have 51 hp need 65+ hp

28 replies to this topic
  • wsmcrobert

Posted December 16, 2006 - 04:07 PM


need some help. i have an '02 xr650r transplanted into a tz250 road racing frame. had it on the dyno today with disappointing results.

current engine mods:

hot cams stage 2 cam
wiseco 12.5 / 1 piston
head work with extremely large valves
mikuni hsr 45 mm carb
straightened intake manifold
custom one off pipe
power mist to-137 fuel (5% oxygen)

Posted Image

we also had some trouble with the main jet.(btw i am using an open carb, no air box). the dyno graph is in mph so it is hard to know the precise rpm but if you look around 85 mph (prob. 5000 rpm) the mixture is very rich, then as the rpm's peak it goes a little lean. this is happening with the throttle wide open from 5k to 8k on the main jet. what could be doing this? carb too big? carb too small? do i need a velocity stack? needle and seat too small?

as i said in the title, i need to get up to around 65 hp to be competitive. and i think that with my current set up i should be more like 55-58 hp. any advice?

  • rebelventurer

Posted December 16, 2006 - 04:24 PM


I think you are having issues with intake velocity!
Why not the crf450 motor?

  • BWB63

Posted December 16, 2006 - 05:06 PM


I am guessing that you have way to big of a needle jet and you air jet is too small. HSR45 then I would try a 1.2 air jet and a Y-4 needle jet, 9dh0j-1 needle?, 22.5~25 pilot? I would also try a smaller carb or stock to see if there is more off, like the cam timing? Porting and polishing this head has given us nothing but trouble. I had a HSR42mm Mikuni on a stock engine and it ran a little wet (engine couldn't burn all the fuel). I agree with: "rebelventurer" 'I think you are having issues with intake velocity!'

  • weskc35k

Posted December 16, 2006 - 05:38 PM


It's about the package and what works.
I am personally not a big valve fanatic but most guys go this way.
Your problem is probably a carb thing but your next doodad after you fix up the glitch should be ignition related so as you burn all that fossil fuel going through your motor.
If you can go back to a stockish head with this cam and see how much difference there is between the setups.
You'll work it out.

  • rcnutt

Posted December 16, 2006 - 06:19 PM


Put the 2-stroke back in it..............

  • BWB63

Posted December 16, 2006 - 09:49 PM


I looked and see nothing about having a 102.4mm piston? You are not 680cc and are looking for more then 54hp ? Tricked out HRC (cam, 11:1 piston) is 51~52rwhp, that is the 64bhp at the engine that the race bikes say thay have, that you see on corrected charts that rider push around as true dyno chart. My 680cc is just over 58rwhp and 72bhp at the engine. If you are at 50 with low end trouble you are having on that chart, once you get the intake figured out you will be close to 54~55rwhp. I have the 3mm oversized intake valves, 11:1 Piston, my cam is about the same but, mine has more lift, I have a bored out Edelbrock (42mm), and a 45,000 volt coil, Nolgoly (I forget how to spell it) and there plug wire (but, I don't think it dose anything) Iridium plug. S/S valves and other stuff. In the end just over 58rwhp. I am about to rebuild and try a few other things to see what happens.

  • wsmcrobert

Posted December 17, 2006 - 08:02 AM


those are some of the things on my list.

bore to 680 cc
over reving ignition module
advace ignition (5-7 degrees? maybe this is handled in the ignition module?)
get a second opinion on my pipe

will adjusting the valve timing add hp or just move around the hp you already have?

i forgot to say that the combustion chamber is re-shaped for the big valves. not much of a squish band left.

has anyone ever read the mikuni carb. tuning manuel? http://www.spankyspa...ing-manual.html

  • RC30

Posted December 17, 2006 - 08:13 AM


Do you speak deutch?


Read this:


  • BWB63

Posted December 17, 2006 - 08:42 AM


those are some of the things on my list.

bore to 680 cc
over reving ignition module
advace ignition (5-7 degrees? maybe this is handled in the ignition module?)
get a second opinion on my pipe

will adjusting the valve timing add hp or just move around the hp you already have?

i forgot to say that the combustion chamber is re-shaped for the big valves. not much of a squish band left.

has anyone ever read the mikuni carb. tuning manuel? http://www.spankyspa...ing-manual.html

I have the manual somewhere.
I didn't go witha over rev box because of the extra mass of the bigger 102.4mm piston. Just didn't think it was cool to take that much mass to those rpm, and I think the valves will float above 8,400rpm even with the extra stiff springs I have.

