hercalmighty Posted August 28, 2013 Report Share Posted August 28, 2013 Hey. I just wanted to know if any of you guys with PVs have cut them to match the exhaust port. I have a feeling someone port my cheetah cylinders and matched the block offs but didnt touch the PVs. So now my PVs dont open any where near enough to match the exhaust port. The thing runs great up top with the block offs but like crap down low. With the PVs the thing has a ton of bottom but goes flat on top. Yes, the PVs are opening and closing. Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted August 28, 2013 Report Share Posted August 28, 2013 You can definitely and should get them done. Might be a builder who can match the PV's to the block off pieces so you don't have to tear down. But ultimately your best result will be to take it apart and match them. Quote Link to comment Share on other sites More sharing options...
lms1977 Posted August 28, 2013 Report Share Posted August 28, 2013 Yes you need to match them take the springs out of them push them up scribe a line and grind them down.. when it was ported did they make the width real wide? How much area is exposed on the sides of the power valve blades? Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted August 28, 2013 Report Share Posted August 28, 2013 Yes you need to match them take the springs out of them push them up scribe a line and grind them down.. when it was ported did they make the width real wide? How much area is exposed on the sides of the power valve blades?Just to be a bit more specific, you would scribe from the inside of the cylinder as well as the exhaust flange side. It will have a contour if done correct. Quote Link to comment Share on other sites More sharing options...
hercalmighty Posted August 28, 2013 Author Report Share Posted August 28, 2013 I'm not sure how much bigger they ported these cylinders. I bought them this way. I tried measuring them compared to the super cub porting layouts that are posted on CP's website. If I go by those measurements they went pretty big. There is quite a bit of blade exposed when the PV is fully opened. I figured that I would use the blockoffs as a template. Yes, I do know that I have to match the curve of the exhaust port. I was seeing if anyone has done it themselves. I do my own case matching and thought it wouldn't be much different to match the PVs to the block offs. Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted August 29, 2013 Report Share Posted August 29, 2013 If you can handle a simple case mod then I would say go for it. It's definitely doable. God speed, and report back with results. Quote Link to comment Share on other sites More sharing options...
camatv Posted August 30, 2013 Report Share Posted August 30, 2013 match the pv's for sure. BUT you will loose bottom end with the lesser pv length.. you can make the pv flow better and still have the bottom you want and have now, it all really depends on how the exhaust was ported. certain shapes in the port work excellent but the have to work with the valve. most times only an as cast cylinder can be done the right way ( or at least the way i do them) most people WAYY overport to make the cylinders work and that leads to the pv's not working as optimal as they can. if you can measure your down pv port duration you should be able to get a before and after number and then can probably make an edjucated change from there. i have numbers that i use the pv hanging in the port when all the way open has lower'd your exhaust port duration. thats the loss in overrev your feeling. Quote Link to comment Share on other sites More sharing options...
hercalmighty Posted September 1, 2013 Author Report Share Posted September 1, 2013 Well i got the PVs cut this weekend and installed. I now have a full range of power and it is working great. nice bottom to top pull. It was a pretty easy fix. Im very happy with the results. Quote Link to comment Share on other sites More sharing options...
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