12.8-1 vs 13.5-1 compression

I have an 07 WR450. I want to raise the compression for more bottom end. But I don't want to run race gas, too hard to get were I live.

My stock compression is 12.3-1.

Will I see much of a gain with 12.8-1 and know I'm safe with pump fuel ?

I know lot's of people are fine running 13.5-1 with pump fuel but is it worth the gamble :busted:

anyone

For that little bit of compression change, you may-as-well just add a tooth to the rear sprocket, really.

13.5 to 1 wow thats getting kinda close to what some diesels run at.

Run 13.5.1 If you want.Big differance over 12.3.You won't need race gas.I'm running a 13.5 and 14.1 in the 250's.No race gas.

The only question that ponders me is how you are looking for more low end on a 450.Maybe because it's a WR.Like said above you can change the gearing to achieve that.If you haven't done any others mods to the WR I would start there first.Open up the pipe(new one is better on this model)/re jet/Open up the air box and get rid of the throttle stop.

13.5 to 1 wow thats getting kinda close to what some diesels run at.

doulbe that an then we are talking diesels run at 25 to 30 CR

Run 13.5.1 If you want.Big differance over 12.3.You won't need race gas.I'm running a 13.5 and 14.1 in the 250's.No race gas.

The only question that ponders me is how you are looking for more low end on a 450.Maybe because it's a WR.Like said above you can change the gearing to achieve that.If you haven't done any others mods to the WR I would start there first.Open up the pipe(new one is better on this model)/re jet/Open up the air box and get rid of the throttle stop.

Bike has all the free mods, YZ full exhaust, airbox opened, rejetted, etc. I've also already added 2 teeth to the rear sprocket.

I race Hare Scrambles A class and we have lots of gnarly tech stuff where I like the low end grunt.

My piston is due for replacement anyways so I figured I might as well bump up compression.

I guess I'll take a chance on the 13.5-1, seems everyone figures it will be fine on pump.

No one with any thoughts on the 12.8-1 ???

Thanks guys :busted:

Bike has all the free mods, YZ full exhaust, airbox opened, rejetted, etc. I've also already added 2 teeth to the rear sprocket.

I race Hare Scrambles A class and we have lots of gnarly tech stuff where I like the low end grunt.

My piston is due for replacement anyways so I figured I might as well bump up compression.

I guess I'll take a chance on the 13.5-1, seems everyone figures it will be fine on pump.

No one with any thoughts on the 12.8-1 ???

Thanks guys :busted:

You could always cut it to 13.5:1 and retard the ignition if it is pinging on pump gas at first.

doulbe that an then we are talking diesels run at 25 to 30 CR

Really? Cummins run at about 17.5:1, my little Detroit is at 21:1 (and that is WAYYY high because it was not designed for turbocharging - most guys drop them to 18:1 when they turbo them). I'd really like to see a diesel that is running anything higher than about 22:1.

Dude it's not gonna ping.These new 250's from 07 on are stock 13.5's. You won't have a problem till 14.5 which is a waste unless your cammed for it.

Bike has all the free mods, YZ full exhaust, airbox opened, rejetted, etc. I've also already added 2 teeth to the rear sprocket.

I race Hare Scrambles A class and we have lots of gnarly tech stuff where I like the low end grunt.

My piston is due for replacement anyways so I figured I might as well bump up compression.

I guess I'll take a chance on the 13.5-1, seems everyone figures it will be fine on pump.

No one with any thoughts on the 12.8-1 ???

Thanks guys :busted:

No one with any thoughts on the 12.8-1 ???

Go big or go home!:thumbsup:

No one with any thoughts on the 12.8-1 ???

Go big or go home!:busted:

Ok cheers I'm convinced 13.5-1 it is :thumbsup:

The only question that ponders me is how you are looking for more low end on a 450.Maybe because it's a WR.

The cams are a big reason. The 5 valve head is a contributing factor to a certain degree. I think thats why Yamaha went with a 4 valve head for the 2010 YZ 450f.

I'm interested to see how tribalbc likes the HP piston. Have you thought about doing the cams too?

The cams are a big reason. The 5 valve head is a contributing factor to a certain degree. I think thats why Yamaha went with a 4 valve head for the 2010 YZ 450f.

I'm interested to see how tribalbc likes the HP piston. Have you thought about doing the cams too?

cams too?:busted:

That would be the iceing on the cake! It would make everything come together like a pear in a apple pie factory..................Wait never mind.:banana:

Wrong anology.:banana:

The cams are quite a bit retarded?:thumbsup:

I bet the WR trans doesn't help...?

I bet the WR trans doesn't help...?

Makes the 450x trans seem like its setup for mx.

doulbe that an then we are talking diesels run at 25 to 30 CR

Diesels run between 6:1 in large stationary engines - 24:1 in passenger vehicles CR NOT 25 -30 CR I went to school for diesel. Your typical diesel pickup or heavy duty truck runs between 16-24:1 CR :busted:

The cams are a big reason. The 5 valve head is a contributing factor to a certain degree. I think thats why Yamaha went with a 4 valve head for the 2010 YZ 450f.

I'm interested to see how tribalbc likes the HP piston. Have you thought about doing the cams too?

Yeah I'm in the process of getting a set of YZ cams from a fellow TTer right now.

I'll probably rebuild in OCT and give a report then :busted:

Yeah I'm in the process of getting a set of YZ cams from a fellow TTer right now.

I'll probably rebuild in OCT and give a report then :busted:

Should be an animal when its done :thumbsup:

im pretty sure all new 250f's have 13.5/1 pistons stock. gave my 07 a little more grunt outta the corners. good luck on the rebuild

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