engine mods performance vs. durability


29 replies to this topic
  • hondacrf150f1

Posted October 28, 2007 - 07:49 AM

#21

no it just stopps at 95-97, and yes pulls very hard till that speed, its almost like the bike's redline is 7600-7800 rpm's not 8300 becaues it doesnt go over that, its really not a problem with me because i dont go over 80 that often.

My dads 03 XR650R is the same way, except he has stock wheels not 17's, his doesnt go over 92...and also doesnt rev over 8000, same story as mine same uncorking mods, same gearing

  • InternalCombustion

Posted October 28, 2007 - 09:07 AM

#22

16-44? Im running 15-45 and my bike doesnt redline? but it does max out around 95, really doesnt go over 7600 RPM's. Its got amazing amounts of torque but it wouldnt even do 107 down hill

no it just stopps at 95-97, and yes pulls very hard till that speed, its almost like the bike's redline is 7600-7800 rpm's not 8300 becaues it doesnt go over that, its really not a problem with me because i dont go over 80 that often. My dads 03 XR650R is the same way, except he has stock wheels not 17's, his doesnt go over 92...and also doesnt rev over 8000, same story as mine same uncorking mods, same gearing


Okay, all my previous posts on this thread were from my Blackberry, so I did not notice your avatar showing you are running 17" rims. The I just read your last post, above. My apologies for that mistake.

Running 17's with 15-45 gearing should give you a 5th-gear redline of about 102-105. You say its real strong right up to 95-ish, then flat, but your Vapor is indicating only 7600-7800. I got the frontend apart on my R right now or I'd take it out and test it and make sure I've not imagined I can redline mine in 5th.

I can say for a fact that before I got my 16-44 sprockets, I was using 15-45, just like you, with 17" rims. On 2 different occassions I redlined it, going uphill on I-81 (the safest, straightest section of rural highway near me), indicating about 101-102. And I wasn't laying down on the tank, only leaning into the wind-blast a bit.

Maybe I'm way off. Again, somebody correct me here but you should be able to redline 5th gear, running 15-45 and 17" rims, with a well-tuned, uncorked 650R, right?

hondacrf, I would be very surprised if your ECM is faulty (cutting off at 7600 rpm vs 8200) but you could test it by going full throttle in 4th and see at what rpm it cuts off. Plugging your numbers into my gearing worksheet, you should see about 87-89 mph when the ECM trips.

Another check would be to go pull your spark plug (assuming you have not been idling the bike a lot recently) and see what color the electrode is. Should be light-brown to tan-ish. If its either darker (too rich) or lighter (too lean), your mixture is off.

Somebody step in here if I'm way off in left field with my thinking...

  • Billahjack

Posted October 29, 2007 - 06:04 PM

#23

Somebody help me here.

A properly uncorked and tuned R with factory gearing should redline in 5th gear, shouldn't it? Mine does.

Okay maybe I've also got an Edlebrock and vented side panel but that doesn't add all that much, I don't think.

JK, make your mods to your engine, but first I'd figure out what's holding your bike back right now. Something just isn't right, in my opinion.

Ride safe.



I couldn't redline my stock uncorked 650R with 14/48 gears and side panel cutout at 3000 feet elevation. It would only hit about 97 mph. Down a slight hill, I could get it up to 103 where the rev limiter hit. When I changed the header/pipe/cam, it would easily hit 103.

14/48 gearing with stock size rear knobby gives you 103 mph (GPS verified) at rev limiter.

Below 6500 RPM, a fresh 650R with uncorking and a good slip-on pipe is pretty close to my Moriwaki full exhaust/HRC Cam/Side panel cut-out. After that, the stock header/cam chokes it up.

Over 6500 rpm, my bike walks away from my buddies stock cam/uncorked bike. I think my header tubes are too large diameter for stock compression which is why my bike is a little softer down low. Perhaps I can get a HRC piston sometime.

  • weskc35k

Posted October 29, 2007 - 11:42 PM

#24

Bill i saw a vid of yours on you tuber,why didn't you build a little kicker in that sucker.
Actually i know why,good stuff.

  • Billahjack

Posted October 30, 2007 - 07:04 AM

#25

It was private property....

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  • jk9270

Posted November 05, 2007 - 05:34 PM

#26

Just a quick update. I got the stage 2 cam 11:1 piston and FMF powerbomb header all installed and cut out the stock side cover to the airbox. Along with the regular uncorking/rejetting and powercore 4 muffler that I already had done. I think the engine is pretty good now.
In a straight up drag race I was able to beat my brother's CRF 450R pretty soundly. By the time I hit 3rd gear he was in the rearview. up to about 40mph it was pretty close, probably more traction than any thing else, as neither bike was hooking up too well from the starts.

One thing is for sure, it takes some doing to kick this bike over now, and the choke just floods the engine when it is cold. I'm not sure if this is a jetting issue or if that is just the way it is going to be.

  • Birdy426

Posted November 06, 2007 - 09:46 AM

#27

How is the bottom end torque? I just finished building an XR400 for a buddy (11:1 Wiseco, 406cc, cam, Mikuni Pumper carb, and XRs only pipe and header). The thing rips. My bud says "Can you get me that much bottom end on my 650R?" He's a pretty big guy and wants to be able to loft the front end rolling on the throttle. I haven't seen his 650, but I assume it's stock. He says that right now it doesn't have the bottom end power to do that. From what I'm reading here, a similar build to what we did for his son's 400 would be the ticket...that is, high comp piston, cam (hot cams? HRC?), header and pipe, open up the air box and rejet. Any thoughts or comments on this approach and expected results?

  • InternalCombustion

Posted November 06, 2007 - 11:54 AM

#28

How is the bottom end torque? I just finished building an XR400 for a buddy (11:1 Wiseco, 406cc, cam, Mikuni Pumper carb, and XRs only pipe and header). The thing rips. My bud says "Can you get me that much bottom end on my 650R?" He's a pretty big guy and wants to be able to loft the front end rolling on the throttle. I haven't seen his 650, but I assume it's stock. He says that right now it doesn't have the bottom end power to do that.


The only mod you buddy needs to make (assuming "big guy" means less than 300+ lbs) to loft the front with just throttle, is to just uncork it.

An uncorked 650R will do throttle-wheelies all day long in 1st, and for some guys, in 2nd and 3rd.

Find out if his is uncorked and if not, walk him through it. Then watch him smile (and get out of his way...)

If it is uncorked and he can't bring the front up at will, there's something out of tune with his setup.

  • jk9270

Posted November 06, 2007 - 12:26 PM

#29

My mods didn't do a lot for the bottom end, there was plenty of power there already. From mid range to top end it is way faster. I agree with Internal, there is something wrong if your buddy can't wheelie in at least 2nd gear just by gooseing the throttle. I can lift my front wheel pretty much whenever I want to now if there is a little bit of traction.

  • Birdy426

Posted November 06, 2007 - 01:38 PM

#30

Thanks for the replies, guys. I will probably pick up his 650 tonight, anfd if it's not uncorked, hit that first. If it is uncorked already, I'll look at the carb for jeting, do leak down and compression checks, and make sure the pipe isn't carboned up, and go from there. Thanks agian for the prompt replies.





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