Power Core IV v2 - Flight Test Report

Test Pilot report from the Super Secret HDTF ( High Desert Test Facility ).... We could tell you where it is, but then we'd have to kill you :D

Warning HIGHLY Subjective Test Report Follows! :)

Test of YZ timed WR400 with FMF PC IV SA "2" vs. YZ400 with original FMF PC IV SA.

I met up with our Lead Flight Test Engineer (LFTE) , Clark Mason at the HDTF at 17:00. The WMEWR ( World's Most Expensive WR ) was prepped and waiting on it's race stand, when the LFTE made his first mistake....."You want to ride it?". Faster than a coyote on a rabbit, I set the PJYZ ( Plain Jane YZ400)

against the nearest Vertical Bike Stabilizer ( VBS aka "Bolder" ) and headed for the WMEWR. Once astride the WMEWR the LFTE commenced with the briefing.... Big surprise, the HOTAS ( Hands on Throttle and Stoppers ) have enough stuff mounted on them for the average F-18. The WMEWR is 250 lbs ready to roll and you can feel the difference, more Titanium and Carbon Fiber than most Jets :D

Preflight Brief completed, we were cleared for flight....After two kicks the one of the other FTE's advised "Kick it like you got some..." Okay Stomp! Bike comes to life. As compared to my YZ400 with a stock head pipe and an FMF PC IV SA. The PC IV SA "v2" is a "little" quieter than original at idle- IMHO. I slipped the bike into gear and headed up the trail. First set of Whoops, the bike starts to drop away....and keeps going....and going.....At this point the Test Pilot initiates a recover maneuver to exit

the Whoops before a departure ( mil speak for departure from controlled flight ) of the WMEWR. The shorten suspension on the WMEWR is VERY noticeable in the Whoops ! After further familiarization maneuvering on the WMEWR, I reenter the Whoops to compete the test point. Throttle response is very

good down low, crisp, feels a little stronger that the PJYZ. The WMEWR seems a little tight on top with this pipe, likes to be short shifted. It was weird riding a bike with more "stuff" on it that felt lighter than my YZ. A quick run up a dirt road confirmed the earlier feeling. Down on top end as compared to the "original" PC IV SA on my YZ, better down low. I think part of the bottom end response may have been due to the P-38 Accelerator Pump and the fact that Clark's bike is PERFECTLY jetted....are you

surprised!? :D With the test points completed I entered the pattern and brought the WMEWR back in for landing. Support staff chained the WMEWR down before it floated off.

Recap, the new PC IV was marginally quieter than the original one and it trades top end for bottom - IMHO.

Good Fun! ( Thanks Clark!)


Chris in the Mojave

'98 YZ400F

[This message has been edited by Chris in the Mojave (edited 04-24-2000).]

Thanks for the gret report.

Can anyone comment on using the stock headpipe and E-series CF promeg? What is the low, mid , and top end like??


I have never (I am sheltered) heard the stock YZ before. Is the SA IV-2 quieter than the stock WR w/ baffle removed? How about compared to the stock WR exhaust intact? You said the PC-IV-2 has better bottom end than the stock YZ, was it noticably stronger or marginally?

This is wicked important. My wife, Alisa, has given me her blessing (PLEASE, PLEASE, PLEASE CAN I HAVE THE FMF PC-IV-2 W/ POWER BOMB HEADER...I'LL DO ANYTHING!!!!!!!!!!!!!!!) to get this exhaust system. Is it worth $500.00 (w/ power bomb header). I CANNOT run my WR w/ the exhaust baffle removed.


99 WR, 84 Kaw 900 Ninja, '82 Honda CB750F clothes hanger, '84 Honda Z50 "Berm Destroyer". Always thinkin' "Hell, this worked on my 2 stroke!!"

Thanks Chris and Clark,

You guys must spend as much time bench racing and laughing as you do riding. The tests you performed sounded great and more trustworthy than the one you get from the dyno or from the local "Pipe Pusher" dealer down the street. Being a ex-navy guy the format brought back some memories from a few years ago. " A " for effort guys. Thanks for the Report. :)


00'WR400 75'Yamaha 250 enduro

White e-Series S-bend 12 discs, Yz timed, rejetted to Clark specs, throttle stop cut, lid removed, Topar Racing top clamp, Tag Metals T2 bars, Scotts damper, Devol disc guard and frame guards, lights removed, Cr routed Fastline brakeline, Acerbis Rally pro hand guards fastened to the top clamp, Gel grips Live in Southwest Ohio

Chris, good report. What you say makes perfect sense. A less restrictive muffler (louder) will make more top end at the expence of low end. More back pressure (quieter) will give you more low end at the expense of ultimate top end power. That is why on Yamaha street bikes (and on Doug Hennry's yz) they use an EXUP valve in the exhaust. The valve partially blocks off the exhaust at lower RPM to build back pressure which helps exhaust velocity to scavenge (pull) the exhaust out of the cylinder. At high RPM the valve opens for top end high flow power. This is why the E-series comes in two versions, low restriction pro-meg for top end and quieter s-bend for midrange. All this is standard four stroke exhaust tuning stuff which leads me to the thing that has been bugging me for a while....

How come some people report here that a louder freer flowing muffler on their WR gives them a boost down low? I suspect that maybe the noise gives the impression that the bike is accelerating faster.


'99 WR400

'92 GSXR 7/11

Visit my photo album AT YOUR OWN RISK!! My photo album

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