Calculations.....
#1718156
12/30/14 09:33 PM
12/30/14 09:33 PM
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Joined: May 2014
Posts: 503
Idaho
1320Dart
OP
mopar
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OP
mopar
Joined: May 2014
Posts: 503
Idaho
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What do you guys use, and/or, get your safe RPM limits for your motors? 
Greg ----------------------------------------------------------------- Cost is irrelevant, making memories is far more valuable! 
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Re: Calculations.....
[Re: 1320Dart]
#1718158
12/30/14 11:12 PM
12/30/14 11:12 PM
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Joined: Jan 2003
Posts: 6,591
Canton, Ohio
Sport440
master
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master
Joined: Jan 2003
Posts: 6,591
Canton, Ohio
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Do what I did, Don't start it for the last 5 years.  Very safe.  Lots of things to be considered, On the low end our stock mopars are good for about 6000 rpm stock. Add better rod bolts 6300 rpm. SB,s even higher. Above that you want better rods ,lighter bob weight, etc. Cam duration/CI size will be a factor as will the heads as to where the engine RPM will Want to be for max performance. You will need to build the lower end to match. Also, Even though a motor can rev higher, it may not be needed for the combo. I lean on keeping it to the conservative side, to race another day. My builds will stay around 6500 RPM and perform 9.6 to 10.5 ets. While I love the sound of a 8000 rpm motor, I don't want the expense of maintaining one. To many things involved for a simple answer.
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Re: Calculations.....
[Re: 1320Dart]
#1718159
12/30/14 11:35 PM
12/30/14 11:35 PM
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Joined: Aug 2003
Posts: 43,163
Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,163
Bend,OR USA
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Quote:
What do you guys use, and/or, get your safe RPM limits for your motors?
I try shifting it when it quits pulling hard, I then look at the playback tach and see what RPM that was  My 518 C.I. pump gas motor wouldn't quit pulling hard until above 7800 RPM according to the playback tach, I got chicken on that motor and made sure to shift it between 7000 and 7400 RPM  It had CAT brand forged steel 6.800 long rods,supposedliy 4340 Chinese forged steel crankshaft at 4.300 stroke with 2.200 rod journals sizes It is still running hard as far as I know, I traded that car off two years ago. The current 505 C.I.motor has a forgd steel Ohio Crankshaft CO 4.25 stroke crank in it with a set of RPM 6.700 long BB Chevy type rods in it, I shift it at 7000 RPM and it has crossed the finish line last year, with 5.86 rear gears (I changed them last winter to 4.56) at or a tiny bit above 7800 RPM, it definetily had its tonque out the last two to three hundred feet in the 1/4 mile   Better to be safe than sorry, shift it early so it lives longer 
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Calculations.....
[Re: Cab_Burge]
#1718160
12/31/14 08:33 AM
12/31/14 08:33 AM
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Joined: May 2014
Posts: 503
Idaho
1320Dart
OP
mopar
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OP
mopar
Joined: May 2014
Posts: 503
Idaho
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If you were to run a 4.5 piston with 7.1 rod on a:
4.375 crank -
4.5 crank -
4.625 crank -
How are you coming up with your "safe" RPM limits?
This is assuming that you have good quality parts.
Greg ----------------------------------------------------------------- Cost is irrelevant, making memories is far more valuable!
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Re: Calculations.....
[Re: 1320Dart]
#1718161
12/31/14 09:56 AM
12/31/14 09:56 AM
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Joined: Jan 2003
Posts: 9,996
Frostbitefalls MN (Rocky&Bullw...
gregsdart
master
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master
Joined: Jan 2003
Posts: 9,996
Frostbitefalls MN (Rocky&Bullw...
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I have a 2432 bob weight, 6.965 Manley rods and a 4.15 stroke. I shift at 7100 and trapped at 7800 for several passes before switching to a much taller tire, now going through at about 7400. Every application will be different. If I were going to build a long stroke motor like a 4.500, using off the shelf h beams I would keep the revs down to 7,000 or less. Unless you plan on using something better than a 440-1 head, you probably won't need any more rpm anyway. "good quality parts" can cover a wide range, so a talk with piston and rod manufacturers would be a good education and would help you select a motor package that will work well for you and live a good long life. What heads are you planning on running? What is the goal for the motor?
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: Calculations.....
[Re: gregsdart]
#1718162
12/31/14 10:21 AM
12/31/14 10:21 AM
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Joined: May 2014
Posts: 503
Idaho
1320Dart
OP
mopar
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OP
mopar
Joined: May 2014
Posts: 503
Idaho
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Quote:
I have a 2432 bob weight, 6.965 Manley rods and a 4.15 stroke. I shift at 7100 and trapped at 7800 for several passes before switching to a much taller tire, now going through at about 7400. Every application will be different. If I were going to build a long stroke motor like a 4.500, using off the shelf h beams I would keep the revs down to 7,000 or less. Unless you plan on using something better than a 440-1 head, you probably won't need any more rpm anyway. "good quality parts" can cover a wide range, so a talk with piston and rod manufacturers would be a good education and would help you select a motor package that will work well for you and live a good long life. What heads are you planning on running? What is the goal for the motor?
Hi Master Greg!
My rods are R&R billet aluminum Pro Mod rods. They are a killer piece! Monte turned me on to them. Pistons aren't ordered yet. But I am going to get them from CP. My heads are B1 Originals. They are flowing in the 420's. The chambers aren't quite done yet. That's why no piston or cam yet. Also it will be on carburated alcohol. I'm hoping for about 15.5 to 1 compression.
Greg ----------------------------------------------------------------- Cost is irrelevant, making memories is far more valuable!
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Re: Calculations.....
[Re: 1320Dart]
#1718163
12/31/14 02:58 PM
12/31/14 02:58 PM
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Joined: Jan 2005
Posts: 3,635
Oakland, MI
dizuster
master
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master
Joined: Jan 2005
Posts: 3,635
Oakland, MI
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With stroke and rod length, you can calculate max g-force for any given RPM. That g-force with piston/rod weight can tell you max load on the rod at TDC. Your piston/rod manufacture should be able to give you a good idea how much load each of your components can take. With that, you can match the RPM/G-force/Load up to the rod/piston maximum design forces. More stroke = more piston speed = more inertia = more load on the rod / bolts Heavier piston = more inertia = more load on the rod / bolts They go hand in hand... Obviously everything has a fatigue life. What is normal piston speed in a NASCAR motor is well below what we would run in a drag motoor. They have to live a long sustained life, where we don't. How often you want to "freshen" the motor, can impact what kind of RPM you're looking to turn. As a ROUGH estimator, you can use average piston speed. It discounts the weight of the parts, and rod length, but it will get you in the ballpark. http://www.wallaceracing.com/piston-speed-velocity.phpCup motors and F1 motors run around 5200FPM average piston speed, drag motor with decent parts can go over this. I read somewhere that 5500FPM is about the safe limit for decent parts, but obviously that depends on piston/rod weight.
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