Does anyone know....
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Stellar HDF Member
Joined: Dec 2009
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Does anyone know....
Greetings my friends. Does anyone know the displacement limitations on a 2008 96ci throttle body? It can only move so much air, so what is the biggest top end you can put on a 96 before you open a whole new can of worms? Thank you in advance for your input, and may God bless.
Seasoned HDF Member
Joined: Sep 2008
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From: San Diego, CA
Are you talking about a street run engine or a racing application?
Are you talking about a drop in big bore kit, or a custom application where you will modify the cases and/or change the stroke?
I am far from an expert in suck matters, but I have modded all my bikes, and done most of the work myself.
For a drop-in, street driven big bore kit on a 96" Twin Cam, I believe the biggest would be 110" (without modifying the cases).
I don't believe a 110" build would need a bigger throttle body... I have seen some 110" builds with a 58mm throttle bodies, most likely based on goals, cams, and headwork. Most 110' builds use 50mm throttle bodies. I believe OEM is 50mm for EFI bikes '07+.
If I am wrong about OEM being 50mm, and you have a 46mm throttle body, changing throttle bodies or injectors isn't hard, just costs a little bit more. I have a 58mm throttle body and 5.3 grams/second injectors on my 124" build.
Contact a shop, like FuelMoto, or the one you favor and trust. Give them your current engine specs, your goals, and they should be able to recommend a big bore kit, with components that compliment each other, that will do the job. They will know and recommend the extra parts you will need to reach your goals...
Good luck with your mod..
Are you talking about a drop in big bore kit, or a custom application where you will modify the cases and/or change the stroke?
I am far from an expert in suck matters, but I have modded all my bikes, and done most of the work myself.
For a drop-in, street driven big bore kit on a 96" Twin Cam, I believe the biggest would be 110" (without modifying the cases).
I don't believe a 110" build would need a bigger throttle body... I have seen some 110" builds with a 58mm throttle bodies, most likely based on goals, cams, and headwork. Most 110' builds use 50mm throttle bodies. I believe OEM is 50mm for EFI bikes '07+.
If I am wrong about OEM being 50mm, and you have a 46mm throttle body, changing throttle bodies or injectors isn't hard, just costs a little bit more. I have a 58mm throttle body and 5.3 grams/second injectors on my 124" build.
Contact a shop, like FuelMoto, or the one you favor and trust. Give them your current engine specs, your goals, and they should be able to recommend a big bore kit, with components that compliment each other, that will do the job. They will know and recommend the extra parts you will need to reach your goals...
Good luck with your mod..
Last edited by hattitude; Sep 21, 2025 at 09:09 AM.
Thread Starter
|
Stellar HDF Member
Joined: Dec 2009
Posts: 2,913
Likes: 2,542
Are you talking about a street run engine or a racing application?
Are you talking about a drop in big bore kit, or a custom application where you will modify the cases and/or change the stroke?
I am far from an expert in suck matters, but I have modded all my bikes, and done most of the work myself.
For a drop-in, street driven big bore kit on a 96" Twin Cam, I believe the biggest would be 110" (without modifying the cases).
I don't believe a 110" build would need a bigger throttle body... I have seen some 110" builds with a 58mm throttle bodies, most likely based on goals, cams, and headwork. Most 110' builds use 50mm throttle bodies. I believe OEM is 50mm for EFI bikes '07+.
If I am wrong about OEM being 50mm, and you have a 46mm throttle body, changing throttle bodies or injectors isn't hard, just costs a little bit more. I have a 58mm throttle body and 5.3 grams/second injectors on my 124" build.
Contact a shop, like FuelMoto, or the one you favor and trust. Give them your current engine specs, your goals, and they should be able to recommend a big bore kit, with components that compliment each other, that will do the job. They will know and recommend the extra parts you will need to reach your goals...
Good luck with your mod..
Are you talking about a drop in big bore kit, or a custom application where you will modify the cases and/or change the stroke?
I am far from an expert in suck matters, but I have modded all my bikes, and done most of the work myself.
For a drop-in, street driven big bore kit on a 96" Twin Cam, I believe the biggest would be 110" (without modifying the cases).
I don't believe a 110" build would need a bigger throttle body... I have seen some 110" builds with a 58mm throttle bodies, most likely based on goals, cams, and headwork. Most 110' builds use 50mm throttle bodies. I believe OEM is 50mm for EFI bikes '07+.
