PR2 YZ450F 62hp @ crank? PIC ADDED

11 replies to this topic
  • Zaj 243

Posted August 28, 2008 - 07:24 PM


Hey all, just picked up an '06 YZ with a PR2 Motor. Its stated to put out 62hp at the crank, and the invoice for the motor work was close to the $2k mark. The bike came with the original piston, valves, springs, and such so I know these have been replaced by PR2. Well i'm inside the engine right now to freshen things up, and I can't find what cost that $2k.

Crank appears stock with stock rod, no visible machining or polishing, except for a loose lower rod bearing :worthy: and main bearings. Cylinder is stock bore, no signs of milled deck or base, appears like the OEM cylinder. The piston p/n cross referenced to a 13.5:1 from JE, with no further machining over a genuine JE unit. Head surface *may* have been milled, the combustion chamber on the very closest edge on the exhaust side is very close to the gasket surface (practically zero "squish" clearance). Valves have the same diameter over stock and appear identical to oems. Springs are painted like stockers and retainers do not have a machined look like most aftermarket replacements i've seen. Cams are stock units, with no signs of being reground but i haven't ruled this out. Exhaust port has no polishing, or the cc, intake appears to have been bead blasted (valve guides included??) and does seem smooth straight to the valve seats, but casting flaws are still intact in the port. What could have been modded that i'm overlooking?

Now to my question: Is the '06 450 putting out hp at the 60ish area stock at the crank? I'm wondering if they just freshened things up rather than building a mod motor. It was stated to be a "reed" replica motor. It is fast but the stock '06s were animals. Anyone with experience feel free to chime in, like to hear ideas and input. Thanks :thumbsup:

  • grayracer513

Posted August 28, 2008 - 07:36 PM


Unless it was done by an estimate, there's basically no way for a shop level concern to actually measure HP at the crank. I also don't know what the at-crank HP of a stock '06 is, but I've seen more than one completely stock bike break 50 RWHP on a Dyno-Jet, including one that hit 49.75 at 5000 ft above sea level.

  • Zaj 243

Posted August 28, 2008 - 08:03 PM


I'm coming off a 426 set up for dirt track, and its set up very well and has no problem hanging with 450's on short tracks. Half miles are where the 450 shines, and i figured i'm killing 2 birds with one stone, upgrading 5 years and getting the mod motor i've dreamed about. Now its looking like i've got a stock 450. How much loss would one guess is lost through transmission and drive chain? Mid to upper 50's at the wheel are desirable for the 450's, not quite where the 426 runs @ 47ish.

  • bigred455

Posted August 28, 2008 - 08:04 PM


Let's take 50 RWHP add 15% for estimate at the crank. Crank HP roughly 57.5,I am sure the factory has it written down at 60hp.

  • Zaj 243

Posted August 28, 2008 - 08:44 PM


Does anyone know if the stock '06 head has little to no step into the combustion chamber off of the gasket surface on the exhaust side?

  • Zaj 243

Posted August 30, 2008 - 02:17 PM


Anyone have any idea what the stock ccv is? Maybe this thing just had the head milled down and a mild port job. Heres a pic of the intake, does it look changed?
Posted Image

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  • bigred455

Posted August 30, 2008 - 07:13 PM


It has definetly been cleaned up.

  • jamiehughes

Posted August 30, 2008 - 07:42 PM


maybe someone pulled the fancy motor out and put in a lightly modified one before they sold it to you... my 06 is a sweet ride in stock form, and pulls really hard...

  • aggiemoto99

Posted August 30, 2008 - 08:59 PM


def has head work....and that is where all your power gains come from.

But 62 at the crank is not that impressive....and for 2k....its really not impressive unless they used all new parts.....which is then ballpark correct.

RH can get 58 wheel hp out of that bike....from what Ive read..

  • Zaj 243

Posted August 30, 2008 - 09:09 PM


Thanks for the responses guys, the only reason I upgraded to this over my 426 was because of the motor work. Glad to see it has some work done. And the motor hasn't been swapped or changed any since the work was done, i've known the bike since it was new. Does anyone happen to know the stock combustion chamber volume for the '06 head? I'd like to get some numbers going here to figure out was piston I should run and if the head has been cut.

  • shortburb

Posted August 31, 2008 - 04:04 PM


, including one that hit 49.75 at 5000 ft above sea level.

The HP# @ 5k ft is corrected right? so its more like low to mid 40s for actual HP...?

  • grayracer513

Posted August 31, 2008 - 04:35 PM


Don't know. Eddie Sisneros posted the graph in late '05.

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