Re: The perfect stroke?
[Re: emarine01]
#385202
07/24/09 04:20 PM
07/24/09 04:20 PM
|
Joined: Aug 2007
Posts: 498 El Dorado Ca
65signet
mopar
|
mopar
Joined: Aug 2007
Posts: 498
El Dorado Ca
|
340 i think is the best, pound for pound stock 383 or 440 car would get beat by a 340 car.
1965 Plymouth Barracuda 273 M/SA 1970 Plymouth Duster 360/904 10.60s with J heads
|
|
|
Re: The perfect stroke?
[Re: Dodgem]
#385204
07/24/09 05:02 PM
07/24/09 05:02 PM
|
Joined: Jan 2003
Posts: 9,892 Weddington, N.C.
Streetwize
master
|
master
Joined: Jan 2003
Posts: 9,892
Weddington, N.C.
|
Generally for a given/desired displacement)modern V8 engines seem to work best (at least in terms of highest average toruqe/broadest overall powerband) with between a .85 and .9 stroke to bore (not bore to stroke which would be the inverse) ratio and at least a ~1.7:1 rod ratio. Big bore short stroke (like a 327 chevy and 340 mopar) used to be considered the hot ticket but with 40+ years of modern cylinder head technology you don't really have to rely on allieviating bore shrouding to keep the VE up at high piston speeds. Case in point look at the modern LS1 motor This is over-simplified of course but in general I believe it to be true that this ratio seems to yield be the best balance between adequate torque, wide powerband and optimum power for a ~6500 rpm valvetrain. But as you spin the motor higher with higher compression, better flowing heads and racier valvetrain, generally/ideally the stroke gets proportionally shorter and the rod gets longer. For every desired torque peak there is also an optimum runner length and cross section, but that goes out hte window whether we're talking Carb, EFI or modern Direct port injection (which doesn't have to carry any fuel in suspension in front of the intake valve. Just as first mass flow and later Direct port injection altered the "rulz", DPI is likely to re-write them yet again because it can alter/vary fuel volume and spray pattern (without vlave interference) as it injects INTO the cylinder. i would look for Modern DFI and V8's moving to 180 degree crankshafts (to reduce rotating mass and balance intake pulses) to be the next big moves in V8 development. Flat cranks have been inherently low on low/middle RPM torque with carburation but I look to DFI to help offset that in order to take advantage of the better high RPM breathing and lower mass. Another trend once they get this sorted will likely be smaller displacenets (3.5-4.0 litre motors making roughly the same useable power as contemporary 5.0-5.5 litres) That should be enough to get some debate (but hopefully not ) going!
Last edited by Streetwize; 07/24/09 05:19 PM.
|
|
|
Post deleted by Defbob
[Re: MR_P_BODY]
#385207
07/24/09 06:04 PM
07/24/09 06:04 PM
|
Anonymous
Unregistered
|
Anonymous
Unregistered
|
|
|
|
Re: The perfect stroke?
[Re: gregsdart]
#385211
07/25/09 12:17 AM
07/25/09 12:17 AM
|
Joined: Jan 2005
Posts: 12,424 Kalispell Mt.
HotRodDave
I Live Here
|
I Live Here
Joined: Jan 2005
Posts: 12,424
Kalispell Mt.
|
It depends on way more parameters than you gave us.
Desired RPM Bore spaceing Valve size Port effeciency relative to valve size Flow
Ideally you want to make sure you have enough flow to feed your desired cubic inches enough to make your desired power and tq.
Example if you want to make 500 hp and 500lbs tq you need to adjust the bore size to unshroud your valves enough to get about 250+ CFM without shrouding the valve then you make the stroke long enough to get your cubic inches up to where it is big enough to make the 500 lbs tq. If you want the same motor to make 600 lbs tq add more stroke. If you want the same motor to make 600 lbs hp you need to make more CFM air flow, if you can do that with out a bigger bore then don't worry about it. I think ultimately you make sure you can get the flow for the power you want, if you need a bigger bore to get a bigger valve then thats what you do, if there is a cubic inch limit then bump you stroke to get the cubes.
Also depends on if you have a hemi or wedge or 2 3 4 or even 5 valves. More valves and valves that open away from the bore can make the same power on a smaller bore then a wedge can, in that case you can use a smaller bore that burns more completly and then use a longer stroke.
Bottom line is more cubes give you more tq, more flow gives you more HP (asumeing flow quality is not trashed). I don't think there is an ideal ratio as long as you can get the flow you need.
I am not causing global warming, I am just trying to hold off a impending Ice Age!
|
|
|
Re: The perfect stroke?
[Re: MR_P_BODY]
#385213
07/25/09 01:29 PM
07/25/09 01:29 PM
|
Joined: Oct 2007
Posts: 4,212 New York
polyspheric
master
|
master
Joined: Oct 2007
Posts: 4,212
New York
|
a longer rod to give a better dwell period at the top
Depends on your definition of "at the top". If it's 10° each way B/ATDC, the difference between a 5" stroke with a very short rod (7" = 1.4:1) and a long rod (10" = 2:1) is very small. By 10°, the long rod has traveled .0474" down, while the short rod has gone another.... .0032" (three thousands and a bit). Putting it another way, between the 2 engines the time to travel down from TDC to .060" is about 1°.
Boffin Emeritus
|
|
|
Re: The perfect stroke?
[Re: emarine01]
#385215
07/25/09 02:36 PM
07/25/09 02:36 PM
|
Joined: Feb 2007
Posts: 6,295 U.S.
moparniac
master
|
master
Joined: Feb 2007
Posts: 6,295
U.S.
|
This exactly why I just put a flux capacitor in my car as it will adjust the jigowats on the fly to effectively balance the rotating mass and any rod ratio combo for maximum power with no chance of grenading the engine!
Mopar Performance
|
|
|
Re: The perfect stroke?
[Re: RobX4406]
#385220
07/26/09 02:42 PM
07/26/09 02:42 PM
|
Joined: Jan 2003
Posts: 7,978 Bethel Ct
AdamR
master
|
master
Joined: Jan 2003
Posts: 7,978
Bethel Ct
|
Quote:
One that leads to a happy ending!
|
|
|
|
|