200X wiseco 10.25:1 Vs 12:1 piston - opinions

[Leevvii]

ATC200X wiseco 10.25:1 Vs 12:1 piston - what is the benefits of each, any suggestions.

[deathman53]

the 12:1 needs race gas, but bottom end will be much better.

[wonderboy]

My opinion: 12:1 was just a bit too much trouble if you just want to ride. 10.25 seems like a nice increase in power, but without the headaches of 12:1. I was always worried about running high enough octane and worried about sitting at idle too long (no airflow through the head to keep it cool). If maximum power is the only goal, then 12:1. Otherwise, I'd run the 10.25.

[christph]

I was wondering the same thing back when I rebuilt my 83 X. I went with the 10:25 because I didn't want to run race gas. I'm happy with it but left wondering how much more performance I would have got with the 12:1. I'm not sure if you have to run full race or 50/50 with that piston. You might contact Mickey Dunlap at Four Stroke Tech for X advice. He has worked on these engines and offers a 250 big bore kit.

[oldskool83]

10:25.1 more then that buy a 350x

[atc300r]

I was talking to a guy at the races about this .He knows another racer that is running a 12:1 on 91 octane.Says he has no problems.

[RIDE-RED 250r]

12:1 is pushing it for pump fuel, generally speaking. You might be able to buy yourself a little leeway by jetting it rich, but in so doing you are dialing back peak performance so you might as well stick with 10.25:1, run 93 octane, hit the trails and enjoy a significant boost in power over stock.

My brother has a 350x with a 10.25:1 and it's a bear, very torquey. Also a miserable SOB to kick over, even if you know what you are doing, his auto-decomp parts failed years back and he took them out...

[yaegerb]

ATC200X wiseco 10.25:1 Vs 12:1 piston - what is the benefits of each, any suggestions.

Race gas for 12:1 and 91 or higher for the 10.25. 12:1 will run too hot IMO without race gas. Mine ran happily on VP C12. Run lower octane at your own risk.

Your motor/wallet will be very happy with a 10.25 on 91 with a little more aggressive cam than stock plus you can keep the VM 24 Keihin.

Unless you are going ballz out with a dedicated racer it's not worth the extra compression.

[Leevvii]

Thanks everyone. Think i'll stay with the 10.25:1, im not racing, just bush bashing. One more question, what octane do you guys in the US, consider to be race fuel? We have 91, 95 and 98 octane available at pumps. I will also need to run a lead replacement in my '84 200x.

[christph]

I consider full race 110 octane.

[RubberSalt]

Christph is right, we typically consider 110 as race gas. An alternative are alcohol based fuels like e85, which is 105 octane and runs cooler than gas typically. Like all fuels, it does require new jetting. e85 and race gas typically require richer jetting.

e85 is the poormans race fuel. Most machines make more power on e85 than 110. The problem with e85 is consistency. Many pumps mix ethanol and gas as you pump. Consistency lacks. VP makes a race version of it, c85, which like all their race gas, is consistent.

If your in the bush, I'd stick with pump gas. Maybe some of that 95-98 (should run cooler). Your not racing, no point to build a racer.

Compression gives a direct increase in power across the entire rpm range. It's usually pretty linear and makes a big difference. You can expect about a 15% increase in power before you factor in the fuel's capability when going from 10.25 to 12:1.

2 stroke pipes, turbos, super chargers, pro chargers, they all add compression. They blow an air/fuel mix into the cylinder under pressure, upping the compression drastically.

[plevib]

That's very interesting. I've never considered running e85 so I didn't realize it was 105 octane. So to someone who has run it, does it gum up carbs pretty bad? How long can you let it sit in the fuel bowl before it turns things green? I've just always avoided it, but being able to run 12:1 for less money than even 87 (I run 91 %100 gas in my small engines) it might be worth draining the carb when the trike sits. ...

[Mickey Dunlap]

For most of my customers I take a 12:1 and round it off so there are no sharp edges, then I'm at 11.5:1 and I run a pretty big cam, makes it go from 10 rwhp to as much as 18 rwhp with my 30mm carb kit and a new stainless head pipe made to up grade the DG pipe. It's all about getting the cylinder pressure down so you can run pump gas. Mine didn't make any more power with race gas with this set up either. With the 10.25 you can't run a big cam with out killing the bottom end and making it rev slow.

[oscarmayer]

the 12:1 needs race gas, but bottom end will be much better.

Incorrect. It needs proper jetting and 93 unleaded pump minimum. I ran it all day long in my old engine I sold. Years. Never had an issue. Again. Tuning is key.


If your not racing it or needing the extra 1-1.25hp then stay with the 10.25:1. In my opinion, the best is 97 octane. Any higher and your not benefiting. Since it sounds like you r trail riding the 10:25:1 will suit you just fine. I recommend you look at upgrading to a mikuni 28mm carb. Also look at upgrading the exhaust. All these mods together will help a lot.


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[Leevvii]

The shop that is reboring my barrel suggests i go with the 12:1, he claims to have done this before on these type of engines, uses 98 oct and all OK. He said that too much engine paint on the fins is a big heating problem with the barrels, maybe moreso than the compression, suggests cutting slots in the front mudgaurd to up the airflow if im concerned. Makes sense. He tells me that the head had been ported previously, and was impressed with the porting. Im stuck with the standard carby, and i assume standard jetting, for the moment, will this be OK [not too lean?] with the 12:1 ?