Big Bore Q & A 

 

1) Forged Pistons – What You Need to Know 

Forged pistons do require some break-in time.  When new, they expand and contract quite a bit as they find their home. Because of this, we recommend a few short, wide-open bursts followed by complete cool-downs — right down to a cold engine — and repeating that cycle multiple times. Regardless of piston type, it’s always a good idea to let your engine warm up by riding at low throttle until the thermostat is circulating. This is especially important after it’s been sitting — whether you’ve been fixing your buddy’s A-arm or just BSing for a while. It’s not just about being forged — these pistons are big, and they need time and care to settle in right.

Nervous About Forged Pistons? You’re Not Alone.

We get it — forged pistons still carry a bit of a reputation from the old days. But a lot has changed since then.

Modern forged piston designs have improved significantly. Plus, today’s EFI systems are incredibly consistent and come with built-in compensations for things like exhaust heat, ambient temps, and cold engine starts — all of which help protect your engine and maintain performance.

That said, if forged still isn’t your thing, we’ve got you covered. Our 1000 big bore kit is available with cast pistons as an alternative

2)  Is a Big Bore Right for Me?

Maybe not — big bores aren’t for everyone. They’re built for a small slice of the snowmobiling world.

But if you’re the kind of rider who craves more punch, quicker throttle response, and wants to leave your buddy in the dust… then yeah, we’re your people.

EFI and tuning are our roots. Today’s sleds get us fired up because they eliminate a lot of the old issues — no more fighting with carbs or ignition setups that used to squeak motors way too easily. With the modern platforms, our Upshift403 big bores are reliable, consistent, and tested every single weekend.

Yes, more power means more wear — that’s just physics. But here’s the reality: most riders spend less than 8% of their engine hours at full throttle, wide open. That means you get the performance boost without constantly beating up your motor.

3) Do I Need to Machine My Crankcase or Send One In? 

1000 Kit: No crankcase machining is required. However, the transfer ports don’t line up perfectly. That said, it still makes nearly full power as-is. If you want to go the extra mile, the 1000 crankcase can be matched by hand.

1070 & 1150 Kits: These share the same machining pattern and do require crankcase work. Some holes need to be filled with liquid aluminum before machining.

For all engines, we recommend sending in your crankcase for machining. We’ve developed a program that channels the gas/oil mixture directly to the PTO and MAG bearings — a feature not present in the Polaris Patriot crankcase. This extra step improves lubrication and long-term durability. We’re happy to work with your local machinist if you prefer to handle it that way, and we may be able to recommend trusted machine shops in the U.S. for our American customers. We also have a limited number of exchange crankcases available.

Note: The Arctic Cat 858 already has this provision built in and does not require crankcase machining.

5) Premixing oil in the gas in the tank –

this is a good idea in any machine.  I know the internet says that a tpi or semi direct engine doesn’t get oil in the crankcase but this is BS.  There is reversion caused by a hurricane in the basement of the two stroke  and it is getting lots of gas/oil from injector in there.   Also gas/oil mixture flows through an injector just fine.  Our tunes are designed with 100:1 in the tank.  We recommend 100:1 in the tank.   We have done dyno tests to show customers the more oil you put in the gas the more power you make.  Oil is the seal!

6) What Octane Fuel Is Required?

We always start with and tune for 100 octane fuel — that’s our baseline. For our big bore kits, we do offer a 91 octane head insert and tune, but truthfully, it makes us a bit nervous. Pump gas quality is unpredictable these days, and it’s hard to rely on what you’re actually getting out of the nozzle.

Our tunes are consistent because they run lean, mean, and right on the edge. If you mess around with lower octane fuel, the ECU will detect knock, dump extra fuel into the motor, and you’ll lose the power you just paid for.

Bottom line: if you want peak performance, stick with 100 octane.

7) Is it hard to pull over?

on a cold day it sure is!  So is a 9R.  The 1000 pulls similar to 9R. 1070 and 1150 are harder cold.

8) Can we send you our crankcase and receive an assembled engine

Yes, for 2025/2026 season we would be happy to assemble your stripped, clean engine for free. Send with out a clutch please.

9) I want to sell my 9R or 850 long block or keep it as a running spare

No problem we have been getting cases off ebay and buying brand new ones.  The case is really all we need to build you a big motor long block.

10) Do I need throttle body relocate 

No but should work towards it, we have two sizes and the big bores benefit top end power from the bigger 60mm

11) What spark plug to run 

Recommend NGK “9” heat range plugs although there has been no problems reported with “8”

12) Which Clutch should I or can I use?

You can use either the P22 or the P85.  The big bores will introduce more harmonics to the clutch so we recommend keeping an eye on both.  The P22 works nice but we are little scared it may give up it’s life expectancy before the P85 so we run mostly P85 on our in house sleds.  

Clutch kits – we can steer you in the right direction, tell you our opinion and put you in touch with colleagues that specialize in clutching.  We do have parts in stock as well they are not on our website right now.  Clutching is a bit of a personal preference.  Some like less weight and let the engine rev faster other want maximum track speed, we can chat