bore vs stroke

[Tim754]

OK so where in 'four stroke land' does a 7000/8000hp ,most only two valve per cylinder, V8 Top fuel dragster fit in ? long ,square or short stroke ?   

[DR]

  I know the bb 454 runs a 4in stroke and 4.25in bore pointing toward slightly over square whilst the 427's ran 4.250in bore and 3.760in stroke so beats me Tim..one is over and one is under and both are/were quite popular drag engines

[mx250]

OK so where in 'four stroke land' does a 7000/8000hp ,most only two valve per cylinder, V8 Top fuel dragster fit in ? long ,square or short stroke ?   

Come on Tim, you know that's unfair - the drag V8's et al break ALL the rules  - and only last about 4 seconds and 2000 revolutions

[Mike52]

All that playing about with bigger valves ,porting , cams and the like is to increase volumetric efficiency.
Tis possible to get 130% ve. A standard car motor [say a 308] used to run about 80%ve when new.
In other words it,s possible to stuff 50% more air/fuel into the same capacity motor with a bit of work [ and a lot of money ]
Or you can just jam a turbo/supercharger on it and supply it with some fuel that carries it,s own oxygen.
Or nitrous.
In the old days the rails were using some wierd rocket fuel that burns without air.
Their 1/4mile times were incredible BUT the fuel was downright dangerous and was banned.
Those tiny remote controlled airplanes running methanol are making up to 1hp per cc.
Imagine.

[oldfart]

Tim, if you watched "Gasoline" this week your very question was answered
In short they burn 18 gallons of fuel ( nitromethane -  the more you can jam in those pots AND still be able to burn it with the motor hydraulicing is how it works )  in just a tad over 4 secounds, young andrew Cowins top fueler makes 1000Hp per pot X 8 = 8000hp .
pay attention to the unburnt fuel pouring out of the headers just prior to launching.

Firko,  these things are awsome   

http://www.youtube.com/watch?v=G7g-z43znlc

[Mike52]

At 8000rpm a rail motor is doing 133revs per sec.
The engine would only do 665 revs in a 5sec 1/4 mile run.
Sounds like a lot more .

[Lozza]

Volumetric efficiency is not as important as combustion efficiency, which co-incidently is around 0.8 in production machines, 0.92-3 in the very best race engines.Volumetric can only fill the cylinder and the cylinder head especialy on a 4T engine.

[lukeb1961]

In the old days the rails were using some wierd rocket fuel that burns without air.
Their 1/4mile times were incredible BUT the fuel was downright dangerous and was banned.

hydrazine perhaps? or something really nasty, like triethylborane?!

[firko]

hydrazine perhaps? or something really nasty, like triethylborane?!

Correct Luke...it was hydrazine. It achieved the wanted HP plus a hell of a lot more  but at the cost of turning engines into lethal bombs. They banned it after a couple of drivers were killed by exploding engines.
http://www.dragzine.com/tech-stories/fuel-cooling-ignition-tech/flashback-friday-the-story-of-the-leathal-fuel-called-hydrazine/

[pancho]

I have been watching this discussion with interest and frustration from a computer away from home since friday last,frustrating 'cause the computer wouldn't let me in!.
 my go - I waited a fair while for some-one to mention bmep.                {nathan s]                                                                                 Volumetric efficiency, well tuned 2/ commonly achieve better than 120% I believe. Not forgeting megaphone effect on 4/                                           Then you have turbo and supercharge.
  The new CAT Diesel truck engine runs 50 psi turbo!
 What about the value of short verses long conrod? [Conrod angle] Plus offset gudgeon.
 Then there is constant pressure verses constant volume [this one is interesting when you think about the latest development in direct petrol injection.]
 One thing here from jc on the psi on the area of a bigger piston got me thinking.
cheers pancho

[Lozza]

Volumertic figures can only happen over a short rpm range when the resonace is in phase, which means the efficiency will be poor when not in phase.
Never seen the downside from a longer rod, desaxation(there you go firko) is not used that often these days and is basicaly a defacto longer rod.

[Mike52]

There was a trick with chev motors where you put in a longer rod and shorter gudgeon height piston.
Trying to remember why.[ getting old and forget half this stuff]
Piston tip over just after tdc on the firing stroke I think , causing loss of hp through friction.

[lukeb1961]

Volumertic figures can only happen over a short rpm range when the resonace is in phase, which means the efficiency will be poor when not in phase.
Never seen the downside from a longer rod, desaxation(there you go firko) is not used that often these days and is basicaly a defacto longer rod.

Herr Stolk - what is this crazy talk? Please explain "desaxation" !

[vmx42]

Herr Stolk - what is this crazy talk? Please explain "desaxation" !

Gudgeon pin offset

[Lozza]

The term is a very old one from some early engine that had a 'desaxe' layout or gudgeoun pin off set. The YZ 85 is the only engine I know now that still uses this today. Gudgeon is offset to the inlet side of the piston.  
With the volumetric thing. resonances and harmonics are only in tune for a few 1000 rpm not across the rev range,