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bob27s -> RE: Jett Q40 LS (8/30/2007 5:12:01 PM)
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I have not run the LS engine yet myself. But Dub has been working on it for pretty much the entire year.
So far... so good....best I can tell you there. The case is basically the same. Just a differnt rod, crank, pistion, sleeve. Design is rather basic... fabricating this beast is not quite so basic.
Also... worth noting for others..... its not really a 'long stroke' engine. This one is basically a square engine (closer matched bore and stroke). The racing engines have historically been under-square (big bore) engines.
As for the crankcases....
It is somewhat of a black art there... we are not 100% sure why the Q40 engines run better in the casting... parts are the same... ground rpm is generally the same..... its just something "that happens" that Dub stumbed on setting up a practice engine. Clearly it is an interaction of a number of things (fluid dyanmics, thermodynamics, metalergy, geometry, phase of moon, etc). But it is something notible, and repeatable --- so thus the recommendation.
The Q-500 BSE engines do run better. More precise bearing alignment is possible, closer control on tolerances seem to be more of a factor. (since you are not performing a secondary operation to create bores and mating features as you do with a casting). Again.... how much of a difference..... its hard to quantify. You really do not see it in the ground rpm or the way the engine behaves. But a consistant 1 or 2 seconds on the race course is proof enough something works better this way.
Bob
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