If I am wrong about OEM being 50mm, and you have a 46mm throttle body, changing throttle bodies or injectors isn't hard, just costs a little bit more. I have a 58mm throttle body and 5.3 grams/second injectors on my 124" build.
Contact a shop, like FuelMoto, or the one you favor and trust. Give them your current engine specs, your goals, and they should be able to recommend a big bore kit, with components that compliment each other, that will do the job. They will know and recommend the extra parts you will need to reach your goals...
Good luck with your mod..
Seasoned HDF Member
Joined: Sep 2008
Posts: 14,144
Likes: 11,219
From: San Diego, CA
Thank you for all that. I don't think I will build too hot of a motor, just know that with almost 85K on the clock now it won't be long before she'll need a top end refresh. been looking at some dyno numbers on some kits and I have to say I never knew the TC96 could be built as impressive as it can be with even just a slight increase in displacement.
Hey, it's only money, right!
Hey, it's only money, right!
FWIW, I recently rebuilt a friend's bike after his crank went bad at 60K miles. I used a new OEM short block, new OEM pistons, cylinders, & lifters. I also used his old heads, cams, intake, exhaust, injectors, and tune. He knows I have the "mod sickness" and thought I had snuck a cam in there during the rebuild... he's happy as hell with his OEM rebuilt engine...
Your 96" is the same as thew 103" but with a smaller bore. You could go 103" with cams, or a very popular 96"/103" big bore kit is a 107".
Fuelmoto offers several levels of big bore kits, as do other vendors. You could do a 103"/107", with a non radical cam and get a really nice seat-of-the-pants increase in performance... The kits often come with new cylinders & pistons, or if you have a good speed shop local, they could do the work for you. You could also have your heads gone through with a basic rebuild. Put it all together and get a good tune. I suspect you would notice a BIG improvement...
I have the "sickness". My current bikes have; Stage I (will change in the near furture), Stage II (bolt-in cam), Stage IV (big bore kit w/headwork), and my bagger with the bigger crate engine. They are all very fun, and yet never "enough"... I would be afraid to add up the costs of engine mods I have made to my bikes since my then new '78 FXS Low Rider
And yet, I would do it all over again... 
My advice.... set a goal, work with a good shop of your choice to pick/match components, and then enjoy the new engine mods...
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Stellar HDF Member
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Everything motor wise is still in the research/planning phase. I know I'm going to build the bottom end as bulletproof as I can with Darkhorse doing that for me with a crank and the Timken bearing upgrade while they have it. I've often thought about leaving it a 96, it's served me well since 2008 and has always been all the bike I needed. More HP and torque would be a hoot to ride I'm sure, but then I have to factor in more frequent tire changes, which equals money. I'm looking at retirement here in the next year or two, hopefully. And what I want to do before that is build the bike I'm going to ride until I just can't ride anymore. And I want to be able to not wrench on it much more than routine maintenance until I have to hang the keys up.
Grand HDF Member
Joined: Sep 2022
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From: Florida
Everything motor wise is still in the research/planning phase. I know I'm going to build the bottom end as bulletproof as I can with Darkhorse doing that for me with a crank and the Timken bearing upgrade while they have it. I've often thought about leaving it a 96, it's served me well since 2008 and has always been all the bike I needed. More HP and torque would be a hoot to ride I'm sure, but then I have to factor in more frequent tire changes, which equals money. I'm looking at retirement here in the next year or two, hopefully. And what I want to do before that is build the bike I'm going to ride until I just can't ride anymore. And I want to be able to not wrench on it much more than routine maintenance until I have to hang the keys up.
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Seasoned HDF Member
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From: poway
Thank you for all that. I don't think I will build too hot of a motor, just know that with almost 85K on the clock now it won't be long before she'll need a top end refresh. been looking at some dyno numbers on some kits and I have to say I never knew the TC96 could be built as impressive as it can be with even just a slight increase in displacement. Hey, it's only money, right!
You can see it here..
https://www.hdforums.com/forum/twin-...000-miles.html
This motor has been a stage 4 103 from about 15000 to 80000 and 107 up to 125000.
IMO when you get around to doing the top end and you want a little more simply pull the top end and if the crank is good install, both runout and lower rod bearings, a mild cam and bore kit, then get it tuned. No need to for timken. The main bearings on my EGC looked fine for 125000 miles.
As far as throttle body goes, if you don't mod the heads the stock ones will be fine. With good flowing heads on a 103 depending on the build you could pick up 4-6 hp on the top end but it really depends on who does the heads, final CR, Air cleaner, exhaust, and cam choice.
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