DragBikeMike
Serious Thumper
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SuzukiSavage.com Rocks!
Posts: 4166
Honolulu
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This is the first in a series of reports outlining a big bore engine project. The project will incorporate a 97mm bore with a modified cylinder head (my Stage III). I will be building a spare engine so I can simply swap out engines and test.
I intend to judge the initial results based on cranking pressure, ease of starting, required fuel, drivability, audible noise, operating temperatures, seat-of-the-pants power, and timed acceleration runs. If the results of the initial evaluation are good, I will continue to run the big engine to see how reliable it is.
The foundation for the big bore engine is a used lower-end assembly I purchased on eBay. It is a five-speed unit form a 1997 LS650. Getting that lower end to Hawaii was an interesting project in itself.
The cylinder is another eBay treasure. I have no idea how old it is, but it was in very poor condition with a scored bore, bent & broken fins, cobby sealing surfaces, and years of baked on crud. It will be matched to a Wiseco 97mm piston assembly, part number 4597M09700 (originally designed for the DR650).
The cylinder head is the take-off from my 2016 LS650. It only had about 3000 miles on it when I replaced it with my Stage II head. It’s in excellent condition and will be a good foundation for the Stage III mods. The Stage III mods will include larger intake valves along with reshaped intake runners, and enlargement of the exhaust port to a full 1.79” to match my Mac header. I will flow test the finished head and post the results.
Target compression ratio (CR) will be 10:1. I expect that combustion chamber volume will be reduced slightly by the larger intake valves. The cylinder will be trimmed or shimmed as necessary to achieve a static CR of 10:1. Low-lift flow will be improved with the Stage III head, so I have chosen the Web 402 cam. It has significantly less duration than the Web 340b (cam I am currently running). The 402 should compliment low end torque. The high end characteristics should remain similar to my current setup due to the enhanced cylinder head flow. It will be interesting to see how it shakes out. The 402 cam requires heavier springs with more travel. Valve guides may have to be trimmed. Valve-to-piston clearance must be verified. The 402 is not a bolt in cam.
I will use acceleration benchmarks from my tight-quench engine and the 94mm Wiseco engine I am currently running. The tight-quench engine was quite a bit faster than the Wiseco pop-top engine. Comparative 2nd & 3rd gear timed runs on the completed 97mm engine should give us a good feel for how the big motor stacks up. Let’s get started.
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