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  #11  
Old 30th June 2008
jmr1283's Avatar
jmr1283 jmr1283 is offline
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Quote:
Originally Posted by aswracing View Post
Small shots of nitrous, say 50hp and less, for relatively short periods of time, like drag racing, don't really require a reduction in compression. Just make sure it's jetted rich enough and you take out some timing. There are ignitions available that will retard the timing when you're on the button.
alright good. now for a another ?, You would though still have to set ur ring gaps, for nitrous. how much % wise of horsepower would u lose while not on the juice? if im wrong please correct me, but isnt it like 3%.


What you're trading off with 15 degree versus 30 degree is squish area vs. dome height. To get enough squish area at 30 degrees to make a real good chamber, you have to raise the dome height a lot. Well, that tends to raise compression. So most of the time, we do 30 degree on race motors and 15 on street motors.

The caveat here is that many aftermarket heads have a fair bit more volume. And you're going for 11 to 11.5:1 anyway. So you may well be able to get a 30 degree in there at a streetable CR and with a good surface area. Depends on the heads.

xb heads

Personally, I would cut them at 15 and make the measurements and run the numbers and then decide.

Well nrhs is gonna have them soon. The only problem is i have 15 pistons already. so if its not gonna do much for me(curbin detenation) id rather stick to the 15's. but if theres a lot of gain. then ill have to.


That's an excellent cylinder, I've used them on multiple builds (Axtell sells the same casting, but they do the machine work and put their name on it). I'd run'em. If you were doing a full-on race motor then yeah, a full cast iron would be better. But that cylinder will work fine on a street bike.
Dan told me the same thing actually. i just wonder longevity.but both u and dan say go with them. that means i go with them.
great stuff aaron. with ur help this motor is gonna rip. oh and any preferred nitrous system.
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  #12  
Old 1st July 2008
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aswracing aswracing is offline
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I wouldn't worry about slightly larger ring gaps costing you power off the bottle. You may get an additional 1 or 2% on your leakdown tester but I'd be real surprised if you can actually find that on the dyno.

What pistons are we talking about here? The 3-13/16 bore Hurricanes that are 15 degrees all the way to the edge and dished in the middle? I can't really tell you if they can be made to work at 99" under an XB head at 11.5:1, without understanding the dome volume. I can tell you that with a motor that size, and a head that starts out with a chamber that small, it's not a given that you can make that work. But if you know about the dome, we can work it out and I can tell you.

If you don't know the dome volume, you (or NRHS) can measure the 1" down volume. Simply pack some wheel bearing grease around the top ring (leave the second and oil rings off), put the piston in the bore 1" down (to the base of the dome), and fill it from a burrette. You can then do the calculations with my CR calculator ... http://www.nrhsperformance.com/nrhscalculator.shtml ... and figure out what chamber volume you need to get to your target CR. An XB head at 3-13/16 bore and big valves can be done anywhere from about 70cc to 80cc, getting outside that range is tough.
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  #13  
Old 2nd July 2008
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jmr1283 jmr1283 is offline
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Quote:
Originally Posted by aswracing View Post
I wouldn't worry about slightly larger ring gaps costing you power off the bottle. You may get an additional 1 or 2% on your leakdown tester but I'd be real surprised if you can actually find that on the dyno.

good stuff, glad to know. So lets say if i dont end up using nitrous rate away, and say never use it. but want to be prepared. and be able to. what would u suggest. set it up, just in case(sinse its not gonna do anything to power or longevity) or make a decision either way. this bike will be more street then strip(suspension, etc) so if im at 130 hp and shot the nitrous then im at say 170hp whats that gonna do with street/strip tires. is it worth the money if im not gonna be able to use it. decisions decisions

What pistons are we talking about here? The 3-13/16 bore Hurricanes that are 15 degrees all the way to the edge and dished in the middle? I can't really tell you if they can be made to work at 99" under an XB head at 11.5:1, without understanding the dome volume. I can tell you that with a motor that size, and a head that starts out with a chamber that small, it's not a given that you can make that work. But if you know about the dome, we can work it out and I can tell you.

i can give u the parts # from zippers,
9662ps
zippers h-d dish dome-.095"
0122230/01 s572/w731 ,or

part # 521-380, this comes of the green sticker, the first list is white, and looks newer. the person that i bought this motor and kit from said, they would run at 12.0 to 1 when u cut the angle squish band.(seems to me it would be more) hope this helps


If you don't know the dome volume, you (or NRHS) can measure the 1" down volume. Simply pack some wheel bearing grease around the top ring (leave the second and oil rings off), put the piston in the bore 1" down (to the base of the dome), and fill it from a burrette. You can then do the calculations with my CR calculator ... http://www.nrhsperformance.com/nrhscalculator.shtml ... and figure out what chamber volume you need to get to your target CR. An XB head at 3-13/16 bore and big valves can be done anywhere from about 70cc to 80cc, getting outside that range is tough.
the only problem is the cylinders are unfinished, so it woudl have to happen after the cylinders been honed. and for me to do it id have to wait to get them back so that wouldnt work because head work and stuff.
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  #14  
Old 30th July 2008
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Originally Posted by jmr1283 View Post
I guess ill just stick to my original idea of a sportster frame. I think im goin to cut out the back bone and weld in a new one that gives more room for this type of motor.
Kinda late but maybe not and it may help another.

I would not raise the backbone I would lower the engine. This will give you a lower center of gravity. The down side of this though is if you are using shocks you will have to watch the swing arm angle. Using struts or a hardtail kit would negate that issue though.

You can lower the motor by making stepped sleeves that fit inside the tubes and extend them the needed amount.
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  #15  
Old 31st July 2008
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jmr1283 jmr1283 is offline
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havent thought about that. most people ive seen have just raised the back bone up. this is goin to be a street drivin bike so taking away ground clearence might become a problem. thats a great idea though rick
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  #16  
Old 8th June 2013
Peterson Peterson is offline
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If you love something or not, but don't forget the functional working of part that you want to change it. As in some cases, the replaced part don't fit as the older one. Hope you don't mind it.

racing accessories
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