8/33 Cam vs Thumper Stage 4 & Stock Piston vs 12:5:1
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  1. #1
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    8/33 Cam vs Thumper Stage 4 & Stock Piston vs 12:5:1

    Hello Fellow KTM Enthusiast

    Few Questions. I currently have an 09 KTM 525XC With FCI Intake and Full All4Racing Exhaust from Bill.

    Friday, I'm taking the Carb out and sending it to Thumper Racing to get bored to 41MM along with Emulsion Tube & R&D Powerbowl.
    After everything is installed I will be talking the bike to FCI in Pamona CA. to get the bike tuned by Garret.

    Debating whether or not I should go ahead and drop in an 8/33 Cam and 12:5:1 Piston while i'm at it or perhaps a Thumper Stage 4 Cam and 12:5:1.
    Does anyone have experience on which setup will be better overall for my build? I mostly ride Dunes as well. (Glamis and Pismo Beach)
    Also, Thumper stage 4 is more than double the price of the 8/33 as well, so I'm taking that into account.

  2. #2
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    On a stock bore 525, even with 12.5/1 Piston and Carb boring, the Thumper Stage 4 Cam will be too much. If you were to do head work, porting, BB or Stroker crank, then I would probably go that route depending on the build specs you want. The 8/33 on your current specs would be a better way to go.

    Also, remember if you go with the Stage 4 Thumper Cam, you will be required to upgrade your valve springs at minimum. With the 8/33 Cam, I would still upgrade your springs to be on the safe side but it may not be necessary.

    The 8/06 with 12.5/1 Compression and Carb boring, is a solid drop in cam (that does not require spring upgrade) that will give you more mid and top and with the compression boost with the new piston will compensate for the bottom end loss.

    Just my 2 cents......

  3. #3
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    Quote Originally Posted by steveo525 View Post
    On a stock bore 525, even with 12.5/1 Piston and Carb boring, the Thumper Stage 4 Cam will be too much. If you were to do head work, porting, BB or Stroker crank, then I would probably go that route depending on the build specs you want. The 8/33 on your current specs would be a better way to go.

    Also, remember if you go with the Stage 4 Thumper Cam, you will be required to upgrade your valve springs at minimum. With the 8/33 Cam, I would still upgrade your springs to be on the safe side but it may not be necessary.

    The 8/06 with 12.5/1 Compression and Carb boring, is a solid drop in cam (that does not require spring upgrade) that will give you more mid and top and with the compression boost with the new piston will compensate for the bottom end loss.

    Just my 2 cents......

    Thanks for your input. On Thumpers website it says the stage 4 cam had a 10% loss on the bottom end but gained most of it back with a 12:5:1 Piston. That's why I was asking. I'd rather play in safe with the 8/33 though then lose any bottom end grunt/torque.

    Second thought would be just to leave the bike as is with FCI, Full Bills Exhaust, Bored 41MM carb and R&D Powerbowl then get it on a dyno for perfect tuning. I mean, Is the 8/33 and 12:5:1 Piston really even worth the $500-$600 investment? Realistically, how much would it really help this 525 out in the dunes and also the potential reliability drop off on the bike which is something I should probably factor in as well.

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  5. #4
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    Steveo told me the same thing back when I didn’t really know anything about these engines and he was right, not to imply I’m an expert now.
    I have a 540 with a 13:1 comp piston and it still makes a whole lot of top with the 8/33 cam,, however it does have other stuff done that will altar it in comparison to yours.
    That setup won’t be much of a reliability issue, CP is a good piston and 8/33 and 8/06 cams come from the factory, not an aftermarket company, both drop in cams. Stay away from the thumper stage 4 unless you go with a fully built engine.
    If it was mine I would just be saving up for a good reliable, decently powerful build all at one time once the engine showed the need for it,
    8/33 cam, port/polish, 12:5:1 piston (13,1 or higher if you don’t mind running race gas), 41mm carb, +1 valves....
    I feel it’s worth mentioning if you go up in compression it will create more heat, I feel that the mino water pump kit should be installed with high compression piston if you go that route, especially in the dunes.
    And I would wait until I did all that to get it on the dyno, shouldn’t be hard jetting for now with a stock internal quad with just intake and exhaust, I bet if you called Bill he could get you dang near spot on.
    I really like my powerbowl, clears that bog right up!
    Last edited by Youngwildandfree; 12-13-2018 at 11:38 PM.

