Piston upgrade for a 103"?
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Cruiser
Joined: Jan 2016
Posts: 160
Likes: 14
From: North of Denver
Piston upgrade for a 103"?
When I tore down the top end to replace the heads I got to looking at the stock pistons in my 103" twin cooled.
I'm thinking that forged pistons would definitely be an upgrade and was also considering moving up from the stock 10:1 to a 10.5:1 (plus the bump from the .030 head gasket).
I'd like some advice on whether or not this is a worthwhile upgrade, pitfalls/ gotcha's, etc., I'd also like to know what my options are for the pistons themselves (Wiseco 40126PS is the only thing I've come across so far).
It's not quite time to do the 107" upgrade yet...but this would be a good way to test 10.5:1 to see if I want that on the 107" kit.
sidenote: 5,000 feet of elevation negates some of that CR and I would expect to carry some type of octane boost when traveling at/near sea-level.
I'm thinking that forged pistons would definitely be an upgrade and was also considering moving up from the stock 10:1 to a 10.5:1 (plus the bump from the .030 head gasket).
I'd like some advice on whether or not this is a worthwhile upgrade, pitfalls/ gotcha's, etc., I'd also like to know what my options are for the pistons themselves (Wiseco 40126PS is the only thing I've come across so far).
It's not quite time to do the 107" upgrade yet...but this would be a good way to test 10.5:1 to see if I want that on the 107" kit.
sidenote: 5,000 feet of elevation negates some of that CR and I would expect to carry some type of octane boost when traveling at/near sea-level.
HDF Community Team
Joined: Jun 2006
Posts: 12,776
Likes: 2,607
From: san antonio
Have to ask. Why are you replacing the heads? What are you replacing them with? What is your thinking of buying pistons when you don't know if piston to cylinder fitment will be correct without boring/honing cylinders to fit pistons? Cart before horse? Why buy pistons now when a 107" is the future plan? Why forged when cast are quite commonly used in bigger bore builds? Personal choice for sure, just curious.
If you want to increase compression, you can use a .030" MLS head gasket and deck stock heads about .030" to get the compression bump you want for 10:1 to 10.5:1; no pistons required. Of course, all said without knowing what heads and/or cams you are running.
Not a worthwhile modification IMHO.
If you want to increase compression, you can use a .030" MLS head gasket and deck stock heads about .030" to get the compression bump you want for 10:1 to 10.5:1; no pistons required. Of course, all said without knowing what heads and/or cams you are running.
Not a worthwhile modification IMHO.
Seasoned HDF Member
Joined: Mar 2010
Posts: 21,115
Likes: 7,638
From: Poolville
IMHO your waisting your money on the pistons if your gonna go to a 107 build on the future. The only difference there would be $200 for the bore job. And if it's a concern on the 10.5:1then get there with a .030" head gasket and if it proves to be to much you can always slip a .045" Gasket in
The important thing here is to make sure the cam you are using is good for that compression ratio.
The important thing here is to make sure the cam you are using is good for that compression ratio.
Thread Starter
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Cruiser
Joined: Jan 2016
Posts: 160
Likes: 14
From: North of Denver
Heads (mentioned in the signature) are SE CNC which were also ported and polished by NRHS. This was done along with the 58mm throttle body as part of a piece by piece approach moving toward a full-blown 107".
The TW-777 is still mild enough to be 'bolt in' and valve clearance isn't an issue even having done the .030 head gaskets. So I've already got that little bump in CR from the stock 10:1.
I'm hoping the cart isn't too far ahead of the horse, at this point the bike only has about 700 miles...so the thought was break-in and conditioning could just as easily be completed with the ring gap having been set on the 10.5 pistons or keeping with stock. Eventually this set of jugs will be torque plated and bored and honed to match the pistons during the 107 build...but in the mean time I'm just 'conditioning' them and looking forward to another step along the way.
