.045 vs .030 head gaskets on 103 build - what about the cylinder o-ring?
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Road Warrior
Joined: Jun 2009
Posts: 1,943
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From: NYC
.045 vs .030 head gaskets on 103 build - what about the cylinder o-ring?
First, I have searched the sight and have some back ground info.....but was wondering what impact using a .030 gasket has in terms of crank stress, ride, and sound of the bike.
my understanding is stock 103 with a .045 gasket results in an approximate compression ratio of 9.6:1 and stock 103 using .030 gaskets result in 10:1 compression ratio.
so does this extra compression push the crank ?
does it change the ride? I have a high compression honda that shakes like a machine gun.
does it change the sound? more cannon ball, no diff, etc
I read one of the Harley PDFs and also read a blurb about changing the ignition module if you exceed 10:1 compression.
what about the cylinder o-ring, are there thickness options there as well?
my understanding is stock 103 with a .045 gasket results in an approximate compression ratio of 9.6:1 and stock 103 using .030 gaskets result in 10:1 compression ratio.
so does this extra compression push the crank ?
does it change the ride? I have a high compression honda that shakes like a machine gun.
does it change the sound? more cannon ball, no diff, etc
I read one of the Harley PDFs and also read a blurb about changing the ignition module if you exceed 10:1 compression.
what about the cylinder o-ring, are there thickness options there as well?
HDF Community Team
Joined: Jun 2006
Posts: 12,773
Likes: 2,603
From: san antonio
First, you can't speak of compression in absolute numbers unless you know your chamber volume. Using a .030" head gasket in lieu of a .045" head gasket will increase static compression by .25 points. So, if your static CR with a .045" head gasket is 9.6, the static CR will increase to 9.85 with a .030" head gasket, not 10.
The main benefit of the thinner head gasket is not the compression bump but the tightening of the "squish" or "quench" band/area in the combustion chamber which results in more efficient and complete combustion and thereby mitigating detonation.
Of course the extra compression "pushes" the crank but to no ill effect.
No, there is no change in ride. Or if there is, you won't notice it over the normal shaking and vibrating that is a characteristic of the 45* vtwin motor.
On a smaller displacement motor, say 88" or 95", you might notice a snappier sharper exhasut note but you would have to really be paying attention to notice. The exhaust note is much more a function of cam timing than compression.
The reference to an "ignition module" indicates that the motor is carbureted. Any upgrades that include increasing compression to 10:1 or incorporating cams would benefit from a programmable ignition module to modify the ignition curve. If the A/F is controlled by an EFI system, a fuel management system like the SERT or TTS is required to modify the ignition curve.
There are no thickness options with the cylinder base o-ring; however, the o-ring can be replaced with base gaskets that are available in different thicknesses.
The main benefit of the thinner head gasket is not the compression bump but the tightening of the "squish" or "quench" band/area in the combustion chamber which results in more efficient and complete combustion and thereby mitigating detonation.
Of course the extra compression "pushes" the crank but to no ill effect.
No, there is no change in ride. Or if there is, you won't notice it over the normal shaking and vibrating that is a characteristic of the 45* vtwin motor.
On a smaller displacement motor, say 88" or 95", you might notice a snappier sharper exhasut note but you would have to really be paying attention to notice. The exhaust note is much more a function of cam timing than compression.
The reference to an "ignition module" indicates that the motor is carbureted. Any upgrades that include increasing compression to 10:1 or incorporating cams would benefit from a programmable ignition module to modify the ignition curve. If the A/F is controlled by an EFI system, a fuel management system like the SERT or TTS is required to modify the ignition curve.
There are no thickness options with the cylinder base o-ring; however, the o-ring can be replaced with base gaskets that are available in different thicknesses.
Tourer
Joined: Jun 2011
Posts: 417
Likes: 3
From: Watauga, TX
Go here and run the numbers to see what a .030 vs .045 will do to your build.
http://bigboyzheadporting.com/TwinCamComp.htm
http://bigboyzheadporting.com/TwinCamComp.htm
Outstanding HDF Member
Joined: Aug 2008
Posts: 2,090
Likes: 7
If you change the head gasket thickness you will need different length pushrods or adjustable pushrods. I'd go with adjustable rods myself, but they also make perfect fit rods for situations like this. It's a matter of choice, but the adjustable give you infinite adjustment for any future upgrades. They also give you the ability to change your lifter preload in the event that your cams are steep ramped. Also, if you change to aftermarket cams, the base circle may be smaller, which again would require a different length pushrod or adjustables.
Seasoned HDF Member
Joined: Mar 2021
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From: backwoods
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Seasoned HDF Member
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From: outskirts of ba habba
Wholly $hit rounded one, it's a 10 year old thread....Suppose it may be irrelevant by now ??
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