High compression pistons vs. screamin' eagle heads
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1st Gear
Joined: Oct 2007
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High compression pistons vs. screamin' eagle heads
I am getting ready to install an andrew EV27 cam in my 94 evo (just turn 10k miles). Many people have said it is just as easy to remove the rocker boxes as it is to utilze the adjustable pushrods. With that said, I already have my tank off ready to go that way. My question is, at that point I've already anticipated removing a portion of the top end, should I just spend a few more bucks and get new heads or HC pistons? I've heard a lot of good things about the wiseco pistons (10:1) .............how much more would be involved to add the new pistons? This sounds pretty affordable compared to heads. I would think the combo of cam and pistons would provide a nice power increase (hopefully around 75HP) while mantaining good reliability.Thoughts?
Road Master
Joined: May 2007
Posts: 851
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From: Mitchellville, Ia.
RE: High compression pistons vs. screamin' eagle heads
That's a good piston, I've used a lot of them. Set the quench while your at it (.030" to .035") to diminish pinging and cool things down. Better to rework you heads rather than buy new.
Tourer
Joined: Dec 2007
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RE: High compression pistons vs. screamin' eagle heads
Well if money is no object then spend away, how fast to you want to go!! The EV27 IMHO is the best cam for an evo engine. It can be a little noisier with it's fast ramps but it makes such a wonderful torque curve. It makes power for the real world not the bench racing type! Since gas is only getting worse I don't know if I would go with 10:1 pistons. I would ask around your area for a good engine builder that understands cam timing, compression, and head flow as all of these need to work in concert. Putting aftermarket heads designed to make 140+ HP will have such big ports that your EV27 cam will be lost. A good engine builder would take your stock head and probably enlarge the valves, increase flow to match the cam so you can pack the cylinder quickly for more low end torque. A nice 9.5:1 ratio piston with .030" head gaskets would give you roughly 170 to 190 cranking pressures which will be fine on pump gas. On an electra glide sport I ran 9.8:1 compression, flowed heads with larger valves and EV27 and dyno'd 76 HP and 81 ft. lbs. torque but what was nice was the nice flat torque curve. This bike would pull the front end in three gears although third came up more because of bouncing it up but hey, there was daylight under that tire!! Oh, and I was using a stock carb and getting 46-48 mpg! I went with the compufire high compression ignition and dual plugs which will start a whole new argument over their worthyness on an evo but no other bike I have owned started easier or ran as smooth.
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1st Gear
Joined: Oct 2007
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RE: High compression pistons vs. screamin' eagle heads
see that is the thing.........money is an object. The pistons seem very affordable. To a novice like me it seems like a fair amount of bang for the buck. I guess my question should really have been how much more labor/time is involved to install pistons during a cam change knowing that I will have the rocker boxes off? Obviously the existing cylinders would need to be honed but how difficult is it to pull them off?
Tourer
Joined: Dec 2007
Posts: 265
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From:
RE: High compression pistons vs. screamin' eagle heads
Until you have enough bullets to do the heads and pistons I would leave them alone for now. The EV27 will help out your stock engine and you will have that part out of the way. When you get more cash then I would go ahead and budget for some head work and pistons etc. You can pull the rocker covers and the rockers off without removing the lower rocker box. This is pretty simple and quickly done. If you do get into the heads then change the valve guide seals to spring loaded viton seals as the HD seals are junk. Going to bee hive springs will also make it a little quieter but as I said, until you have the cash to do it right I would just do the cam for now.
Road Master
Joined: Jan 2006
Posts: 1,221
Likes: 40
From: Chester NY
RE: High compression pistons vs. screamin' eagle heads
As other said. EV27with a compresion bump, setting squench, a qaulity valve job, you will love the bike again. This is all i ever do to evos. Next one i have coming in will gett a woods 6 stick to compare to.
Cruiser
Joined: Dec 2007
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From:
RE: High compression pistons vs. screamin' eagle heads
You may want to consider, if your pulling your heads to replace your base gaskets I am in the procsess of doing what you are, tore my 94 Heritage apart yesterday. Will do the heads just clean up the stock pistons replace the base gaskets and change cam, my cylinders looked fine 28,000 miles I will end up around 9.5 -1 compression when finished. Lot of good info here though.
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1st Gear
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RE: High compression pistons vs. screamin' eagle heads
thanks all - it doesn't sound like it istalling the pistons is an obvious choice that would only take a few more minutes to do while changing the cam.
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Tourer
Joined: Feb 2008
Posts: 383
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From: Richmond BC.
RE: High compression pistons vs. screamin' eagle heads
In theory pistons are fairly easy to install but before doing that you need to check your piston to wall clearance, then gap the rings give it a quick hone to break the glaze. If your barells are worn at all then you will have to get oversize pistons which means your barrels need to be bored make sure you have the machine shop use torque plates to keep the barrels true. The pistons are marked front and back plus make sure the orientation is correct there are many different methods some have an arrow to the front some to the cam etc etc. The rings also have an up and down to them some with a dot some with a bevel inside also the top and second rings are different but easy to get mixed up then staggering of the gaps not to the front or rear. Bottom line get all the instructions make sure you understand them clearly and if not get someone who knows to help you. When taking off the heads make sure you undo the head nuts evenly follow the torque sequence when taking them off it's just as important as when you torque them, really easy to damage a stud. Clean all of the surfaces with Laquer thinner clean the barrels with hot soapy water and rinse well to get all the metal out of the inside then coat with oil right away so they don't rust. These are just some of the steps. Allow yourself some time and do it right then it will last for years.
Stage III
Joined: Mar 2010
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Any of you guys still around?... I'm looking at doing the same mods to my 87 Evo... SE heads andrews ev27 cam but was told to order 9.5:1 pistons... according to Wiseco's site the stock 8.5:1 pistons will give me 9.5:1 with the SE heads.. which I have read everywhere... but vtwinperformance.biz calls for 10.5:1 wiseco pistons for the SE heads and I've been told and read this will lead to starting issues or the need for reliefs....
But my buddy helping me with the build keeps telling me to order 9.5:1 pistons. is he confused ???(JE makes them) If stock 8.5:1 with SE heads will raise it to 9.5:1 will 9.5:1 pistons be raised to 10.5:1 with the SE heads?
someone help me settle this argument ????
Thanks
But my buddy helping me with the build keeps telling me to order 9.5:1 pistons. is he confused ???(JE makes them) If stock 8.5:1 with SE heads will raise it to 9.5:1 will 9.5:1 pistons be raised to 10.5:1 with the SE heads?
someone help me settle this argument ????
Thanks