Author Topic: Overhead cams (Read 754 times)

agent 009 · « **on:** June 01, 2005, 11:41:13 PM »

These were around before ww2, but out of curiosity, how many WW2 V-12's had these? 605 did. merlin had 1 cam, Griffon? twin?

Captain Virgil Hilts · « **Reply #1 on:** June 02, 2005, 12:54:52 AM »

The Allisons were overhead cam 4 valve per cylinder with pent roof dual plug chambers. They even had roller cam followers and forged pistons.

agent 009 · « **Reply #2 on:** June 02, 2005, 01:35:31 PM »

Interesting. Pent roof? what is that?

Captain Virgil Hilts · « **Reply #3 on:** June 02, 2005, 01:40:27 PM »

Something SIMILAR to a hemi. Only more like the roof of a house.
The intake valves are on one side of the roof, the exhaust valves on the other.

agent 009 · « **Reply #4 on:** June 02, 2005, 04:55:10 PM »

Cool. How bout relative value of round top pistons vs flat?

SkyLab · « **Reply #5 on:** June 02, 2005, 07:36:35 PM »

Quote

Originally posted by agent 009
Cool. How bout relative value of round top pistons vs flat?

It’s hard to evaluate one engine component to another in a simple one vs. another comparison.

It is how the components work together in an engine that matters.

Your question would have been answered early in the design stage of the engine since the choice would effect so many other parts of the complete design.

In particular the combustion chamber design.

Some designs favor flat toped pistons, others round or shaped piston tops.

Captain Virgil Hilts · « **Reply #6 on:** June 02, 2005, 09:01:12 PM »

Quote

Originally posted by agent 009
Cool. How bout relative value of round top pistons vs flat?

Ideally, you want a flat top piston with the smallest combustion chamber possible, the shallower the better. It decreases valve shrouding, decreases piston weight, and improves flame travel. That's for gasoline and alcohol, and to some extent diesel. Nitromethane is a little different.

pasoleati · « **Reply #7 on:** June 02, 2005, 09:07:38 PM »

As far as I know, there were only 3 high power (at least several hundred hp) engine designs with double OHC to see mass production in WW two and two of these were Soviet: the Mikulin AM-series aircraft engines,the V-2 tank diesel and the Ford V-8 tank engine (developed from their V-12 aircraft engine project). I don´t have adequate data on torpedo boat plants (otherwise excellent Fast Fightinmg Boats by Fock is silent on engine detail design), but e.g. the Italian Isotta design might have been a DOHC engine.

KurfÃ¼rst · « **Reply #8 on:** June 03, 2005, 04:22:06 AM »

Well you could say French instead of Soviet, ie. the origin of those engines. Good ole USSR.

gripen · « **Reply #9 on:** June 03, 2005, 05:01:42 AM »

Hm... Mikulin AM-series engines were originally developed from the BMW VI. But many advanced features of the AM-series were purely russian origin like throttle system which the Germans directly copied to the Jumo and DB engines.

gripen

pasoleati · « **Reply #10 on:** June 03, 2005, 09:46:38 AM »

Quote

Originally posted by Kurfürst
Well you could say French instead of Soviet, ie. the origin of those engines. Good ole USSR.

Not in this case. Though the crappy Klimov (never got past about 1250 hp reliably) was of French origin, Mikulin was indeed based on the BMW VI, but to put things into perspective the BMW VI produced some 600 hp while e.g. the AM-42 was doing some 2000 hp from the same displacement.

As for the V-2 diesel, it is interesting to note that this engine had 34% lower specific fuel consumption (according to German stats) than the great Maybach fuel Molochs fitted in German tanks and had a torque rise of over 20% compared to Maybach´s less than 10% (again from German stats), both of great importance to tank engines.