Molnar crankshaft power limit
#2847581
11/17/20 01:26 PM
11/17/20 01:26 PM
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Joined: Jan 2003
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JERICOGTX
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What is the HP limit of a Molnar crankshaft. Or should I say one that you would be comfortable with?
69 GTX
68 Road Runner
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Re: Molnar crankshaft power limit
[Re: cesar perez]
#2847612
11/17/20 02:00 PM
11/17/20 02:00 PM
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Posts: 3,082 St. Paul , Mn.
tubtar
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I would suspect that a big block crank could go into 4 digits , but not too far. The usual suspects come into play too...............reciprocating weight , tune , etc.
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Re: Molnar crankshaft power limit
[Re: dvw]
#2847622
11/17/20 02:15 PM
11/17/20 02:15 PM
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Joined: Jan 2003
Posts: 4,275 Morrow, OH
markz528
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I trust my builder (Tony Bischoff @ BES). I'm at 1060 hp with a 574 CI.
67 Coronet 500 9.610 @ 139.20 mph 67 Coronet 500 (street car) 14.82 @ 94 mph 69 GTX (clone) - build in progress......
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Re: Molnar crankshaft power limit
[Re: dvw]
#2847626
11/17/20 02:23 PM
11/17/20 02:23 PM
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gregsdart
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Tom will tell you HP means squat. He will ask you bob weight, rpm limit, and if it's a power adder motor. Mine runs a Molnar 4.500/2.200 crank and their 7.100 rods. Bob weight is 2222. Motor has a 7400 chip. Over 300 passes. Car has been 9.0#150@3350#. Doug Glad to read this. I am pondering a whole new rotating assembly and was about to call molnar. Same deal; 4.5 stroke 7.10 rods. Would use a 7400 chip also.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: Molnar crankshaft power limit
[Re: gregsdart]
#2847686
11/17/20 04:04 PM
11/17/20 04:04 PM
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markz528
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Tom will tell you HP means squat. He will ask you bob weight, rpm limit, and if it's a power adder motor. Mine runs a Molnar 4.500/2.200 crank and their 7.100 rods. Bob weight is 2222. Motor has a 7400 chip. Over 300 passes. Car has been 9.0#150@3350#. Doug Glad to read this. I am pondering a whole new rotating assembly and was about to call molnar. Same deal; 4.5 stroke 7.10 rods. Would use a 7400 chip also. My chip will be 8000. I run Oliver rods. I was trying to buy a Callies crank and that didn't go too good. Tony was not concerned with the Molnar crank.
67 Coronet 500 9.610 @ 139.20 mph 67 Coronet 500 (street car) 14.82 @ 94 mph 69 GTX (clone) - build in progress......
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Re: Molnar crankshaft power limit
[Re: JERICOGTX]
#2847808
11/17/20 07:56 PM
11/17/20 07:56 PM
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Joined: Oct 2007
Posts: 4,209 New York
polyspheric
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In theory, the crank's stiffness (bending resistance) goes down with: 1.greater length (SB is stiffer than BB, other dims omitted, increased bore pitch) 2. longer stroke 3. reduced main or rod journal diameter (BBC rod journal) When in doubt, larger radius at the journal edges helps. I wrote some comments on journal overlap on my site: http://victorylibrary.com/mopar/journal.htm
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Re: Molnar crankshaft power limit
[Re: polyspheric]
#2847813
11/17/20 08:04 PM
11/17/20 08:04 PM
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JERICOGTX
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My plan is to run a 4.375 stroke, with Oliver rods. Won’t be spinning it much over 7000.
69 GTX
68 Road Runner
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Re: Molnar crankshaft power limit
[Re: JERICOGTX]
#2847828
11/17/20 08:50 PM
11/17/20 08:50 PM
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LA360
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Tom Molnar is quite happy to chat about t I am sure. He worked at Oliver before starting up on his own. Email him via his website or try contacting him directly on Facebook. Really knowlegable as you expect.
Alan Jones
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Re: Molnar crankshaft power limit
[Re: J_BODY]
#2848026
11/18/20 10:27 AM
11/18/20 10:27 AM
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Wookie316
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I have one for my 572 that is in the works. It should be an 850ish package shifting around 6800-7000. Bought on the recommendation of others. I think I will be happy.
1971 Plum Crazy Super Bee. 572 World Aluminum block with a Cope 727 & Dana 4.10 out back. 9.88 @ 138 with a 1.35 60 NA. Dialed back to 10.0’s. 4000 lbs with me in it.
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Re: Molnar crankshaft power limit
[Re: dvw]
#2848045
11/18/20 11:04 AM
11/18/20 11:04 AM
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Tom will tell you HP means squat. He will ask you bob weight, rpm limit, and if it's a power adder motor. Mine runs a Molnar 4.500/2.200 crank and their 7.100 rods. Bob weight is 2222. Motor has a 7400 chip. Over 300 passes. Car has been 9.0#150@3350#. Doug 100% my experience when I asked about an HP limit on rods. Tom is the best!
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Re: Molnar crankshaft power limit
[Re: dvw]
#2848091
11/18/20 12:33 PM
11/18/20 12:33 PM
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fbs63
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Tom will tell you HP means squat. He will ask you bob weight, rpm limit, and if it's a power adder motor. Mine runs a Molnar 4.500/2.200 crank and their 7.100 rods. Bob weight is 2222. Motor has a 7400 chip. Over 300 passes. Car has been 9.0#150@3350#. Doug If I was doing this combo I would use a Molnar crank and rods up to 900hp and 7500-7800rpm. Tom has put a LOT of R&D and analysis into his products. If you are wanting to make more power or turn more RPM I would use aluminum rods. They are WAY easier on everything else. R&R, BME or GRP are good choices. They will last 300 passes as long as they are heat soaked before the first pass and you don't motor down on them. All the OLD myths about aluminum rods are just that. MYTHS.
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Re: Molnar crankshaft power limit
[Re: fbs63]
#2848123
11/18/20 01:15 PM
11/18/20 01:15 PM
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Joined: Oct 2007
Posts: 4,209 New York
polyspheric
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300 passes was Bill Jenkins' limit as well
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Re: Molnar crankshaft power limit
[Re: polyspheric]
#2848300
11/18/20 06:53 PM
11/18/20 06:53 PM
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gregsdart
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300 passes was Bill Jenkins' limit as well I am surprised the rod manufacturers don't trust the general public with some accurate method of determining a life span of thier aluminum rods. Some formula based on piston weight, piston speed and any other factor that has a mesurable affect on rod life would be great. There is a great deal of difference in actual life span between a pro stocker and a lawn mower! Take for instance a motor i built back in 1986. 440 stock crank offset ground to 4 inch with a 2.100 sbc bearing. BME 396 forging rods made up with 7.15 c to c length. This motor never saw more than 6500 rpm and had a very light piston. I bet the life of those rods was(or is!) Thousands of runs due to low rpm, moderate stroke and light piston. I ran into the guy i sold that shortblock to about ten years later and he said it was still running great!
Last edited by gregsdart; 11/18/20 06:56 PM.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: Molnar crankshaft power limit
[Re: gregsdart]
#2848339
11/18/20 09:00 PM
11/18/20 09:00 PM
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Joined: Oct 2007
Posts: 4,209 New York
polyspheric
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I bet the life of those rods was(or is!) Thousands of runs due to low rpm, moderate stroke and light piston
Exactly
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