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cseay1
Samba Member
Joined: March 22, 2012
Posts: 1341
Location: Elkwood VA
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 Posted: Thu Jul 24, 2014 2:52 pm Post subject: |
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I was thinking about your problem as I was driving my 2000 Ram 3500 24V Cummins Dually.. which by the tach redlines at 3300 rpm. I started searching to find out why the Cummins redlines so lo and found this
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| The longer the stroke, the greater distance the piston must move during each stroke. At a given RPM, that means the piston has to travel faster (higher average velocity) to cover that distance than it would if the stroke was shorter. Now remembering that the piston is essentially stopped at both TDC and BDC, to achieve that higher average velocity during the stroke, the piston must accelerate faster during the first half of the stroke and decelerate faster during the second half. This increased acceleration and deceleration takes energy - lots of it. Fortunately, the negative torque of accelerating the piston is largely balanced by the positive torque of the deceleration, but the loads on the crankshaft, piston, the piston pin, connecting rod, and rod bearing during all four strokes of a four-cycle engine increase dramatically with increases in stroke (or piston speed). |
The longer stroke may be using up more energy at high rpm. Not sure if I am being helpful here, but it is interesting nonetheless.
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Chris
1968 Karmann Ghia coupe - build log here: Chris' 68 Ghia Build Log - From the Woods back to the Street
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johnnypan
Samba Member
Joined: October 24, 2007
Posts: 7431
Location: sackamenna
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| Posted: Thu Jul 24, 2014 3:04 pm Post subject: |
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| advinnie wrote: |
| Yes mate i built it and have put just over 500 mile on it now. It is a massive improvement over the stock 1600 engine. It pulls hard in every gear untill 5000 rpm where it just stops accelerating. |
Thats your torque curve..
74 crank 90.5 slugs? with what you have now for components? increase the bore and you flatten the torque curve..it will perform closer to what you want.. but you need to think...would better flowing heads help your 1699?yep..could you try better heads and not lose a dime if you decide to go bigger? yep..
I say work with what you got for every bit of power you can, dial that engine in, then go bigger if you have too...shit, it aint even broke in yet..do it this way and learn speed..that way when you build a monster it will run like a monster.. |
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williamM
Samba Member
Joined: August 07, 2008
Posts: 4333
Location: southwest Arizona
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| Posted: Thu Jul 24, 2014 3:45 pm Post subject: |
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 Distant misty memory  --"search Ring speed" has to do with the performance of certain ring design when asked to perform long stroke with high revs.
2 strokes had high revs and some went to longer strokes with ring problems that the engineers worked hard to fix.
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modok
Samba Member
Joined: October 30, 2009
Posts: 26790
Location: Colorado Springs
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| Posted: Thu Jul 24, 2014 5:38 pm Post subject: |
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That's true but my 1904 SP has wide rings and it seems to rev much higher than it ever should.
Take a look at the carbs and re-bend the ACC pump squirter tube up outa the venturi. If too close it will suck fuel out of there and go rich. Rich kills the top end. This is well known problem but not discussed often enough. |
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