well, i had it on the dyno today with disappointing results. i got 51 hp and i want 65+ also, the plumbing did'nt work out too well for the oil tank. i'm going to be making another tank and mount it outside the frame on the right side of the bike so that the hose feeding the oil back to the motor is much shorter. the 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) 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? with my current set up i think that i should be in the 55-58 hp range. i have heard of xr650r motors getting 70 rwhp. i am sure that is with the 680cc kit and probably an over-reving ignition module. i don't know if the over-rev ignition module changes the timing. any input on that? is there a way to advance the timing like an offset woodruff key? move the pick-ups? any advice would be appreciated! thanks!
My guess is, way ported head and big valves are your problem. Tons of flow isn't always good. If you lose intake velocity, you lose power. There have been lots of arguments about this guys engine building. After reading it, I agree. http://www.mototuneusa.com/think_fast.htm
My suggestion is to hook up the RPM lead so you can get a torque curve. I've built one of these when they first can out using the HRC power-up kit. We found power to a bit disapointing too, mid fifties I think but the torque was awesome. Even though the peak power was low the bike was fast on the track because it had such a wide curve. I don't know how the Hot Cam compares to the kit cam but the bike I did needed more cam to make more power. If your torque curve sucks you may have issues that need fixed, cam timing off, low compression, ex-pipe design, ect. The carb looks to me like it needs the main air correction jets changed. You can change the fuel curve by changing the relationship between the main air and main fuel jets. Bigger main airs lean more on top but also lean out everywhere. So if you go smaller on the main airs it will get richer on top and a little richer in the middle requiring you to step down on the main fuel jets too. It'll take a little tweaking to get this right but it doesn't have to be absolutely dead on, close is good enough carburation changes from day to day and the difference for close to dead on is minuscule in this application so don't pull your hair out over it. That little dip at the end of the curve looks odd to me was the engine missing or is that just the way it looks when it hits the limiter?
Just my opinion, but you won't find much power using the Hot Cams. They design them to work with stock parts and to be "drop in," which leaves a lot of potential power laying on the table. From the specs on the Hot Cams site they show about .383" lift on the intake, vs. .374" stock but they added 20 degrees of duration. The duration is going to help some but you need more lift to take advantage of the valves and head work. What size are your valves? You need the lift to be ~30% of the diameter of the valve, minimum. I'm guessing you need something more like the Megacycle 106x1 which is .435" lift @ 268 degrees.
+1 on that. Hotcams are OK, but the crew at Megacycle are the best. :up: I don't know enough about jetting to help troubleshoot but a previous poster did a great job with that already. You could also go to any number of XR speciality tuning shops that are all down in SoCal. Preciscion Concepts comes to mind. They build and run the HRC factory bikes for Baja and the BITD series. http://www.precisionconceptsracing.com/html/contact_us.html
You might find it interesting to read what these guys did to get 70hp from a Ducati Supermono: http://www.sigmaperformance.com/supermono_tech_1.htm In brief, because singles breath in big gulps, they need big holes: ie big bore pipes, and they ran a 54mm throttle body. Ok, allow that 54mm with a butterfly in it is more like a 50mm flatslide, but that's still 10% bigger than you have... hence 21% bigger area... Mind you, they were running bigger valves, more lift, etc etc... I have a deep suspicion that 65hp is just beyond hope for a 650 Honda
+ 1 red is stock green is hi comp piston, cam, pipe blue is borynac's 680 (the above image and info are shamelessly stolen from ADV Rider.) Alot more info from here: http://www.xr650r.borynack.com/HorsePowerMods.htm
alot of great information since my last post. thank you so much!! here's where i'm at now: i got my new oil tank made and it works really well. i had the bike running and ready to head off to wsmc last month when i thought i heard the valves making a lot of noise. i pulled off the valve adjustment covers and looked at my cam and it was wasted. i dropped the motor and pulled off the valve cover and the rocker arms were wasted too. remember how i said that my first oil tank did not deliver enough oil to the motor? well it took out my valve train. i wonder how the main bearings are. the valves were bearly lifting. i had the rocker arms welded and resurfaced and ordered a new hot cam (same one). then the machinest who redid the rocker arms told me to order new cam bearings too, which i did today. also the guy who built my new oil tank built me a new pipe too (mark mcday, used to build pipes for muzzy). he thought my old pipe was extremely under sized. so, once i get all my parts i'll put her back together and i'm hoping to be out at wsmc later this month.
Besides the larger oil tank, can you run larger oil line and fittings? Good thing WSMC's noise limit is 105 (or is it 108?) db! That sucker is gonna be loud! I've got a non-running SR500 that we hope to build for WSMC 500 Singles. With any luck we'll get it all together sometime this year.
Any updates? I ran my Honda FT591-powered TZ250 at VIR last weekend. The braking and cornering were fun, but I was wiped in the straights by the other V6LW, DSB, and Clubman bikes. I dynoed my motor at 48 hp, which seems low to me given the mods. Oh, well, I'll spend the season learning to ride it and worry about hp in the offseason, I guess.
I think general concensus over here (back when supermonos were popular) was that the Honda engines were generally not up to it for road racing... and the FT (ascot) engine was an all-round dog. All the successful bikes were running yamaha XT600-660 motors, or Euro stuff (Husky, KTM, Rotax/BMW). At 48hp, you've basically got a very heavy 125...
