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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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  #1  
Old 10th July 2022
DrMotorcycle DrMotorcycle is offline
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Default Cams for a Turbo XL1200H

Well, I've had my Draw-Thru turbo Sportster on 12PSI of boost w/mechanical water/methanol injection for the past month or so and I'm already bored . Check my post history for more information on the bike. A quick summary is it's a Draw-Thru Turbo Setup, HSR42 w/dual thunderjets (one is pump gas, the other is 50/50 water methanol), and a T25/T28 Hybrid Turbo W/Carbon Seal.

Anyways, I knew I'd be at the point of wanting more power pretty quickly coming from (180hp) sportbikes, so I started looking around at the current cam offerings from all of the different companies. Seems to me that if I were to keep it simple, the Fueling Reaper 505/515 is the best all around choice; They can be bolted straight in, they have very mild overlap (26*), 108.5/109 lobe centers, and a 239/248 split duration; is it me, or does this seem like it was almost meant for a turbo setup? Strongly leaning this direction right now.

Andrews n4/.497 SE's Seem too aggressive on the Overlap + Duration for a Turbo setup, N2/N3 Give up too much lift in comparison to the Fueling 505/515, and every other cam past the .500 lift range is going to take some headwork to not be a waste of time (correct me if I'm wrong).

What says you?
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  #2  
Old 23rd July 2022
Turbo Sporty 48 Turbo Sporty 48 is offline
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Default

Check out the 551 cams.
Buel made them Harley adopted them, I think.
Best turbo cam for the money.
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  #3  
Old 24th July 2022
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aswracing aswracing is offline
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Quote:
Originally Posted by DrMotorcycle View Post
Well, I've had my Draw-Thru turbo Sportster on 12PSI of boost w/mechanical water/methanol injection for the past month or so and I'm already bored . Check my post history for more information on the bike. A quick summary is it's a Draw-Thru Turbo Setup, HSR42 w/dual thunderjets (one is pump gas, the other is 50/50 water methanol), and a T25/T28 Hybrid Turbo W/Carbon Seal.

Anyways, I knew I'd be at the point of wanting more power pretty quickly coming from (180hp) sportbikes, so I started looking around at the current cam offerings from all of the different companies. Seems to me that if I were to keep it simple, the Fueling Reaper 505/515 is the best all around choice; They can be bolted straight in, they have very mild overlap (26*), 108.5/109 lobe centers, and a 239/248 split duration; is it me, or does this seem like it was almost meant for a turbo setup? Strongly leaning this direction right now.

Andrews n4/.497 SE's Seem too aggressive on the Overlap + Duration for a Turbo setup, N2/N3 Give up too much lift in comparison to the Fueling 505/515, and every other cam past the .500 lift range is going to take some headwork to not be a waste of time (correct me if I'm wrong).

What says you?
Proper cam selection for a turbo setup starts with understanding the turbo's differential pressure ratio, i.e. how much exhaust pressure is needed to generate how much intake pressure.

Very inefficient turbos have a ratio of 2:1 or greater. You have to really limit the overlap in that situation. But the closer you get to 1:1, the more the cams can start looking like normally aspirated cams. Read Vizard's books, he goes into more detail on all this.

Stock 1994 XL1200 heads (if that's what you're running) nose over on the flow bench by the time you reach .450 of lift. In other words, the valve is far enough out of the way that it's no longer the thing that's constraining the flow. You can continue to lift it farther, but the flow won't increase.

To take advantage of high lift you need bigger valves. Big valve heads, with good ports and a valve job that pushes the valve size, can be set up such that the flow doesn't nose-over until north of .600 lift. That's when it makes sense to use high lift cams.
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  #4  
Old 1 Week Ago
DrMotorcycle DrMotorcycle is offline
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Quote:
Originally Posted by aswracing View Post
Proper cam selection for a turbo setup starts with understanding the turbo's differential pressure ratio, i.e. how much exhaust pressure is needed to generate how much intake pressure.

Very inefficient turbos have a ratio of 2:1 or greater. You have to really limit the overlap in that situation. But the closer you get to 1:1, the more the cams can start looking like normally aspirated cams. Read Vizard's books, he goes into more detail on all this.

Stock 1994 XL1200 heads (if that's what you're running) nose over on the flow bench by the time you reach .450 of lift. In other words, the valve is far enough out of the way that it's no longer the thing that's constraining the flow. You can continue to lift it farther, but the flow won't increase.

To take advantage of high lift you need bigger valves. Big valve heads, with good ports and a valve job that pushes the valve size, can be set up such that the flow doesn't nose-over until north of .600 lift. That's when it makes sense to use high lift cams.
Thanks for the advice. I told my Uncle to give you guys a call about a motor that he's putting together for his Buell S1 that threw a rod. He's doing a (I think?) 90" setup on it and I think I recall that he said he's going to have you guys do the bottom end.

There were some Redshift 585's on ebay that I sent him a link to, as we often do for each other when we see good deals. He bought them . Said he talked with someone at Hammer and Ordered Springs and Adjustable's w/collapse-able tubes IIRC.

I digress. The reason I bring this up is that he also owns an M2 cyclone that he Nicknamed "Psiclone" that has one of my draw-thru turbo setups on it. Since he bought the 585 cams, he now has a set of .497's that were in the S1 as original equipment that need a new home. Pretty sure the plan as of now is for him to pull out his 497's and have me install them in his M2 while I'm doing a top-end gasket swap (bike has 67k miles!). He mentioned wanting to possibly install a set of low-comp turbo pistons, IDK if you have a drop-in solultion or not.


So long story short, I'll be testing the N4's pretty soon on the Turbo Buell M2 fairly soon.
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