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[tmitchellofpg]

I read that the 05 has 9 to 1 and the 06 has 8 1/2 to 1 compression. Why the difference?  Was the 9 to 1 in 05 causing some kind of problems?
Tom

[Taildraggerdave]

I think the 05's made so much power the MoCo wanted to tame the engine down a bit to keep from smoking the big back tire on the 06's.......

[AUSSIE_FLSTFSE]

I read that the 05 has 9 to 1 and the 06 has 8 1/2 to 1 compression. Why the difference?  Was the 9 to 1 in 05 causing some kind of problems?
Tom

I actually thought that both motors were identical, but after checking the only difference is the actual bare cylinder heads. These heads were a new part for 2006 & must have reduced the CR by a little. Maybe something to do with the EPA. Both motors seem to still make similar power & I think if you rode 2 stock bikes you would not notice a difference in power between them. As far as I know there are no issues with the 05 CR but I also did not think it was 9:1. I believe it is 8.8:1

Cheers
Aussie




GENERAL INFORMATION 
 Manufacturer   Harley-Davidson® 
 
 Model Year   2005 
 
 Model   FLSTFSE Screamin’ Eagle® Fat Boy® 
   
 
 Color   Two-Tone Platinum Mist / Slate 
 
 
 ENGINE 
 Engine   Twin Cam 103B™ 
 
 Displacement   103.0 in.³ 
 
 Bore x Stroke   3.87 in. x 4.37 in. 
 
 Torque   100.4 ft. lbs. @ 4000 rpm 
 
 Compression Ratio   8.8:1 
 
 Fuel System   Electronic Sequential Port Fuel Injection (ESPFI) 
 
 Clutch   Multi-plate clutch with diaphragm spring in oil bath 
 
 Exhaust   Slash down 
 
 DIMENSIONS 
 Length   94.3 in. 
 
 Weight   689.0 lbs. 
 
 Ground Clearance   4.8 in. 
 
 Wheelbase   64.5 in. 
 
 Fuel Capacity   5.0 gal. 
 
 Seat Height   24.7 in. 
 
 DRIVETRAIN 
 Transmission   5-speed transmission   
 
 Final Drive   Carbon fiber belt   
 
 
 BRAKES/WHEELS/TIRES 
 Brakes   Front: 11.5 in. x 0.20 in.
 Rear: 11.5 in. x 0.23 in.   
 
 Tires   Front: MT90B16 72H
 Rear: 150/80B16 71H 
 

[grc]

Not aware of any "real" compression ratio change.  As Aussie noted, the CR never was 9:1, even though many including H-D often rounded the numbers off rather than quote the more precise 8.8:1 ratio.  All big twin cylinder heads were changed between '05 and '06, but that was at the ports (see attachment).

Jerry

[AUSSIE_FLSTFSE]

Not aware of any "real" compression ratio change.  As Aussie noted, the CR never was 9:1, even though many including H-D often rounded the numbers off rather than quote the more precise 8.8:1 ratio.  All big twin cylinder heads were changed between '05 and '06, but that was at the ports (see attachment).

Jerry

Thanks Jerry, I had forgot about the port change. I now remember that because I looked into the 50mm SE throttle body & it was only suited to the 2006 ports.

Cheers
Aussie