fci intake is a must have

13.5:1 will need 105+ octane

 

No money in the budget for FCI. 105 octane? Is safe to run leaded fuel?

 

FCI would help more than a TB bore and you can also run 1 layer head gasket with stock piston and bump your compression to 12.5:1 and run pump 93 octane and make just as much power as a 13.5:1 with 110. There's a discussion about it going on in this forum.

 

Fci is a lot more money than tb bore. I am aware of the single layer gasket mod anc im just not sure thats the route I want to take.

 

Compression is your biggest help in the bottom and mid range.

The TB bore wont hurt the bottome end but it dosnt help it either, its more for the upper RPM range

some good porting would also be a big help when you can get the money to do it

 

Def getting port work done. Just still on the fence about what cr piston to get. Will 12.75:1 require race gas?

 

Air plane fuel is to dry and will pit holes in the piston. Other than that, sounds like my bike.

 

I had Baldwin mill my CP 13.75:1 MX piston down to 13.2 or so (I can't remember) so I can run both mix (50/50) and straight C12. If you are saying the FCI isn't in the budget, consider that a weekend of racing could burn 3-4 gallons of race fuel @ $10-15/gallon. Doesn't seem too bad, but I wasn't even racing this year and burned through 15 gallons of C12! And, I was mixing it 50/50 for 12 of those 15 gallons!! Once you run compression above 13.5-13.75:1, it will require race fuel in most instances and will start to run you $20-30 per ride. (I'm thinking about 2 gallons per ride). If you run a National... I'd expect a fuel 5-6 gallons for 1 class.

Agreed: get the head done. My plan to get an FCI before I have the TB bored.

Just a thought, if you went with the YZ450F cam and bored the TB, you would be shifting the powerband say 1000-2000 RPMs lower (helping it pull out of a corner), while maintaining the additional power from the bored TB? I am hoping to dyno the YZ450F cam soon so I might have some insight later on. Nothing is proven, but it's a thought.

 

You can play around with sprocket combos and get that grunt out of turns to seat bounce a double I'm running a 13T now it's what came on my bike I'm going to swap it for a 14T soon. I just got the GYTR cams and going to test those as well I haven't tried a YZF cam but I got the 06 yfz cam now. I love the FCI my next go is a port job. You can mix 50/50 with a 13:1 piston but I would rather run 110 striaght

 

it will be great if you tell us your opinion for the gytr cams compare to the 06 yfz cam

 

Boring a throttle body needs to be done with an Intake or you are wasting money. Best bet if on a budget do the intake then port the head and bore the TB but boring b4 an intake and running a stock head will not let that TB do what it is capable of.

 

I went with a 12.75:1cp piston. I dont want to chase after race fuel every weekend. I guess I could hold off on the TB bore and put that money towards an FCI.

 

Got the bike all broken down. Checked the valve lash before I tonook apart. The exhaust side was perfect amd the intak was side was at the upper limit but not to bad. Everythin else looked fine. The throttle body was a pain getting out. So as far as mods im going to get the port work done, cp 12.75:1 piston, +3mm taper bore and get the cylinder honed. Im just going to run my Pro Flo intake for now and get the FCI later down the road. Thanks for everyones input. I will keep updating as the rebuild comes along.

 

Got another question. When I checked the con rod bearing it had very slight side to side movement but no up and down play. Is that good?

 

yep, thats how they should be

 

Who is doing the porting and next time you take down an engine may I suggest cleaning it first, dirt in the motor no good

 

Mixxer is doing the head work. And yes I did power wash my bike before I took it apart but there is a lot of dirt built up in hard to reach areas like under the fenders where all and such. I dont like forcing water into the areas with all the electrical stuff.

