somebody correct me if im wrong but high compression helps bottom end torque but hurts topend horsepower and vice versa with low compression
not 100% sure about that just what i was thinking
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| Author: | davehix [ Fri May 29, 2009 11:57 am ] |
| Post subject: | compression |
hey whats a good compression to run in the woods. lets hear what some of you guys run. |
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| Author: | Kyle [ Fri May 29, 2009 12:42 pm ] |
| Post subject: | Re: compression |
hehe anything above 10 you gonna need some race fuel least i think. a lot of people stick around 9-9.5 for pumper gas. mine is 12.98:1 |
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| Author: | bruce 1 [ Fri May 29, 2009 4:52 pm ] |
| Post subject: | Re: compression |
Comp = cheep HP 14.78/1 |
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| Author: | ridenrace6 [ Fri May 29, 2009 5:41 pm ] |
| Post subject: | Re: compression |
somebody correct me if im wrong but high compression helps bottom end torque but hurts topend horsepower and vice versa with low compression not 100% sure about that just what i was thinking
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| Author: | gasman [ Fri May 29, 2009 5:47 pm ] |
| Post subject: | Re: compression |
bruce 1 wrote: Comp = cheep HP 14.78/1 i'd hate to see a plug blow out of that thing with that kinda compression you could kill somebody with it.lol  but serious what octane fuel do you have to run with that much compression?chad 
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| Author: | aboone993 [ Fri May 29, 2009 5:48 pm ] |
| Post subject: | Re: compression |
I have heavy 4 seater trail buggy so I set mine at 8.5/1 for low end chuggin' and engine life longevity and to be able to run pump gas |
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| Author: | ridenrace6 [ Fri May 29, 2009 5:56 pm ] |
| Post subject: | Re: compression |
is it better to run shims under the cylinders or copper gaskets under the heads to lower the compression |
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| Author: | aboone993 [ Fri May 29, 2009 6:01 pm ] |
| Post subject: | Re: compression |
I had to run both because my heads had been cut down for higher comp. but if you can get enough clearance with just one of them I would go with the copper head gasket . its a easier job and helps seal the jug to the head ...JMO |
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| Author: | kyjr.buggy1 [ Fri May 29, 2009 6:21 pm ] |
| Post subject: | Re: compression |
I run about 13:1 in mine. Kyle's right, anything much more than 10:1 will need to run on racing fuel. At least blended racing fuel with 93 octane pump gas. -Dakotah/koko |
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| Author: | aboone993 [ Fri May 29, 2009 6:36 pm ] |
| Post subject: | Re: compression |
I thought about what I said about having to run both head gaskets and barrel shims and it was confusing I could have ran all barrel shims but I wanted to have a head gasket for its sealing ability so I had to use both to get my deck hight where it needed to be |
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| Author: | Baddvw [ Fri May 29, 2009 9:17 pm ] |
| Post subject: | Re: compression |
The way you guys saw my motor ran at Wellsville, that is 9.5:1 compression with top-secret fuel  
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| Author: | ridenrace6 [ Sat May 30, 2009 1:04 am ] |
| Post subject: | Re: compression |
ridenrace6 wrote: somebody correct me if im wrong but high compression helps bottom end torque but hurts topend horsepower and vice versa with low compression not 100% sure about that just what i was thinking surely somebody can answer this and if so what is a happy medium and is there anyway to check like with a compression gauge without tearing down the motor i would really like to now what size i needed so that i can get them and pushrods beforhand and put it right back together with as little down time as possible
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| Author: | Odyknuck [ Sat May 30, 2009 9:12 am ] |
| Post subject: | Re: compression |
High compression is overrated. Its fine up untill you run out of race fuel. You can not just stop at the local station and fill up. Personally i would keep compression down (8 or 9:1) were you can run pump gas. Your motor will last longer and be less expensive to run. Gas is only down in price right now. It will continue to climb. The last time I bought race fuel it was 7 Bucks a gallon. There really is not that much power to gain for the price to be paid. A good set of ported heads will yield you way more HP and Torque than raising compression. Invest the money were it really counts. |
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| Author: | Odyknuck [ Sat May 30, 2009 9:15 am ] |
| Post subject: | Re: compression |
Because of Cam overlap checking with a compression gauge will only tell you the static. You would really need to pull the heads and CC them and find the deck hieght to really know. ridenrace6 wrote: ridenrace6 wrote: somebody correct me if im wrong but high compression helps bottom end torque but hurts topend horsepower and vice versa with low compression not 100% sure about that just what i was thinking surely somebody can answer this and if so what is a happy medium and is there anyway to check like with a compression gauge without tearing down the motor i would really like to now what size i needed so that i can get them and pushrods beforhand and put it right back together with as little down time as possible |
