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Sportster Motorcycle Motor - Top End Discuss Sportster Motorcycle Top End issues. Rockerboxes, Valves, Cylinders, Pistons, Rings, Lift Rods, etc...

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  #21  
Old 21st October 2011
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This is why I used Cometic gaskets. My bike runs great with n6's, home ported xb's, hybrid exhaust, and S&S. I was just making sure we were all clear about why milling was not going to work for what you wanted. Higher compression yes and squish band change no with milling.
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  #22  
Old 21st October 2011
Turbo Sporty 48 Turbo Sporty 48 is offline
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Ok, .030" or 0.040" Cometics will bump the compression and improve the squish?
Stock are 0.050"?
All I need are the cams.
See how good you guys are!!!
Simple solution and a good outcome.

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Originally Posted by rottenralph View Post
This is why I used Cometic gaskets. My bike runs great with n6's, home ported xb's, hybrid exhaust, and S&S. I was just making sure we were all clear about why milling was not going to work for what you wanted. Higher compression yes and squish band change no with milling.
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  #23  
Old 21st October 2011
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You would want the 30k Cometics but I still think it is a waste of time and money. There is just not that much to be had from a .3 gain in compression. If you are going to pull the head and you really think you need more compression spend the money on pistons and get something closer to 10.5. That coupled with a cam change will give you something you can feel. There is no way I would pull down a good running engine for a third of a point of compression.
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  #24  
Old 21st October 2011
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Quote:
Originally Posted by Sporty 48 View Post
Here is a simple example: http://www.muller.net/mullermachine/docs/squish1.html
and NRHS:http://www.nrhsperformance.com/tech_squish.shtml

Hammer about 2/3 of the way down the page, edge squish band:http://hammerperf.com/xlporting.shtml
Hmm, I'm not sure what you're getting at with the term "edge" squish band. Are you saying there are designs where the squish band happens in the center of the chamber? I haven't seen that, but I have no doubt somebody somewhere has tried it.

In these bikes though, the squish area is always on the sides, i.e. there's one on the spark plug side and one on the pushrod side. From the factory, they are flat (0 degree) to work with the flat top piston. We can angle them, though, and match that to a piston that has an angled dome. The advantage to angling them is twofold: the fuel squeezes out at a more direct path to the flame front, and the shelf is reduced which helps fuel come into and exhaust go out of the cylinder better.

The downside to angling is that for a given dome height, you give up squish band surface area, unless the dome is raised to compensate. That of course generally means more compression. For that reason, 30 degree chambers are generally used on race bikes with high compression ratios. If you go 30 degrees with a short dome, you have very little surface area to the squish band. So for street motors, a shallower angle like 15 degrees is usually preferred.

But angling the squish really does nothing to make the squish tighter. As mentioned, thinner gaskets are the most direct route to that. Milling the cylinder, using thinner base gaskets (or eliminating them altogether),or using a piston with a taller compression height, also accomplish this. Sledge Hammer pistons are made with a slightly larger than stock compression height for this reason.
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  #25  
Old 21st October 2011
Turbo Sporty 48 Turbo Sporty 48 is offline
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Hammer Performance,
What is the simplest way to get 10.0:1 CR, 15 degree squish bands with Harley cast pistons? Plan on using .497 cams.
The rev limiter is set at 6,250 rpm.
I see the ridge around some of your pistons, why?
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  #26  
Old 22nd October 2011
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The easiest way to get 10 to 1 on the late model bikes is to shuffle thinner base and or head gaskets and leave your heads and pistons alone.

I think what you are referring to as edge squish bands are angled squish bands and they are not intended to be used with flat top pistons like those you are using. They are intended for special pistons which have an angle in the dome or crown that mates up with the angle cut in the head. When combined with flat tops they will eliminate your existing squish bands. More than one site sponsor sells 10.5 to one pistons which is pretty much the upper limit of what you can get away with your preferred cam. The aftermarket pistons not only have more compression but they have larger valve pockets which will allow a wider selection of cams. They can be purchased in a flat top or to be used with an angled squish band. It is your engine and your money but I think you are overestimating what a third of a point of compression is going to do for you. Another thing to consider, just because someone got 90 rwhp from an engine like yours with an exhaust like yours and a .497 cam and 10 to 1 compression, don't assume you will. It does not always work that way. There are plenty of guys on here with more cam, more compression, and better heads that have not achieved that.
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  #27  
Old 22nd October 2011
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That would be me. on the cams, ignition, carb, exhaust, and every other part known to man. I also have home ported heads but I am not sure if they are good or not.
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  #28  
Old 22nd October 2011
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You get an A for effort Ralph and as a result of your efforts you have a pretty good idea of how easy it will be to get 90hp with a .497 drop in cam, 10 to 1 compression, and no head porting. Possible but more like a great opportunity for disappointment. In my opinion the EFI bikes give up power pretty easy. 1250 kit, 575 cam, stage 2 heads, decent exhaust, tuning, 100ish hp.
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  #29  
Old 22nd October 2011
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I wanna have sex with RottenRalph's bike. Rocketmangb's bike is beautiful too, but man Ralph's bike is sex on wheels.

Gearheads get a bad rap, you guys are -I LUV XLF!--I LUV XLF!--I LUV XLF!--I LUV XLF!-ing smart. Much respect. I hope I can put the pieces together to understand my machine the way you guys do. I'm trying.

I may be drunk.
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  #30  
Old 22nd October 2011
Turbo Sporty 48 Turbo Sporty 48 is offline
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Maru,
Already said paper hp means nothing. Dynos can print out a lot of B.S., just used that one as an example.
Andrews said in an email to me that 10.0:1, .497 and regular gas was a go.
The hottest cam, the highest compression and that will still burn regular gas if it is required.
The squish band is my little ace in the hole to make it happen.
It could also very well be that as currently configured with high test gas the existing motor will produce more power than the motor with my goals achieved and regular gas.
However, if high octane gas is available, well I should be able to develop a tune to take advantage of that.
Let it also be repeated, I really want that cool loping idle of a slightly warm cam? The .497 does cause the idle to stutter a little. Cool.

Quote:
Originally Posted by maru View Post
Another thing to consider, just because someone got 90 rwhp from an engine like yours with an exhaust like yours and a .497 cam and 10 to 1 compression, don't assume you will. It does not always work that way. There are plenty of guys on here with more cam, more compression, and better heads that have not achieved that.
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