R/S ratio
02-05-2007, 02:21 PM
#21
1.0 BAR
Join Date: Jul 2006
Posts: 414
Re: R/S ratio
Waffles: There's no such thing as a square r/s ratio. A rod ratio of 1 is, in practice, impossible, since the piston would hit the crankshaft. A "square motor" is one with the same stroke as it has bore, and the only way it makes more torque is with the added displacement if you're moving up in stroke. Hell, if you were to make a square D-series you'd end up with like a 1.3 liter motor.
And there's no disproportion in power curves compared to torque curves, since one is just a function of the other.
EDIT: Crap, I was wrong, streetfiend was right. Upon further research, I have found:
.
See? I can admit when I'm wrong. Still think my joke was funny though.
And there's no disproportion in power curves compared to torque curves, since one is just a function of the other.
EDIT: Crap, I was wrong, streetfiend was right. Upon further research, I have found:
Another advantage of the increased rod ratio is the amount of dwell time of the piston at TDC. While technically, the pistons are at TDC and BDC for an infinately small amount of time on both engines, the effective amount of time they stay at TDC is increased on a long rod engine. For example, if you consider 5 degrees before and after the actual TDC on the crankshaft to be the effective TDC, then in a long rod engine the piston will move less during this 10 degree sweep than in a short rod engine. This is again because the long rods have a lower change in angle for any given change in angle of the crankshaft. At BDC however, the dwell time is actually decreased with longer rods, though this is not as big of a concern on forced-induction engines. So, there is a "happy medium" for the rod ratio here, which seems to be about 1.80. Increasing dwell time increases the amount of time that the valves can stay open, which increases the volumetric efficiency of the engine (the effectiveness of the engine to move air in and out of the cylinder).
See? I can admit when I'm wrong. Still think my joke was funny though.
02-05-2007, 03:30 PM
#22
0.0 BAR
Join Date: Nov 2006
Posts: 0
Re: R/S ratio
There are reliefs cut into the crankshaft journals to allow for clearance in near square bore-stroke ratios, such as some boxer engines (bmw's flat four bike). But yea a r/s ratio of one is going to give you a more linear hp/tq curve, only in theory, seeing as volumetric efficiency is never 100% in a naturally aspirated motor, which is why most engines have a longer stroke than bore. But when you get into turbo...
02-05-2007, 03:42 PM
#23
1.0 BAR
Join Date: Jul 2006
Posts: 414
Re: R/S ratio
...Get a rope? How are you going to cut a relief big enough to allow the piston to occupy the same damn space as the journal. Nig nog.
Better yet, how do you cut reliefs into journals that doesn't eat the main/rod bearings? Jesus.
Better yet, how do you cut reliefs into journals that doesn't eat the main/rod bearings? Jesus.
02-05-2007, 05:39 PM
#25
0.0 BAR
Join Date: May 2005
Posts: 0
Re: R/S ratio
Originally Posted by Walter
not..they aren't the same.
Wrong Walter, think about it. Unless the crankshaft is not rotating in a circular fashion or the connecting rods magically change length throughout the crankshaft rotation, they are the same.
02-05-2007, 09:06 PM
#26
0.0 BAR
Join Date: Nov 2006
Posts: 0
Re: R/S ratio
They forge the crank like that that. The piston head is made shorter and the counterweights ------ further. This is a near square bore-stroke. You're right in that a perfectly square one would occupy the same space. But that's why someone thought up a "crankless engine" more of a connecting-rod-less engine, but the use of a bumpstick to displace the piston allows to extremely proportional bore-stroke ratios. Revetec produces it I believe, don't get me wrong- the design is a vibrating nightmare but it allows square bore-stroke ratios.
02-08-2007, 06:54 PM
#29
0.0 BAR
Join Date: Feb 2003
Posts: 0
Re: R/S ratio
Originally Posted by iceracercrx
After years of building motors there is no perfect R/S. You can change things to make your curves better in some spots and worse in others.
Just build your engine/setup and be a man about cranking on the boost controller.
02-09-2007, 12:33 AM
#30
0.0 BAR
Join Date: May 2005
Posts: 0
Re: R/S ratio
Originally Posted by Joseph Davis
Ding ding ding.
Just build your engine/setup and be a man about cranking on the boost controller.
Just build your engine/setup and be a man about cranking on the boost controller.
Nah, there is a perfect R/S ratio for each engine. It's perfect when it complements everything else on the motor.
But ----, for me, here on HMT it's all about the ------ BOOST.
