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high octane/ thinking about a wobble bobble

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B Barenie

03-19-2007 22:16:21

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Chads:
10.00" rod , 5.25" stroke = 1.91 -1 con/rod ratio!
Thinking about welded rods, stock motor, with shorter connecting rods ! going to cut rods down to 9", 1.71 ratio !
More piston speed, better breathe !
Stock motor !
What do ya tink !

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b barenie

03-21-2007 03:45:59

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Re: high octane/ thinking about a wobble bobble in reply to B Barenie, 03-19-2007 22:16:21

At what ratio does a large stroke motor start to loose what was gained, because of an unacceptable ratio 1.25-1.33 ?

I have heard my times, that it's all about cubes.
Do you experienced engine builders really achive that much more out of extremely expensive products, assembled on these motors ?

Will a pulling motor operate thru out the torque curve better at 9.5-10.00-1 comp ratio than at 12-1 ? If you can control compression, than why go so high? Is this a fool's myth

Thank's for the great discussion !

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mlpankey

03-21-2007 20:03:34

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Re: high octane/ thinking about a wobble bobble in reply to b barenie, 03-21-2007 03:45:59

i like the way you think . personally i do everything they say not to do. i run quiet a bit of stroke the rods are short becuse the pins in the oil ring . i also run 13.5:1 dynamic compression with the biggest intake valve machine able to fit with out hitting the cylinder wall. i make considerable power enough that i twist crankshafts into. i have not found a builder yet that can mathmatically formulate how compression doesnt help torgue and power . theres some who in internet pulling world that believe theres hydraulic lock with high compression . the only way i see that happening on a updraft engine is if the head gasket blows putting water in it.now i know this will definately raise a discussion.

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ChadS

03-22-2007 07:14:17

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Re: high octane/ thinking about a wobble bobble in reply to mlpankey, 03-21-2007 20:03:34

Must be why you see alot of 13.1 engines with only 175 psi of cyl pressure!!

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mlpankey

03-22-2007 13:13:52

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Re: high octane/ thinking about a wobble bobble in reply to ChadS, 03-22-2007 07:14:17

never had a 13.1 run so low must need valve job. loosing nearly 100 pounds if only 175psi. for example had three intake valves sucked into seat still showed 235psi on lowest cylinder.

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ChadS

03-22-2007 14:34:11

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Re: high octane/ thinking about a wobble bobble in reply to mlpankey, 03-22-2007 13:13:52

Naa,,, its when a they let the overlap of the cam allow the intake charge to half escape outthe exhaust before its drawn into the cyl, dropping cyl pressure, and it can have 13 to 1 compression ratio, and only test 175 psi, and run on low octane fuel. Fuel, combustion chamber, piston head design are some of the things to ponder over when trying to get a high cyl pressure to run. We used to run flat top pistons and be inthe 285-290 psi range at cranking speed,,,,, it ran very strong! Now we use a deep dish piston and put the explosion into the tops of the piston, giving it room, and a path to burn. makes a bit less compression, but makes bout the same power as the higher cyl pressure. Chad

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Rusty Junk TX

03-20-2007 19:39:07

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Re: high octane/ thinking about a wobble bobble in reply to B Barenie, 03-19-2007 22:16:21

In this game of tractor pulling and rpm's around 3000 or less (less than half that for a Deere), I would rather pry on that rock (sled) with a long pry bar or screw driver (connecting rod) than a short one because you can get more leverage on it. Just have a good crankshaft, cam it and time it right.

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03-20-2007 08:06:26

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Re: high octane/ thinking about a wobble bobble in reply to B Barenie, 03-19-2007 22:16:21

Piston speed will only change with RPM or stroke! Rod ratio will change the dwell, Piston speed will be a rather complex expression if you start trying to exert the rod/stroke ratio in to it.

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B-maniac

03-20-2007 17:59:00

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Re: high octane/ thinking about a wobble bobble in reply to LW, 03-20-2007 08:06:26

You people are WAAAAAYYYY over thinking these principles and laws of physics. These are low rpm tractor engines. At 3000 rpm or less , all you need is cubic inches (big bore/long stroke) the longest rod you can get in there (to reduce side loading on cylinder and keep the stress angle straightest between the piston and crank throw) and plenty of fuel and air. Leave the "brain surgery" to Warren Johnson and his 8000 rpm 500 cid pro-stock engines. Like buick&deere said , have a cam ground for the added dwell that a long rod gives you and take advantage of it. Keep it simple and if you want to overthink something probably your track savvy and driving could possibly use some.

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HOW

03-20-2007 15:11:29

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Re: high octane/ thinking about a wobble bobble in reply to LW, 03-20-2007 08:06:26

how can the dwell be changed but not the speed if the R.P.M. and stroke are the same, if dwell is a unit of time would this change piston speed?????!

