PowerBomb and Power Core IV-2----YES

10 replies to this topic
  • Clark_Mason

Posted June 16, 2000 - 02:50 PM


I ran this combination using 14/47 gearing which is 6% taller than stock. Used my standard 80mi test loop. System performance was excellent. This combination has excellent low, mid and very good top end. I hit 92mph before running out of straight road. It pulls real hard off the bottom and through the mid range just like my e-series promeg with the tapered header but is quieter. The system is not a quiet system but it is quieter than White Brothers e-series, Yoshimura, DSP, and others. It is not a quiet as the MegaMax II but it is a top drawer performer. It is staying on my bike. If I do get sound tested I feel I will have a 50/50 chance of passing at 99-101db. I will keep a quiet exhaust in case I need it. I was vary pleased with the fit finish and performance of this system-it pumped out mega torque and carbureated perfectly.

I ran the PC IV-2 for a while with the stock header and was not overwhelmed at all. The PowerBomb really woke things up and makes the system seem more torquey-revvy read responsive, I liked it.

I was using the following jetting on my 99WR with YZ cam timing:

Fuel Screw = 1.25
Needlw = DVP #4
Main Jet = 185

Riding altitude 1200 to 3500 feet.


  • Kevin_in_New_Hampshire

Posted June 16, 2000 - 03:56 PM


Like I said in an earlier post, FMF told me they are making a quiet end cap for this pipe very soon. The ETA has yet to be announced however.
Guestimating, how much louder is this setup over your mega max?

Also, how much of an improvement over stock exhaust w/ the baffle insert REMOVED??

Would the mega max fit onto the PB header?

[This message has been edited by Kevin in New Hampshire (edited 06-16-2000).]

  • Airastro

Posted June 16, 2000 - 04:13 PM



Sounds like your test results mirror mine from an earlier post on my YZ426. I did not have the luxury of testing a bunch of different pipes prior, just the stock one and the FMF HI-Flo. I was also extremely pleased with the results. this thing just rips- very noticible on an mx track when you need quick acceleration out of a tight corner to clear a jump.

  • Mech

Posted June 16, 2000 - 09:12 PM


Hey clark,
Does the power bomb fit with the stock exhaust and the E-series S bend? Thanks. :)

  • Clark_Mason

Posted June 17, 2000 - 06:58 AM


To all

1) The PowerBomb header is the same outside diameter as the stock header. So I would assume it will fit in any application where the stock headpipe can be used. For example White Brothers with the stock exhaust seal, MegaMax II with the provided spacer, etc.

2) The MegaMaxII can be made very quiet with the quiet core and then opened up with no quiet core and more disks. The most disks I ran in the mega max was 13 and at that number it was just slighly quieter than the PB/PC-2 combination. If you need quiet the megamaxII is the most flexible as far as tuning. The PB/PC=2 combo is a better performer but not by that much if quiet is your priority. Now if FMF comes out with a removable replaceable quiet endcap for the PC-2 that will pass the 99db forrest service limit then they would have it made. But for today if you want a minor weight savings, tuneable power and a quiet exhaust the MM-II is tought to beat.

3) My Carbon Fiber e-series pro meg using the WhitBrothers titantium taper headpipe is also an outstanding system and I feel it offers better very top end performance and basically the same performance everywhere else as the PB/PC-2 but its much louder at least to the rider.


[This message has been edited by Clark Mason (edited 06-17-2000).]

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  • WR400_Jay

Posted June 17, 2000 - 02:21 PM


Clark Thanks for all the testing analysis data on the pipes you have run. I recently picked up a used Megamax II just to be mouse like quiet in the woods if I ever have to be. I normally run and e-Series S-bend shorty with 10-12 discs. The power is awesome but it is very loud.

I have one question for you though. I see you are running a 185 main at the higher altitude you live at and I was wondering if you have ever fouled because of it. I have a flatspot/hiccup between 3/4 and 7/8 throttle and I wonder if I need to go a little richer. I live at about 500-700ft and I'm running a dvr needle 4th position, 48 pilot 1.5 turn and a 180 main

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

  • Clark_Mason

Posted June 17, 2000 - 03:13 PM



Experiment with the mainjet and the needle clip position. First try a 178 MJ then a 182 and run the same course. You may dial it right off. If it is not a noticable improvment then go back to the 180 and vary the clip one position each way take notes you should be able to get it perfect.

With YZ cam timing I will run between a 178 to a 190 main depending on altitude. Remember my bike has been CNC ported and may be able to take a little richer main jet than stock. I believe that a stock WR with YZ timing would run between a 175 and 182 mainjet depending on altitude (10000ft to sea level) above 10000feet maybe a 172 or a 170.


[This message has been edited by Clark Mason (edited 06-17-2000).]

  • James_Dean

Posted June 17, 2000 - 09:05 PM


Try the YZ426 needle, richens the flat spot exactly as you described it. EKR#4 according to the service manual. Service guy said part #5JG14916-ER is EKR (even though the parts dept shows EVR). I prefer the slightly richer(down low)EKP#4, #5JG14916-EP.
James Dean

  • Gordon

Posted June 19, 2000 - 04:14 AM


Clark how would you rate this pipe against the DSP and The Big Gun? The opinion out there has always been that noise = horsepower? I know there are a few (very few) that have beat this. Never on my toys. Have you ever tested the stock YZ pipe? When you did your testing did you stay close to the same gearing? On this test it appears you went a bit higher on the gearing, which bodes well for the pipe. What pipe would you use if noise and spark arrester were not an issue? Have you ever heard of Uptite Racings pipe. Suposally it dyno tested 7 horse power over the stock YZ pipe. It is a reverse megaphone. I tried this pipe and it is like riding with open headers. So loud I wouldnt care it it added 20 horsepower. Just curious. We all appreaciate your testing

  • Clark_Mason

Posted June 19, 2000 - 04:45 PM


Actually the taller gearing would work against my intreset in excellent low end / mid range perfromance.

The best pipe I personally tested was the Yoshimura all titantium race pipe with the SA in place. It was light 4.5lbs total and ran great everywhere. I suspect the DSP would be identical or very close. The Yosh was too loud for me. I ride out of my garage and do a lot of street to get to dirt roads/trails and the loud pipes on the street constant droaning in the ears is too much plus my neighbors need to be considered.

I have never run the stock YZ pipe.

As to Uptite and George Earl pipes I have worked with George on pipes in the past 95 KTM 400 and 97 ATK 605. His pipes work excellent but usually are top end horsepower reverse cone design and very loud. I'm staying or trying to shy away from loud.

I'm trying to balance noise and performance and its hard since the pipe people have not truly focesed on the noise side of the equation but I belive they are now getting the picture and over the next 1-2yrs will have the products.


  • Kevin_in_New_Hampshire

Posted June 19, 2000 - 05:31 PM


Ever get your hands on a Staintune?

[This message has been edited by Kevin in New Hampshire (edited 06-19-2000).]


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