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| Author: | Kyle [ Sat May 30, 2009 9:54 am ] |
| Post subject: | Re: compression |
Odyknuck wrote: Because of Cam overlap checking with a compression gauge will only tell you the static. You would really need to pull the heads and CC them and find the deck hieght to really know. Yep thats the ONLY way to really know. I had never CC'd a head before and Greg showed me how you do it with water pretty neat ol trick. Then dial indicator for deck height. Here is a cool calculator you can figure it out with after you find all the numbers. http://www.aircooled.net/gnrlsite/resou ... /calcs.htm |
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| Author: | ridenrace6 [ Sat May 30, 2009 7:10 pm ] |
| Post subject: | Re: compression |
thanks guysfor the info  i was afraid id have to pull it apart though just wanted to be sure before i and sidnt have too 
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| Author: | wbsouth [ Sun May 31, 2009 1:02 am ] |
| Post subject: | Re: compression |
I ran around 12:1 on my 2500cc and mixed the fuel half and half that way i could still afford to ride lol.. |
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| Author: | bruce 1 [ Sun May 31, 2009 7:41 pm ] |
| Post subject: | Re: compression |
gasman wrote: bruce 1 wrote: Comp = cheep HP 14.78/1 i'd hate to see a plug blow out of that thing with that kinda compression you could kill somebody with it.lol but serious what octane fuel do you have to run with that much compression?chad 116. no mix. Just bought 10 drums. You have to match your fuel with your comp. I can lug mine in 3rd gear in the woods down to 500 to 700 rpm with no problem. I know a lot of guys that have low comp. motors but still run race gas. That can hurt your motor as much as high comp. with pump gas. |
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| Author: | ridenrace6 [ Mon Jun 01, 2009 12:40 am ] |
| Post subject: | Re: compression |
never heard of to much octane so to speak huerting anything but i knew too little would i talked to the guy that built my engine the other day and he said best he remembered itwas either 10 or 10.5 to1 so what gas mix or octane would be best or should i lower it with copper head gaskets and if so how much for running pump gas?????? |
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| Author: | bruce 1 [ Mon Jun 01, 2009 6:54 am ] |
| Post subject: | Re: compression |
http://www.renegadepro1.com/racing_fuels.html This web site should help. |
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| Author: | chris38375 [ Mon Jun 01, 2009 11:19 am ] |
| Post subject: | Re: compression |
ridenrace6 wrote: ridenrace6 wrote: somebody correct me if im wrong but high compression helps bottom end torque but hurts topend horsepower and vice versa with low compression not 100% sure about that just what i was thinking surely somebody can answer this and if so what is a happy medium and is there anyway to check like with a compression gauge without tearing down the motor i would really like to now what size i needed so that i can get them and pushrods beforhand and put it right back together with as little down time as possible low compresion is for luggin motors,thats how mine is built,100 thosands deck height,high compression means higher rpm |
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| Author: | D.B.I..KY [ Wed Jun 03, 2009 12:23 pm ] |
| Post subject: | Re: compression |
You will gain HP across the the rpm range with compression. But detonation is what you have to be careful of. In the heat of summer with less than 60% it will start to detonate quicker. Lower RPM than a day that's 70 and 90%. I run race fuel only on 12.5+ motors. On motors 10.5 to 12.5 I run 60/40 pump gas/alky and drop the heat range on the plugs. 10.5 and lower gets pump gas. Good stuff in the heat. cheep in the cool. Race gas in the winter takes too long for the oil to get hot enough to burn the water/fuel out of it. Race gas in an 8.5 motor will hurt HP, due to combustion and egt too low to make power. You just have to find the sweet spot for your combo. JMO |
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| Author: | turboblue [ Wed Jun 03, 2009 1:03 pm ] |
| Post subject: | Re: compression |
Octane number ratings are the fuels resistance to detonation. Higher number fuels light off harder than lower octane fuels. That's why race gas is used in high compression engines. It won't light till the plug fires. Using race gas in an engine that doesn't need it wastes money and actually runs poor compared to pump gas. Run only as much octane as you need to eliminate detonation......no matter how good it smells burning.....
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| Author: | ZONK [ Fri Jun 12, 2009 12:34 pm ] |
| Post subject: | Re: compression |
turboblue wrote: Octane number ratings are the fuels resistance to detonation.
Higher number fuels light off harder than lower octane fuels. That's why race gas is used in high compression engines. It won't light till the plug fires. Using race gas in an engine that doesn't need it wastes money and actually runs poor compared to pump gas. Run only as much octane as you need to eliminate detonation......no matter how good it smells burning..... |
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