fox_forma Posted February 14, 2008 Report Share Posted February 14, 2008 I have a dune port on my cylinders and I was going to combine it with my coolhead that has 18cc domes. Once I put it all together I was running into issues with the coolhead leaking and thus decided to go back to the stock head. Now with the coolhead I had just over 150psi in each cylinder with the dune port along with +4 timing. I thought this was low for 18cc domes but I guess the port work really dropped down the comp readings. With the coolhead leaking and just being a PITA I decided to just bolt up the stock head and now i'm reading around 110psi in each cylinder. Once again I imagine its due to the port work. I would like to get my compression up a little more so should I just go with getting my head milled or possibly go with a newer design cool head that uses the stock studs as mine was the one that was 2 pieces and used the extended studs. Plus I just didnt like the design of that cool head, to many o-rings and issues. Will there be any real big factor running a cool head with smaller domes vs getting the head milled some? Also how much should I mill it? Quote Link to comment Share on other sites More sharing options...
dajogejr Posted February 14, 2008 Report Share Posted February 14, 2008 I have a dune port on my cylinders and I was going to combine it with my coolhead that has 18cc domes. Once I put it all together I was running into issues with the coolhead leaking and thus decided to go back to the stock head. Now with the coolhead I had just over 150psi in each cylinder with the dune port along with +4 timing. I thought this was low for 18cc domes but I guess the port work really dropped down the comp readings. With the coolhead leaking and just being a PITA I decided to just bolt up the stock head and now i'm reading around 110psi in each cylinder. Once again I imagine its due to the port work. I would like to get my compression up a little more so should I just go with getting my head milled or possibly go with a newer design cool head that uses the stock studs as mine was the one that was 2 pieces and used the extended studs. Plus I just didnt like the design of that cool head, to many o-rings and issues. Will there be any real big factor running a cool head with smaller domes vs getting the head milled some? Also how much should I mill it? What is your elevation.... With 18cc domes and no porting...fresh motor...it should be high 180s low 190s at or near sea level. Porting may drop that 10 PSI or so...but a dune port "Shouldn't" drop down your compression that much. A very aggressive drag port could lower it, but probably still not that much. Did you check squish? What kind of compression tester are you using? Dune port shouldn't lower it that much...... Do yourself a favor, call Dave Noss @ Noss machine. See if he can help you get the head sealed. Normally, it's a pinched Oring, or you need a dab of RTV on the nut/studs to get it to seal. I had problems getting mine to seal, but to be 100% honest I never called Dave to try and rectify it....give him a shot. Did you get a fresh bore, did you get new pistons, have you checked clearances, have you check ring end gap? Quote Link to comment Share on other sites More sharing options...
Wildcardracing Posted February 14, 2008 Report Share Posted February 14, 2008 You're probably close (with porting and 18cc domes) to where your compression should be. I run 18's on my bike at 5000' with porting and am in the 145psi range. My bike had 100psi even with the stock head. Could be a difference in comp guages too, just as long as both cylinders read the same. The elevation there is around 3000' right? Quote Link to comment Share on other sites More sharing options...
00tbanshee Posted February 14, 2008 Report Share Posted February 14, 2008 (edited) if you don't want to mess around with the cool head sell it and get your stock head re cc'ed.i ran a stock head redone by rudy kurts 2 yrs ago and last season ran a stock head redone for my 4mil from kevin.never blow any head gaskets on either one.loved them.also the one rudy did was cut for 19cc and ran 185 compression with it Edited February 14, 2008 by 00tbanshee Quote Link to comment Share on other sites More sharing options...
dajogejr Posted February 14, 2008 Report Share Posted February 14, 2008 You're probably close (with porting and 18cc domes) to where your compression should be. I run 18's on my bike at 5000' with porting and am in the 145psi range. My bike had 100psi even with the stock head. Could be a difference in comp guages too, just as long as both cylinders read the same. The elevation there is around 3000' right? No...something else is wrong. Mesa, AZ is 1200 feet... http://en.wikipedia.org/wiki/Mesa,_Arizona Quote Link to comment Share on other sites More sharing options...
Wildcardracing Posted February 14, 2008 Report Share Posted February 14, 2008 No...something else is wrong.Mesa, AZ is 1200 feet... http://en.wikipedia.org/wiki/Mesa,_Arizona My bad, thought they were higher. Wonder if he held the throttle wide open for the test, part that throws me is "110 in both cylinders" usually when u loose compression it's in one or the other not equally. Quote Link to comment Share on other sites More sharing options...
dajogejr Posted February 14, 2008 Report Share Posted February 14, 2008 Hey...no prob. I'm from MI...so I had no idea, had to look it up myself. That bike will run a TON better w/ 150PSI than 110, but I think there is a different problem...something isn't measuring up. A typical dune port might drop static compression a few PSI, maybe up to 10...not much more than that though.... Quote Link to comment Share on other sites More sharing options...