  6. #5
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    I agree, definitely install the Mino hi flow water pump. The piston and 8/33 Cam would be totally worth it and a very nice power upgrade on your bike. My 525 is fast, fun and very rideable at Glamis with stock piston and 8/06 Cam, FCI, R&D Float bowl, jetted carb and exhaust. Much faster than any Big 3 450 or even a Big 3 Raptor 700. But I also have a fully built Raptor 778 with 80 HP, so I enjoy riding that in G even more than the KTM.

    2 things I would not budge on if this were my build. #1, I would upgrade my Valve springs with the 8/33 Cam, #2, with 12.5/1 Compression Piston, I would run minimum 100 Octane at Glamis or a 50/50 Race Gas/Pump Gas mix. I wouldn’t even chance detonating the Piston. Been there done that. It’s different in the sand and if they tune it right on the optimal afr, you will be pushing it. So why chance it to run straight cheap and crappy California pump gas. Mix it.

  7. #6
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    Quote Originally Posted by steveo525 View Post
    I agree, definitely install the Mino hi flow water pump. The piston and 8/33 Cam would be totally worth it and a very nice power upgrade on your bike. My 525 is fast, fun and very rideable at Glamis with stock piston and 8/06 Cam, FCI, R&amp;D Float bowl, jetted carb and exhaust. Much faster than any Big 3 450 or even a Big 3 Raptor 700. But I also have a fully built Raptor 778 with 80 HP, so I enjoy riding that in G even more than the KTM.<br>
    <br>
    2 things I would not budge on if this were my build. #1, I would upgrade my Valve springs with the 8/33 Cam, #2, with 12.5/1 Compression Piston, I would run minimum 100 Octane at Glamis or a 50/50 Race Gas/Pump Gas mix. I wouldn’t even chance detonating the Piston. Been there done that. It’s different in the sand and if they tune it right on the optimal afr, you will be pushing it. So why chance it to run straight cheap and crappy California pump gas. Mix it.
    Thanks for all the advice gentleman. I just ended up booking an appointment for the 8th of January with CT Racing in Los Angeles. They are gonna start with the carb boring, powerbowl and emulsion tube. Going to talk with Allen about everything else engine wise. Sounds like he is an RFS engine guru from everything I've read. Told him on the phone what I was looking (I.E. more mid-top-overrev without sacrificing low end torque/grunt.) He said he would probably be making me a custom grind cam along with higher comp. wossner piston. He said with the carb boring,those two engine mods and tuning the bike will scream throughout the powerband while really waking the mid-top end up. I guess we shall see.

  8. #7
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    Sounds good, good luck!

  9. #8
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    Ask Allen about his head work (+1 valves, 5 angle valve job and port work). I had Allen do the head on my 540, big HP gain.
    08 525 xc with 540 KTM big bore kit
    08 525 xc
    09 505 sx

  10. #9
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    Quote Originally Posted by JRSTI View Post
    Ask Allen about his head work (+1 valves, 5 angle valve job and port work). I had Allen do the head on my 540, big HP gain.

    How is the reliability with these engine modifications you have working out? I'll have the big three mods done to the bike come NY, Carb Modding and 41mm bore, Full Bill Exhaust and FCI plus tuning. As much as I want to perhaps mod the engine while Allen has it with a 12:5:1 Piston, custom grind cam, valves, porting etc. I just don't want to risk liability. Plus, Its not like the 525 really need more power for Christ sake lol. Already a flipping rocket. More of a WANT VS NEED at this point if anything

  11. #10
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    All The headwork is just controlling air flow and improving it. More air= more top end. With the stock cylinder be careful how big you go on the porting, valves, and carb bore in relation to the cam. It’s possible you turn it into losing bottom and gaining top instead of gains everywhere.
    You aren’t hurting anything reliability wise. Especially with a reputable builder.

