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MM puller Comp. ratio

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Tractor puller

04-08-2003 19:57:51




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I have built several tractor pulling engines in the last ten years, but I cant figure out why Moline pullers are scared of compresion. Some say they wont lug, why not? I put togeather a 10.5 ratio 425 incher for a UB and it works great. Olivers make a bunch of ponies around the 13.5 mark as do farmalls. Whats all this talk about and why wont a 12.5 Moline work? WE run racing gas, and turn from ten to twenty % over factory high idle. Why wont a High comp MM lug hard? does it belong to a union or what?

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LW

04-10-2003 18:53:27




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 Re: MM puller Comp. ratio in reply to Tractor puller, 04-08-2003 19:57:51  
I must have missed something? We were talking about a 425 cid 4 cyl not a big engine right?I think the real key here is that the 4cyl crankcase has a limit of how much stress it can handle be it fromcyl pressure or the torque, the latter being the big issue in my opinion, a longer arm (the stroke) will wip more, putting higher loads, but is the real issue still just the fact that a 700+cid 4cyl engine at 12:1 would make more power than the crankcase can handle with only 3 mains and its design.

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curious

04-12-2003 06:22:03




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 Re: Re: MM puller Comp. ratio in reply to LW, 04-10-2003 18:53:27  
well if there is problems with the crankcase, is there anything that can be done to help strengthen it??



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Dieselbear

04-12-2003 12:52:51




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 Re: Re: Re: MM puller Comp. ratio in reply to curious, 04-12-2003 06:22:03  
You can put a gridle on the bottom.



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Bill

04-09-2003 19:56:20




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 Re: MM puller Comp. ratio in reply to Tractor puller, 04-08-2003 19:57:51  
When you get around to building some big motors you will find out why. Up over 700 inches and 12 to 1 comp will usually send the crank out the bottom or you will hammer the mains out about once a year.



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Dieselbear

04-10-2003 09:33:02




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 Re: Re: MM puller Comp. ratio in reply to Bill, 04-09-2003 19:56:20  
I agree with Bill, 9 to 10:1 is plenty on a big cube motor. that is if you expect it to last for awhile.



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Pete Brandel

04-08-2003 21:02:41




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 Re: MM puller Comp. ratio in reply to Tractor puller, 04-08-2003 19:57:51  
I know exactly what you are talking a about.I pulled a MM U for about 10 years.My first motor was a 447 cube (4.810 bore x 6.185 stroke).With 10A4206 heads on it had about 260 psi compression.This produced about 100 horsepower on the dyno.I bumped the compression up to 295 psi with 10A4207 heads.That produced about 110 horse.COMPRESSION is HORSEPOWER.My U had 16.9x38 cut tires.The motor would pull down to about 1000 rpm and just hang there until the tire broke loose.Very seldom did it ever pull down lower than that and when it did I never choked it off.Again the tires would let loose.I then stroke it to 7 inch which is 508 cubes.I wanted to keep the compression in that 290-295 range so I used 10A4213 heads.That produced 130 hp.My theory is with more horsepower early in the pull,you will have more momentum,and it will take a lot more to pull the motor down with that horsepower.There is a point where you can have too much compression.I have been told by many that after 300 psi you start going the other way.I was told by a lot of MM people that I was running too much compression but it worked good for my combo.Of course with that compression you have to run Cam 2 racing fuel straight.

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Andy

04-09-2003 19:29:30




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 Re: Re: MM puller Comp. ratio in reply to Pete Brandel, 04-08-2003 21:02:41  
Does the Cam 2 racing fuel totaly eliminate preignition at that psi? Did you have problems holding the heads down? Thanks.



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Captainhookerus

04-08-2003 20:39:01




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 Re: MM puller Comp. ratio in reply to Tractor puller, 04-08-2003 19:57:51  
There are a lot of wannabees out there that run regular gas or LPG. Too much compression with garbage fuel won't work. My MM's like 12 to 1 and higher.
Ken



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glr62

04-20-2003 01:14:13




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 Re: Re: MM puller Comp. ratio in reply to Captainhookerus, 04-08-2003 20:39:01  
try the dyno trick. can't get the load on or off quick enough!!!



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LW

04-08-2003 20:35:18




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 Re: MM puller Comp. ratio in reply to Tractor puller, 04-08-2003 19:57:51  
I don't know who you have talked to but we have one running at 11.8, one at 10, one at 11. , one at 13.2 and they all run good the 11.8 to 1 engine runs stock rpm's 408cid makes 112hp lugs real good , the problem I have usually found is most people run way to much ign timing on molines. LW



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