YZ Activity - Wanted: More Upper Energy

The Question - Just finished reading your TRX primer info. Great job. Bottom line for me is this: I'm road racing a YZ80 motor, which of course is designed for off-road use. I don't need bottom end, and mid-range is okay but not really necessary for the particular track I'm building this engine for. What I really need is top end HP, and lots of it. I'm at max legal limit on displacement thanks to bore and stroke, and running 185 psi compression. I have no problem using race gas only. I've mapped my ports, and used a degree wheel to establish port timing.

So where do I go now for top HP improvements?? And by the way, which software are you liking best at this point? I've tried the TSR DOS stuff, and it's okay, but clunky, and doesn't really tell me what to do once I've got all my numbers. Thanks for any insight.

Pat

P.S. I saw your formulas page where it lists a formula to determine speed based on rpm and gear ratio. Seems that the formula you have would work for, say, a direct drive auto, but it doesn't say how to determine gear ratio (for motorcycles/ATV's). I use the

following (okay, it's a little long, but it eventually arrives at the right numbers):

FORMULA FOR CALCULATING SPEED IN GEAR:

RPM / PRIMARY RATIO / SECONDARY RATIO / GEAR RATIO x CIRCUMFERENCE / 12 x 60 / 5280 = MPH

Where Primary ratio=driven gear (on clutch basket) divided by primary gear (on crankshaft)

Secondary ratio=rear sprocket teeth divided by countershaft sprocket teeth

Circumference = circumference of rear wheel(s)

Example: Using a hypothetical rear tire circumference of 78", at a redline of 9,500 in 1st gear, we get:

9500 / 1.672 / 4.1769 / 2.188 x 78 / 12 x 60 / 5280 = 45.92 mph

The Response - You may need to design the engine around a higher BMEP to reveal its true potential. What is the actual output from the engine as it is now? Since you have TSR software look heavily into the pipe making programs. I would think a custom pipe could reveal some missing HP. You may need to spend more time developing combustion chamber design as well (check into MSV and proper squish clearance). There is no limit. Since I don't know what has been done or your level of expertise to perform modifications it is hard for me to speculate. Serious HP is found in exhaust port modifications, carburation (jetting properly), and

transfer port aim and design. I like flat top pistons and flat top ports that send their charge (more) across the crown for this kind of operating range. This tends to favor peak power rather than power range.

Thanks for the speed formula. The ones listed on that page are automobile formulas. In the example you provided - the resulting speed is very high. That's not the YZ80 we're talking about here is it? If it is that thing must really rock! You are correct in the way it is done - unless I've missed something too. I'll have to add it to my formula page if you don't mind.

Rick

You're welcome to use my "crude" speed formula. By the way, the example wasn't for my 80 (I wish!). I can't remember offhand what numbers I used -- either an R1 or a FZR600. It's been a while. My 80 runs a tick over 89 mph in 6th gear with the Streets of Willow gearing on it (both using the formula and the radar gun). Now if I could just get a few more ponies.... Thanks again for the very informative web site.

Pat

I thought those numbers were kind of high for a 80 cc bike - but I thought it may be possible if the rest of the gears were very closely spaced. The last street bike I rode was a RZv500. I had to slip the clutch to about 50 mph or it didn't like it at all. I can remember it reaching well into the triple digits with just a single gear change.

Eighty nine MPH sounds fast for that bike. How fast is the competition going anyway? Are you getting smoked down the straights or off the corners? I last raced at Willow in 1982 - ugh... I'm getting old...

Rick

Don't feel bad. The last time I rode the big track at Willow was in '85, which was a season after I was racing an RZ500 actually. We ran the 24 hour there in '85 on a 600. We're all getting old. That's why I race 80's now. Much more fun with less all-out go-for-blood competition, and when you fall down, you usually get back up and keep going. I'm the current class champion, but the only guy running what most people would consider a "dirt bike" (see www.wmking.com/yz802.htm). Everyone else is running the RS125 or TZ125 chassis with an 80 motor. So at 6'1" and 200 pounds, I lose a lot in aerodynamics to the little guys on the fully faired bikes. Another reason I need hp.

Even with the current motor, I've got plenty of mid-range, and on the smaller tracks I have no problem. Plenty of pull off the corners. The only place I'm really hurting is Streets of Willow, where the long front straight allows the guys with horsepower to pull me up the hill (they've got about 4-5 mph on me at the end of the straight--not much I can do about the aerodynamics, or at least that I want to do, so I have to resort to motor). I can reel them back in in the back section, but they get away again down the straight. After five laps or so, they gain enough on the straight that I can't make it up in the 'infield' anymore. So my goal is to build a top-end-only motor for Willow, and keep my other motor for the smaller tracks.

Thanks again,

Pat

Very nice pictures and web site you've got there. The first thing I thought when I saw the bike was that it sits very high. Even with the suspension mods you made it seems like you're pushing more wind and perhaps not cornering as fast as you could if the bike were lower to the ground. This may be deceptive though since it seems like your bike is lighter - it may not matter as much. After looking at the pictures of the different races it was easy to notice the other bikes are putting down more tire to the track as well - their tires are wider and (perhaps) shorter.

Having said that about cornering, I'm sure you know that you'll gain more by going faster in the fast sections of the track than going faster in the slow sections - maybe that's why you're looking for more top end. I remember many a Yamaha 500 cc (GP) rider looking for more on top when chasing the much faster Honda's down the straights. It could take a complete lap to gain back what was lost during a run down the straight (if it happened at all). One way Kanamoto <sp> could keep the ill handling Honda out front was to give it a brutal top end and pray for tracks with long straights! It seems Yamaha was never willing to compromise the lower speed handling to favor the top end. They just relied on riders with bigger balls to ride them deeper into the turns, brake later and get on the gas earlier to make up the deficit. There were years when it paid off.

Since Bill's pipes did your engine work I assume you told him your intention for the engine - road racing. Otherwise you'd likely get a motocross pipe - and that kind of pipe favors the mid or upper mid over the top. As you know motocrossers need a wide power spread - you don't. I know Bill's can make you a custom pipe and port for additional high RPM power. Perhaps just cutting the barrel for a few degrees of additional exhaust timing would help. More exhaust area means more high RPM power.

Other than that, you know the Zen masters might say "Feel lighter." It has been proven that one can overcome the heat of the desert by visualizing ones self being cooler. The reverse is also true - it can be done in cold situations and visualizing a warm place - I wonder if it would help to visualize ones self lighter (and more aerodynamic) as well - I know it couldn't hurt :)

Rick

- I never heard from this fellow again, I wonder if the Zen line was too much.

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