12:1 piston?

[trailrider894]

hey guys, i am racing mx next year, and am starting to order some parts, i am wondering what octane i need to run with a 12:1 piston? i don't live near a bike shop or a gas station that sells more than 97 ocatane, so can i use an octane booster? or?

[Scro]

97 octane will suffice. I've ran 93 octane on a 12.5:1 piston with no issues.

[trailrider894]

How much of a power gain will i get for having a 12:1 compared to stock?

[400exshop]

you will fill a big diff.

[trailrider894]

any other input?

[400man]

have you picked out a bigger cam to use with the new piston?

[slightlybent47]

I have a 12:5/1 but I run 110 most of the time, sometimes when I want to save fuel I’ll run 110 with pump gas at a 50/50 mix.
Do a 416 0r a 426 12:5/1 with a stage two cam p&p with a 450 carb and you will be hanging on tight.

[trailrider894]

Slightlybent, can you give me all the info of things i would need to do a 426? and would i need to get a new cylinder sleeve? or can the current one be bored out? What else will i need to know? I didn't have a full engine rebuild in mind, because i am focusing on suspension right now. But i guess i might as well do the engine over this winter.

[CJM]

Bore the engine out to 426, shouldnt need a new jug.

Biggest thing I will say is do a cam, port and polish, 450R carb, and the piston of course. Also add a spal puller fan so you can keep her cool.

[trailrider894]

So you do not need to re-sleeve in order to bore?

[trailrider894]

and is there someplace that i can send it too that has a quick turn around time?

[trailrider894]

and what size piston would that require?

[CJM]

Nope, dont need to re-sleeve it.
88mm iirc is the piston size
Any machien shop should be able to bore it, ct racing, gt thunder and others do esxcellent work. I did gt thunder and got the HD studs when I did my 416 build-took like 2 weeks total.

[slightlybent47]

I think CJM is write you don’t need a sleeve for the 416 or the 426. I’d say suspension first. If you’re going into the motor anyway it’s not going to be that much more to do it rite. You can do like I did and do the 416 without the hd head studs and that will save a little on the build. My 416 has stock studs and has never failed. Doing a 426 and with the high compression you may want the hd studs for insurance. The p&p can be anywhere from mild to full race cut depending on how much you want out of it, I went with a little more then a recreational p&p but not a full race cut. And with the 12/1 and p&p you will need a t least a stage 2 cam to open up that mid range and get that air flowing better.
Now here is where some disagree with this combo you could go with a full pipe and it will probably open up the mid range rpm even more but with a stock head pipe and a good slip on I think you keep a little more of that good low end torque. But if you go bigger then the 426 I think the bigger pipe will be better overall.

I had all my motor work done by a local guy in our org that did a real good job on mine because I’m the only one down here that runs the ex and I have run the crap out of it for two years just to compete with all the 450’s and it has ran perfect the whole time. It still starts like it did when it was new and in stock form and it has been very dependable. and i can still putt around in the pits and on the trails with no problum with it.
Now that my 416 is old hat, I wish I done the 426 but I wanted to leave room for another build before I had to put a sleeve in.
Next build I may just bump it up to a 440 and be dune with it.

I can say that the 416 has been good to me though and ran strong but when I put the 450 carb on it really woke it up. the stock carb is sluggish in my opinion and I felt that way from the day I bought it. Even after i had the motor work done.

And if I’m rite you need the piston first before you have it bored so the machinist can bore to that piston.

I can say I don’t regret having it done.


Good luck I hope that is of some help to you.

[CJM]

Yes, you will need the piston in order to have it bored to match.

[trailrider894]

Is there a kit or something i kan buy? and is a 11:1 or 12:1 better?

[CJM]

I got my wiseco piston kit on from magic racing for 155 bucks. I went with them cause they are pretty reputable.

I got my hotcam from apex racing on ebay.

My gaskets are from cometic and I sprung for the best ones they had.

As for 11:1 vs 12:1: I wanted to run pump gas on my 416 build with no issues so I went with 11:1, maybe you could squeak by with 12:1 and 93 octane but I chose to play it safe. With my 416 kit, 11:1 piston, stg 2 hotcam, open airbox (well outerwears but still) and slip on lexx exhaust even vs my friends stock with stg 1 hotcam mine rips!

Its like night and day and for a trail rider it suits me just fine. Remember, power is important but suspension and handling help you out way more. I switched from stock to 450R shocks and its like night and day.

[slightlybent47]

I’ve never had the chance to ride and compare the two but I like the higher compression and I have a good sores for race fuel available. But some say 97 will work just fine but I have never ran it that low, 5 gallons of 110 mixed 50/50 with 93-97 will last a long time and you will get quite a bit of riding on 10 gallons of fuel. You could even go with a 25/75 mix and stretch it even farther. Though I’m no expert I would say the higher compression should have a bit more torque but I’m just guessing at that. Maybe someone else can be more help on that.

[slightlybent47]

i'm actualy running a 12.5/1

[Black450ER]

If you are going wide open for long stretches (desert racing) then go with the 11:1, other than that, the 12:1 will be great!

[CJM]

In my case I do not have any place to get over 93 octane without going to my local track. Some seem to have it available locally.

That and there is alot of dunes here (NJ pine barrens) so yea 11:1 is cooler too.

Whichever you choose you will be happy.

[trailrider894]

What would you do for a motocross setup?

[CJM]

Power is king of course if your racing, 12:1 would probably be better, but 11:1 is no slouch either-your call really. Difference is 12:1 may need better than 93 octane to run properly.

I would get your suspension redone if your gonna race, get some works triple rates or similar and have your stocks rebuilt/revalved for ya. It wont be cheap but will help you control better and thus you can ride faster.

[trailrider894]

so like a 426 12:1 with a cam and P&P would be good?

[slightlybent47]

Originally posted by trailrider894
so like a 426 12:1 with a cam and P&P would be good?

Throw in a good slip on and grind the stock headers and a 450 carb and you’ll be getting blisters from hanging on.

If your sig is rite you need +2 up front and +4 on the back, the stock width is going to put you serious disadvantage on a mx track, much more so then less power. When I went wider I immediately was able to take corners a full gear higher and much faster then when it was stock. And that was with a stock motor. On average most passes and wins seem to come down to getting in and out of corners during a race.
Welcome to the money pit! But really all the money is well worth it when you’re upping your game and progressing as a rider.

[trailrider894]

just ordered a +4 axle after reading your post... getting it in the mail in the next few days!!! Then looking for a good set of +2's. lol anyone have a good used set?

[slightlybent47]

Oh heck you have the pipe and header. I should have seen that earlier. http://planetsmilies.net/not-tagged-smiley-10206.gif (http://planetsmilies.net) I’d look at used a arms, there should be plenty around. I’m not sure but you may have to get rid of the timing key if you do that build. And as long as there not bent they will be fine. Mine were used when I got them. If you do that motor and suspension you’ll be quite happy with it I’m sure.

[CJM]

Yea 426 MAY need the timing key either reduce to wheelies custom 3 degree key or key removed totally.

bent is right tho, better the suspension like I said will help you win races.