13.1 compression on pump gas?

[sportraxkid]

Hey everyone im getting a good deal on a 04 yfz from a local machine shop. They are puting a new crankshaft rod etc. in the bottom end and they bored the top end to a true 450 and are using a 13.1 wiseco piston. The bike also has a new full cpi exhaust system and cpi intake and K&N filter. I was thinking about getting some hotcams for it to while the engine is still apart. How big of a difference would the cam's make and would it be ok to run it on premium(91 octane here). I ran 91 in my 11.1 440ex for 3 years and I know some people who run it in there 13.1 compression yfz's but want to know what you guy's think? btw I am runing it at about 5000ft and 90% of the riding is in sand.

[EvilJester400EX]

You need to run high octane gas. I tried running one of my YFZ's that has 13:1 on 93 octane and it just didn't work.

[GPracer2500]

At that elevation you might be able to get away with 93 pump--you'll have to test to know. Also, if the crankcases aren't back together yet you might want to talk to the machine shop about doing the oiling modification.

[Bill Fuller]

Why would they be boring it to make it a "true" 450??If they are replacing the crank then why not put in the WR crank?I wouldn't try to run it with pump gas.I would have them keep the stock size bore and stick with the lower compression piston.Make sure they do the oil mod!!Sounds to me like this quad has already fried the crank/piston once....My bet is the cylinder was trash and they figure to bore it to save money on buying a new one,:rolleyes: You can buy a new cylinder for around $200 and I bet they have more then that in it by the time the bore and re-nikisil(sp).Make sure they are replacing the crank bearings AND timing chain.Before you spend money on the cams try the cam mod.It's free!

[sportraxkid]

The engine is being bore 1mm over which makes it a true 450 and the crank and rod is being replaced with a new crank and hot rod. They bought the bike at a auction with a bad motor. all the bearing's etc and the rest of the quad is in great shape he just didn't ever service it. And will someone please tell me how to do this oil mod?

[sportraxkid]

oh and what is the cam mod?

[GPracer2500]

The oil mod involves drilling a small oil squirter to spray an "under oiled" portion of the engine. The cases must be split to do the mod but the mod itself isn't all that involved. I think most tuning shops charge $75 or less to do it if you just bring in your disassembled crankcase. The YZ450F dirt bike has had it for a few years (I think). The 07' YFZs also got it, so I've heard.

The "cam mod" is simply retarding the exhaust cam timing by 1 tooth from stock. That puts the cam timing to the same spec as the YZ450F dirt bike. AFAIK, there's no reason not to do the cam mod on a YFZ.

[Bill Fuller]

If they don't replace the crank bearings then I wouldn't buy it.Sounds to me like they don't know what they are doing.By installing the WR crank it will be a true 450 no bore needed.

Good Luck

[Kennethyfz450]

Hey bill when are you heading back down to LBL. e-mail me sometime kennethb@scrtc.com




WR crank brings the 04-05 to a true 450.
WR crank makes the 06 450's rev faster by converting over to that crank; however, I wouldn't break down my 06 engine to install a WR crank like some folks have to get a little more rev. (Find a trail tech -6 flywheel first, and see if that helps your reving craves)

I went with a WR crank and Athena big bore and my bike hauls booty now:D

However, I also have KMS fuel injection installed too.

Anyhow the dealer you took your yfz to doesn't seem to know what he is talking about.

[sportraxkid]

Originally posted by Bill Fuller
If they don't replace the crank bearings then I wouldn't buy it.Sounds to me like they don't know what they are doing.By installing the WR crank it will be a true 450 no bore needed.

Good Luck

They are not making it a 450 because they just want to.If they put in a wr crank that would make it a 460. The cylinder was shot so they bored it 1 mm over and are installing a new crankshaft so of coarse they are putting in new bearings. Lindsay Machine is the best motorcycle engine builder in utah. I have had them bore about 5 different cylinder's for me and anyone who has had engine work in utah will tell you they do awesome work. He has been waiting for a gasket set to come in so im going to call him and ask him if he can do the oil mod and the timing.

sorry for the confusion about the bearing's I was talking about axle bearings, Tie rods etc.