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  #46 (permalink)  
Old 10-24-2012, 12:26 AM
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Originally Posted by hcompton View Post
American's use long stroke big piston low rpm v8s. ferrari and other high rpm engine use shorter stokes and higher piston speed to make more power. 1.5 covers higher output v8 like bmw, merc but 1.2 is very fair for road use.

You cant make more power without higher piston speed, more displacement or boost. Nothing else makes any difference at all sep where things were built with a restriction of some type.

looked at another way 2 hp per ci would mean a stock 5.0 litre ford mustang from 1989 would make 604hp. or a 350 would be 700 hp.


A short stroke engine has a slower piston speed moving up and down the cylinder then a long stroke engine running at the same rpm is what I think you meant to say! the formula is: Piston speed ft. per min.= (stroke in inches x rpm)/6

Jester

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Last edited by painted jester; 10-24-2012 at 12:47 AM.
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  #47 (permalink)  
Old 10-24-2012, 11:23 AM
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Originally Posted by zildjian4life218 View Post
Okay so I consider myself still a newbie when it comes to the hotrodding world we all love so I am coming to you for input. My buddy has a foxbody that he road races and is looking for more power. His dad told him that he can get a 331ci $700 eagle rotating assembly and put it in a "boss" 302 block with some certain head and it will make 450hp (which I could understand) but he then said and spin it 9-10k rpm all day long with no problems.... I feel as though this is..... well seems like rather out of reach assuming its probably a cast crank with steel i beam rods and hypereutectic pistons but hey I could be wrong... it has happened before and im sure its not the last. Can someone with more experience as me chime in on this? I just wanna know how far off the road I am or am not.
You are right! It takes a lot of rocket science by the time an engine starts getting into the mid 6000 RPM catagory. This just goes crazy about 7000 RPM and CRAIZER above that point.

Structural strength of the block, crankshaft, rods and pistons becomes a huge issue not so much from the 450 hp thought that drives you to a lot of stuff made from 4340 steel like the crank and rods, high quality forged pistons with lightened tool steel floating pins, internal balance, very expensive dampers like the Rattler or Fluid Damper (cannot use the latter on NASCAR tracks because of imbalance issues after hot soaking). This would take ported aftermarket heads to feed the CFM requirements with a pretty exotic valve train to track the cam at those RPMs. Basically from 7000 RPM up you've got to dry sump the engine as the windage gets to be such a power limiter, you've got to put the crankcase under a continious vacuum and you've got to remove the oil that isn't in the galleys. Removal gives the oil time to rest and degass inside the crankcase it gets mixed with the air and gasses in there which actally makes a stiff brown mousse that is several times more viscus than the pure oil, this will cavitate in the pump and within the bearing clearances quickly destroying both pump and bearings followed by a massive engine failure as the bottom end comes out. All 4-bolt mains and crank girdles are not only necessay to keep the bottom end ridged enough that wandering dimension changes won't cause enough distortion to blow the engine, but another unadvertised purpose they serve is to bust up the rotating assembly is a failure does happen to soak up some of the energy to where the crank assembly isn't sailing about the track till its energy is used up. So dry sumping is used to extra capacity with storage away from the rotating mass to give the oil time to vent off before going back into the engine among other things.

So yes you can build a cheap high RPM engine by just buying a radical cam, stuff springs and some top end and exhaust goodies, but without the rocket science everywhere else it won't be together for long.

Bogie
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