at first i though the cycliners where hemispherical which would make the pistons a strange shape. i was wrong. this is interesting though. Why aren't our heads hemi? our heads are kinda triangular right? They aren't flat right?

 

The Hemi head had a very effecient combustion chamber design, allowing for true crossflow characteristics placing the spark plug directly in the center of the 2 valves and in the most effective place in relation to the combustion chamber.

 

Yes, but on race slicks. It was near impossible to break the 13 barrier on those bias-ply tires. A lot of the skill involved in racing those cars had to do with holding back on power during the launch.

Mr. Roland Leong was one of the record holders at our local drag strip with the fastest Hemi-powered car back in the days. In 1966, his car was unbeatable at NHRA.

 

[QUOTE=Hyper-X,Oct 27 2004, 02:46 PM]Yes, but on race slicks.

 

i think the HEMI has 2 spark plugs per cylinder. i might be wrong.

 

and still fast as f today. Combining modern technology including fuel injection and standalone engine management systems, it's more than enough to whoop on the new stuff.

They still have crate motor kits available with some 472 Hemi and 528 Hemi engines making 525 and 610 hp respectively, ready to drop in.

 

that thang gotta hemi?

 

itryan, it's the combustion chamber that's a hemispherical design. The S2000 uses a variation of the "pent roof" design, which allows for more than just two valves. (For what it's worth, the pent-roof allows for center placed spark plugs as well - that's not exclusive to the hemispherical shape.)

The hemi style has an issue related to the large combustion chamber the shape produces. From what I've read, the chamber is so large that the flame front doesn't have time propogate through the entire volume and burn all the fuel before it leaves the exhaust valve. Hence, it would never pass modern emissions tests. The HEMI engines used in the Ram trucks and such get around this by using TWO spark plugs, to produce a mutli-front flame.

I'm not sure about the hemispherical shape being all that efficient - my understanding of cylinder head design says that car companies spend lots of time and effort doing computer modeling of flame front propogation and the like during a combustion event to ensure a thurough and even burning of the fuel. Some designs have issues with hot spots forming, which leads to detonation... Of course, for all I know, it could be perfect. However one thing is obvious - it places a limit on the compression ratio that can be achieved.

 

A guy here in Australia (terry Sainty) makes top fuel engines from scratch, ie: Block, carnk, heads everything.

He tried 4 valve twin cam, 3 valve single etc after 10 years of trying to perfect those. He came back to a 2 valve "HEMI" design. The others could not handle the forces or temperatures involved in an 8000hp motor.

 

Then again, I rather doubt that F1 engines use a hemi design. Different designs for different purposes.