fox_forma Posted February 14, 2008 Author Report Share Posted February 14, 2008 it been a real pain lately to really even wrench on the bike due to several things but figured I would throw it all back together and see what happens. As for the tester itself, I forget the brand but its a fairly good one and it has always been correct on my previous bikes so I don't think the tester is the issue. Both cylinders are reading exactly the same and everything looks good in the cylinders. I also forgot to mention I haven't even ran the bike yet due to the cool head issues and just waiting on other parts so I also assume the rings will seat once ran through for a little. I poured a little 2t oil in the cylinders to try and seal them up for the testing that way but who knows. The cylinders look good and still have the cross hatches in them but measurements haven't been taken. Haven't checked the squish yet, maybe tonight or this weekend if I can make time. I was reading a bunch of other threads and topics on compression and came across a few where some people were in the same situation with new port work and there compression dropped a good amount. If I do stick with the cool head I am selling this one and going with a low profile one which uses the stock studs, I'm tired of changing out those damn studs anymore so its either new head or machine my stocker. Considering a stock bike makes around 125psi compression, with added port work couldn't that bring it down to about where I'm at now with a stock head? I'm about to start over and sell everything and just port my stockers and go from there. Quote Link to comment Share on other sites More sharing options...
Wildcardracing Posted February 14, 2008 Report Share Posted February 14, 2008 it been a real pain lately to really even wrench on the bike due to several things but figured I would throw it all back together and see what happens. As for the tester itself, I forget the brand but its a fairly good one and it has always been correct on my previous bikes so I don't think the tester is the issue. Both cylinders are reading exactly the same and everything looks good in the cylinders. I also forgot to mention I haven't even ran the bike yet due to the cool head issues and just waiting on other parts so I also assume the rings will seat once ran through for a little. I poured a little 2t oil in the cylinders to try and seal them up for the testing that way but who knows. The cylinders look good and still have the cross hatches in them but measurements haven't been taken. Haven't checked the squish yet, maybe tonight or this weekend if I can make time. I was reading a bunch of other threads and topics on compression and came across a few where some people were in the same situation with new port work and there compression dropped a good amount. If I do stick with the cool head I am selling this one and going with a low profile one which uses the stock studs, I'm tired of changing out those damn studs anymore so its either new head or machine my stocker. Considering a stock bike makes around 125psi compression, with added port work couldn't that bring it down to about where I'm at now with a stock head? I'm about to start over and sell everything and just port my stockers and go from there. That explains a lot right there, once your rings seat you'll pick up 5-10psi and it'll then be around 120 with the stock head. Loosing 5lbs with a port is deffinately not unheard of. As for your head ?, just have the stocker milled and rechambered...It will do the same thing as a cool head just wont look as nice. Quote Link to comment Share on other sites More sharing options...
fox_forma Posted February 15, 2008 Author Report Share Posted February 15, 2008 (edited) I was compression testing it before even firing so I knew what fuel to use, didnt want to go in blind with just premium unleaded and have issues. Looks like the head will be dropped off tomorrow for some work. How much should I ask for to get shaved off? Edited February 15, 2008 by fox_forma Quote Link to comment Share on other sites More sharing options...
Snopczynski Posted February 15, 2008 Report Share Posted February 15, 2008 (edited) Exhaust port height, elevation, and base gasket thickness will effect compression. As well as having a warm engine, accurate gauge, and holding the throttle wide open. Edited February 15, 2008 by Snopczynski Quote Link to comment Share on other sites More sharing options...
Wildcardracing Posted February 15, 2008 Report Share Posted February 15, 2008 I wouldn't just have joe-machinist do my head, have a builder who knows how to chamber the domes properly do it. If you're just having it milled off then no more than .020". You won't get much gain unless it has more milled and is rechambered. Maybe 130 psi. Quote Link to comment Share on other sites More sharing options...
fox_forma Posted February 15, 2008 Author Report Share Posted February 15, 2008 I wouldn't just have joe-machinist do my head, have a builder who knows how to chamber the domes properly do it. If you're just having it milled off then no more than .020". You won't get much gain unless it has more milled and is rechambered. Maybe 130 psi. I didnt plan on having just any machinist do the work, next to my work is a shop that the guy specializes in Banshee's, at least thats all he mostly has in his shop and they aren't your normal stockers so I'm sure he is trust worthy. Obviously I will discuss everything over with him first so it gets done correctly. He's always had parts I needed and has always been helpful in the past so hopefully he comes through on this as well. I just want this damn thing to run. Quote Link to comment Share on other sites More sharing options...
IrideA250R Posted February 15, 2008 Report Share Posted February 15, 2008 I've seen 2 compression gauges vary by as much as 25 PSI before too on the same engine 5 minutes apart.. Just something to keep in mind....not all gauges are created equal. Quote Link to comment Share on other sites More sharing options...
fox_forma Posted February 15, 2008 Author Report Share Posted February 15, 2008 I've seen 2 compression gauges vary by as much as 25 PSI before too on the same engine 5 minutes apart.. Just something to keep in mind....not all gauges are created equal. This I fully understand, but my gauge has always seemed to be accurate with my other bikes so I dont see why it wouldnt with this one but I guess to be safe I will track down a second gauge to verify. Quote Link to comment Share on other sites More sharing options...
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