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mitchel450
4fiddy Racer
Joined: 11 Feb 2008
Posts: 208
Location: At condellos
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 Posted: Wed Nov 18, 2009 9:52 am Post subject: Compression 450R |
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| Gday. Chasing info into what is recomended when going higher comp piston. I think standard in YFZ450R is 11.6:1. I can get 12.4:1 and 14.1 but I think you need 100oct for the 14.1. Any info would be good. Bike is used for motocross. Cheers |
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t&l performance
The Day Starts With OZATV !
Joined: 07 Sep 2008
Posts: 1131
Location: perth
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| Posted: Wed Nov 18, 2009 10:03 am Post subject: |
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go 12.4.1 and u will be better to run avgas 100 octane 14.1 u would need full on race fuel
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mitchel450
4fiddy Racer
Joined: 11 Feb 2008
Posts: 208
Location: At condellos
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| Posted: Wed Nov 18, 2009 11:29 am Post subject: High comp piston |
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| So it wont run properly on say bp ultimate with a 12? |
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phrozin
Blaster class
Joined: 15 Jan 2008
Posts: 111
Location: earth
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| Posted: Wed Nov 18, 2009 12:43 pm Post subject: Re: High comp piston |
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| mitchel450 wrote: | | So it wont run properly on say bp ultimate with a 12? |
I run the 98 stuff on my kawa its stock comp is 12.1 no issues but 14.1 is in the danger zone on pump gas, rule of thumb 11.1 to 12.1 would be ok on high oc pump gas "98"or 100, 12.1 to 13.1 av gas <-- is say avgas as some 100 aint 100oc but av gas is hard to get as the gov has made the sale for non aviation illegal 13.1 up some thing like vp racing fuel but get you wallet out its expencive |
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Hudson
4fiddy Racer
Joined: 12 Feb 2006
Posts: 287
Location: This Week... Back in Texas
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| Posted: Wed Nov 18, 2009 1:29 pm Post subject: |
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12.4:1 can be done with MA legal fuel but it's got alot to do with tuning and making sure it's not pinging. I'm pretty sure that you can only get a piggy back computer for the Yamaha and not the reprogramable type that a few of the other manufactures offer so it will take some dyno time and someone who knows what they are doing to get the most out of it. Higher comp will definately give you a HP boost but there is other things to do to a 450 that will make you faster on a track other than engine mods.
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bullet
The Day Starts With OZATV !
Joined: 09 Sep 2006
Posts: 1518
Location: Middleton SA
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| Posted: Wed Nov 18, 2009 3:10 pm Post subject: |
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Hudsons right. 12.4 should not be a problem but it is important not to just consider those numbers.
They are just the static compession ratio.
Actual cylinder pressure is what you are chasing.
Things like cam timing etc have a dramatic effect on volumetric efficiency and pre-combustion pressures.
So some engines might well easily go near 14:1 on pump gass with the right performnce cams.
Such cam profiles mean the valves are rarely shut and they are usually very high rpm peaky engines.
Put a std cam back in one of these engines and it will go pop sure.
Stay safe and careful under 12.4:1
buy new tyres if you want to go faster 
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Linc
Roostin Away
Joined: 17 Feb 2006
Posts: 999
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| Posted: Wed Nov 18, 2009 3:18 pm Post subject: |
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I think 12.4:1 would be just fine. My 05' TRX is 13:1 with the HRC cam and runs all day on BP-Ultimate 98oct. My Bro's LTR was 12.8:1 and was fine as well.
Linc |
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PeteW
Moderator
Joined: 09 Feb 2006
Posts: 1877
Location: Doreen, Vic
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| Posted: Wed Nov 18, 2009 8:41 pm Post subject: |
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Stay away from the 14:1 unless you can gauruntee a supply of race fuel and you are not planning on racing MA events with it......
12.4 is pretty safe for a Yam Motor but make sure the work around it is done to make the comp increase worth while.... How much other work has been done to your quad, Shocks? Arms? etc?
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mitchel450
4fiddy Racer
Joined: 11 Feb 2008
Posts: 208
Location: At condellos
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| Posted: Tue Nov 24, 2009 11:35 am Post subject: Compression |
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| Yeah need it to be able to race. Did clubman this year, moved to intermediatesfor 2010. Bike got PEP's all round, full motoworks system. gytr filter and adapter with lid off and power comander3. Also got aftermarket axle. damper, stem etc. Bike goes alright, just looking at getting a bit more power. Want to do cams also, but another guy said to get head flow ported and cams and leave the stock piston in, but get dynoed. Bike running map that yamaha gave me for pipe and filter. |
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