Basic 1250 kit
Road Captain
Joined: Mar 2009
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883 heads have shallower chambers than 1200 heads, and the valves are longer to reach them. This puts the valves closer to the pistons to begin with, as compared to 1200 heads, and thus puts you in more danger of piston-to-valve (p-v) contact.
The operative cam specs for assessing your risk are the "TDC Lift" figures. These numbers describe how far the valves are open as the piston passes through top dead center between the exhaust stroke and the intake stroke. The higher those TDC lift specs, the more likely you are to get piston to valve contact. Whenever you run TDC lifts of more than about .200 on either valve, with stock 883 heads, you are taking a chance.
P-V clearance has nothing to do with max lift, as many people mistakenly assume. Max lift always occurs with the pistons well down the bore. It's the TDC lift specs that you have to be concerned about.
The N4's have TDC lifts of .216 intake and .189 exhaust. Although those numbers are totally fine for 1200 heads, in my experience they cause the pistons to kiss the valves about half the time when used with stock 883 heads. Many guys who are using them with stock 883 heads are getting contact and don't even know it, until they take it apart and see the marks in the valve pockets. It's often subtle enough that the only symptom is some excessive noise.
An alternative to the N4's, that's designed for a similar power band but has TDC lifts of .137/.150 and therefore are totally safe for stock 883 heads, is the Feuling 505/515 grind. So if you're looking for that kind of a power band (mid to top end at the expense of bottom end), that's the safer choice.
The operative cam specs for assessing your risk are the "TDC Lift" figures. These numbers describe how far the valves are open as the piston passes through top dead center between the exhaust stroke and the intake stroke. The higher those TDC lift specs, the more likely you are to get piston to valve contact. Whenever you run TDC lifts of more than about .200 on either valve, with stock 883 heads, you are taking a chance.
P-V clearance has nothing to do with max lift, as many people mistakenly assume. Max lift always occurs with the pistons well down the bore. It's the TDC lift specs that you have to be concerned about.
The N4's have TDC lifts of .216 intake and .189 exhaust. Although those numbers are totally fine for 1200 heads, in my experience they cause the pistons to kiss the valves about half the time when used with stock 883 heads. Many guys who are using them with stock 883 heads are getting contact and don't even know it, until they take it apart and see the marks in the valve pockets. It's often subtle enough that the only symptom is some excessive noise.
An alternative to the N4's, that's designed for a similar power band but has TDC lifts of .137/.150 and therefore are totally safe for stock 883 heads, is the Feuling 505/515 grind. So if you're looking for that kind of a power band (mid to top end at the expense of bottom end), that's the safer choice.
Grand HDF Member
Joined: Dec 2012
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From: river
I dont believe youre knocking HP because you now have a stock 1200 Sportster pushing 70ish hp give or take. To each his own!
HDF Community Team
Joined: Aug 2019
Posts: 1,816
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From: Santa Ana, CA
How do you guys know your HP numbers? Dyno? Guess? I have no idea what HP my bikes running at. Heck, I don't even have a speedometer so I couldn't even tell you how fast I'm going at any given time. Ignorance is bliss. So when I get pulled over and the cop asks me "Do you know how fast you were going back there?", my only response will be "No sir, I do not. But it felt pretty fast"
Grand HDF Member
Joined: Mar 2023
Posts: 4,360
Likes: 1,344
From: Westland, Michigan
The Hd generic dyno sheet is conservative but the bike still isn't putting out anything I'd call amazing
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Road Captain
Joined: Jul 2020
Posts: 592
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From: SE PA
How do you guys know your HP numbers? Dyno? Guess? I have no idea what HP my bikes running at. Heck, I don't even have a speedometer so I couldn't even tell you how fast I'm going at any given time. Ignorance is bliss. So when I get pulled over and the cop asks me "Do you know how fast you were going back there?", my only response will be "No sir, I do not. But it felt pretty fast"
To the OP, Aaron's post is about as good as it's gonna get, he's a wealth of knowledge. A friend of mine has those Feuling 505/515 cams in a 1200. They will hit later in the rev range than the stock W cams will. Depends where you want your power. W cams ain't bad for a lot of people, I'd go with the 505/515s if you like to run it hard. The 1250 kit alone will make a dramatic difference coming from a 883.
Last edited by MattLS6; Sep 22, 2023 at 01:27 PM.
Grand HDF Member
Joined: Dec 2012
Posts: 3,782
Likes: 1,202
From: river
How do you guys know your HP numbers? Dyno? Guess? I have no idea what HP my bikes running at. Heck, I don't even have a speedometer so I couldn't even tell you how fast I'm going at any given time. Ignorance is bliss. So when I get pulled over and the cop asks me "Do you know how fast you were going back there?", my only response will be "No sir, I do not. But it felt pretty fast"
Dyno and drag strip for my hp numbers.