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Hemi engine ? All of this confusion about semi hemi has gotten me to put my 5 cents in too. Hemi engine is not a new concept, it is actually very old. This is the little I know, very quick blurbs. In around 1917 there was an engine that powered some aircraft for British fighters it was a V12 with dual overhead cam for each head. It was unbalanced, assembled in many peices , had gears to drive the cams, engineering was extremely primitive in those days so the engine output was limited to 75 horses. Italian race cars like Buggati and others began to experiment with Hemi engines and dual overhead cams in the 20's and 30's they were moving away from the "flat heads" that were common. American cars did not have these designs, except in some airplane designs and special military vehicles, the British were far ahead in this aspect. Italian cars and some special Mercedes were in the forefront in the building of hemi engines in the 1930's . In 1932 Ford started to cast it's V8 engine with a flatheads but their experimental side of the house built several dual overhead cam V8 engines, these were not put out because they were extremely expensive, unreliable and unecessarly complicated for regular cars of the times. The flat head was common through the 30's, 40's and early 50's. The VW bug engine in the 1930's was one of the most advanced production engines of it's time since the valves were in the head and not in the block and it even had an unheard of oil pump (very rare in those days). German, English, and Italian specialty production cars only used Hemi's with overhead cams since the 1930's . One American company with it's production engine was able to compete with the world in racing (German, English and Italian) was Offenhouser . See picture: http://www.replicaengines.com/products/offenhauser.htm It started as a machineshop in the 1930's a was pumping out its racing engines like hotcakes, every racer wanted it's dual overhead cam Hemi engine with pop up pistons. In the 1940's Offenhouser even experiemented with Fuel injection due to the need for speed. All American racecars used the Offenhauser engine without exeption and this left the Europeans in the dust. It made racers win every race against the Europeans. The Offenhouser engine was later replaced by the Ford Coswoth engine in the late 50's thru the 80's. All formula racers are dual overhead cam with hemi chambers and dome pistons. Back to production cars, In the late 40's Chrysler, Desoto, Packard started to build an engine with the Hemi characteristics to install in their top of the line production cars. They had a single in engine cam with canted valves in the head. The canted valves in the head, simulated the design that the race cars had. the spark plugs were at an angle and not well placed. Head design was expensive and required a complicated valvetrain. The production lasted around 12 years and was replaced by a cheaper production design which was commonly known as the 440 with a wedge combustion chamber design. At this time , virtually all European engines were of the true Hemi design. During the mid production of the Chrysler semihemi engine , the company was buildingthe top of the line Hemi that everyone knows well , this engine was for their top of the line cars and speed demons from the 50's,60's and 70's . Production ended in the 80's but started again as a crate engine in 1999 since the demand was high for drag racers with the top speed of 300 mph in 6 seconds more or less. This engine from Chrysler is in high demand because it is chunkier, has forged guts requres less mechanical parts to make it a HEMI , most engines today (latest) run long rubber belts or chains to do the dual overhead cam hemi thing but will not take up to 15000 rpm take offs that dragsters need sometimes . Not Marketing this engine is of the highest demand for all super dragsters. Go to one of those dragster events, notice most have the sparkplug wires in the middle of the top of the giant valve covers , that is the Chysler hemi engine. Fun to watch tme flames blow out the exhaust. Ford and Chevy Motorsports have similar (very special, non production) products in their catalogs. Bottom line for this design was cost and our high production product industry was falling behind by producing more products of cheaper design that would be accepted by the consumer. Ford and Chevy tried to simulate this design earlier by the design of their big block engines (429/460 and 454) they used canted valves in their design to simulate the semi Hemi and their motorsorts division even had full hemi designs for their racing customers. They had specialty engines with modified heads and pistons to match for example Ford had modified 390 (427 FE block) in their GT 40's and modified 302's in later GT 40's competing against all the Supercars in Europe (Ferraris, Porches, Lambrogini's etc..) Ford beat them all in the Lemans and Grand Touring Super races, it was a combination of modified (semi hemi)combustion chambers, pistons, size and good breathing the American design was closing on the Europeans. Look in the Summit Racing catalog , Hemi is tops. All american 4 bangers had the Hemi design in the late 70's, the Japanese made it standars in all of their cars in the 80's. All 4 strock motorcycle engines have been of the Hemi design since the 60's. All American car engines are Hemi designs , like the Cadillac's Northstar , Fords Triton engines just to name a couple. Why has the world gone Tru Hemi ? Combustion efficiency. The Hemi Combustion chamber coupled with the dome pistons are of a matched design that are machine to prevent all hotspots and squeeze the gasses staight up into the top of the dome where the spark plug is located. Gasses explode very symetrically pushing the piston in a symetrical fashion. With this design, racers have been able to pump out up to 5000 horspower out of an American V8 engine for drag racing. The lack of hot spots has given these engines the capability to increase compression up to 15 to 1 ratio without destroying the engine. Some aftermarket companies (including for VW's) have been designing pistons contours to match the head's combustion chambers of older engine designs to create burn symetry and prevent damaging hotspots. As everyone is discussing semi Hemi cut heads in our aircooled engines and not knowing the history of why , I thought Id give you this story. If Semi Hemi works to lower compression of an engine good, it will work for the daily driver who wants a longer lasting engine because the bottom engine end gets less stress heads do not pull them bolts as much and less knocking makes happier valves. I know because I experiemented with a 460 (8 liter) engine in my 67 T-bird (RIP) . I got it to make a compression of 12 :1 ratio it was a lightening fast Corvette killer, made Porsches look lame , left them in my exhaust. This engine only lasted a few months of Zoom but it was fun. It was a rebuilding nightmare, then I lowered the compression by adding several copper head gaskets and the compression was reduced to 9:1 it gave me several years of trouble free service (300 miles per day) until it was stolen and driven off a bridge. To take advantage of a semi hemi cut VW head , when lots of power is wanted using higher compression, one needs to make the piston top to match , semi hemi in my opinion is superior in removing hot spots but can only be taken advantage if the piston is made/designed for it when high power is desired . These are not gimmicks but old fashion engineering, the why's was just confusing everyone. I have worked on so many types of engines (Fiats, Jaguars, Mercedes, Beamers , Volvos old Ferraris, Dodge,Chevy, Fords, trucks, motorcycles etc...all old stuff) and people that I observed and experienced all of this. Hemi is new to production cars in the last 30 years. These engines can be improved but the secret is in the piston/combustion chamber design , flowing the intake and exhaust is for speed but the combustion burn is for the efficiency in the use of fuel. Thats my 5 cents. LEON MARTINEZ SAN DIEGO AND TIJUANA ------------------------------------------------ To unsubscribe, E-mail to: <type3-off@vwtype3.org> For more help, see http://vwtype3.org/list/