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Tractor Pulling Discussion Forum

Octane

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Fantasy 560

03-15-2004 16:29:58




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I have a four cylinder engine with 200 psi on the compression tester, what octane of gasoline would be the best? Thank you for any help.




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ChadS

03-16-2004 19:22:04




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 Re: Octane in reply to Fantasy 560, 03-15-2004 16:29:58  
If the carb is right, it will run fine on 94. 200psi is a borderline for octane levels. It will take a fuel a bit more potent than pump gas. Just my opinion, ChadS



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a puller

03-16-2004 19:36:29




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 Re: Re: Octane in reply to ChadS, 03-16-2004 19:22:04  
hey chads, how many rpm do you think a JD A or G with stock stroke can rap?? I have some people that don't think 2000 rpm is possible, and some that think 1500 is crazy?!?



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ChadS

03-16-2004 20:27:39




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 Re: Re: Re: Octane in reply to a puller, 03-16-2004 19:36:29  
Safely,,,,and everything in good order, and everyday, 20% is not out of the question. I have seen alot of JD over 2000 rpm. Sounds like a chain saw! LOL I just don't like seeing the big flywheel spinning that fast, unless it is rebalanced, and made to run that fast. in our deadweight club there is a G JD that has a double flywheel and runs over 2500rpm. God help us if it ever came apart. 1500?? yeah I can live with that, maybe 1800 for the high side, but would have to be confident in the condition of the tractor's parts. Chad

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Fantasy 560

03-16-2004 14:48:00




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 Re: Octane in reply to Fantasy 560, 03-15-2004 16:29:58  
The head is a allis chalmers flat head, and I am running flat top pistons, all that is left is about 3/16 of a inch between head and piston. I am running a stock cam shaft. I hope this helps. Any help is again appreciated, thank you.



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CASEPOWER

03-15-2004 17:25:53




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 Re: Octane in reply to Fantasy 560, 03-15-2004 16:29:58  
It is not about compression but about cylinder pressure and combustion chamber design. Aspects affecting cylinder pressure are compression, timing, intake temperature, camshaft design and others. Knock or detonation takes all these into effect then add quench of cylinder head design and fuel. You can run extremely high compression but the cylinder pressure can drop because of camshaft design. You can also run high compression but then retard the timing. These are all factors that come into play. There is no set rule, and every situation is different. Start on high octane pump gas and go from there. Racing fuel is not a magic potion. Think of the octane rating as a detonation number. The higher octane fuel only allows you to run a high compression. The higher compression is were the power comes from, not a magic fuel.

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a puller

03-15-2004 19:35:33




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 Re: Re: Octane in reply to CASEPOWER, 03-15-2004 17:25:53  
I would run something at least 100+ octane, up to 110. I can't say for sure, but we like to run aviation fuel which is 100 in our JD a's. my cousin runs this and adds that 104+turbo octane booster..or whatever its called...We have a JD G that has about 210-220 that we run 110 in and it does real good...we could run less, but it's less hassel for the little power gain to just buy it from the torco barrel. I have seen that the 2cyl. tractors seem to take more octane for the compression then the 4 and 6 cyl. ones do....hope this helps...

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CASEPOWER

03-15-2004 20:24:00




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 Re: Re: Re: Octane in reply to a puller, 03-15-2004 19:35:33  
It is proven that a bigger bore will detonate before a smaller bore at the same compression. That's could be why.



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a puller

03-15-2004 20:49:12




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 Re: Re: Re: Re: Octane in reply to CASEPOWER, 03-15-2004 20:24:00  
I didn't know that..thanks for the info. I wonder why that is??? I would think the opposite because it is farther for the flame to travel.....maybe it has to do with the heat issue?? thanks alot and maybe some more light coudl be shed on this topic..lol..



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EFV

03-16-2004 20:06:43




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 Re: Re: Re: Re: Re: Octane in reply to a puller, 03-15-2004 20:49:12  
Big bore engines require more octane because as the fuel travels across the bore it separates .
Gaoline is a mixture of octane rating particles.
Think of it as blend fertilizer. Lower rated parts detonate easier.



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TimC

03-16-2004 14:22:19




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 Re: Re: Re: Re: Re: Octane in reply to a puller, 03-15-2004 20:49:12  
If the flame has to travel across a 4.5 inch bore or more for a JD it takes longer, requiring more total ign advance causing more heat. I'd also guess on a big bore like a jd the storke and rods are longer so there is less quench because in the old days they had lead and didn't want the piston to get that close to the head to creat a good quench area and condition.



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buickanddeere

03-17-2004 06:44:49




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 Re: Re: Re: Re: Re: Re: Octane in reply to TimC, 03-16-2004 14:22:19  
The main factor is the two cylinders have much less combustion chamber surface area for the same displacement that a four of six cylinder has. Much less heat is absorbed from the mixture on the compression and the powerstroke for that matter. The warmer mixture is more prone to auto ignite. The large combustion chamber without a quench area can get into a flame front collision problem. Or pre-ignition from the large flame front's shock wave taking so long to travel all the way cross such a large area. Some success has been had with a wedge shaped piston top making a quench on the intake valve side. And a MSD ignition system can slightly reduce igntion spark advance requirements.

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