  • wsmcrobert

Posted April 09, 2007 - 08:22 PM


well, did some more work,

new stage II cam (i fried my first one)
new cam end bearings
new pipe by mark mcday
new oil tank by mark mcday
removed idle gear and kick start assy.
found my carb problem (vacuum leak:blush:)
added velocity stack

picked up: nearly 10 hp :thumbsup: now i'm up to 60.6 hp (also won the first race i entered it in, formula singles)
http://mylaps.com/re...s.jsp?id=485118 where it says "best speed" that is my average speed. wsir is a 2.5 mile road course. i was bouncing off the rev-limiter on 15/37 gearing (130 mph give or take) for race day dropped 2 on the rear and stayed off the rev limiter.

i am still building and have some questions:

1. is it possible to remove the counterbalancer and re-balance the crank? how bad does if vibrate?

2. i made a mistake in my first post. i have a wiseco 11:1 piston. all things being equal what are the pros and cons of advancing the ignition (say 3 or 5 degrees fixed by either an offset woodruff key or moving the pick-up and keeping the stock ignition) versus a higher compression piston and not advancing the ignition?

3. does anyone have any hard facts (like dyno graphs) for the vortex ignition?

thanks :worthy:

Posted Image

4th gear, 16 / 37 gearing

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  • Thumpmeister

Posted April 09, 2007 - 09:11 PM


This might not help... But, I'm sure everyone here remembers the dual carb set-ups honda put on their bikes in the mid-80's. I've had a couple of those, and the dual-carb xr250 I had went as good (or better) than an xr 400.

What if you could get a dual-carb set-up on your brp? Maybe one off of an older xr 600? Just a thought...

  • HawkGT

Posted April 09, 2007 - 09:30 PM


Thanks for sharing the graphs!

What fuel are you using with the 11:1 and the HC stg 2? I assume your not running an auto-decomp unit? Do you know what dynamic compression your running (cranking comp)?


  • 4Takt

Posted April 10, 2007 - 06:48 AM


That's pretty cool. Can you share a picture of your bike? Thanks.

  • wsmcrobert

Posted April 10, 2007 - 08:11 PM


i have'nt checked the cranking compression yet. i'll probably do that before this weekend (while i prime the oil pump)

i am using power mist to-137 (i am a dealer). it is 5 % oxygen 120+ octane. i'm thinking of using the d-832, 12% oxygen 120+ octane. powermist dot com

here's what it looks like: i'm getting it ready for the races this weekend in vegas.

Posted Image

Posted Image

  • InternalCombustion

Posted April 11, 2007 - 05:41 PM


Forgive me if you already posted this: what class are you racing this bike in?

Sweet ride.

You obviously have an over-active (and intuitively accurate) imagination.


  • RC30

Posted April 13, 2007 - 09:02 AM


Posted Image

:worthy: Sexy machine :thumbsup:

  • wsmcrobert

Posted April 13, 2007 - 02:08 PM


race classes:

formula singles, a formula class, only limit is that it must be a 4-stroke single. everything else is unlimited.
foumula twins light weight. again a formula class, except this class allows unlimited displacement singles and i think up to 700 cc twins (sv650 mostly but they can be 80 hp so they are tough)
formula 40 light weight (becuase i'm over 40 years old) but i'm outclassed. it is basically a formula 2 race for those over 40.
formula 2, but again outclassed (600 cc in-line 4 cyl. machines 120+ hp)

d-super stock (a 500 cc twins class)
d-super bike (a 500 cc twins class)
formula 2 (sv650 and 125 gp - really should be called formula 3)
light weight twins super bike (an sv650 class)
clubman (a catch all class; singles, air cooled twins, older street 2-strokes)

i checked cranking compression. it is 148 lbs.

still looking for help guys, i need to decide if i'm going to go for a higher compression piston or play with the ignition. which is better? maybe i should go for the ignition box, because i still have'nt decided if i'm going to bore to 102.4 mm

  • drop

Posted April 13, 2007 - 02:23 PM


I think you're going to be out gunned in all but the formula single class no?

  • weskc35k

Posted April 13, 2007 - 06:16 PM


Go a big high comp piston first,ignition stuff to fine tune it.

  • HeadTrauma

Posted May 04, 2007 - 09:32 AM


Is it possible that you are using too much octane considering the comparatively low 11:1 compression? Have you tried anything in the 100 or 105 range? You're making a lot of power already, but you might pick up some more if it doesn't actually need all that octane to keep from pinging.

The rules said "must be 4-stroke single, all else unlimited." Does that mean forced induction allowed? :applause:

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