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yes it DOES

03-20-2007 08:45:45

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Re: high octane/ thinking about a wobble bobble in reply to LW, 03-20-2007 08:06:26

shorter rods will increase PEAK piston speed

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03-21-2007 01:17:25

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Re: high octane/ thinking about a wobble bobble in reply to yes it DOES, 03-20-2007 08:45:45

OK then show me the math that will prove it.

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Drew

03-21-2007 05:16:06

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Re: high octane/ thinking about a wobble bobble in reply to LW, 03-21-2007 01:17:25

The only way I can think of off the top of my head would be to make a chart of piston position vs. crankshaft position in degrees. How I would calculate it would be to find the third leg of a triangle, the first two legs being formed by half the crank throw and the connecting rod. You need to know the law of sines and law of cosines to be able to do this. Make a table showing the position every 3 or 5 deg. and you should be able to see a difference.

If I scratch my head long enough I may be able to get my graphing calculator to make a graph of piston position vs. crank degrees to see the speed difference.

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03-21-2007 14:56:05

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Re: high octane/ thinking about a wobble bobble in reply to Drew, 03-21-2007 05:16:06

That's exactly the point I was making its a constanly changing variable If you figure all engines at a 90 deg. crank angle ( at max thrust) then piston speeds will not change by changing rod angle.

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Drew

03-21-2007 06:17:40

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Re: high octane/ thinking about a wobble bobble in reply to Drew, 03-21-2007 05:16:06

After I got my head out of my a$$ this morning I dont think you can use the law of cosines because you do not know the included angle between the crankshaft throw and the connecting rod. To find the distance from the center of the crankshaft main to the wrist pin, you have to break the trangle formed by the connecting rod, crank throw and the distance from the crank main to the wrist pin into two right triangles; then you can use the pythagorean theorem to find the distance from the crank main to the wrist pin. Repeat for every degree of crankshaft position you want to check at.

Its just slightly time consuming :-)

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B Barenie

03-21-2007 19:25:47

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Re: high octane/ tgoing hot in reply to Drew, 03-21-2007 06:17:40

At 70 degree's after tdc piston hits max speed, usinging a shorter rod length, I assume, speed would increase, as would volume fill.

Need some help !
long rod-short rod !
Question ! stock motor-low rpm, need hp !

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Green M n 100hp H's

03-21-2007 21:40:20

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Re: high octane/ tgoing hot in reply to B Barenie, 03-21-2007 19:25:47

BUY WEIGHTS!!! All that power N tire spinnin you gots to put it on the ground!!!!! Double weld up the drawbar n tighten your seat belt!! man! They gonna have to add more weight to the sled!!! They aint gonna stop ya Bud! Your gonna drive right by em all!

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B Barenie

03-22-2007 16:49:49

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Re: high octane/ tgoing hot in reply to Green M n 100hp H's, 03-21-2007 21:40:20

Chads :
When talking to an Idiot, best not to get involved in conversation !
Then you have two Idiot's sounding like one Idiot,
talking about an Idiot >

Have a good day !

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Maybe,,,

03-20-2007 15:30:44

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Re: high octane/ thinking about a wobble bobble in reply to yes it DOES, 03-20-2007 08:45:45

If the longer rod helps low end, maybe a shorter rod helps higher rpm power? Would suffer lack of low end though,,, Pistons that make up the difference, and make the cyl pressure as high as you can,may be something to look at closer. In theory, the pistons might be moving faster than what stock would be,, longer rods slow em down just a bit,,

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buickanddeere

03-20-2007 07:07:52

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Re: high octane/ thinking about a wobble bobble in reply to B Barenie, 03-19-2007 22:16:21

The long rod/short rod debate will exist as long as there are piston engines. Cam timing will make up for any difference in dwell time if you tell the grinder what you have. Long rods exert less thrust on the cylinder walls. Something to think about with wild overbores or thin sleeves. An out of round cylinder leaks pressure past the rings. Less HP lost to friction with long rods as well.

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High Octane

03-20-2007 07:24:06

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Re: high octane/ thinking about a wobble bobble in reply to buickanddeere, 03-20-2007 07:07:52

I know the longer rods do well in my "STOCK" M motor. How about moving some of the chamber into the piston tops in a high compression situation??

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mlpankey

03-20-2007 03:24:29

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Re: high octane/ thinking about a wobble bobble in reply to B Barenie, 03-19-2007 22:16:21

well pro stock nhra boys been doing it for years .piston doesnt dwell long before being jurked back down pulling more air/fuel into cylinder .rod ratio is one thing that lets a motor live at high rpms . antique tractor pulling doesnt see high rpms .my rod ratio works out to be 1.3.1.

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