 

dynamic compression can be added via the intake cam also.... the cam duration and lobe center will change the point where filling and trapping of the intake charge is most efficient...

and by dynamic , that means the amount of charge that is actually being compressed, not just the static compression ratio of the piston.... if you dont have fill and trapping of a charge, it doesnt matter what the static compression ratio is.... because you could have high static comp and still not literally be compressing anything....

the intake cam from the 08 yf450f dirt bike (or any year cam with same part #) will bias the powerband for more bottom and midrange pull compared to the yfz intake cam... if you still need more torque, that is an inexpensive way to get it $140~150....

 

good call on the cylinder honing.... that cylinder has seen lots of use to be that smooth and shiny....

fresh rings would never seat without a fresh hone there....

12.75:1 is still fine for premium pump fuel

and TB bore would go before FCI for motocross use....

 

About every other ride, I take all of the plastics off, tank off, and pressure wash the whole bike. You would be surprised where mud will hide. And it gives you a good look at everything from the wiring harness passing by the stem (a common spot for the harness to rub) to find cracks in your subframe, etc.

It sucks, but pays off in the end.

 

Yeah I probably shouod have gotten it s little cleaner. I didnt think it was that bad until I started tearing into it and finding mud and dirt crammed into every little space.

 

Head is almost done. Taking the cylinder and piston to Power Seal tomorrow to get homed and matched up. Still waiting on thd TB. Here are some pics of the head.

 

Got the head and TB back. Cylinder is at the shop. Hope to get it all back together next weekend.

 

Are you running stock valves

 

Yeah valvetrain is all stock. Was told when the head was apart that everything was in excellent shape so no need to replace anything.

 

the oem yamha valves are the very best in the business....

light / quality titanium....
back cut profile for best flow....

they last longer than anything i have seen in 30+ years....

so, ... longest life and highest flow profile.... what's not to love there?!

all the +1 ti valves i have seen have a lousy profile that inhibits low to mid lift flow numbers....

the +1 KW steel valves have a good copy of the yamaha back cut flow profile.... but they need stiff springs to control the extra weight.... and they wear a lot faster than the yamaha ti valves do... a lot....

 

I'm not saying you don't know what you are talking about mixxer but a ton of shops are going to +1 or +2 valves dyno numbers don't lie and I know my head makes more power then just a ported head and flows better

 

i have posted gains in lots of dyno runs years ago for everyone to see....

if the valves dont have the back cuts, you lose flow immediately in low to mid lift.... that's what back cut valves are even made for in the first place... nothing new there... nothing to prove either...

so... on built engines with oversized valves the DO have the BACK CUTS.... like the steel kibblewhites.... i had posted that you could take a 58hp machine to 60hp with +1 valves.... but then you have a lot of money invested in seat cutting... valves ...and heavy springs.... and all that for a setup that wears out valves much faster than oem...

nothing lasts as long as oem ti with the oem perfectly matched springs...

so anyways... i have never been in a hurry to get rid of the best valvetrain in the industry for all the cost in doing so, for a 2 hp gain...

now... thats a good setup with everything done right... but i have seen lots of people with big valve setups that werent done right... and they dont get any real gain.... so for the cost of getting rid of the best valvetrain ever... i have just always told people that the $$ would be best spent elsewhere....

in the trx450r.org dyno section i had done a TRX head for him that i said would be 60hp with his setup... mailman is the member name....and it pulled 60hp a year ago.... this year he wanted to go +1 with a shop out there putting the valves in... i told him it would add 1~2 hp on his machine... and he recently posted his new dyno graphs showing exactly that...

it isnt a guaranteed 1~2 hp either... it depends on the level of build your machine is at.... a 40hp machine with oversize valves isnt going to get 42 out of the mod.... but a 58hp machine will go to 60 because at that level it can make use of it...

hondas dont have anywhere near the the quality or flow design of the yamaha setup... so if i was changing the super ti yamaha valves... i personally wouldnt want to give up the excellent profile or the unmatched wear characteristics of oem yamaha.... you have to consider all that you have vs the cost and gain you will get... and what you are giving up for the $$ spent too

 

Don't forget about e-85 fuel. That's what I plan on running in my 13.75:1

 

Would an e85 setup benefit more.from oversized valves?