Quote:
Originally Posted by APEmike
I know how to make it happen.
Its a matter of finding the difference in wrist pin height and making up for it with a spacer plate between the block and upper case. Spacer plates are custom, but not expensive. As for boring and replating Nikasil bores goes, I deal with it daily. Its a long-ish process though where I work but its not hard, nor OVERLY expensive.
The other think you need to worry about is engine balance. New pistons dont weigh the same as stock pistons so you will have to get the rotating assembly re-balanced. A gram or two can make a pretty big difference in balance at 13,000 rpm.
Gaskets and a spacer plate are really no trouble at all to have made.
The trick to more power however is all in the head, and our problem is that the valvetrain materials are junk. They werent made for performance, they are cheap, lawnmower grade, welded valve head-to-stem low quality steel junk. I am currently working on trying to find a way to make some real race quality stainless valves, but it is slow going.
The way to go would be to find a real good spring (i know a couple different ones that work), titanium retainers (that nobody makes, yet) stainless valves(working on them), in standard or oversize depending on application, porting from someone who knows what they are doing(my friend/co-worker), some more compression as it is way too low for a modern street motorcycle(JE or Wiseco, pick one for the sticker you like more), and a cam to match the work and what the bike is being used for. Web Cam will be happy to make you a custom grind.
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Mike pin to piston deck (on squish band) is 3.5mm shorter compared to 250's. Comparing stock parts. I measured 250's high comp pistons to have up to 1mm more material on squish depending on their base compression ratio values, could be up to 4.5mm for a 13,5:1 piston
So that can be easily overcome by a base spacer...
Nice idea, I thought so myself, but when I checked thoroughly piston travel, I noticed that a spacer larger than 1-2mm would leave the bottom of the piston skirt go under the block (and I am talking about the 250's short skirted high compression pistons, the 300's stockers are on the limit as they are).
The cylinder block (and most importantly its walls) is of the exact same height while now the piston has a longer travelling distance up and down and I bet that is one of the main reasons their 300 piston design has shorter skirts and still reach the bottom edge of the walls...
Anyway,measuring the 300's open-decked cylinder block wall, I found it to be about 4.5mm thick...
So these observations make me wonder about a couple of things, I hope you can help me understand better...
1. How much overbore do you believe would be reliable for that kind of cylinder wall thickness ? +2mm ? And if only that much, do you believe it is really worth the process ? I mean for the 250's iron sleeves it is probably good value for money (and extra power), but for aluminum nikasil replating on a 300 ?
2. What could be done if the available high-comp, short-skirted 250 short-stroke oriented pistons almost have their bottom tips coming out and under the block walls inside the 300's longer piston travel even without using any base spacer ?
Maybe your answers will help me make a breakthrough with my project, so I am really looking forward to your post, thank you in advance !