The Next Phase The lower end is assembled, I've discovered the port timing and I've made a port map. I also know the actual compression ratio (UCCR). I can say I'm well into the second phase of this engine rebuild. In this section I'll discover the reed valve's parameters and go over a couple of other things.
The reed valve is defined by the parameters given in the drawing. The reed petal material is fiberglass. Its thickness is .42 mm. The tip lift at the edge of the petal is 10 mm. The radius of the reed valve stop plate is 57 mm. Since the new target peak power range is 8000 RPM this calculates out as the engine having a natural frequency of 133 Hz (8000 RPM / 60 Seconds = 133).   For reed valve data to be entered into software programs it is necessary to explain the terminology used to express the different dimensions of the reed cage. It is represented this way within a couple of software programs. SVCC The swept volume of one cylinder - CC's (cm^3). RDBA The reed block full V angle - degrees. RDTH The thickness of the reed petal - mm. RDNO The total number of reed petals on the reed block. RDPNO The total number of reed valve port windows. RDWD The width of a single reed petal - mm. RDPW The actual width of each reed valve port window - mm. CRAD The corner radius of the window of the reed valve port window - mm. RDLN The distance from the tip of the reed petal to the point in is clamped. RDPL The actual height of a single reed valve port window - mm. RDPS The distance from where the reed valve port starts to the point the reed petal is clamped - mm. SPRD The radius of the reed valve stop plate.
Power Targets I think I can safely design a porting and pipe arrangement, cylinder head and reed valve/carburation combination to achieve my objective using 92 octane pump gas . I will be able to keep the compression ratio at or around 12.25 : 1, with the static compression coming in at about 155 to 160 psi at sea level. This will require reshaping and removing space from the combustion chamber so that its volume (when the piston is at TDC) is about 17.6 cc's - about 4.8 cc's less that it has now. The Yamaha supplied data states that this engine puts out 15.2 ft.- lb. torque at 7000 RPM with a peak horsepower reading of 17 @ ???. I calculated the BMEP (Brake Mean Effective Pressure) for this engine from this data. The Blaster has a BMEP of just 85 psi in stock form. That's very low (read - inefficient). Actually the horsepower and torque figures that Yamaha supplied seem to be a little on the high side - perhaps they were recorded at the crankshaft or sprocket. At any rate this engine is in a mild state of tune. Even when whipping along at 7000 RPM its piston speed is a lazy 2618 FPM (Feet Per Minute). When I increase the engine speed to my new peak power target speed of 8000 RPM the piston speed is still on the low (safe) side at 2992 FPM - I'll let the over rev run to 9000. Going by the maximum 4000 FPM rule, an engine with a short stroke like this can turn as fast as 10700 RPM. I think that's a little high for the 92 octane version of this engine but for the other simulated engine builds using the design parameters I outlined I'll take advantage of this built in feature a little bit more. For the 50/50 pump/race gas engine I'll use 8400 RPM as the target for peak power, with overrev to 9400 RPM. For the High Output 110 octane version I'll use 8700 as the target for peak power, with overrev to 9700 RPM. Without liquid cooling I don't think there's any way this engine can rid itself of heat fast enough to take advantage of its almost 11000 RPM ceiling. I have heard a few good things about the jetting kit that LRD sells for use in stock Blaster carburetors so I decided to give it a try. They asked me a few questions about my Blaster's engine modifications to be sure the jetting they ship me is correct. They were most interested in knowing if it had an after market air cleaner (yes) or a tuned exhaust pipe (uh-huh). I told them I was going to run premix instead of oil injection so that will be a major factor when determining the jet sizes to ship me. I understand the kit consists of a different pilot and needle, and ships with a larger main jet as well. It will be interesting to see how close they can get it. I am interested in putting a larger carburetor on the quad, and in fact have a 34 mm PJ here that is a "take off" from Bill's 88 TRX250R. However I found it impossible to get the larger carburetor into the stock rubber mounting boot. I know I could "hog it out" using a porting tool but those modifications never last very long on intake boots. In time it will crack, suck air and perhaps seize the top end. When I checked around I found a mounting boot that would accommodate the larger flat slide carb but the cost was what I would call prohibitive. With about a hundred dollars going to that single part alone it would not make me happy. I know I can locate or find a cheaper way to mount that piece. I'll search around and see what I can come up with. I removed the oil injector on this engine. Not because it was a bad unit or had any problems associated with it - but because its just easier to carry all the same kind of gas. Jason's dad Bill mentioned a couple of times how it would be easier if all the bikes ran the same fuel setup, so I complied by ordering an oil pump block off plate. I should have taken the 10 minutes it would take to make the darn thing but since I had LRD on the phone and they had some all made up I told them to send me one. A couple of weeks ago I was talking with a man I met (Gary) through the Internet who just happens to be a two stroke engine builder about my need of dynamometer time when this project is finished. I need to be able to test these design parameters. I talked to him about securing some time on his dynamometer which he uses primarily for motorcycles. I'm unclear whether we will be able to run the Blaster on it or not (at this point) because it hooks up to the rear sprocket of a motorcycle for its testing procedures. We just don't know if it will work or not - but we'll give it a try. It was during this conversation I mentioned that I would love to test the stock carburetor and the larger 34 mm carburetor for peak power output. Gary thought it would be worth testing. We also talked about the possibility of adding auxiliary boost ports to the intake side of the engine. He thought it would be very interesting to test this engine before and after the addition of these holes. I agree. I have seen a few Blaster barrels that were ported for this type of power output and it seems like it would not be a bad idea to add them - especially since those who port these engines on a day to day basis are adding these ports (surely they must be backing up their work with dyno numbers). I agree with Gary that these modifications should be tested, but given the type of project this is and the amount of time and money available to complete it, I doubt there will be time enough to test all the things I would like to. I was also talking to someone else a few days ago (or was it email) about these auxiliary ports. It seems that some people are taking a heliarc welder to the outside of the barrels to build up the material in the area the holes get drilled so they can make them larger. I won't be adding any aluminum to this barrel but I do plan to add the ports. Yesterday I received an email from a man named Jeff who noticed my discovery of the piston position when at BDC in relation to the port windows - the piston is not completely uncovering the ports. To quote him, he said " In the late 80's and early 90's it was found that this, I'll call it overlap, helped in reducing the under vortices that are created when gases flow up, around and out into the cylinder area." He also went on to say that "This is documented in S.A.E. research papers. If I remember right the gases adhere to the 'step' rather than form a vortex. I can look up the paper number if you need it." I'll mail him back about that because I'd like to read more about it and its application. Though this engine has quite a bit of port time/area it will certainly need a boost to get the additional power I'm shooting for - I don't think widening the ports will do it alone, it seems like the ports will have to be raised as well. I'll have to run the numbers through the software to see what combinations I can come up with that will lead me toward my goal. In the mean time I'll measure the ports dimensions the best I can so I can enter the data into the software programs.   The vertical port walls look like this. I entered the data I collected after measuring the Blaster vertical divider walls onto my little drawing. Some of the software programs will accept data like this to help calculate the amount of port area.
To measure the reed cage I needed the help of these tools. The intake boot has a "boss" which can be drilled for the addition of a boost bottle. That's another thing the two-stroke software can do for this engine.	Yes it is possible. Two monitors, both platforms (Mac & PC) running from within my Power Mac. At the top of this page is the reed cage picture I just drew - shown here on the left monitor. I'm getting ready to run some numbers on the PC.

Date Last Modified: 8/8/99
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