Surfrjag Posted August 16, 2014 Report Share Posted August 16, 2014 I like aluminum oxide 36 grit Quote Link to comment Share on other sites More sharing options...
Atomic Monkey Posted August 20, 2014 Author Report Share Posted August 20, 2014 I cut the exhaust tonight and there was an area at the top of the port that was level with the deck surface, starting at the liner to about 1/2" in b4 it turns down. Should I recut that feature into the roof again? Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted August 20, 2014 Report Share Posted August 20, 2014 (edited) Depends. Think in terms of how to get the rings to make as smooth a transition. Mock the cylinder up and physically roll the crank to see what's happening. Plus if it is where you want it now duration/height wise, that will change by removing more material. This may/may not be condusive to the type of power you're wanting. Edited August 20, 2014 by trickedcarbine Quote Link to comment Share on other sites More sharing options...
Atomic Monkey Posted August 20, 2014 Author Report Share Posted August 20, 2014 I'm talking about the roof of the port itself, not the chamfer in the liner. The roof its flat, its got about a 1/2" lead-in before it turns down towards the pipe... maybe it turns the return pulse flat across the piston, and puts it under the fresh charge??? Seems like that could be the theory, then the return pulse would follow the same path the incoming charge does.... maybe. Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted August 20, 2014 Report Share Posted August 20, 2014 Well, if the liner side of things is cool then I'd definitely get the ceiling and floor of the port entry pretty flat. You are correct about it reacting with the charge in that area but you don't nesaccarily need a perpendicular area off the bore for that to happen properly. I definitely have seen good results with the flat floor and roof of the port when it is blended totally straight from chamfer to flange. Quote Link to comment Share on other sites More sharing options...
registered user Posted August 21, 2014 Report Share Posted August 21, 2014 ive seen a few that go in flat and turn down. i never cut the flat part back in. this drawing doesnt appear to go in flat either Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted August 21, 2014 Report Share Posted August 21, 2014 No need for the perpendicular or flat entry point in the exhaust port. The smoother the transition the better. In that CP drawing, do you see the floor where the contour starts to slope down under that letter C. I have even seen that massaged out on the few cubs I've seen. Quote Link to comment Share on other sites More sharing options...
registered user Posted August 21, 2014 Report Share Posted August 21, 2014 i think alot of stuff people do (my self included) looks good on paper but doesnt do much in actuality. like messaging off that floor lip. piston is only at bdc for a very brief moment, remainder of the stroke the piston is above the floor and creating a ledge of its own. doubtful it would matter if you messaged off the floor lip or not Quote Link to comment Share on other sites More sharing options...
Atomic Monkey Posted August 21, 2014 Author Report Share Posted August 21, 2014 Well what I ended up doing was opening up the the port all the way around. I did grind away the bottom lip, and the roof and side have a slight perpendicular lead-in just so I could keep where the port comes throught the liner fairly square. That way when its bored it doesn't really affect the timing. Everything is nice and blended well, I think it turned out well. I'll post up some pics tomarrow! Quote Link to comment Share on other sites More sharing options...
Atomic Monkey Posted August 21, 2014 Author Report Share Posted August 21, 2014 Here's the exhaust, just need to get in there and smooth out all the chatter marks Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted August 21, 2014 Report Share Posted August 21, 2014 Swank Quote Link to comment Share on other sites More sharing options...
registered user Posted August 22, 2014 Report Share Posted August 22, 2014 sweet. used cylinders are cheap enough you can get another set if you go past the point of no return but ive learned its best to make smaller more logical modifications rather than just grinding the fuck out of everything and hoping it works. plus youll learn more along the way Quote Link to comment Share on other sites More sharing options...
Surfrjag Posted August 22, 2014 Report Share Posted August 22, 2014 the other side of the port makes more of a difference. lets see that and the transfer entry's and windows Quote Link to comment Share on other sites More sharing options...
registered user Posted August 22, 2014 Report Share Posted August 22, 2014 (edited) window makes more of a difference than the tunell ? im not sure i could agree with that . without a well shaped tunell , the window meens almost nothing as far as im concearned. i believe this to be even more important with transfer ports. anybody thats been around 2t enngines over the decades has seen transfer ports and all the ports in general evolve over time. alot more science behind it than what people think i would dare guess most 250's back in the day would be lucky to see 35-40hp. all the modern ones are 45-50. theyre more power today because of a few reasons and superior tunell shapes is one of em Edited August 22, 2014 by registered user Quote Link to comment Share on other sites More sharing options...
Atomic Monkey Posted August 22, 2014 Author Report Share Posted August 22, 2014 Well things are definately different behind the windows, especially in the transfer tunnels. Pretty much to direct the flow to where I believe it should go, and to support the little bit of additional displacement. The exhaust was raised and lowered (with the help of a couple of people... Thank You very much!), but not widened much in an effort to keep the motor from being really "peaky". I also opened up and blended the exhaust to the pipe flange. In some respects material removal has been conservative to retain velocity, and in other areas its biased towards higher flow rates to support larger carbs, higher RPMs, etc. This is an experiment, and I'm already planning on getting new cylinders... with what I've learned so far, I don't care for how the intakes are done. Quote Link to comment Share on other sites More sharing options...
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