I haven't bought pistons yet...that was part of my question, is it worth buying 10.5 pistons and what are my options (Wiseco or who else)?
It was my understanding that forged pistons are an upgrade in material (forged vs. cast), total weight and the friction coatings...maybe that's my misunderstanding.
The TW-777 is still mild enough to be 'bolt in' and valve clearance isn't an issue even having done the .030 head gaskets. So I've already got that little bump in CR from the stock 10:1.
I'm hoping the cart isn't too far ahead of the horse, at this point the bike only has about 700 miles...so the thought was break-in and conditioning could just as easily be completed with the ring gap having been set on the 10.5 pistons or keeping with stock. Eventually this set of jugs will be torque plated and bored and honed to match the pistons during the 107 build...but in the mean time I'm just 'conditioning' them and looking forward to another step along the way.
I haven't bought pistons yet...that was part of my question, is it worth buying 10.5 pistons and what are my options (Wiseco or who else)?
It was my understanding that forged pistons are an upgrade in material (forged vs. cast), total weight and the friction coatings...maybe that's my misunderstanding.
Stellar HDF Member
Joined: May 2009
Posts: 2,066
Likes: 97
From: Northern VA
Forged aren't really an upgrade in your case. Sure they maybe handle more compression but they also require looser cylinder fit. So you wouldn't even be able to put forged in without working on your cylinders. And your rings were seated many, many miles ago. Probably within the first 10 miles. If you pull the pistons out you might as well go 107 because you'd be boring/honing at that point regardless.
Cast piston to cylinder fit is usually around 0.0005-0.001"
Forged is usually around 0.0025"
Cast piston to cylinder fit is usually around 0.0005-0.001"
Forged is usually around 0.0025"
HDF Community Team
Joined: Jun 2006
Posts: 12,776
Likes: 2,607
From: san antonio
Eventually this set of jugs will be torque plated and bored and honed to match the pistons during the 107 build...but in the mean time I'm just 'conditioning' them and looking forward to another step along the way. I haven't bought pistons yet...that was part of my question, is it worth buying 10.5 pistons and what are my options (Wiseco or who else)?
It was my understanding that forged pistons are an upgrade in material (forged vs. cast), total weight and the friction coatings...maybe that's my misunderstanding.
It was my understanding that forged pistons are an upgrade in material (forged vs. cast), total weight and the friction coatings...maybe that's my misunderstanding.
Looks like you have a decent configuration; save the $$ and ride the bike until you are ready for the 107" upgrade. Making these modifications in steps is often time consuming and can get expensive.
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107" would kill several birds with 1 stone. (just don't tell your local Fish & Game people....haha)
Scott
Scott
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Thread Starter
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Cruiser
Joined: Jan 2016
Posts: 160
Likes: 14
From: North of Denver
Are you guys sure the SE 110" bolt in kit wouldn't be the better way to go?
...just joking
Any suggestions on the 'best' forged 10.5:1 piston for a 107" build? Axtell, MTC, Wiseco?
Anybody have any feedback on having used the IC FuelMoto jugs as opposed to having my own re-worked?
...just joking
Any suggestions on the 'best' forged 10.5:1 piston for a 107" build? Axtell, MTC, Wiseco?
Anybody have any feedback on having used the IC FuelMoto jugs as opposed to having my own re-worked?
Seasoned HDF Member
Joined: Mar 2010
Posts: 21,115
Likes: 7,638
From: Poolville
Are you guys sure the SE 110" bolt in kit wouldn't be the better way to go?
...just joking
Any suggestions on the 'best' forged 10.5:1 piston for a 107" build? Axtell, MTC, Wiseco?
Anybody have any feedback on having used the IC FuelMoto jugs as opposed to having my own re-worked?
...just joking
Any suggestions on the 'best' forged 10.5:1 piston for a 107" build? Axtell, MTC, Wiseco?
Anybody have any feedback on having used the IC FuelMoto jugs as opposed to having my own re-worked?