts in 4-stroke reciprocating piston engines are much easier to design. Even then there are engine concepts or designs that create a lot of headache for the engineer. Generally speaking the easiest to design systems are four cylinder, straight six cylinder and V8 engines.
Obviously the FIRE engines are four cylinder engines and therefore the discussions hinge around them.
Even then it helps appreciating the FIRE concept more to know what some of the principally other concepts comprise of. It should be noted that the cross flow design of the FIRE engine is not unique to the FIRE engines as other manufacturers use it successfully too.
The reason why Fiat designed the FIRE engines as cross flow is the catalogue of advantages over other designs. More details are written in other sections, but two design features of other engines should be mentioned.
The first is the Siamese centre port design, which creates big problems for the exhaust designer. The centre port is bigger than the other two ports and the design is strictly speaking a 4 in 3 in 1 design. This is not all bad news but with such designs never as much power can be extracted as with individual ports and the amount of failures when trying to get the best possible solution has cost the top tuners a lot of money. The results after all these years of tuning Mini engines are more than respectable.
The other design feature is the one found in the old Fiat 899/903cc pushrod engine that dates back to 1953. Exhaust port and inlet port share the same side. Apart from the fact that things can be rather cramped, the best routing of the inlet manifold as well as the exhaust manifold is not possible. Additionally the inlet manifold picks up excessive heat from the exhaust, which is on the 899/903cc design still one of the better designs. Although better than many other designs in this way because on some other designs exhaust manifold and inlet manifold even share some of the bolts ? it is only second best design.
Obviously the FIRE engines are four cylinder engines and therefore the discussions hinge around them.
Even then it helps appreciating the FIRE concept more to know what some of the principally other concepts comprise of. It should be noted that the cross flow design of the FIRE engine is not unique to the FIRE engines as other manufacturers use it successfully too.
The reason why Fiat designed the FIRE engines as cross flow is the catalogue of advantages over other designs. More details are written in other sections, but two design features of other engines should be mentioned.
The first is the Siamese centre port design, which creates big problems for the exhaust designer. The centre port is bigger than the other two ports and the design is strictly speaking a 4 in 3 in 1 design. This is not all bad news but with such designs never as much power can be extracted as with individual ports and the amount of failures when trying to get the best possible solution has cost the top tuners a lot of money. The results after all these years of tuning Mini engines are more than respectable.
The other design feature is the one found in the old Fiat 899/903cc pushrod engine that dates back to 1953. Exhaust port and inlet port share the same side. Apart from the fact that things can be rather cramped, the best routing of the inlet manifold as well as the exhaust manifold is not possible. Additionally the inlet manifold picks up excessive heat from the exhaust, which is on the 899/903cc design still one of the better designs. Although better than many other designs in this way because on some other designs exhaust manifold and inlet manifold even share some of the bolts ? it is only second best design.