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[OILCAN1]

WHEN MY BIKE GOES IN THIS WINTER FOR THE ENGINE UPGRADE I AM PLANNING ON NEW CAMS. I AM PLANNING ON USING THE SE 251 CAMS. I ALREADY HAVE THE SE 50MM TB FREE FLOWING AIRCLEANER AND RACE TUNER. CURRENTLY RUNNING COBRA TRUE DUALS WITH SUPERTRAPP SLIPONS. PROBABLY GOING TO GO TO TRUE DUALS(THNDERHEADER OR DD FATCAT). ANY WAY DOES ANYONE HAVE SUGGESTIONS ON COMPRESSION WHEN USING THE 251 CAMS.  PISTONS OR HEADSHAVING? WHAT WORKS BETTER AND WHY?

[skyhook]

10.2 to 10.6 depending on altitude, heat, tuning, available fuel, etc...shaved heads, flattops, and .030" head gaskets are the best way to get there...better swirl and less detonation...the 93cc cvo heads can be welded to reduce volume to achieve the desired compression

[sadunbar]

WHEN MY BIKE GOES IN THIS WINTER FOR THE ENGINE UPGRADE I AM PLANNING ON NEW CAMS. I AM PLANNING ON USING THE SE 251 CAMS. I ALREADY HAVE THE SE 50MM TB FREE FLOWING AIRCLEANER AND RACE TUNER. CURRENTLY RUNNING COBRA TRUE DUALS WITH SUPERTRAPP SLIPONS. PROBABLY GOING TO GO TO TRUE DUALS(THNDERHEADER OR DD FATCAT). ANY WAY DOES ANYONE HAVE SUGGESTIONS ON COMPRESSION WHEN USING THE 251 CAMS.  PISTONS OR HEADSHAVING? WHAT WORKS BETTER AND WHY?

The Thunderheader and D&D Fatcats are not Tru Duals - they are 2 into 1 pipes.  I think you would be happy with the D&D Fatcat...

[OILCAN1]

SORRY TYPO I MEANT 2 INTO 1.  I CURRENTLY AM RUNNING TRUE DUALS AND AM LOOKING AT GOING TO A 2 INTO 1. WHY DO YOU LIKE THE D&D BETTER?

[sadunbar]

SORRY TYPO I MEANT 2 INTO 1.  I CURRENTLY AM RUNNING TRUE DUALS AND AM LOOKING AT GOING TO A 2 INTO 1. WHY DO YOU LIKE THE D&D BETTER?

The Thunderheader typically has a mid range rpm torque "dip" that tuners struggle to eliminate.  D&D Fatcats generally produce a nice smooth torque curve when matched with a good torque producing cam...

[OILCAN1]

OK I'm with you on the D&D pipes, what are your thoughts on compression? I'm trying to figure out wheter to put SE 10.5 pistons in it when it goes in for the upgrade.

[RedDevil]

I have the Vance & Hines Pro Pipes on my Street Glide and they perform very nicely with the Heavy Breather.  Good low and mid torque.  As you can see by signature below (V&H on the SEUC also), I'm a little partial to Vance and Hines.  

  

[skyhook]

the 10.5 dome pistons are definitely the cheapest/easiest way to get compression...the cometic .030" head gasket is a good idea checking clearances of course

[sadunbar]

OK I'm with you on the D&D pipes, what are your thoughts on compression? I'm trying to figure out wheter to put SE 10.5 pistons in it when it goes in for the upgrade.

My thought on compression are likely contrary to most.  I shy away from anything more then 10:1.  Most would probably say 10.5:1 is good to go.  I am just a bit more conservative.  Less compression is easier on valves, valve seats, cylinder walls, rings, ect...  Compression is a cheap (cost) and simple way to gain power, but is a bit harder on the components.

[Mr D]

My thought on compression are likely contrary to most.  I shy away from anything more then 10:1.  Most would probably say 10.5:1 is good to go.  I am just a bit more conservative.  Less compression is easier on valves, valve seats, cylinder walls, rings, ect...  Compression is a cheap (cost) and simple way to gain power, but is a bit harder on the components.

My .02 worth, I agree with Sadunbar, Slight lower compression will yield longer engine life, Are you sold out using the SE 251's ? It is probably the best (Saying Sparingly) bolt in Harley offers But it yields a slight higher compression to get all the buck from that grind. I would look at a grind from Zippers or Head Quarters, They offer great bolt in lower compression using cams with excellent performance, I feel there are better options available to you for cams other than HD's. As far as exhaust..... Fat Cat All the way over Thunderheader, More consistent power curve with the Fatty 
Hope that helps ??

[Rooster]

I had 251's and domed pistons for 10.5-1 compression ran way to hot and pinged like crazy. I would stay with lower compression and flat top pistons on a bagger especially riding 2-up and loaded. Good luck in whatever you choose.

[OILCAN1]

So I understand the basic philosophy of engines and how they work but the technical chit gets a little over my head will the stock pistons work OK with the 251 cams or do I need different ones? And yes I am stuck with using HD parts as my wife is the marketing coordinator for a Harley dealership.

[skyhook]

stock pistons won't work very good with 251 cam...you could use the 10.5 pistons and if concerned about too much compression ask the builder to lower compression to 10.2 by machining the heads or pistons...the most popular cams for cvo 110" are zippers 575 and yuill bros 14

[OILCAN1]

What do you mean by machining the heads or the pistons? If you mill the heads wont this raise compression?

[skyhook]

enlarge the combustion chamber or remove material from the piston dome...don't forget the .030" head gaskets...if it's a dealer they'll try to use thicker ones...no good...if you don't already have the cams, the zippers or yuill will work better with stock pistons