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PSI of compression, how much if enough?

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redhead

02-02-2002 16:32:34




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I've been envolved in several IH pulling builds where the final compression was anywhere from 175-215 psi. The results were good, and a combonation of pump premium and race gas worked very well. Now, we're thinking about pushing the envelope to 240-250 psi for the next engine. What's everyones opinion? Is this too much for a super stock 4.5 mph class? Will it lug down? Will 100-115 octane keep it from detonating? Hope to hear some good/respectable comments! Thanks.

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G Taylor

02-03-2002 16:36:19




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 Re: PSI of compression, how much if enough? in reply to redhead, 02-02-2002 16:32:34  
As long as power isn't lost because combustion has to travel around an extreme lump on the piston & detomnation isn't a problem ,go as high as you want. Gets to the point of diminishing returns after the 11 or 12 to 1 ratio however.



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JOhn

02-02-2002 20:23:32




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 Re: PSI of compression, how much if enough? in reply to redhead, 02-02-2002 16:32:34  
Well...with anything above 200psi, It seems to do more harm them good, at least on 2 cylinders.
John



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ihcSuperM

02-02-2002 21:23:06




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 Re: Re: PSI of compression, how much if enough? in reply to JOhn, 02-02-2002 20:23:32  
I dont' know about the deeres but on the 4 bangers the more compression you have the better from my experiences. The more compression the better. I have a Super M with a 298 cid making 70 HP. I don't think you can get any more wihtout going into water jacket or getting in the bottom of the motor. That is the main advantage to running a 450 LP head. That small wedge type combustion chamber and a flat top piston are an awsome combination. I would try to stay in the 220 to 240 range. Anything over 250 and it is taking more power to make that compression. It can also be tough on your starter. Also, you can run straight Cam2 (115) and never have a problem. Just don't run to lean. I would back the fuel adjustment screw on the carb out until you can flood the engine and then go in on the screw until you aren't flooding anymore. Running a high compression engine to lean is the fastest way to burn a valve. If you can't flood the engine, you need to open up the jet in your carb. The stock jet is .058". Try going up about .006" at the time. It doesn't seem like much but it is. Also, vaccum is very important. For best results, you want about 19-20 on the vaccum gage at high idle. If you are to high, open up the ventura about .015" at a time until you get it where you need it. This will give you the best lug. Remember, you need the air moving as quickly as possible to vaporize the fuel and deliver it into the combustion chamber.

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Bob

02-02-2002 20:35:04




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 Re: Re: PSI of compression, how much if enough? in reply to JOhn, 02-02-2002 20:23:32  
I agree John, with my arrangement it would go from a put-put to a boom-boom



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JOhn

02-03-2002 09:48:24




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 Re: Re: Re: PSI of compression, how much if enough? in reply to Bob , 02-02-2002 20:35:04  
we have an A that has 1/4" of stroke added and .045 aluminums with about 185psi running 110 octane with 56hp.



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Bob

02-02-2002 17:20:24




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 Re: PSI of compression, how much if enough? in reply to redhead, 02-02-2002 16:32:34  
I have a 880 oliver 265 waukasha with 245-265 compression. I run half avaition fuel (115 octane) and half menthole-hydrate (wood alcohol) Its works great, no detonation problems, just hard to mask that sweet honey smell thats all



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JDGnut

02-02-2002 19:37:20




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 Re: Re: PSI of compression, how much if enough? in reply to Bob, 02-02-2002 17:20:24  
Bob... on your AV gas.. is that the Low Lead fuel sold at airports?? most of the AV gas is 100octane.. Low lead... or are U just usin the AV gas a name for the High Octane... JDGnut



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Bob

02-02-2002 20:12:08




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 Re: Re: Re: PSI of compression, how much if enough? in reply to JDGnut, 02-02-2002 19:37:20  
Its high octane (115) racing fuel I get it at the local drag shop



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redhead

02-02-2002 19:21:25




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 Re: Re: PSI of compression, how much if enough? in reply to Bob, 02-02-2002 17:20:24  
I can smell it now Bob. The only problem is we have fuel rules, and we are checked pretty often!



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Bob

02-02-2002 20:15:06




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 Re: Re: Re: PSI of compression, how much if enough? in reply to redhead, 02-02-2002 19:21:25  
I hear ya all right. Most of the pulls i go to dont have much in the way of fuel rules so till they do i will just keep playin



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JDGnut

02-04-2002 15:33:43




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 Re: Re: Re: Re: PSI of compression, how much if enough? in reply to Bob, 02-02-2002 20:15:06  
I know U mentioned that U have fuel rules.. U need to check to see how hot the fuel can be.. most are written to keep from running Alcohol... not the racing fuel..
JDGnut



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