Without turning this into either an essay or debate....
first the odds of making 15/1 CR in a pushrod anything with a 4" bore and 2"
stroke are probably worse than winning Powerball. Second the block deck
heights are generally designed around a 1.6 to 1.8 rod ratio with the
original stroke as it is in the range that will make a broad power band and
support various displacements with 10 or 15% of the original easily. If you
have a 3.5 stroke with a 6" rod the ratio a very nice 1.71 now with the 2"
stroke that rod needs to be only 3.42 inches long. It will pretty hard to
connect things with that short a rod or even clear crank counter weights.
Most 2" stroke engines with a 4" bore would probably have to run in 11000
to 14000 rpm range to generate enough velocity in commonly available
cylinder heads used for more common 3 to 3.5" strokes even worse the rod
ratios needed to connect the piston to the crank and reach the top of the
deck will be both crazy long and heavy something a very high RPM engine
needs to avoid. The problems are numerious and the real cost just not
justified unless the only goal is to make it start up and happy that it runs
is enough. The main issue is the entire geometry gets all out of wack if
that is an engineering term... everything done to connect the various parts
just becomes one band-aid sort of fix after another.
Dave
----- Original Message -----
From: "Rick Byrnes" <Rick@RBMotorsports.com>
To: "Dave Dahlgren" <dahlgren536@comcast.net>; <drmayf@mayfco.com>;
<land-speed@autox.team.net>
Sent: Tuesday, February 22, 2011 11:28 AM
Subject: Re: [Land-speed] Destroking a Crankshaft...
> Dave, could you be a little more specific.
>
> In a naturally aspirated engine, lets say a 4" bore with a 2" or 2.5"
> stroke.
> I would also assume compression of around 15:1.
>
> Push rod, and valve train technology improved so much in the past ten
> years, running the engine to higher speeds should not be an issue, and
> many of us are already using expensive lightweight components.
>
> What dynamics would prevent making really good power.
>
> Serious question. I'm not trying to be a smart ass.
_______________________________________________
Land-speed@autox.team.net
Donate: http://www.team.net/donate.html
Archive: http://www.team.net/archive
Forums: http://www.team.net/forums
|