11:1CR on 91 octane
#1
02-04-2016 | 10:29 PM
Thread Starter
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Cruiser
Joined: Jan 2016
Posts: 160
Likes: 14
From: North of Denver
SE High Compression Pistons
I just dropped off my heads for some finishing touches and got to looking thru the parts list for the winter upgrade. Once I had the whole list reviewed it dawned on me that really the only thing I won't have touched in the top end or cam chest will be the pistons and cylinders (bottom end stays stock). I gave a gander through the 2016 Screamin' Eagle parts catalog and they have listed a set of high compression pistons specifically for the 103" twin cooled heads (27000007).
Anybody have any actual numbers on the HP/TQ increase from these SE pistons?
Here in CO at elevation 91 octane is premium:
My questions are...Is there a justifiable performance increase & is 91 enough to prevent knocking at the listed 11.25:1 compression ratio?
Other factors:
I put this in the Rushmore category as it is specific to the 103TC models...if it needs moved please suggest.
Anybody have any actual numbers on the HP/TQ increase from these SE pistons?
Here in CO at elevation 91 octane is premium:
My questions are...Is there a justifiable performance increase & is 91 enough to prevent knocking at the listed 11.25:1 compression ratio?
Other factors:
- 2015 FLHTK twin cooled w/ ACR (EZ-start will negate ACR in the map)
- I'll be using .030" head gaskets but that won't increase CR measurably
- Cams are .585" (S&S MR103)
- SE CNC heads (1.875" intake, 1.575" exh)
I put this in the Rushmore category as it is specific to the 103TC models...if it needs moved please suggest.
Last edited by GibsonSG; 02-05-2016 at 08:38 AM. Reason: Title change
#3
02-05-2016 | 03:46 PM
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Cruiser
Joined: Jan 2016
Posts: 160
Likes: 14
From: North of Denver
Octane at elevation
The octane requirements drop at elevation, so I don't think 91 would be such a bad thing at 5,280+ but...
I had some very good conversations with S&S and NRHS and their input has once again proven invaluable.
@11.25:1 the ability to tune a bike is focused on the 5,000+ RPM range. At that RPM range a cam would have to stay open long enough and have valves large enough to 'breath'. The MR103 is not optimal above 10.5:1 and the SE CNC heads are only setup for .585" max, not the >.6" need for intake/exhaust.
As much as I would like to find a reason to swap pistons the SE HC pistons are not a good match for my needs in a 'Touring' bike.
Serious consideration is being given to the S&S 103" forged 5.2cc pop-up dome having the cylinder honed to match a +.005 for cleanup, or run the stock setup thru a conditioning phase and then move to a 107" with pistons to match and evaluate the cam needs as to what I've liked or disliked about the MR103 to that point.
Safe riding!
I had some very good conversations with S&S and NRHS and their input has once again proven invaluable.
@11.25:1 the ability to tune a bike is focused on the 5,000+ RPM range. At that RPM range a cam would have to stay open long enough and have valves large enough to 'breath'. The MR103 is not optimal above 10.5:1 and the SE CNC heads are only setup for .585" max, not the >.6" need for intake/exhaust.
As much as I would like to find a reason to swap pistons the SE HC pistons are not a good match for my needs in a 'Touring' bike.
Serious consideration is being given to the S&S 103" forged 5.2cc pop-up dome having the cylinder honed to match a +.005 for cleanup, or run the stock setup thru a conditioning phase and then move to a 107" with pistons to match and evaluate the cam needs as to what I've liked or disliked about the MR103 to that point.
Safe riding!
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