I sinserly appologize to all for what I'm about to say. It looks like you've spent a ton of time and money to make a really really slow TZ250 that has a service life of half the 2stroke engine. Why? Don't get me wrong, I'm all for engineering projects, but why not shoot to have something better when you're done than what you started with. A barely running TZ motor will punt out an EASY 70bhp and weigh a whole lot less so why replace it with a boat anchor of a motor? Honestly people why not just put a Rebel 250 motor in a GSXR frame?
The torque of a big single is too much of an allure for some. But wtf would I know? Other than I rode a singe for 3 laps last September and then went out and bought a KTM 560.
This has been covered a few times, but what the heck. 1.) Different classes, different standards. This ain't for 250GP racing. It's for Clubman/Formula Singles racing. 2.) You don't need a portable weather station and a box of 2,000 jets to keep a 4-stroke single running well. 3.) A powerband a mile wide that rolls on nice and smooth. 4.) Parts you can get from a dealer down the street. 5.) Longer service intervals (don't know where you're getting the 1/2 service life of a 2-stroke). Even a built 4-stroke lasts longer than a roadrace 2-stroke. 6.) IMHO a big thumper sounds bitchin'. 7.) When you can't get motor parts for your 250 any more, let us know. Someone will buy your rolling chassis for...a 4-stroke. Peace!
I'm challenged by #5 and #7--parts for FT500 motors are drying up fast. I like the thumper because there is some challenge in finding correct gearing. You have to work with relatively low rpm, so you have to find the right gearing that will be tall enough to provide speed while using the motor's torque. Kind of like a 2-smoke, only backwards.
Does anyone have the number for tigcraft? I keep trying to go to their web site and I get an apache error so nothing comes up. I am half way interested in one of their frames. Thanks for the help. Chris
I don't have the # but I do have e-mail: Dave Pearce at Tigcraft e-mail: [email protected] - E P.S. Those minimoto rigs are the shiznit if you have a 450 engine!
Yeah, well, here's the thing. You've got the chassis, right? So when the FT500 engine is kaput you have a wide variety of replacements to choose from. Air cooled: SR/TT500 = Widely used in flattracking. Tons of performance parts are availabe. You'll see 45hp or so with a 540 kit. SRX/TT600 = Very popular engine but now, alas, harder and harder to find. Lots of roadracing performance to be had. I've heard of 60+hp on radically built SRX engines. XR600R = Next to the SRX/TT, the best 600 thumper IMHO. Dead reliable. Unchanged for years it excelled at flat out desert racing. Loads and loads of performance parts are available. The first generation (late 80's) motors are starting to show up very consistently on eBay. A freshly rebuilt one just went for $300 or so. A Thumper racing 660 kitted XR600 engine dynos at 65hp. Generally speaking, you can get 45hp - 55hp out of one without alot of effort of $$$$. My motor with a slip-on and rejetted stock carb makes 'bout 40 - 45 (seat of the pants dyno). XR650L = Derived from the XR600R but, somehow, less powerful in stock form. The engine has *never* changed since it's introduction. Can be woken up nicely but the extra weight of the started motor really blows. It's nice of you want to the magic button, though! Water cooled: 250's: Small, light, great fit for a 125GP chassis. Low HP (per se), high maintenance. The smaller the motor, the more maintenance required when it comes to roadracing applications. 426/450's: Rapidly becoming the standard. 45 - 55 hp right out of the box. Small. Loads and loads of parts and tuning knowledge. Expensive 'cause they are new. You're looking at something like $1500 for one used. Well, expensive compared to a $300 - $700 XR600/XR650L engine. XR650R: The modern XR600R. Reliable, makes decent power, performance parts galore. Doesn't make as much raw HP as the Yam 660 (as this thread attests) but it's a Honda. Which means, generally speaking, you can rely on it not to strand you in the middle of Baja OR leave you at the racetrack with a broken engine. I saw a Barker built Aprilia 250 Cup bike with a XR650R engine in it. Awesome, awesome, awesome. Yam 660/700: The best engine out there, IMHO. Someone like Tim Barker can get 70+ hp out of one pretty reliably. Parts are common. They sound awesome. You won't fit one in a 125GP frame but a FZR400 or RS/TZ250 chassis is a great fit. A well built bike (like the Weiss SZR660) will tear apart built SV650's.
I usually don't respond to people trying to argue, but what the heck; 1 plenty of bikes to race in plenty of different classes already exist why take a fast bike and make it slow to be competative?2 I forgot what your logic was, sorry. You need a tiny little battery powered weatehr station that is available at any Radio Shak for under $20, whats the big deal? And I probably used 4 jets all of last season which probably took a combined total of 15 minutes to change (whole season). And as far as the thing blowing up, read the post, the thing wasted a valve train before he even got to the track with it. A GP bike needs a piston every 300 miles so depending on how many races you do you may spend $100 on pistons per year (about 20min each to change) and do the crank in the off season at your leasure. All in all the amount of time and money that has already been spent on this bike could last you a long time on a smoker. As for when I can no longer get parts? That won't be for a very long time and when it does happen it will be because factory made 4 stroke GP bikes will be available. That'll make your little homade bikes, well, as obsolete as the smokers. But you are right about ine thing; singles sound good,but 2 strokes sound better. Unless your name is Ron Wood