  12. #11
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    Not to say the headwork is bad at all, it’s awesome to have done, you will benefit from it more with a bigger bore tho.

  13. #12
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    Very reliable.

    Here are the mods I have.
    41mm Carb with Thumper mods.
    KTM 540 big bore kit.
    KTM 806 cam
    CT Head work (+1 valves, 5 angle valve job and port work).
    Akro full exhaust

    On FCI's dyno it made 55 hp.

    I have since gone to the KTM 833 cam. I have not taken it back to FCI to see it gained any more hp.
    08 525 xc with 540 KTM big bore kit
    08 525 xc
    09 505 sx

  14. #13
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    Updates: KTM 525XC

    Thanks for all the info fellas. Took the bike into CT Racing Last Week. The bike hadn't been running right ever since I purchased it. Valves ended up being shot due to dirt I'm assuming from previous owner seeing how I've only used it once. Caused them to seize on and off I guess. Makes sense by what the bike had been doing a few months back in Glamis with the power completely cutting in and out.

    Allen at CT has been extremely helpful. It was already costing me $1100 to fix the current problem with OEM parts, plus install the R&D Float Bowl, Emulsion Tube, so I just went ahead and did CT GNCC Ktm Race Package which after dialing in and tuning will only be $900 more than stock fix price. Kit includes, Carb rebuilding/boing to 41mm, Dyno Tuning, CNC porting of cylinder head, CNC Radius 5 angle valve job for +1mm over size valves, Set of new +1mm Valves, Performance Lightweight Valve Spring Kit with Titanium Retainers, Webcam MX Stage 3 Performance Camshaft, Diamond Honing cylinder and fitting a JE 13:1 Hi Compression racing piston, Complete Top End Gasket kit, Jet Set, Disassembly clean and prep head and assemble head.

    Mods on Bike:
    -Ktm Bill Exhaust
    -FCI
    -O-Ring Mod, R&D Float Bowl, Emulsion Tube, 41MM Carb Boring
    -CT GNCC Race Package Ran on 100 Octane Gas

    Hoping this thing finally runs properly and like a raged ape. Will be testing in Glamis over presidents day.

    Last edited by evman; 02-09-2019 at 12:17 AM.

  15. #14
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    That is good news. Keep us updated, interested to see what HP it makes on CT's dyno.
    08 525 xc with 540 KTM big bore kit
    08 525 xc
    09 505 sx

  16. #15
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    Quote Originally Posted by JRSTI View Post
    That is good news. Keep us updated, interested to see what HP it makes on CT's dyno.

    Will Do! He was getting 51HP on his last 525 with CT Full Pipe, Airbox Boot Out and Tuning. Which is inline with most dyno's I've seen.

    Mine was pulling only 43HP, which is very low for a tuned, full piped, FCI modded 525 on the first dyno I took it to, but the guys were clueless, so not sure how accurate it was. Plus the valves were already shot which could've made a large impact on those numbers as well.

    Be cool to see mid 50's+ HP, 37tq-40tq. I'll honestly just be stoked for the bike to run properly. My old stock 525 with jetting ran quite a bit harder than current piped, FCI, 525.

  17. #16
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    Just got 525 back from CT Racing today. Will be testing her out all weekend in Glamis. Excited to see how she does in the dunes.

    Pre-Build Mods & Semi Functioning Valves:
    -Ktm Bill Full Exhaust
    -FCI
    -Jetting
    -Dyno: 43.1 HP & 33.02 TQ

    NEW Mods Post CT Build:
    -O-Ring Mod, R&D Float Bowl, Emulsion Tube, 41MM Carb Boring
    -CT GNCC Race Package Ran on 100 Octane Gas
    -Dyno: 60.7 HP and 40.3 TQ


 

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